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1558
2816319
2816253
2026-06-20T04:00:22Z
Farhan Kamal Azeemi 133
3095208
2816319
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text/x-wiki
{{Please leave this line alone (sandbox heading)}}
{{Infobox university
| name = Aviation Institute of Management
| short_description = Private aviation education institution in Karachi, Pakistan
| image =
| caption =
| established = 2016
| type = Private
| CEO = Dr. Wali Mughni, PhD, FRAeS, SBt
| location = Karachi, Sindh, Pakistan
| address = CILT House, Palace Road, Gulistan-e-Jauhar, Karachi
| website = [https://aim.edu.pk aim.edu.pk]
| registered = Government of Sindh
}}
The **Aviation Institute of Management** (**AIM**) is a private aviation education institution established in 2016 in Karachi, Sindh, Pakistan. Headed by Dr. Wali Mughni, PhD, FRAeS, SBt, as Chief Executive Officer and Chairman, AIM is Pakistan's only institute representing Embry-Riddle Aeronautical University (ERAU), the world's largest and most reputable aviation and aerospace university<ref>[1]</ref>.
== History ==
In 2016, Aviation Institute of Management was established as a partnership concern primarily by Dr. Wali Mughni (CEO), Prof. Wali Durrani (late), and Capt. Hadi Rizvi. Later, other members joined, and the organization was converted to a private limited concern in April 2018<ref>[2]</ref>.
AIM is registered with the Government of Sindh<ref>[1]</ref>.
== Leadership ==
=== Dr. Wali Mughni (CEO and Chairman) ===
Dr. Wali Mughni, PhD, FRAeS, SBt, is CEO and Chairman of AIM, a retired fighter pilot, and recipient of the Sher Afghan (Top Gun) title and Sitara-e-Basalat. With over 40 years of experience in aviation and education, he leads AIM in shaping the next generation of aviation professionals. He exclusively represents his alma mater Embry-Riddle Aeronautical University (USA) in Pakistan. He was a consultant to the Aviation Ministry, Government of Pakistan. Dr. Mughni was the lead architect and writer who authored Pakistan's National Aviation Policy – 2015. He worked for NASA as a researcher, IBM as an IT business consultant, and Pakistan Air Force as a fighter pilot. He was the Top Gun (Sher Afghan) award winner of Pakistan Air Force and was also awarded the country's highest peacetime operational award, Sitara-e-Basalat<ref>[2]</ref>.
=== Founding Members ===
The core founding team includes:
* **Prof. Wali Durrani (Late)**: One of Pakistan's most experienced, competent, and qualified educationists. He held the appointment of Registrar, Karachi University, and CEO/Rector/VC of universities including Hamdard, KASBIT, IoBM. He was a consultant for Pakistan Civil Aviation Authority's schools and colleges, a "Management & Financial Advisor" to the Sindh High Court, and an "Organizational Reform Expert" and "Budget & Planning Expert" with Federal Ministry of Law for "Access to Justice Program in Pakistan"<ref>[2]</ref>.
* **Capt. Hadi Rizvi**: An operational pilot with over 50 years of operational and instructional flying experience in PAF, PIA, and other training organizations. He holds MA English and Law degrees, is a world-renowned English poet and prolific writer, and serves as Aviation Management faculty for graduate and undergraduate programs<ref>[2]</ref>.
* **Mr. Azeez Siddiqui**: A veteran aviation professional with over 43 years in PIA and Saudi Airlines, holding positions from planning to operations to strategy development. He is also a faculty member at AIM<ref>[2]</ref>.
* **Dr. Nazir Ahmed Vaid**: A serial social entrepreneur assisting AIM in establishing and growing the business and promoting varied educational activities<ref>[2]</ref>.
* **Mr. Ahsan Qureshi**: A qualified educationist with multifaceted experience in projects and business development, the youngest core team member and promising administrator of the institution<ref>[2]</ref>.
Other core faculty members include Capt. Afsar Malik, Engr. Zafarullah Khan, Engr. Zia ul Haq, Col. Navaid Ahsan, Capt. Amin Desai, Dr. Bilal Siddiqui, Dr. Noor Memon, Air Cdre (R) Tariq Ashraf, Brig (R) Farooq Shaukat, Ms. Sonia Kazim, Ms. Samreen Fahad, and Mr. Taha Khan<ref>[2]</ref>.
== Academic Programs ==
AIM offers diverse aviation education programs:
=== Diploma Programs ===
* **Diploma in Aviation Business Administration**
* **Diploma in Business Administration**
* **Dual Diploma** (Diploma in Business Administration + Diploma in Aviation Business Administration)
=== Certificate Programs ===
* Multiple aviation and management certificates conducted by AIM
* **Graduate Certificate in Aviation (Asia-focus)** by Embry-Riddle Aeronautical University - Aviation Management program focusing on aviation industry in Asia, conducted by highly qualified ERAU faculty from Singapore/USA
* Various aviation management short certificate programs facilitated by AIM
* **Professional Certificate in Aviation Administration**
* **Professional Certificate in Aviation Management**
* **Certificate in Aviation Business Administration (CABA)**
=== Degree Programs ===
* **BS/MBA (Aviation)**
* **BS/MS (Aeronautics)**
* **BS/MS Aerospace Engineering**
* All degree programs offered by Embry-Riddle Aeronautical University (online programs)
* **Bachelor's Degrees** (online by ERAU, USA)
* **Master's Degrees** (online by ERAU, USA)
=== Workshops and Seminars ===
Planned workshops include:
* Crew Resource Management
* Human Factors
* Threat & Error Management
* Emotional Intelligence
* Safety Management Systems
* Aviation Security Management
=== THE AVIATORS ===
**THE AVIATORS** is a project of AIM designed to induct secondary-level students after a thorough psychometric test for career development in the Aviation industry. It offers preparatory classes for careers in aviation, leading to BS (Aviation Management) & Diploma in Aviation Business Administration, with summer camps, short courses, diploma classes, and online classes available for international students<ref>[1]</ref>.
=== Aviationizing Club ===
AIM operates **The Aviationizing Club**, established to promote aviation through learning and fun activities<ref>[1]</ref>.
== Special Features ==
=== Industry-Academia Bridge ===
AIM is linked with the aviation industry and aims to bridge the widening gap between the aviation industry and academia. The institute liaises and coordinates with the industry regularly to ensure:
* Industry needs are synchronized with current teachings and curricula
* Students get opportunities for appropriate internships
* Graduating students get fair chances of gainful employment in the industry
* Meaningful Research & Development is carried out for the industry<ref>[1]</ref>.
=== Scholarships ===
AIM offers scholarships to deserving students in the form of **Qard-e-Hasana**. When students graduate and get gainfully employed, they commit to pay back the dues to the institute in an affordable manner<ref>[1]</ref>.
=== Student Support ===
AIM ensures that no student is left behind and offers zero semester classes at affordable rates to candidates who need help to improve. The prerequisite is simply the displayable passion to learn<ref>[1]</ref>.
AIM specializes in Aviation and Management Sciences and prides itself for having the services of distinguished aviation experts and professionals of the country in its management team and faculty<ref>[1]</ref>.
== Statistics ==
| Metric | Number |
|--------|--------|
| Faculty Members | 25 |
| Programs | 24 |
| Trained Professionals | 172 |
| International Partners | 15 |
== Mission ==
"The organization's mission is to train, educate and groom our youth so as to make them acceptable aviation professionals in the global aviation industry. AIM aims to be a regional leader in aviation and aerospace education, training and Human Resource Development. Our mission is to teach the science, practice and business of aviation and aerospace, preparing students for productive careers and leadership roles in business, government agencies and the military. AIM shall build and retain its reputation as a regional leader in aviation and aerospace education from secondary school level to higher education."<ref>[1]</ref>
== Core Values ==
The core values govern AIM's academic and co-curricular programs and its operating ethos. These values ground and enliven the institute's identity, heritage, and commitment to knowledge for personal enhancement, progress of society, the nation, and the global community<ref>[1]</ref>.
* **Respect**: Understanding and valuing diverse perspectives of every person; every individual, big or small in status, deserves respect
* **Excellence**: Striving for excellence in everything using intellectual, social, physical, spiritual, and ethical competencies
* **Compassion**: Standing with and embracing others in suffering or difficult times to experience greater compassion from Almighty Allah
* **Service**: Using gifts and abilities to advance community well-being
* **Hospitality**: Working with graciousness, welcoming new ideas and people of all backgrounds and beliefs
* **Integrity**: Realizing the greater good in actions and programs, looking at work holistically as united with others across societies
* **Diversity**: Fostering an open, welcoming climate for diverse people, ideas, and perspectives; promoting constructive discourse engaging faculty, staff, and students<ref>[1]</ref>
=== Learning for Here and Hereafter ===
**Learning for Life and beyond** encourages pursuing knowledge and truth throughout lives in ways that improve communities and strengthen understanding of each other. AIM has a commitment to education as a means of facilitating people to live meaningful and decent living. The institute enrolls students of all ages, color, creed, religion, ethnicity, and treats all without bias or discrimination<ref>[1]</ref>.
== Aviation Awareness Exhibition 2026 ==
On January 25, 2026, AIM hosted its Aviation Awareness Exhibition at Happy Palace, Karachi. The event was covered by Geo News and brought together experts, innovators, and industry leaders to shape a brighter tomorrow for Pakistan's aviation sector<ref>[3]</ref>.
== Location ==
AIM is located at CILT House, Palace Road, Gulistan-e-Jauhar, Karachi, Sindh, Pakistan. The institute operates Monday–Saturday, 9:00 AM – 5:00 PM<ref>[4]</ref>.
== Contact ==
* Phone: +92 321 897 9014, +92 333 086 6166
* Website: [https://aim.edu.pk aim.edu.pk]
== Goals & Objectives ==
AIM offers the best possible learning environment, a conducive atmosphere, and an opportunity for all students to get educated, trained, and groomed:
* **To teach** the science, practice, and business of aviation and aerospace
* **To prepare** students for productive careers and leadership roles in business, government agencies, and commercial organizations
* **To groom** students to become internationally accepted professionals in the global aviation industry
* **To liaise and coordinate** with the industry regularly to ensure industry needs sync with teachings, students get internships, graduating students get employment, and meaningful R&D is carried out<ref>[1]</ref>
== References ==
<references>
<ref name="1">[https://aim.edu.pk Aviation Institute of Management]. Retrieved June 20, 2026.</ref>
<ref name="2">[https://aim.edu.pk/faculty/ Organization & its Founding Members]. Aviation Institute of Management. Retrieved June 20, 2026.</ref>
<ref name="3">[https://www.youtube.com/watch?v=LxPqcaTZHWk Aviation Awareness Exhibition 2026]. YouTube. January 24, 2026. Retrieved June 20, 2026.</ref>
<ref name="4">[https://aim.edu.pk/contact/ Contact]. Aviation Institute of Management. Retrieved June 20, 2026.</ref>
<ref name="5">[https://asia.erau.edu/about-asia/partnerships Embry-Riddle Educational Partner - AIM]. Embry-Riddle Aeronautical University. Retrieved June 20, 2026.</ref>
</references>
p7pyf94lfcdo3o3o4t8vw9llmry16gi
2816320
2816319
2026-06-20T04:02:59Z
Farhan Kamal Azeemi 133
3095208
2816320
wikitext
text/x-wiki
{{Please leave this line alone (sandbox header)}}
{{
| name = Aviation Institute of Management
| short_description = Private aviation education institution in Karachi, Pakistan
| image =
| caption =
| established = 2016
| type = Private
| CEO = Dr. Wali Mughni, PhD, FRAeS, SBt
| location = Karachi, Sindh, Pakistan
| address = CILT House, Palace Road, Gulistan-e-Jauhar, Karachi
| website = [https://aim.edu.pk aim.edu.pk]
| registered = Government of Sindh
}}
The **Aviation Institute of Management** (**AIM**) is a private aviation education institution established in 2016 in Karachi, Sindh, Pakistan. Headed by Dr. Wali Mughni, PhD, FRAeS, SBt, as Chief Executive Officer and Chairman, AIM is Pakistan's only institute representing Embry-Riddle Aeronautical University (ERAU), the world's largest and most reputable aviation and aerospace university<ref>[1]</ref>.
== History ==
In 2016, Aviation Institute of Management was established as a partnership concern primarily by Dr. Wali Mughni (CEO), Prof. Wali Durrani (late), and Capt. Hadi Rizvi. Later, other members joined, and the organization was converted to a private limited concern in April 2018<ref>[2]</ref>.
AIM is registered with the Government of Sindh<ref>[1]</ref>.
== Leadership ==
=== Dr. Wali Mughni (CEO and Chairman) ===
Dr. Wali Mughni, PhD, FRAeS, SBt, is CEO and Chairman of AIM, a retired fighter pilot, and recipient of the Sher Afghan (Top Gun) title and Sitara-e-Basalat. With over 40 years of experience in aviation and education, he leads AIM in shaping the next generation of aviation professionals. He exclusively represents his alma mater Embry-Riddle Aeronautical University (USA) in Pakistan. He was a consultant to the Aviation Ministry, Government of Pakistan. Dr. Mughni was the lead architect and writer who authored Pakistan's National Aviation Policy – 2015. He worked for NASA as a researcher, IBM as an IT business consultant, and Pakistan Air Force as a fighter pilot. He was the Top Gun (Sher Afghan) award winner of Pakistan Air Force and was also awarded the country's highest peacetime operational award, Sitara-e-Basalat<ref>[2]</ref>.
=== Founding Members ===
The core founding team includes:
* **Prof. Wali Durrani (Late)**: One of Pakistan's most experienced, competent, and qualified educationists. He held the appointment of Registrar, Karachi University, and CEO/Rector/VC of universities including Hamdard, KASBIT, IoBM. He was a consultant for Pakistan Civil Aviation Authority's schools and colleges, a "Management & Financial Advisor" to the Sindh High Court, and an "Organizational Reform Expert" and "Budget & Planning Expert" with Federal Ministry of Law for "Access to Justice Program in Pakistan"<ref>[2]</ref>.
* **Capt. Hadi Rizvi**: An operational pilot with over 50 years of operational and instructional flying experience in PAF, PIA, and other training organizations. He holds MA English and Law degrees, is a world-renowned English poet and prolific writer, and serves as Aviation Management faculty for graduate and undergraduate programs<ref>[2]</ref>.
* **Mr. Azeez Siddiqui**: A veteran aviation professional with over 43 years in PIA and Saudi Airlines, holding positions from planning to operations to strategy development. He is also a faculty member at AIM<ref>[2]</ref>.
* **Dr. Nazir Ahmed Vaid**: A serial social entrepreneur assisting AIM in establishing and growing the business and promoting varied educational activities<ref>[2]</ref>.
* **Mr. Ahsan Qureshi**: A qualified educationist with multifaceted experience in projects and business development, the youngest core team member and promising administrator of the institution<ref>[2]</ref>.
Other core faculty members include Capt. Afsar Malik, Engr. Zafarullah Khan, Engr. Zia ul Haq, Col. Navaid Ahsan, Capt. Amin Desai, Dr. Bilal Siddiqui, Dr. Noor Memon, Air Cdre (R) Tariq Ashraf, Brig (R) Farooq Shaukat, Ms. Sonia Kazim, Ms. Samreen Fahad, and Mr. Taha Khan<ref>[2]</ref>.
== Academic Programs ==
AIM offers diverse aviation education programs:
=== Diploma Programs ===
* **Diploma in Aviation Business Administration**
* **Diploma in Business Administration**
* **Dual Diploma** (Diploma in Business Administration + Diploma in Aviation Business Administration)
=== Certificate Programs ===
* Multiple aviation and management certificates conducted by AIM
* **Graduate Certificate in Aviation (Asia-focus)** by Embry-Riddle Aeronautical University - Aviation Management program focusing on aviation industry in Asia, conducted by highly qualified ERAU faculty from Singapore/USA
* Various aviation management short certificate programs facilitated by AIM
* **Professional Certificate in Aviation Administration**
* **Professional Certificate in Aviation Management**
* **Certificate in Aviation Business Administration (CABA)**
=== Degree Programs ===
* **BS/MBA (Aviation)**
* **BS/MS (Aeronautics)**
* **BS/MS Aerospace Engineering**
* All degree programs offered by Embry-Riddle Aeronautical University (online programs)
* **Bachelor's Degrees** (online by ERAU, USA)
* **Master's Degrees** (online by ERAU, USA)
=== Workshops and Seminars ===
Planned workshops include:
* Crew Resource Management
* Human Factors
* Threat & Error Management
* Emotional Intelligence
* Safety Management Systems
* Aviation Security Management
=== THE AVIATORS ===
**THE AVIATORS** is a project of AIM designed to induct secondary-level students after a thorough psychometric test for career development in the Aviation industry. It offers preparatory classes for careers in aviation, leading to BS (Aviation Management) & Diploma in Aviation Business Administration, with summer camps, short courses, diploma classes, and online classes available for international students<ref>[1]</ref>.
=== Aviationizing Club ===
AIM operates **The Aviationizing Club**, established to promote aviation through learning and fun activities<ref>[1]</ref>.
== Special Features ==
=== Industry-Academia Bridge ===
AIM is linked with the aviation industry and aims to bridge the widening gap between the aviation industry and academia. The institute liaises and coordinates with the industry regularly to ensure:
* Industry needs are synchronized with current teachings and curricula
* Students get opportunities for appropriate internships
* Graduating students get fair chances of gainful employment in the industry
* Meaningful Research & Development is carried out for the industry<ref>[1]</ref>.
=== Scholarships ===
AIM offers scholarships to deserving students in the form of **Qard-e-Hasana**. When students graduate and get gainfully employed, they commit to pay back the dues to the institute in an affordable manner<ref>[1]</ref>.
=== Student Support ===
AIM ensures that no student is left behind and offers zero semester classes at affordable rates to candidates who need help to improve. The prerequisite is simply the displayable passion to learn<ref>[1]</ref>.
AIM specializes in Aviation and Management Sciences and prides itself for having the services of distinguished aviation experts and professionals of the country in its management team and faculty<ref>[1]</ref>.
== Statistics ==
| Metric | Number |
|--------|--------|
| Faculty Members | 25 |
| Programs | 24 |
| Trained Professionals | 172 |
| International Partners | 15 |
== Mission ==
"The organization's mission is to train, educate and groom our youth so as to make them acceptable aviation professionals in the global aviation industry. AIM aims to be a regional leader in aviation and aerospace education, training and Human Resource Development. Our mission is to teach the science, practice and business of aviation and aerospace, preparing students for productive careers and leadership roles in business, government agencies and the military. AIM shall build and retain its reputation as a regional leader in aviation and aerospace education from secondary school level to higher education."<ref>[1]</ref>
== Core Values ==
The core values govern AIM's academic and co-curricular programs and its operating ethos. These values ground and enliven the institute's identity, heritage, and commitment to knowledge for personal enhancement, progress of society, the nation, and the global community<ref>[1]</ref>.
* **Respect**: Understanding and valuing diverse perspectives of every person; every individual, big or small in status, deserves respect
* **Excellence**: Striving for excellence in everything using intellectual, social, physical, spiritual, and ethical competencies
* **Compassion**: Standing with and embracing others in suffering or difficult times to experience greater compassion from Almighty Allah
* **Service**: Using gifts and abilities to advance community well-being
* **Hospitality**: Working with graciousness, welcoming new ideas and people of all backgrounds and beliefs
* **Integrity**: Realizing the greater good in actions and programs, looking at work holistically as united with others across societies
* **Diversity**: Fostering an open, welcoming climate for diverse people, ideas, and perspectives; promoting constructive discourse engaging faculty, staff, and students<ref>[1]</ref>
=== Learning for Here and Hereafter ===
**Learning for Life and beyond** encourages pursuing knowledge and truth throughout lives in ways that improve communities and strengthen understanding of each other. AIM has a commitment to education as a means of facilitating people to live meaningful and decent living. The institute enrolls students of all ages, color, creed, religion, ethnicity, and treats all without bias or discrimination<ref>[1]</ref>.
== Aviation Awareness Exhibition 2026 ==
On January 25, 2026, AIM hosted its Aviation Awareness Exhibition at Happy Palace, Karachi. The event was covered by Geo News and brought together experts, innovators, and industry leaders to shape a brighter tomorrow for Pakistan's aviation sector<ref>[3]</ref>.
== Location ==
AIM is located at CILT House, Palace Road, Gulistan-e-Jauhar, Karachi, Sindh, Pakistan. The institute operates Monday–Saturday, 9:00 AM – 5:00 PM<ref>[4]</ref>.
== Contact ==
* Phone: +92 321 897 9014, +92 333 086 6166
* Website: [https://aim.edu.pk aim.edu.pk]
== Goals & Objectives ==
AIM offers the best possible learning environment, a conducive atmosphere, and an opportunity for all students to get educated, trained, and groomed:
* **To teach** the science, practice, and business of aviation and aerospace
* **To prepare** students for productive careers and leadership roles in business, government agencies, and commercial organizations
* **To groom** students to become internationally accepted professionals in the global aviation industry
* **To liaise and coordinate** with the industry regularly to ensure industry needs sync with teachings, students get internships, graduating students get employment, and meaningful R&D is carried out<ref>[1]</ref>
== References ==
<references>
<ref name="1">[https://aim.edu.pk Aviation Institute of Management]. Retrieved June 20, 2026.</ref>
<ref name="2">[https://aim.edu.pk/faculty/ Organization & its Founding Members]. Aviation Institute of Management. Retrieved June 20, 2026.</ref>
<ref name="3">[https://www.youtube.com/watch?v=LxPqcaTZHWk Aviation Awareness Exhibition 2026]. YouTube. January 24, 2026. Retrieved June 20, 2026.</ref>
<ref name="4">[https://aim.edu.pk/contact/ Contact]. Aviation Institute of Management. Retrieved June 20, 2026.</ref>
<ref name="5">[https://asia.erau.edu/about-asia/partnerships Embry-Riddle Educational Partner - AIM]. Embry-Riddle Aeronautical University. Retrieved June 20, 2026.</ref>
</references>
77odoqyr6mfpye1cd02ycs5n4x2mns2
2816321
2816320
2026-06-20T04:06:33Z
Farhan Kamal Azeemi 133
3095208
2816321
wikitext
text/x-wiki
{{Please leave this line alone (sandbox header)}}
The '''[https://aim.edu.pk/ Aviation Institute of Management]''' '''(AIM)''' is a private aviation education institution established in 2016 in Karachi, Sindh, Pakistan. Headed by Dr. Wali Mughni, PhD, FRAeS, SBt, as Chief Executive Officer and Chairman, AIM is Pakistan's only institute representing Embry-Riddle Aeronautical University (ERAU), the world's largest and most reputable aviation and aerospace university<ref>[1]</ref>.
== History ==
In 2016, Aviation Institute of Management was established as a partnership concern primarily by Dr. Wali Mughni (CEO), Prof. Wali Durrani (late), and Capt. Hadi Rizvi. Later, other members joined, and the organization was converted to a private limited concern in April 2018<ref>[2]</ref>.
AIM is registered with the Government of Sindh<ref>[1]</ref>.
== Leadership ==
=== Dr. Wali Mughni (CEO and Chairman) ===
Dr. Wali Mughni, PhD, FRAeS, SBt, is CEO and Chairman of AIM, a retired fighter pilot, and recipient of the Sher Afghan (Top Gun) title and Sitara-e-Basalat. With over 40 years of experience in aviation and education, he leads AIM in shaping the next generation of aviation professionals. He exclusively represents his alma mater Embry-Riddle Aeronautical University (USA) in Pakistan. He was a consultant to the Aviation Ministry, Government of Pakistan. Dr. Mughni was the lead architect and writer who authored Pakistan's National Aviation Policy – 2015. He worked for NASA as a researcher, IBM as an IT business consultant, and Pakistan Air Force as a fighter pilot. He was the Top Gun (Sher Afghan) award winner of Pakistan Air Force and was also awarded the country's highest peacetime operational award, Sitara-e-Basalat<ref>[2]</ref>.
=== Founding Members ===
The core founding team includes:
* **Prof. Wali Durrani (Late)**: One of Pakistan's most experienced, competent, and qualified educationists. He held the appointment of Registrar, Karachi University, and CEO/Rector/VC of universities including Hamdard, KASBIT, IoBM. He was a consultant for Pakistan Civil Aviation Authority's schools and colleges, a "Management & Financial Advisor" to the Sindh High Court, and an "Organizational Reform Expert" and "Budget & Planning Expert" with Federal Ministry of Law for "Access to Justice Program in Pakistan"<ref>[2]</ref>.
* **Capt. Hadi Rizvi**: An operational pilot with over 50 years of operational and instructional flying experience in PAF, PIA, and other training organizations. He holds MA English and Law degrees, is a world-renowned English poet and prolific writer, and serves as Aviation Management faculty for graduate and undergraduate programs<ref>[2]</ref>.
* **Mr. Azeez Siddiqui**: A veteran aviation professional with over 43 years in PIA and Saudi Airlines, holding positions from planning to operations to strategy development. He is also a faculty member at AIM<ref>[2]</ref>.
* **Dr. Nazir Ahmed Vaid**: A serial social entrepreneur assisting AIM in establishing and growing the business and promoting varied educational activities<ref>[2]</ref>.
* **Mr. Ahsan Qureshi**: A qualified educationist with multifaceted experience in projects and business development, the youngest core team member and promising administrator of the institution<ref>[2]</ref>.
Other core faculty members include Capt. Afsar Malik, Engr. Zafarullah Khan, Engr. Zia ul Haq, Col. Navaid Ahsan, Capt. Amin Desai, Dr. Bilal Siddiqui, Dr. Noor Memon, Air Cdre (R) Tariq Ashraf, Brig (R) Farooq Shaukat, Ms. Sonia Kazim, Ms. Samreen Fahad, and Mr. Taha Khan<ref>[2]</ref>.
== Academic Programs ==
AIM offers diverse aviation education programs:
=== Diploma Programs ===
* **Diploma in Aviation Business Administration**
* **Diploma in Business Administration**
* **Dual Diploma** (Diploma in Business Administration + Diploma in Aviation Business Administration)
=== Certificate Programs ===
* Multiple aviation and management certificates conducted by AIM
* **Graduate Certificate in Aviation (Asia-focus)** by Embry-Riddle Aeronautical University - Aviation Management program focusing on aviation industry in Asia, conducted by highly qualified ERAU faculty from Singapore/USA
* Various aviation management short certificate programs facilitated by AIM
* **Professional Certificate in Aviation Administration**
* **Professional Certificate in Aviation Management**
* **Certificate in Aviation Business Administration (CABA)**
=== Degree Programs ===
* **BS/MBA (Aviation)**
* **BS/MS (Aeronautics)**
* **BS/MS Aerospace Engineering**
* All degree programs offered by Embry-Riddle Aeronautical University (online programs)
* **Bachelor's Degrees** (online by ERAU, USA)
* **Master's Degrees** (online by ERAU, USA)
=== Workshops and Seminars ===
Planned workshops include:
* Crew Resource Management
* Human Factors
* Threat & Error Management
* Emotional Intelligence
* Safety Management Systems
* Aviation Security Management
=== THE AVIATORS ===
**THE AVIATORS** is a project of AIM designed to induct secondary-level students after a thorough psychometric test for career development in the Aviation industry. It offers preparatory classes for careers in aviation, leading to BS (Aviation Management) & Diploma in Aviation Business Administration, with summer camps, short courses, diploma classes, and online classes available for international students<ref>[1]</ref>.
=== Aviationizing Club ===
AIM operates **The Aviationizing Club**, established to promote aviation through learning and fun activities<ref>[1]</ref>.
== Special Features ==
=== Industry-Academia Bridge ===
AIM is linked with the aviation industry and aims to bridge the widening gap between the aviation industry and academia. The institute liaises and coordinates with the industry regularly to ensure:
* Industry needs are synchronized with current teachings and curricula
* Students get opportunities for appropriate internships
* Graduating students get fair chances of gainful employment in the industry
* Meaningful Research & Development is carried out for the industry<ref>[1]</ref>.
=== Scholarships ===
AIM offers scholarships to deserving students in the form of **Qard-e-Hasana**. When students graduate and get gainfully employed, they commit to pay back the dues to the institute in an affordable manner<ref>[1]</ref>.
=== Student Support ===
AIM ensures that no student is left behind and offers zero semester classes at affordable rates to candidates who need help to improve. The prerequisite is simply the displayable passion to learn<ref>[1]</ref>.
AIM specializes in Aviation and Management Sciences and prides itself for having the services of distinguished aviation experts and professionals of the country in its management team and faculty<ref>[1]</ref>.
== Statistics ==
| Metric | Number |
|--------|--------|
| Faculty Members | 25 |
| Programs | 24 |
| Trained Professionals | 172 |
| International Partners | 15 |
== Mission ==
"The organization's mission is to train, educate and groom our youth so as to make them acceptable aviation professionals in the global aviation industry. AIM aims to be a regional leader in aviation and aerospace education, training and Human Resource Development. Our mission is to teach the science, practice and business of aviation and aerospace, preparing students for productive careers and leadership roles in business, government agencies and the military. AIM shall build and retain its reputation as a regional leader in aviation and aerospace education from secondary school level to higher education."<ref>[1]</ref>
== Core Values ==
The core values govern AIM's academic and co-curricular programs and its operating ethos. These values ground and enliven the institute's identity, heritage, and commitment to knowledge for personal enhancement, progress of society, the nation, and the global community<ref>[1]</ref>.
* **Respect**: Understanding and valuing diverse perspectives of every person; every individual, big or small in status, deserves respect
* **Excellence**: Striving for excellence in everything using intellectual, social, physical, spiritual, and ethical competencies
* **Compassion**: Standing with and embracing others in suffering or difficult times to experience greater compassion from Almighty Allah
* **Service**: Using gifts and abilities to advance community well-being
* **Hospitality**: Working with graciousness, welcoming new ideas and people of all backgrounds and beliefs
* **Integrity**: Realizing the greater good in actions and programs, looking at work holistically as united with others across societies
* **Diversity**: Fostering an open, welcoming climate for diverse people, ideas, and perspectives; promoting constructive discourse engaging faculty, staff, and students<ref>[1]</ref>
=== Learning for Here and Hereafter ===
**Learning for Life and beyond** encourages pursuing knowledge and truth throughout lives in ways that improve communities and strengthen understanding of each other. AIM has a commitment to education as a means of facilitating people to live meaningful and decent living. The institute enrolls students of all ages, color, creed, religion, ethnicity, and treats all without bias or discrimination<ref>[1]</ref>.
== Aviation Awareness Exhibition 2026 ==
On January 25, 2026, AIM hosted its Aviation Awareness Exhibition at Happy Palace, Karachi. The event was covered by Geo News and brought together experts, innovators, and industry leaders to shape a brighter tomorrow for Pakistan's aviation sector<ref>[3]</ref>.
== Location ==
AIM is located at CILT House, Palace Road, Gulistan-e-Jauhar, Karachi, Sindh, Pakistan. The institute operates Monday–Saturday, 9:00 AM – 5:00 PM<ref>[4]</ref>.
== Contact ==
* Phone: +92 321 897 9014, +92 333 086 6166
* Website: [https://aim.edu.pk aim.edu.pk]
== Goals & Objectives ==
AIM offers the best possible learning environment, a conducive atmosphere, and an opportunity for all students to get educated, trained, and groomed:
* **To teach** the science, practice, and business of aviation and aerospace
* **To prepare** students for productive careers and leadership roles in business, government agencies, and commercial organizations
* **To groom** students to become internationally accepted professionals in the global aviation industry
* **To liaise and coordinate** with the industry regularly to ensure industry needs sync with teachings, students get internships, graduating students get employment, and meaningful R&D is carried out<ref>[1]</ref>
{{
| name = Aviation Institute of Management
| short_description = Private aviation education institution in Karachi, Pakistan
| image =
| caption =
| established = 2016
| type = Private
| CEO = Dr. Wali Mughni, PhD, FRAeS, SBt
| location = Karachi, Sindh, Pakistan
| address = CILT House, Palace Road, Gulistan-e-Jauhar, Karachi
| website = [https://aim.edu.pk aim.edu.pk]
| registered = Government of Sindh
}}
== References ==
<references>
<ref name="1">[https://aim.edu.pk Aviation Institute of Management]. Retrieved June 20, 2026.</ref>
<ref name="2">[https://aim.edu.pk/faculty/ Organization & its Founding Members]. Aviation Institute of Management. Retrieved June 20, 2026.</ref>
<ref name="3">[https://www.youtube.com/watch?v=LxPqcaTZHWk Aviation Awareness Exhibition 2026]. YouTube. January 24, 2026. Retrieved June 20, 2026.</ref>
<ref name="4">[https://aim.edu.pk/contact/ Contact]. Aviation Institute of Management. Retrieved June 20, 2026.</ref>
<ref name="5">[https://asia.erau.edu/about-asia/partnerships Embry-Riddle Educational Partner - AIM]. Embry-Riddle Aeronautical University. Retrieved June 20, 2026.</ref>
</references>
9yl614ky2g6zsuflq1077z16de1opu9
2816322
2816321
2026-06-20T04:09:24Z
Farhan Kamal Azeemi 133
3095208
2816322
wikitext
text/x-wiki
{{Infobox university
| name = Aviation Institute of Management
| short_description = Private aviation education institution in Karachi, Pakistan
| image =
| caption =
| established = 2016
| type = Private
| CEO = '''Dr. Wali Mughni, PhD, FRAeS, SBt'''
| location = Karachi, Sindh, Pakistan
| address = CILT House, Palace Road, Gulistan-e-Jauhar, Karachi
| website = <nowiki>[</nowiki>https://aim.edu.pk aim.edu.pk<nowiki>]</nowiki>
| registered = Government of Sindh
}}
'''Aviation Institute of Management''' ('''AIM'''') is a private aviation education institution established in 2016 in Karachi, Sindh, Pakistan. Headed by '''Dr. Wali Mughni, PhD, FRAeS, SBt''' as Chief Executive Officer and Chairman, AIM is Pakistan's only institute representing '''Embry-Riddle Aeronautical University''' (ERAU), the world's largest and most reputable aviation and aerospace university [1].
== History ==
In 2016, Aviation Institute of Management was established as a partnership concern primarily by '''Dr. Wali Mughni''' (CEO), '''Prof. Wali Durrani''' (late), and '''Capt. Hadi Rizvi'''. Later, other members joined, and the organization was converted to a private limited concern in April 2018 [2].
AIM is registered with the '''Government of Sindh''' [1].
== Leadership ==
=== Dr. Wali Mughni (CEO and Chairman) ===
'''Dr. Wali Mughni, PhD, FRAeS, SBt''' is CEO and Chairman of AIM, a retired fighter pilot, and recipient of the '''Sher Afghan''' (Top Gun) title and '''Sitara-e-Basalat'''. With over 40 years of experience in aviation and education, he leads AIM in shaping the next generation of aviation professionals. He exclusively represents his alma mater '''Embry-Riddle Aeronautical University''' (USA) in Pakistan. He was a consultant to the Aviation Ministry, Government of Pakistan. Dr. Mughni was the lead architect and writer who authored '''Pakistan's National Aviation Policy – 2015'''. He worked for '''NASA''' as a researcher, '''IBM''' as an IT business consultant, and '''Pakistan Air Force''' as a fighter pilot. He was the Top Gun (Sher Afghan) award winner of Pakistan Air Force and was also awarded the country's highest peacetime operational award, Sitara-e-Basalat [2].
=== Founding Members ===
The core founding team includes:
* '''Prof. Wali Durrani (Late)''' - One of Pakistan's most experienced, competent, and qualified educationists. He held the appointment of Registrar, Karachi University, and CEO/Rector/VC of universities including Hamdard, KASBIT, IoBM. He was a consultant for Pakistan Civil Aviation Authority's schools and colleges, a "Management & Financial Advisor" to the Sindh High Court, and an "Organizational Reform Expert" and "Budget & Planning Expert" with Federal Ministry of Law for "Access to Justice Program in Pakistan" [2].
* '''Capt. Hadi Rizvi''' - An operational pilot with over 50 years of operational and instructional flying experience in PAF, PIA, and other training organizations. He holds MA English and Law degrees, is a world-renowned English poet and prolific writer, and serves as Aviation Management faculty for graduate and undergraduate programs [2].
* '''Mr. Azeez Siddiqui''' - A veteran aviation professional with over 43 years in PIA and Saudi Airlines, holding positions from planning to operations to strategy development. He is also a faculty member at AIM [2].
* '''Dr. Nazir Ahmed Vaid''' - A serial social entrepreneur assisting AIM in establishing and growing the business and promoting varied educational activities [2].
* '''Mr. Ahsan Qureshi''' - A qualified educationist with multifaceted experience in projects and business development, the youngest core team member and promising administrator of the institution [2].
Other core faculty members include Capt. Afsar Malik, Engr. Zafarullah Khan, Engr. Zia ul Haq, Col. Navaid Ahsan, Capt. Amin Desai, Dr. Bilal Siddiqui, Dr. Noor Memon, Air Cdre (R) Tariq Ashraf, Brig (R) Farooq Shaukat, Ms. Sonia Kazim, Ms. Samreen Fahad, and Mr. Taha Khan [2].
== Academic Programs ==
AIM offers diverse aviation education programs:
=== Diploma Programs ===
* '''Diploma in Aviation Business Administration'''
* '''Diploma in Business Administration'''
* '''Dual Diploma''' (Diploma in Business Administration + Diploma in Aviation Business Administration)
=== Certificate Programs ===
* Multiple aviation and management certificates conducted by AIM
* '''Graduate Certificate in Aviation (Asia-focus)''' by Embry-Riddle Aeronautical University - Aviation Management program focusing on aviation industry in Asia, conducted by highly qualified ERAU faculty from Singapore/USA
* Various aviation management short certificate programs facilitated by AIM
* '''Professional Certificate in Aviation Administration'''
* '''Professional Certificate in Aviation Management'''
* '''Certificate in Aviation Business Administration (CABA)'''
=== Degree Programs ===
* '''BS/MBA (Aviation)'''
* '''BS/MS (Aeronautics)'''
* '''BS/MS Aerospace Engineering'''
* All degree programs offered by Embry-Riddle Aeronautical University (online programs)
* '''Bachelor's Degrees''' (online by ERAU, USA)
* '''Master's Degrees''' (online by ERAU, USA)
=== Workshops and Seminars ===
Planned workshops include:
* Crew Resource Management
* Human Factors
* Threat & Error Management
* Emotional Intelligence
* Safety Management Systems
* Aviation Security Management
=== THE AVIATORS ===
'''THE AVIATORS''' is a project of AIM designed to induct secondary-level students after a thorough psychometric test for career development in the Aviation industry. It offers preparatory classes for careers in aviation, leading to BS (Aviation Management) & Diploma in Aviation Business Administration, with summer camps, short courses, diploma classes, and online classes available for international students [1].
=== Aviationizing Club ===
AIM operates '''The Aviationizing Club''', established to promote aviation through learning and fun activities [1].
== Special Features ==
=== Industry-Academia Bridge ===
AIM is linked with the aviation industry and aims to bridge the widening gap between the aviation industry and academia. The institute liaises and coordinates with the industry regularly to ensure:
* Industry needs are synchronized with current teachings and curricula
* Students get opportunities for appropriate internships
* Graduating students get fair chances of gainful employment in the industry
* Meaningful Research & Development is carried out for the industry [1].
=== Scholarships ===
AIM offers scholarships to deserving students in the form of '''Qard-e-Hasana'''. When students graduate and get gainfully employed, they commit to pay back the dues to the institute in an affordable manner [1].
=== Student Support ===
AIM ensures that no student is left behind and offers zero semester classes at affordable rates to candidates who need help to improve. The prerequisite is simply the displayable passion to learn [1].
AIM specializes in Aviation and Management Sciences and prides itself for having the services of distinguished aviation experts and professionals of the country in its management team and faculty [1].
== Statistics ==
{| class="wikitable"
|+ '''AIM Statistics'''
|-
| '''Metric'''
| '''Number'''
|-
| Faculty Members
| 25
|-
| Programs
| 24
|-
| Trained Professionals
| 172
|-
| International Partners
| 15
|}
== Mission ==
"The organization's mission is to train, educate and groom our youth so as to make them acceptable aviation professionals in the global aviation industry. AIM aims to be a regional leader in aviation and aerospace education, training and Human Resource Development. Our mission is to teach the science, practice and business of aviation and aerospace, preparing students for productive careers and leadership roles in business, government agencies and the military. AIM shall build and retain its reputation as a regional leader in aviation and aerospace education from secondary school level to higher education." [1].
== Core Values ==
The core values govern AIM's academic and co-curricular programs and its operating ethos. These values ground and enliven the institute's identity, heritage, and commitment to knowledge for personal enhancement, progress of society, the nation, and the global community [1].
* '''Respect''' - Understanding and valuing diverse perspectives of every person; every individual, big or small in status, deserves respect
* '''Excellence''' - Striving for excellence in everything using intellectual, social, physical, spiritual, and ethical competencies
* '''Compassion''' - Standing with and embracing others in suffering or difficult times to experience greater compassion from Almighty Allah
* '''Service''' - Using gifts and abilities to advance community well-being
* '''Hospitality''' - Working with graciousness, welcoming new ideas and people of all backgrounds and beliefs
* '''Integrity''' - Realizing the greater good in actions and programs, looking at work holistically as united with others across societies
* '''Diversity''' - Fostering an open, welcoming climate for diverse people, ideas, and perspectives; promoting constructive discourse engaging faculty, staff, and students [1].
=== Learning for Here and Hereafter ===
'''Learning for Life and beyond''' encourages pursuing knowledge and truth throughout lives in ways that improve communities and strengthen understanding of each other. AIM has a commitment to education as a means of facilitating people to live meaningful and decent living. The institute enrolls students of all ages, color, creed, religion, ethnicity, and treats all without bias or discrimination [1].
== Aviation Awareness Exhibition 2026 ==
On January 25, 2026, AIM hosted its '''Aviation Awareness Exhibition''' at Happy Palace, Karachi. The event was covered by '''Geo News''' and brought together experts, innovators, and industry leaders to shape a brighter tomorrow for Pakistan's aviation sector [3].
== Location ==
AIM is located at '''CILT House, Palace Road, Gulistan-e-Jauhar, Karachi, Sindh, Pakistan'''. The institute operates Monday–Saturday, 9:00 AM – 5:00 PM [4].
== Contact ==
* Phone: +92 321 897 9014, +92 333 086 6166
* Website: <nowiki>[</nowiki>https://aim.edu.pk aim.edu.pk<nowiki>]</nowiki>
== Goals & Objectives ==
AIM offers the best possible learning environment, a conducive atmosphere, and an opportunity for all students to get educated, trained, and groomed:
* '''To teach''' the science, practice, and business of aviation and aerospace
* '''To prepare''' students for productive careers and leadership roles in business, government agencies, and commercial organizations
* '''To groom''' students to become internationally accepted professionals in the global aviation industry
* '''To liaise and coordinate''' with the industry regularly to ensure industry needs sync with teachings, students get internships, graduating students get employment, and meaningful R&D is carried out [1].
== References ==
[1] Aviation Institute of Management. https://aim.edu.pk. Retrieved June 20, 2026.
[2] Organization & its Founding Members. Aviation Institute of Management. https://aim.edu.pk/faculty/. Retrieved June 20, 2026.
[3] Aviation Awareness Exhibition 2026. YouTube. January 24, 2026. https://www.youtube.com/watch?v=LxPqcaTZHWk. Retrieved June 20, 2026.
[4] Contact. Aviation Institute of Management. https://aim.edu.pk/contact/. Retrieved June 20, 2026.
[5] Embry-Riddle Educational Partner - AIM. Embry-Riddle Aeronautical University. https://asia.erau.edu/about-asia/partnerships. Retrieved June 20, 2026.
sw4lc0xcer4cvmbki0wsrkio2w3ya1w
Meher Baba/Teachings and methodology
0
47483
2816325
1422972
2026-06-20T11:52:41Z
~2026-35893-18
3095850
2816325
wikitext
text/x-wiki
[[File:Baba dictating.jpg|thumb|240px|Meher Baba conveying points using his alphabet board that are later written up by a disciple. Dr. Abdulla Ghani Munsiff right.]]
:''For a list of External Resources see [[Meher Baba]].''
== No new religion ==
Meher Baba said repeatedly that he did not wish to establish a new cult or religion, but rather to revitalize the great religions of the world.
* ''"I have not come to establish anything; I have come to put life into the old."'' [http://www.ambppct.org/meherbaba/the-final-declaration.php]
* ''"My object in coming to the West is not with the intention of establishing new creeds or spiritual societies and organizations. I see the structure of all the great religions of the world toppling... I intend to bring together all religions and cults like beads on one string and revitalize them for individual and collective needs."'' (Meher Baba, Paramount New Reel, London, 1932) [http://www.youtube.com/watch?v=rt4xVI2odKw]
* ''"I have come not to establish any cult, society or organization - nor to establish a new religion. The Religion I shall give teaches the knowledge of the One behind the many. The Book which I shall make people read is the book of the heart, which holds the key to the mystery of life."'' [http://www.avatarmeherbaba.org/erics/prusa.html]
Although Meher Baba did not establish a new religion, he does have a small number of devotees. An estimation is that there are about 100,000 in India, and consirderably fewer in the rest of the world. In spite of Meher Baba's small movement and pilgrimages to his various centers around the world, followers of Meher Baba take conscious pains not to organize into a formal religion with membership rolls, ritual requirements, priesthood, etc. There is no initiation or central authority or hierarchy. The [[w:Avatar Meher Baba Trust|Avatar Meher Baba Perpetual Public Charitable Trust]] in Ahmednagar, India was established by Meher Baba to administrate his estate in [[w:Meherabad|Meherabad]] and [[w:Meherazad|Meherazad]] India. In addition The Trust performs other duties ascribed to it by Meher Baba in his Trust Deed of providing pilgrim facilities near his tomb, administrating several chartered charitable organizations, protecting copyrights of Baba's works, and spreading Meher Baba's name and written messages.
== Emphasis on a feeling of Oneness ==
Meher Baba taught that the cause of current human difficulties stems from artificial man-made divisions and an intense feeling of separateness. We find many examples of such divisiveness in our modern world, including extreme religious and sectarian conflicts, exaggerated nationalism and race prejudice, castes, political disharmony, the divide between religion and science, and the pulling apart of spiritual and secular life. Baba addressed this problem in three main ways. First he upheld those metaphysical views of Vedanta, Sufism, and Western Mysticism which teach that divisions are an illusion caused by ignorance of the true nature of reality. His major book, ''[[w:God Speaks|God Speaks: the Theme and Purpose of Creation]]'', as well as several of his smaller books of discourses and messages, ''The Everything and the Nothing'', ''Life At Its Best'', and ''Beams on the Spiritual Panorama'', address this subject almost exclusively. The following are some exemplary quotes by Meher Baba on the topic of Oneness.
* ''"I tell you all, with my Divine Authority, that you and I are not WE, but ONE."'' [http://www.ambppct.org/meherbaba/meher-babas-call.php]
* ''"The time has come for the preordained destruction of multiple separateness which keeps man from experiencing the feeling of unity and brotherhood."'' (Meher Baba, ''Final Declaration'', September 30, 1954)
* ''"God is everywhere and does everything. God is within us and knows everything. God is without us and sees everything. God is beyond us and IS everything. God alone IS."'' [http://www.ambppct.org/meherbaba/god-is.php]
*'' "It is my God-ordained work to awaken humanity to the inviolable unity and inalienable divinity of all life. Know that you are in essence eternal, and heirs to infinite knowledge, bliss and power. In order to enjoy your unlimited state all that is necessary is to shed your ignorance which makes you feel that you are separate from the rest of life. The separative ego or "I" can disappear only through divine love, which will be my gift to mankind."'' [http://www.ambppct.org/meherbaba/unity-of-life.php]
* ''"When longing is most intense separation is complete, and the purpose of separation, which was that Love might experience itself as Lover and Beloved, is fulfilled; and union follows. And when union is attained, the lover knows that he himself was all along the Beloved whom he loved and desired union with; and that all the impossible situations that he overcame were obstacles which he himself had placed in the path to himself. To attain union is so impossibly difficult because it is impossible to become what you already are! Union is nothing other than knowledge of oneself as the Only One."'' [http://www.ambppct.org/meherbaba/god-is-love.php]
The second way that Baba approached the feeling of division and disharmony was to make a great effort to syncretize three principle branches of mysticism: Vedanta, Sufism, and Mysticism.
#[[w:Vedanta|Vedanta]] is the main mystical branch of Hinduism. Meher Baba upheld the school of Vedanta known as [[w:Advaita Vedanta|Advaita]]. This view holds that the underlying absolute reality is in fact One and indivisible, while apparent diversity is an effect of ignorance and a total illusion. The purpose of life, ultimately, is to experience reality as it really is by shedding illusions over many lives. Advaita Vedanta was first perfected by the Indian medieval philosopher [[w:Adi Shankara|Adi Shankara]].
#[[Sufism and Islamic Mysticism|Sufism]] is the mystical branch of Islam. Baba upholds the school of Sufism known as ''Wahdat-ul-Wujood'' (Arabic: Literally, unity of existence) formulated by the Arab Muslim mystic and philosopher [[w:Ibn Arabi|Ibn Arabi]].
#[[w:Mysticism|Mysticism]] includes those diverse branches of western thought expressed most often in the poetic mystical works of philosophers and poets like [[w:Baruch Spinoza|Spinoza]], [[w:Ralph Waldo Emerson|Emerson]], [[w:Johann Wolfgang von Goethe|Goethe]], [[w:Novalis|Novalis]] and others who upheld views of Metaphysical Unity.
The third way Baba encouraged unity was to integrate spiritual life into ordinary life, which he saw as artificially divided.
In his book ''[[w:Discourses (Meher Baba)|Discourses]]'', and in other works, Meher Baba takes pains to mend the divide between so-called spiritual life and ordinary life. Meher Baba emphasized that, in order to be meaningful, spiritual life must be practical and applied in daily living. He discouraged monastic isolation and ascetic practices for most people.
* ''"For the spiritual aspirant, however, it is not enough to exercise merely intellectual discrimination between the false and the true. Though intellectual discrimination is undoubtedly the basis for all further preparation, it yields its fruit only when newly perceived values are brought into relation with practical life."'' (Discourses, 6th ed. Vol. 3, p. 115, Meher Baba, 1967)
* ''"So the purely intellectual search for God or the hidden spiritual reality, has its reverberations in the practical life of a man. His life now becomes a real experiment with perceived spiritual values."'' (Discourses, 6th ed. Vol. 2, p. 16, Meher Baba, 1967)
It is important not to misinterpret Baba's concern that "newly perceived values are brought into relation with practical life" as meaning he endorses a blurring of the lines between church and state. Meher Baba was opposed to the mixing of religion and politics. Rather, Meher Baba was emphasizing that the spiritual values of the ''individual'' be expressed in daily life, such as in treating others well, being honest, etc.
== Meher Baba's definite claim to be the Avatar ==
Meher Baba was not hesitant to say what he took himself to be. He said he was the [[w:Avatar|Avatar]], the same soul that takes birth again and again thorughout the ages every 700-1400 years. He said he was [[w: Zoroaster |Zoroaster]], [[w:Rama|Rama]], [[w:Krishna|Krishna]], [[w:Gautama Buddha|Buddha]], [[w:Jesus|Jesus]], and [[w: Muhammad|Muhammad]] and that he has now appeared on Earth as Meher Baba.
* ''"Age after age, when the wick of Righteousness burns low, the Avatar comes yet once again to rekindle the torch of Love and Truth. Age after age, amidst the clamor of disruptions, wars, fear and chaos, rings the Avatar's call: 'Come all unto me.' Although, because of the veil of illusion, this Call of the Ancient One may appear as a voice in the wilderness, its echo and re-echo nevertheless pervades through time and space to rouse at first a few, and eventually millions, from their deep slumber of ignorance. And in the midst of illusion, as the Voice behind all voices, it awakens humanity to bear witness to the Manifestation of God amidst mankind. The time is come. I repeat the Call, and bid all come unto me."'' [http://www.ambppct.org/meherbaba/meher-babas-call.php]
* ''"All this world confusion and chaos was inevitable and no one is to blame. What had to happen has happened; and what has to happen will happen. There was and is no way out except through my coming in your midst. I had to come, and I have come. I am the Ancient One."'' [http://www.ambppct.org/meherbaba/universal-message.php]
* ''"Irrespective of doubts and convictions, and for the Infinite Love I bear for one and all, I continue to come as the Avatar, to be judged time and again by humanity in its ignorance, in order to help man distinguish the Real from the false. Invariably muffled in the cloak of the infinitely true humility of the Ancient One, the Divine Call is at first little heeded, until, in its infinite strength, it spreads in volume to reverberate and keep on reverberating in countless hearts as the Voice of Reality. Strength begets humility, whereas modesty bespeaks weakness. Only he who is truly great can be really humble. When, in the firm knowledge of it, a man admits his true greatness, it is in itself an expression of humility. He accepts his greatness as most natural and is expressing merely what he is, just as a man would not hesitate to admit to himself and others the fact of his being man. For a truly great man, who knows himself to be truly great, to deny his greatness would be to belittle what he indubitably is. For whereas modesty is the basis of guise, true greatness is free from camouflage."'' [http://www.ambppct.org/meherbaba/meher-babas-call.php]
* ''"Thus it is that God as man, proclaiming Himself as the Avatar, suffers Himself to be persecuted and tortured, to be humiliated and condemned by humanity for whose sake His Infinite Love has made him stoop so low, in order that humanity, by its very act of condemning God’s manifestation in the form of Avatar should, however, indirectly, assert the existence of God in His Infinite Eternal state."'' [http://www.ambppct.org/meherbaba/the-highest-of-the-high.php]
== Meher Baba's Metaphysics ==
Meher Baba unequivocably upheld the idea of Unity of Being. Everything was, is, and remains, in the Oversoul. Baba states that Evolution is the soul's journey through ignorance to inevitably find its real nature and identity with God. To illustrate this, here is an excerpt from his book ''God Speaks'' in which he is describing the state of consciousness a soul experiences while identifying itself as a plant in the course of its evolution.
* ''"When the consciousness of the soul associates now with the most-first species of vegetable-form, the soul, thus conscious, tends to identify itself with that form and actually finds itself as that species of vegetable-form, quite oblivious of the reality that it (soul) is infinite, eternal and without form—eternally in the Over-Soul (Paramatma)."'' (''God Speaks: The Theme and Purpose of Creation'', by Meher Baba, 2nd ed. p. 17)
To summarize Meher Baba's theme: the beginning of creation is caused by God's original urge to know himself, expressed in the question "Who am I?" This results in an imagined journey which culminates when the soul, experiencing itself as a fully evolved human being, and after innumerable lifetimes of searching, comes to know and actually experiences its true answer, "I am God." This, Baba says, is called God Realization and to have this experience is the ultimate destiny of all individual souls and the true purpose of creation.
For a more in-depth review of Meher Baba's metaphysics see the Wikipedia article on Meher Baba's main book ''[[w:God Speaks|God Speaks]]''.
== Further Reading ==
{{wikipedia|Meher Baba}}
For a list of external resources see [[Meher Baba]].
[[Category: Meher Baba Studies]]
eolvfyjdf57fc98m4eubt5634imv8me
Computer Skills/Fundamentals/Typing
0
60198
2816291
2808933
2026-06-19T13:02:43Z
Abidkhanyusafzai
3095603
/* Multimedia */ increased the source of learning
2816291
wikitext
text/x-wiki
{{:{{BASEPAGENAME}}/Sidebar}}
'''Typing''' is the process of entering or inputting text by pressing keys on a typewriter, computer keyboard, mobile phone, or calculator.<ref>[[Wikipedia: Typing]]</ref>
Learners should practice typing for fifteen minutes each day until their typing speed is at least 30 words per minute.
== Multimedia ==
* [https://www.typing.com/student/lessons Typing.com: Learn to Type]
* [https://monkeytype.com/ Monkeytype]
* [https://typingbattles.com/ Typingbattles.com: Type Faster Battle Harder]
== Activities ==
* Complete the [https://www.typing.com/student/lessons Typing.com lessons.]
* Use [https://monkeytype.com/ Monkeytype.com] , and practice typing daily until you can reach 30 words per minute consistently.
* Use [https://typingbattles.com/ TypingBattles.com] for pressure typing and different type of tests daily.
== See Also ==
* [[Elementary Typing]]
* [[Introduction_to_Computers/Input_Devices |Input Devices]]
* [[Wikipedia: Typing]]
== References ==
{{reflist}}
{{subpage navbar}}
{{CourseCat}}
[[Category:Computer Skills]]
[[Category:Typing]]
[[Category:Completed resources]]
3t5n0tdecs9whjxwayxtqqyouvy8hy0
2816292
2816291
2026-06-19T13:13:27Z
MathXplore
2888076
Reverted edit by [[Special:Contributions/Abidkhanyusafzai|Abidkhanyusafzai]] ([[User_talk:Abidkhanyusafzai|talk]]) to last version by [[User:SunKissedMocha|SunKissedMocha]] using [[Wikiversity:Rollback|rollback]]
2808933
wikitext
text/x-wiki
{{:{{BASEPAGENAME}}/Sidebar}}
'''Typing''' is the process of entering or inputting text by pressing keys on a typewriter, computer keyboard, mobile phone, or calculator.<ref>[[Wikipedia: Typing]]</ref>
Learners should practice typing for fifteen minutes each day until their typing speed is at least 30 words per minute.
== Multimedia ==
* [https://www.typing.com/student/lessons Typing.com: Learn to Type]
* [https://monkeytype.com/ Monkeytype]
== Activities ==
* Complete the [https://www.typing.com/student/lessons Typing.com lessons.]
* Use [https://monkeytype.com/ Monkeytype.com] , and practice typing daily until you can reach 30 words per minute consistently.
== See Also ==
* [[Elementary Typing]]
* [[Introduction_to_Computers/Input_Devices |Input Devices]]
* [[Wikipedia: Typing]]
== References ==
{{reflist}}
{{subpage navbar}}
{{CourseCat}}
[[Category:Computer Skills]]
[[Category:Typing]]
[[Category:Completed resources]]
rmlo6eamspueufw9d1hcmsogmo5uq5p
Modular arithmetic
0
127829
2816294
2708623
2026-06-19T13:26:25Z
~2026-35635-36
3095607
/* Transitivity */
2816294
wikitext
text/x-wiki
Modular arithmetic is a type of arithmetic on finite subsets of the natural numbers
==Definition==
For <math>n \in \mathbb{Z}</math> then
:<math>a=b\mod{n}</math> iff <math>n|(a-b)</math>
This is read as "a is congruent modulo n to b".
===Examples===
If <math>n=6</math> then
:<math>13=1\mod{6}</math>
:<math>10=4\mod{6}</math>
:<math>1=13\mod{6}</math>
If <math>n=13</math> then
:<math>26=0\mod{13}</math>
:<math>42=3\mod{13}</math>
==Calculation==
An easy way to calculate in mod{n} is <math>a=b\mod{n} \iff </math> they have the same remainder when divided by <math>n</math>.
==Equivalence==
Congruence modulo n is an equivalence relation.
===Reflexivity===
Let <math>n,a \in \mathbb{Z}</math>.
Then <math>(a-a)=0</math> and <math> n|0</math> so <math> n|(a-a)</math>.
Thus <math> a=a\mod{n}</math>.
===Symmetry===
Let<math>n,x,y \in \mathbb{Z}</math> such that <math> x=y\mod{n}</math>.
Then <math>n|(x-y)</math>.
Since <math>(x-y)=(-1)*(y-x), n|(y-x)</math>.
Thus <math>y=x\mod{n}</math>.
===Transitivity===
Let<math>n,x,y,z \in \mathbb{Z}</math> such that<math> x=y\mod{n} \land y=z\mod{n}</math>.
Then <math>n|(x-y) \land n|(y-z)</math>.
Then <math>n|((x-y)+(y-z)</math>.
Thus <math>n|(x-z)</math> and <math>x=z\mod{n}</math>.
hlqq3qyejlzs307wu1m317erqdboc68
Understanding Arithmetic Circuits
0
139384
2816298
2816214
2026-06-19T14:01:09Z
Young1lim
21186
/* Adder */
2816298
wikitext
text/x-wiki
== Adder ==
* Binary Adder Architecture Exploration ( [[Media:Adder.20131113.pdf|pdf]] )
{| class="wikitable"
|-
! Adder type !! Overview !! Analysis !! VHDL Level Design !! CMOS Level Design
|-
| '''1. Ripple Carry Adder'''
|| [[Media:VLSI.Arith.1A.RCA.20250522.pdf|A]]||
|| [[Media:Adder.rca.20140313.pdf|pdf]]
|| [[Media:VLSI.Arith.1D.RCA.CMOS.20211108.pdf|pdf]]
|-
| '''2. Carry Lookahead Adder'''
|| [[Media:VLSI.Arith.2A.CLA.20260619.pdf|A]], [[Media:VLSI.Arith.2B.CLA.20260619.pdf|B]] ||
|| [[Media:Adder.cla.20140313.pdf|pdf]]||
|-
| '''3. Carry Save Adder'''
|| [[Media:VLSI.Arith.1.A.CSave.20151209.pdf|A]]||
|| ||
|-
|| '''4. Carry Select Adder'''
|| [[Media:VLSI.Arith.1.A.CSelA.20191002.pdf|A]]||
|| ||
|-
|| '''5. Carry Skip Adder'''
|| [[Media:VLSI.Arith.5A.CSkip.20250405.pdf|A]]||
||
|| [[Media:VLSI.Arith.5D.CSkip.CMOS.20211108.pdf|pdf]]
|-
|| '''6. Carry Chain Adder'''
|| [[Media:VLSI.Arith.6A.CCA.20211109.pdf|A]]||
|| [[Media:VLSI.Arith.6C.CCA.VHDL.20211109.pdf|pdf]], [[Media:Adder.cca.20140313.pdf|pdf]]
|| [[Media:VLSI.Arith.6D.CCA.CMOS.20211109.pdf|pdf]]
|-
|| '''7. Kogge-Stone Adder'''
|| [[Media:VLSI.Arith.1.A.KSA.20140315.pdf|A]]||
|| [[Media:Adder.ksa.20140409.pdf|pdf]]||
|-
|| '''8. Prefix Adder'''
|| [[Media:VLSI.Arith.1.A.PFA.20140314.pdf|A]]||
|| ||
|-
|| '''9.1 Variable Block Adder'''
|| [[Media:VLSI.Arith.1A.VBA.20221110.pdf|A]], [[Media:VLSI.Arith.1B.VBA.20230911.pdf|B]], [[Media:VLSI.Arith.1C.VBA.20240622.pdf|C]], [[Media:VLSI.Arith.1C.VBA.20250218.pdf|D]]||
|| ||
|-
|| '''9.2 Multi-Level Variable Block Adder'''
|| [[Media:VLSI.Arith.1.A.VBA-Multi.20221031.pdf|A]]||
|| ||
|}
</br>
=== Adder Architectures Suitable for FPGA ===
* FPGA Carry-Chain Adder ([[Media:VLSI.Arith.1.A.FPGA-CCA.20210421.pdf|pdf]])
* FPGA Carry Select Adder ([[Media:VLSI.Arith.1.B.FPGA-CarrySelect.20210522.pdf|pdf]])
* FPGA Variable Block Adder ([[Media:VLSI.Arith.1.C.FPGA-VariableBlock.20220125.pdf|pdf]])
* FPGA Carry Lookahead Adder ([[Media:VLSI.Arith.1.D.FPGA-CLookahead.20210304.pdf|pdf]])
* Carry-Skip Adder
</br>
== Barrel Shifter ==
* Barrel Shifter Architecture Exploration ([[Media:Bshift.20131105.pdf|bshfit.vhdl]], [[Media:Bshift.makefile.20131109.pdf|bshfit.makefile]])
</br>
'''Mux Based Barrel Shifter'''
* Analysis ([[Media:Arith.BShfiter.20151207.pdf|pdf]])
* Implementation
</br>
== Multiplier ==
=== Array Multipliers ===
* Analysis ([[Media:VLSI.Arith.1.A.Mult.20151209.pdf|pdf]])
</br>
=== Tree Mulltipliers ===
* Lattice Multiplication ([[Media:VLSI.Arith.LatticeMult.20170204.pdf|pdf]])
* Wallace Tree ([[Media:VLSI.Arith.WallaceTree.20170204.pdf|pdf]])
* Dadda Tree ([[Media:VLSI.Arith.DaddaTree.20170701.pdf|pdf]])
</br>
=== Booth Multipliers ===
* [[Media:RNS4.BoothEncode.20161005.pdf|Booth Encoding Note]]
* Booth Multiplier Note ([[Media:BoothMult.20160929.pdf|H1.pdf]])
</br>
== Divider ==
* Binary Divider ([[Media:VLSI.Arith.1.A.Divider.20131217.pdf|pdf]])</br>
</br>
</br>
go to [ [[Electrical_%26_Computer_Engineering_Studies]] ]
[[Category:Digital Circuit Design]]
[[Category:FPGA]]
n2bbqxq5ihrbx5k55bchak9wofngvpm
Complex analysis in plain view
0
171005
2816303
2816221
2026-06-19T14:12:06Z
Young1lim
21186
/* Geometric Series Examples */
2816303
wikitext
text/x-wiki
Many of the functions that arise naturally in mathematics and real world applications can be extended to and regarded as complex functions, meaning the input, as well as the output, can be complex numbers <math>x+iy</math>, where <math>i=\sqrt{-1}</math>, in such a way that it is a more natural object to study. '''Complex analysis''', which used to be known as '''function theory''' or '''theory of functions of a single complex variable''', is a sub-field of analysis that studies such functions (more specifically, '''holomorphic''' functions) on the complex plane, or part (domain) or extension (Riemann surface) thereof. It notably has great importance in number theory, e.g. the [[Riemann zeta function]] (for the distribution of primes) and other <math>L</math>-functions, modular forms, elliptic functions, etc. <blockquote>The shortest path between two truths in the real domain passes through the complex domain. — [[wikipedia:Jacques_Hadamard|Jacques Hadamard]]</blockquote>In a certain sense, the essence of complex functions is captured by the principle of [[analytic continuation]].{{mathematics}}
==''' Complex Functions '''==
* Complex Functions ([[Media:CAnal.1.A.CFunction.20140222.Basic.pdf|1.A.pdf]], [[Media:CAnal.1.B.CFunction.20140111.Octave.pdf|1.B.pdf]], [[Media:CAnal.1.C.CFunction.20140111.Extend.pdf|1.C.pdf]])
* Complex Exponential and Logarithm ([[Media:CAnal.5.A.CLog.20131017.pdf|5.A.pdf]], [[Media:CAnal.5.A.Octave.pdf|5.B.pdf]])
* Complex Trigonometric and Hyperbolic ([[Media:CAnal.7.A.CTrigHyper..pdf|7.A.pdf]], [[Media:CAnal.7.A.Octave..pdf|7.B.pdf]])
'''Complex Function Note'''
: 1. Exp and Log Function Note ([[Media:ComplexExp.29160721.pdf|H1.pdf]])
: 2. Trig and TrigH Function Note ([[Media:CAnal.Trig-H.29160901.pdf|H1.pdf]])
: 3. Inverse Trig and TrigH Functions Note ([[Media:CAnal.Hyper.29160829.pdf|H1.pdf]])
==''' Complex Integrals '''==
* Complex Integrals ([[Media:CAnal.2.A.CIntegral.20140224.Basic.pdf|2.A.pdf]], [[Media:CAnal.2.B.CIntegral.20140117.Octave.pdf|2.B.pdf]], [[Media:CAnal.2.C.CIntegral.20140117.Extend.pdf|2.C.pdf]])
==''' Complex Series '''==
* Complex Series ([[Media:CPX.Series.20150226.2.Basic.pdf|3.A.pdf]], [[Media:CAnal.3.B.CSeries.20140121.Octave.pdf|3.B.pdf]], [[Media:CAnal.3.C.CSeries.20140303.Extend.pdf|3.C.pdf]])
==''' Residue Integrals '''==
* Residue Integrals ([[Media:CAnal.4.A.Residue.20140227.Basic.pdf|4.A.pdf]], [[Media:CAnal.4.B.pdf|4.B.pdf]], [[Media:CAnal.4.C.Residue.20140423.Extend.pdf|4.C.pdf]])
==='''Residue Integrals Note'''===
* Laurent Series with the Residue Theorem Note ([[Media:Laurent.1.Residue.20170713.pdf|H1.pdf]])
* Laurent Series with Applications Note ([[Media:Laurent.2.Applications.20170327.pdf|H1.pdf]])
* Laurent Series and the z-Transform Note ([[Media:Laurent.3.z-Trans.20170831.pdf|H1.pdf]])
* Laurent Series as a Geometric Series Note ([[Media:Laurent.4.GSeries.20170802.pdf|H1.pdf]])
=== Laurent Series and the z-Transform Example Note ===
* Overview ([[Media:Laurent.4.z-Example.20170926.pdf|H1.pdf]])
====Geometric Series Examples====
* Causality ([[Media:Laurent.5.Causality.1.A.20191026n.pdf|A.pdf]], [[Media:Laurent.5.Causality.1.B.20191026.pdf|B.pdf]])
* Time Shift ([[Media:Laurent.5.TimeShift.2.A.20191028.pdf|A.pdf]], [[Media:Laurent.5.TimeShift.2.B.20191029.pdf|B.pdf]])
* Reciprocity ([[Media:Laurent.5.Reciprocity.3A.20191030.pdf|A.pdf]], [[Media:Laurent.5.Reciprocity.3B.20191031.pdf|B.pdf]])
* Combinations ([[Media:Laurent.5.Combination.4A.20200702.pdf|A.pdf]], [[Media:Laurent.5.Combination.4B.20201002.pdf|B.pdf]])
* Properties ([[Media:Laurent.5.Property.5A.20220105.pdf|A.pdf]], [[Media:Laurent.5.Property.5B.20220126.pdf|B.pdf]])
* Permutations ([[Media:Laurent.6.Permutation.6A.20230711.pdf|A.pdf]], [[Media:Laurent.5.Permutation.6B.20251225.pdf|B.pdf]], [[Media:Laurent.5.Permutation.6C.20260619.pdf|C.pdf]], [[Media:Laurent.5.Permutation.6C.20240528.pdf|D.pdf]])
* Applications ([[Media:Laurent.5.Application.6B.20220723.pdf|A.pdf]])
* Double Pole Case
:- Examples ([[Media:Laurent.5.DPoleEx.7A.20220722.pdf|A.pdf]], [[Media:Laurent.5.DPoleEx.7B.20220720.pdf|B.pdf]])
:- Properties ([[Media:Laurent.5.DPoleProp.5A.20190226.pdf|A.pdf]], [[Media:Laurent.5.DPoleProp.5B.20190228.pdf|B.pdf]])
====The Case Examples====
* Example Overview : ([[Media:Laurent.4.Example.0.A.20171208.pdf|0A.pdf]], [[Media:Laurent.6.CaseExample.0.B.20180205.pdf|0B.pdf]])
* Example Case 1 : ([[Media:Laurent.4.Example.1.A.20171107.pdf|1A.pdf]], [[Media:Laurent.4.Example.1.B.20171227.pdf|1B.pdf]])
* Example Case 2 : ([[Media:Laurent.4.Example.2.A.20171107.pdf|2A.pdf]], [[Media:Laurent.4.Example.2.B.20171227.pdf|2B.pdf]])
* Example Case 3 : ([[Media:Laurent.4.Example.3.A.20171017.pdf|3A.pdf]], [[Media:Laurent.4.Example.3.B.20171226.pdf|3B.pdf]])
* Example Case 4 : ([[Media:Laurent.4.Example.4.A.20171017.pdf|4A.pdf]], [[Media:Laurent.4.Example.4.B.20171228.pdf|4B.pdf]])
* Example Summary : ([[Media:Laurent.4.Example.5.A.20171212.pdf|5A.pdf]], [[Media:Laurent.4.Example.5.B.20171230.pdf|5B.pdf]])
==''' Conformal Mapping '''==
* Conformal Mapping ([[Media:CAnal.6.A.Conformal.20131224.pdf|6.A.pdf]], [[Media:CAnal.6.A.Octave..pdf|6.B.pdf]])
go to [ [[Electrical_%26_Computer_Engineering_Studies]] ]
[[Category:Complex analysis]]
6ap69h9epnngf6cjv1ttdd0yjjolcsr
Research in programming Wikidata/Business enterprise
0
223822
2816317
2629121
2026-06-20T02:50:38Z
Sàádî
3095758
([[c:GR|GR]]) [[File:Главный офис Tele2 Россия (Москва).jpg]] → [[File:Moscow, Leningradskoye Highway 39A.jpg]] [[c:COM:FR#FR1|Criterion 1]] (original uploader’s request)
2816317
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This article is devoted to the study Wikidata objects "commercial organizations". With the help of SPARQL queries, computed on the objects of the type "commercial organizations" in the Wikidata, the following tasks have been solved: maked a list with organizations by branches distribution in the form of a bubble chart, counted the quantity of organizations by countries, drawn the graph of existing organizations and their subsidiaries. Conclusions were drawn regarding the completeness of the Wikidata on this topic, including a map of the organizations of the world.
== Instances of object "Business enterprise" ==
* Objects: [[d:Q4830453|business enterprise (Q4830453)]]
Using the following queary we can get list of all commercial organizations.
<syntaxhighlight lang="SPARQL">#added 2017-02
#List of `instances of` "business enterprise"
SELECT ?lang ?langLabel
WHERE
{
?lang wdt:P31 wd:Q4830453.
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" }
}
</syntaxhighlight>
[https://query.wikidata.org/#%23List%20of%20%60instances%20of%60%20%22business%20enterprise%22%20%0ASELECT%20%3Flang%20%3FlangLabel%0AWHERE%0A%7B%0A%20%20%20%20%3Flang%20wdt%3AP31%20wd%3AQ4830453.%0A%20%20%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%20%7D%0A%7D SPARQL-query], 109383 Results
<span style="color:green">👍</span>> The most complete and elaborated business enterprise on the Wikidata are: [[d:Q95|Google]], [[d:Q312|Apple]],
[[d:Q2283|Microsoft]]
<span style="color:red">👎</span>> Almost empty and uninformative business enterprise on the Wikidata are: [[d:Q40987|Pininfarina]], [[d:Q46065|ANHUI EXPRESSWAY COMPANY LIMITED]], [[d:Q45812|Futura et Marge]]
The defect of the resulting list is that objects turned out to be nameless on the Wikidata (No label defined). Let's try to get a list of organizations where "label" field will be non-empty.
<syntaxhighlight lang="SPARQL">#List of `instances of` "business enterprise" only with a label.
SELECT ?item ?item_label
WHERE
{
?item wdt:P31 wd:Q4830453
; rdfs:label ?item_label.
FILTER (LANG(?item_label) = "en").
}
</syntaxhighlight>
[https://query.wikidata.org/#SELECT%20%3Fitem%20%3Fitem_label%0AWHERE%0A%7B%0A%20%20%20%20%3Fitem%20wdt%3AP31%20wd%3AQ4830453%0A%20%20%20%20%3B%20rdfs%3Alabel%20%3Fitem_label%20.%20%0A%0A%20%20%20%20FILTER%20%28LANG%28%3Fitem_label%29%20%3D%20%22en%22%29%20.%20%0A%7D SPARQL-query], 74556 Results
== Distribution of organizations by industry ==
Each organization specializes some industry. In order to understand which industry, for example, is the most popular (that is, how many organizations work in this industry), we can build a diagram.
Type of result: bubble diagram.
Are used:
* object [[d:Q4830453|business enterprise (Q4830453)]] (business enterprise),
* property [[d:Property:P452|industry (P452)]] (industry).
<syntaxhighlight lang="SPARQL">
#enterprise industry ranking
#defaultView:BubbleChart
SELECT ?industry ?company (count(*) as ?count)
WHERE
{
?org wdt:P31 wd:Q4830453.
?org wdt:P452 ?industry.
OPTIONAL {
?industry rdfs:label ?company
filter (lang(?company) = "en")
}
}
GROUP BY ?industry ?company
ORDER BY DESC(?count) ASC(?company)
</syntaxhighlight>
[https://query.wikidata.org/#%23enterprise%20industry%20ranking%0A%23defaultView%3ABubbleChart%0ASELECT%20%3Findustry%20%3Fcompany%20%28count%28%2a%29%20as%20%3Fcount%29%0AWHERE%20%0A%7B%0A%20%20%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%0A%20%20%20%20%3Forg%20wdt%3AP452%20%3Findustry%20.%0A%20%20%20%20OPTIONAL%20%7B%0A%09%09%3Findustry%20rdfs%3Alabel%20%3Fcompany%0A%09%09filter%20%28lang%28%3Fcompany%29%20%3D%20%22en%22%29%0A%09%7D%0A%7D%0AGROUP%20BY%20%3Findustry%20%3Fcompany%0AORDER%20BY%20DESC%28%3Fcount%29%20ASC%28%3Fcompany%29%0A SPARQL query], 864 Results.
After analysis of this diagram (Fig. 1), we can conclude that the number of organizations involved in a particular industry. It is possible to build a table based on the data obtained (make a list of the 5 most popular industries):
<table border="1">
<caption>TOP5 most popular industries</caption>
<tr>
<th>Industry name</th>
<th>Quantity of organizations</th>
</tr>
<tr><td>automative industry</td><td>1149</td></tr>
<tr><td>retail</td><td>843</td></tr>
<tr><td>telecommunications</td><td>648</td></tr>
<tr><td>video game industry</td><td>633</td></tr>
<tr><td>manufacturing</td><td>506</td></tr>
</table>
[[File:Diagram of organizations of the world by industry.jpg|thumb|Fig. 1: Diagram of organizations of the world by industry|center|900px]]<br style="clear: both;">
Let's answer the question: What and how many industries exist in Russia?
<syntaxhighlight lang="SPARQL">
#enterprise industry ranking in Russia
#defaultView:BubbleChart
SELECT ?industry ?company (count(*) as ?count)
WHERE
{
?org wdt:P31 wd:Q4830453.
?org wdt:P452 ?industry.
?org wdt:P17 wd:Q159. #Russia country
OPTIONAL {
?industry rdfs:label ?company
filter (lang(?company) = "en")
}
}
GROUP BY ?industry ?company
ORDER BY DESC(?count) ASC(?company)
</syntaxhighlight>
[https://query.wikidata.org/#%23enterprise%20industry%20ranking%0A%23defaultView%3ABubbleChart%0ASELECT%20%3Findustry%20%3Fcompany%20%28count%28%2a%29%20as%20%3Fcount%29%20%0AWHERE%20%0A%7B%0A%20%20%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%0A%20%20%20%20%3Forg%20wdt%3AP452%20%3Findustry%20.%0A%20%20%20%20%3Forg%20wdt%3AP17%20wd%3AQ159.%20%23Russia%20country%0A%20%20%20%20OPTIONAL%20%7B%0A%09%09%3Findustry%20rdfs%3Alabel%20%3Fcompany%0A%09%09filter%20%28lang%28%3Fcompany%29%20%3D%20%22en%22%29%0A%09%7D%0A%7D%0AGROUP%20BY%20%3Findustry%20%3Fcompany%0AORDER%20BY%20DESC%28%3Fcount%29%20ASC%28%3Fcompany%29%0A SPARQL-query], 60 Results.
<table border="1">
<caption>TOP5 most popular organizations in Russia</caption>
<tr>
<th>Industry name</th>
<th>Quantity of organizations</th>
</tr>
<tr><td>retail</td><td>78</td></tr>
<tr><td>automative industry</td><td>13</td></tr>
<tr><td>arms industry</td><td>10</td></tr>
<tr><td>aerospace industry</td><td>9</td></tr>
<tr><td>video game industry</td><td>9</td></tr>
</table>
It can be concluded that such industry as retail in Russia dominates over the rest, and very seriously. If the quantity of organizations in this area reaches 78, then in the next industry (automotive industry), only 13 organizations work.
For comparison, we can build a list of existing industries of some other country (for example, Norway).
<syntaxhighlight lang="SPARQL">
#enterprise industry ranking in Norway
#defaultView:BubbleChart
SELECT ?industry ?company (count(*) as ?count)
WHERE
{
?org wdt:P31 wd:Q4830453.
?org wdt:P452 ?industry.
?org wdt:P17 wd:Q20. #Norway country
OPTIONAL {
?industry rdfs:label ?company
filter (lang(?company) = "en")
}
}
GROUP BY ?industry ?company
ORDER BY DESC(?count) ASC(?company)
</syntaxhighlight>
[https://query.wikidata.org/#%23enterprise%20industry%20ranking%20in%20Norway%0A%23defaultView%3ABubbleChart%0ASELECT%20%3Findustry%20%3Fcompany%20%28count%28%2a%29%20as%20%3Fcount%29%20%0AWHERE%20%0A%7B%0A%20%20%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%0A%20%20%20%20%3Forg%20wdt%3AP452%20%3Findustry%20.%0A%20%20%20%20%3Forg%20wdt%3AP17%20wd%3AQ20.%20%23Norway%20country%0A%20%20%20%20OPTIONAL%20%7B%0A%09%09%3Findustry%20rdfs%3Alabel%20%3Fcompany%0A%09%09filter%20%28lang%28%3Fcompany%29%20%3D%20%22en%22%29%0A%09%7D%0A%7D%0AGROUP%20BY%20%3Findustry%20%3Fcompany%0AORDER%20BY%20DESC%28%3Fcount%29%20ASC%28%3Fcompany%29%0A SPARQL-query], 41 Results.
The dominant industry here is [[d:Q187939|manufacturing (Q187939)]].
== Number of organizations by country ==
Next query displays number of commercial organizations in each country in the world.
Are used:
* object [[d:Q4830453|business enterprise (Q4830453)]] (business enterprise),
* property [[d:Property:P17|country (P17)]] (country).
<syntaxhighlight lang="SPARQL">
SELECT ?countryLabel (count(?org) as ?count)
WHERE
{
?org wdt:P31 wd:Q4830453.
?org wdt:P17 ?country.
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" }
}
GROUP BY ?country ?countryLabel
ORDER BY DESC (?count)
</syntaxhighlight>
[https://query.wikidata.org/#SELECT%20%3FcountryLabel%20%28count%28%3Forg%29%20as%20%3Fcount%29%0AWHERE%0A%7B%0A%20%20%20%20%3Forg%20%20wdt%3AP31%20wd%3AQ4830453.%0A%20%20%20%20%3Forg%20wdt%3AP17%20%3Fcountry.%0A%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%20%7D%0A%20%7D%0A%20%20GROUP%20BY%20%3Fcountry%20%3FcountryLabel%0A%20%20ORDER%20BY%20DESC%20%28%3Fcount%29%0A SPARQL-query], 198 Results
== Organizations and their subsidiaries ==
It is necessary to build a graph from existing organizations, including subsidiaries.
Are used:
* object [[d:Q4830453|business enterprise (Q4830453)]] (business enterprise),
* property [[d:Property:P355|subsidiary (P355)]] (subsidiary).
<syntaxhighlight lang="SPARQL">
#subsidary graph
#defaultView:Graph
SELECT ?org ?orgLabel ?subsidiary ?subsidiaryLabel
WHERE
{
?org wdt:P31 wd:Q22687
; rdfs:label ?item_label.
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" }
OPTIONAL { ?org wdt:P355 ?subsidiary. }
FILTER (LANG(?item_label) = "en")
}
</syntaxhighlight>
[https://query.wikidata.org/#%23neighboring%20countries%20graph%0A%23defaultView%3AGraph%0ASELECT%20%3Forg%20%3ForgLabel%20%3Fsubsidary%20%3FsubsidaryLabel%0AWHERE%0A%7B%0A%20%20%20%20%3Forg%20wdt%3AP31%20wd%3AQ22687%0A%20%20%20%20%3B%20rdfs%3Alabel%20%3Fitem_label%20.%0A%0A%20%20%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%20%7D%0A%20%20%20%20OPTIONAL%20%7B%20%3Forg%20wdt%3AP355%20%3Fsubsidary%20.%20%7D%0A%20%20%20%20FILTER%20%20%28LANG%28%3Fitem_label%29%20%3D%20%22en%22%29%20%0A%7D%0A SPARQL-query], 428 Results(edges).
The resulting graph of neighbors (Fig. 2) consists of hanging vertices and isolated vertices. It is necessary to construct a graph where these vertices are absent.
[[File:Diagram of subsidiaries of the world.jpg|thumb|Fig. 2: Diagram of subsidiaries of the world|center|900px]]<br style="clear: both;">
<syntaxhighlight lang="SPARQL">
#neighboring countries graph
#defaultView:Graph
SELECT ?org ?orgLabel ?subsidiary ?subsidiaryLabel
WHERE
{
?org wdt:P31 wd:Q22687
; rdfs:label ?item_label.
?org wdt:P355 ?subsidiary.
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" }
FILTER (LANG(?item_label) = "en")
}
</syntaxhighlight>
[https://query.wikidata.org/#%23neighboring%20countries%20graph%0A%23defaultView%3AGraph%0ASELECT%20%3Forg%20%3ForgLabel%20%3Fsubsidary%20%3FsubsidaryLabel%0AWHERE%0A%7B%0A%20%20%20%20%3Forg%20wdt%3AP31%20wd%3AQ22687%0A%20%20%20%20%3B%20rdfs%3Alabel%20%3Fitem_label%20.%0A%20%20%20%20%3Forg%20wdt%3AP355%20%3Fsubsidary%20.%20%0A%20%20%0A%20%20%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%20%7D%0A%0A%20%20%20%20FILTER%20%20%28LANG%28%3Fitem_label%29%20%3D%20%22en%22%29%20%0A%7D%0A SPARQL-query], 55 Results(edges).
== Fullness of the Wikidata ==
According to the category [[w: en: List_of_companies_of_Russia | List of companies of Russia]] there are at least 208 commercial organizations in English Wikipedia in Russia. We can note that there is a rating of the largest companies of Russia that is listed. It can be concluded that even big organizations have not been included in this list, not talking about small and medium ones.
It is impossible to obtain relevant data on the number of commercial organizations, because their number grows every day, and information about them is not represented in the public domain. For example, the USRLE, which provides data for a fee. {{Sfn|EGRUL|2017}}
The quantity of commercial organizations entered in the state register as newly created, in 2014 amounted 420.5 thousand, according to data on the site of the Federal Tax Service (FTS). In June, 2015 came into force orders of the Ministry of Finance of Russia that the data of existing organizations and information about them no longer applies in public. The data can be provided only to state authorities, local self-government bodies and so on. Therefore, it is not possible to obtain reliable data on the quantity of available organizations.
There is an opportunity to explore fullness with the help of the Wikidata. It is necessary to remember the total number of organizations (from the beginning) on the Wikidata (about 110 000, as their number is constantly growing). A typical user who has a general understanding of organizations may be interested to see how an organization looks or where it is located on the map.
To see how many organizations have an image (that is, the 'image' field is filled in), we need to write the following script.
<syntaxhighlight lang="SPARQL">
#List of organizations with image
SELECT ?org ?orgLabel ?image
WHERE
{
?org wdt:P31 wd:Q4830453. #instance of orgs
?org wdt:P18 ?image #has image
SERVICE wikibase:label { bd:serviceParam wikibase:language "en"}
}</syntaxhighlight>
[https://query.wikidata.org/#%23List%20of%20organisations%20%0A%0ASELECT%20%3Forg%20%3ForgLabel%20%3Fimage%0AWHERE%0A%7B%0A%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%20%23instance%20of%20orgs%0A%20%20%3Forg%20wdt%3AP18%20%3Fimage%0A%20%20%0A%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%7D%0A%7D SPARQL-query], 2913 Results.
It can be concluded that the number of organizations with the image is 2913. This is not so much, which indicates about incompleteness of information.
Let's build a table of (maybe) popular user requests for organizations (depending on who is interested in some things about the organization). Also, we sort it by descending the results.
<table border="1">
<caption>Table of requests in Wikidata</caption>
<tr>
<th>Request name</th>
<th>Quantity of results</th>
</tr>
<tr><td>inception</td><td>30995</td></tr>
<tr><td>founded by</td><td>5722</td></tr>
<tr><td>subsidiary</td><td>3398</td></tr>
<tr><td>subsidiary</td><td>2913</td></tr>
<tr><td>location</td><td>577</td></tr>
<tr><td>motto</td><td>2</td></tr>
</table>
The results of this table indicate that the quantity of necessary information about organizations is very small, considering their total number on the Wikidata.
There is an opportunity to investigate organizations in Russia too.
We can try to get a list of organizations in Russia with the help of the Wikidata.
<syntaxhighlight lang="SPARQL">
#List of organizations
SELECT ?org ?orgLabel
WHERE
{
?org wdt:P31 wd:Q4830453. #instance of organizations
?org wdt:P17 wd:Q159. #Russia country
SERVICE wikibase:label { bd:serviceParam wikibase:language "en"}
}</syntaxhighlight>
[https://query.wikidata.org/#%23List%20of%20organisations%20%0A%0ASELECT%20%3Forg%20%3ForgLabel%20%3Flocation%0AWHERE%0A%7B%0A%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%20%23instance%20of%20orgs%0A%20%20%3Forg%20wdt%3AP17%20wd%3AQ159.%20%23Russia%20country%0A%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%7D%0A%7D SPARQL-query], 577 Results.
There are 577 organizations that were output by the query. For example, the user wants to see how these organizations are located on the map. It is necessary to write a script.
<syntaxhighlight lang="SPARQL">
#Map of organizations
#defaultView:Map
SELECT ?org ?orgLabel ?location
WHERE
{
?org wdt:P31 wd:Q4830453. #instance of orgs
?org wdt:P17 wd:Q159. #Russia country
?org wdt:P625 ?location #display location
SERVICE wikibase:label { bd:serviceParam wikibase:language "en"}
}</syntaxhighlight>
[https://query.wikidata.org/#%23List%20of%20organisations%20%0A%23defaultView%3AMap%0A%0ASELECT%20%3Forg%20%3ForgLabel%20%3Flocation%0AWHERE%0A%7B%0A%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%20%23instance%20of%20orgs%0A%20%20%3Forg%20wdt%3AP17%20wd%3AQ159.%20%23Russia%20country%0A%20%20%3Forg%20wdt%3AP625%20%3Flocation%0A%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%7D%0A%7D SPARQL-query], 9 Results.
Result: very few records with geographic coordinates in Russia. We can get a map of organizations not only in Russia, but of all organizations in the world by using the following script.
<syntaxhighlight lang="SPARQL">
#List of organizations
#defaultView:Map
SELECT ?org ?orgLabel ?location
WHERE
{
?org wdt:P31 wd:Q4830453. #instance of orgs
?org wdt:P625 ?location
SERVICE wikibase:label { bd:serviceParam wikibase:language "en"}
}</syntaxhighlight>
[https://query.wikidata.org/#%23List%20of%20organisations%20%0A%23defaultView%3AMap%0A%0ASELECT%20%3Forg%20%3ForgLabel%20%3Flocation%0AWHERE%0A%7B%0A%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%20%23instance%20of%20orgs%0A%20%20%3Forg%20wdt%3AP625%20%3Flocation%0A%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%7D%0A%7D SPARQL-query], 511 Results.
The result (Fig. 3), again, is very small, only 511 organizations. The quantity of organizations with location is even less than the total number of all organizations in Russia.
[[File:World organizations map.jpg|thumb|Fig. 3: World organizations map|center|900px]]<br style="clear: both;">
Analyzing the data obtained, it can be concluded that the information about organizations on the Wikidata are only partially filled. There is not enough information to do any definite conclusions about the organizations and their components. A small amount of information can be explained by the chaotic appearance and disappearance of organizations (it is not easy to survive in such conditions of competition and the existing economy). But the information even about such major organizations (Apple, Microsoft, Intel) is incomplete and needs to be improved (for example, the Intel organization does not have a motto on Wikidata).
== Future work ==
# Output 20 organizations with the largest revenue.
# Output as a diagram how many commercial organizations are appear each year.
# What is the distribution of the quantity of commercial organizations by industry in different countries.
== Test ==
<quiz display=simple>
{ The following commercial organizations are listed: [[w:Tele2|Tele2]], [[w:Lada|Lada]], [[w:Aviakor|Aviakor]], [[w:Uralmash|Uralmash]].
Correlate the organization's data with the images below.
|type="()"}
|1 (Tele2),|2 (Lada),|3 (Aviakor),|4 (Uralmash)
+--- [[Image:Moscow, Leningradskoye Highway 39A.jpg|240px|]]
---+ [[Image:MainBildingUralmash.jpg|240px|]]
-+-- [[Image:Lada Kalina (1118).jpg|240px|]]
--+- [[Image:Tu154-aviakor.jpg|240px|]]
{ Such commercial organizations are known: MegaFon, [[w:Svyaznoy|Svyaznoy]], [[w:EurosetEvroset]], Sportmaster. Years of the creation of commercial organizations are known: 1992, 1995, 1997, 2002. <br>
Arrange the organization's data in order of increasing date of their creation (1st place is the oldest organization, 4th place is the newest one).<br>
|type="()"}
|1 place (1992),|2 place (1995),|3 place (1997),|4 place (2002)
---+ [[Image:MegaFon logo Russian.svg|120px|]] MegaFon
-+-- [[Image:SvyaznoyLogo.png|120px|]] Svyaznoy
--+- [[Image:Euroset.png|120px|]] Evroset
+---Sportmaster
{ Arrange countries in ascending order of the number of organizations (on the 1st place: least number of organizations):
|type="()"}
| 1 | 2 | 3 | 4
-+-- Sweden
+--- United Kingdom
---+ USA
--+- Germany
</quiz>
SPARQL-queries with answers:
*
[https://query.wikidata.org/#%23List%20of%20organizations%20%0ASELECT%20%3Forg%20%3ForgLabel%20%0AWHERE%0A%7B%0A%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%20%23instance%20of%20organizations%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%7D%0A%7D List of all organizations],
*
[https://query.wikidata.org/#%23List%20of%20organisations%20%0A%0ASELECT%20%3Forg%20%3ForgLabel%20%3Finception%0AWHERE%0A%7B%0A%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%20%23instance%20of%20orgs%0A%20%20%3Forg%20wdt%3AP571%20%3Finception%0A%20%20%20%20%20%20%20%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%7D%0A%7D List of all organizations with years of creation],
*
[https://query.wikidata.org/#%23List%20of%20organisations%20%0A%0ASELECT%20%3Forg%20%3ForgLabel%20%3Fimage%0AWHERE%0A%7B%0A%20%20%3Forg%20wdt%3AP31%20wd%3AQ4830453.%20%23instance%20of%20orgs%0A%20%20%3Forg%20wdt%3AP17%20wd%3AQ159.%20%23country%20%3D%20Russia%0A%20%20%3Forg%20wdt%3AP18%20%3Fimage%0A%20%20%0A%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22en%22%7D%0A%7D List of all organizations In Russia with image],
*
[https://query.wikidata.org/#SELECT%20%3Forg%20%3Fcountry%20%28count%28%2a%29%20as%20%3Fcount%29%0AWHERE%0A%7B%0A%09%3ForgLabel%20wdt%3AP31%20wd%3AQ4830453%3B%0A%20%20%20%20%20%20%20%20wdt%3AP17%20%3Forg.%0A%20%20%09OPTIONAL%20%7B%0A%09%09%3Forg%20rdfs%3Alabel%20%3Fcountry%0A%09%09filter%20%28lang%28%3Fcountry%20%29%20%3D%20%22ru%22%29%0A%09%7D%0A%7D%0AGROUP%20BY%20%3Forg%20%3Fcountry%0AORDER%20BY%20DESC%28%3Fcount%29%20%0A List of organizations by country in descending order]
== References ==
*{{cite web
|url=https://www.nalog.ru/rn77/service/egrip2/
|title = Access to EGRUL and EGRIP
|year = 2017
|ref = {{harvid|EGRUL|2017}}
}}
*{{cite web
|last1 = Andrew Krizhanovsky, Nikita Nikolaev
|title = Коммерческие организации
|trans-title = Business Enterprise
|url = https://www.authorea.com/users/86022/articles/177807-wd-business-enterprise2
|publisher = Authorea
|year = 2017
}}
[[Category:Research in programming Wikidata|{{SUBPAGENAME}}]]
[[Category:Business]]
h3grishxzscm9xnhkka38texd9rs3x5
Module:String2
828
241542
2816316
2558028
2026-06-20T01:14:20Z
Uzume
187172
Update from [[d:Special:GoToLinkedPage/enwiki/Q16914835|master]] using [[mw:Synchronizer| #Synchronizer]]
2816316
Scribunto
text/plain
require ('strict');
local p = {}
p.trim = function(frame)
return mw.text.trim(frame.args[1] or "")
end
p.sentence = function (frame)
-- {{lc:}} is strip-marker safe, string.lower is not.
frame.args[1] = frame:callParserFunction('lc', frame.args[1])
return p.ucfirst(frame)
end
p.ucfirst = function (frame)
local s = frame.args[1];
if not s or '' == s or s:match ('^%s+$') then -- when <s> is nil, empty, or only whitespace
return s; -- abandon because nothing to do
end
s = mw.text.trim( frame.args[1] or "" )
local s1 = ""
local prefix_patterns_t = { -- sequence of prefix patterns
'^\127[^\127]*UNIQ%-%-%a+%-%x+%-QINU[^\127]*\127', -- stripmarker
'^([%*;:#]+)', -- various list markup
'^(\'\'\'*)', -- bold / italic markup
'^(%b<>)', -- html-like tags because some templates render these
'^(&%a+;)', -- html character entities because some templates render these
'^(&#%d+;)', -- html numeric (decimal) entities because some templates render these
'^(&#x%x+;)', -- html numeric (hexadecimal) entities because some templates render these
'^(%s+)', -- any whitespace characters
'^([%(%)%-%+%?%.%%!~!@%$%^&_={}/`,‘’„“”ʻ|\"\'\\]+)', -- miscellaneous punctuation
}
local prefixes_t = {}; -- list, bold/italic, and html-like markup, & whitespace saved here
local function prefix_strip (s) -- local function to strip prefixes from <s>
for _, pattern in ipairs (prefix_patterns_t) do -- spin through <prefix_patterns_t>
if s:match (pattern) then -- when there is a match
local prefix = s:match (pattern); -- get a copy of the matched prefix
table.insert (prefixes_t, prefix); -- save it
s = s:sub (prefix:len() + 1); -- remove the prefix from <s>
return s, true; -- return <s> without prefix and flag; force restart at top of sequence because misc punct removal can break stripmarker
end
end
return s; -- no prefix found; return <s> with nil flag
end
local prefix_removed; -- flag; boolean true as long as prefix_strip() finds and removes a prefix
repeat -- one by one remove list, bold/italic, html-like markup, whitespace, etc from start of <s>
s, prefix_removed = prefix_strip (s);
until (not prefix_removed); -- until <prefix_removed> is nil
s1 = table.concat (prefixes_t); -- recreate the prefix string for later reattachment
local first_text = mw.ustring.match (s, '^%[%[[^%]]+%]%]'); -- extract wikilink at start of string if present; TODO: this can be string.match()?
local upcased;
if first_text then
if first_text:match ('^%[%[[^|]+|[^%]]+%]%]') then -- if <first_text> is a piped link
upcased = mw.ustring.match (s, '^%[%[[^|]+|%W*(%w)'); -- get first letter character
upcased = mw.ustring.upper (upcased); -- upcase first letter character
s = mw.ustring.gsub (s, '^(%[%[[^|]+|%W*)%w', '%1' .. upcased); -- replace
else -- here when <first_text> is a wikilink but not a piped link
upcased = mw.ustring.match (s, '^%[%[%W*%w'); -- get '[[' and first letter
upcased = mw.ustring.upper (upcased); -- upcase first letter character
s = mw.ustring.gsub (s, '^%[%[%W*%w', upcased); -- replace; no capture needed here
end
elseif s:match ('^%[%S+%s+[^%]]+%]') then -- if <s> is a ext link of some sort; must have label text
upcased = mw.ustring.match (s, '^%[%S+%s+%W*(%w)'); -- get first letter character
upcased = mw.ustring.upper (upcased); -- upcase first letter character
s = mw.ustring.gsub (s, '^(%[%S+%s+%W*)%w', '%1' .. upcased); -- replace
elseif s:match ('^%[%S+%s*%]') then -- if <s> is a ext link without label text; nothing to do
return s1 .. s; -- reattach prefix string (if present) and done
else -- <s> is not a wikilink or ext link; assume plain text
upcased = mw.ustring.match (s, '^%W*%w'); -- get the first letter character
upcased = mw.ustring.upper (upcased); -- upcase first letter character
s = mw.ustring.gsub (s, '^%W*%w', upcased); -- replace; no capture needed here
end
return s1 .. s; -- reattach prefix string (if present) and done
end
p.title = function (frame)
-- http://grammar.yourdictionary.com/capitalization/rules-for-capitalization-in-titles.html
-- recommended by The U.S. Government Printing Office Style Manual:
-- "Capitalize all words in titles of publications and documents,
-- except a, an, the, at, by, for, in, of, on, to, up, and, as, but, or, and nor."
local alwayslower = {['a'] = 1, ['an'] = 1, ['the'] = 1,
['and'] = 1, ['but'] = 1, ['or'] = 1, ['for'] = 1,
['nor'] = 1, ['on'] = 1, ['in'] = 1, ['at'] = 1, ['to'] = 1,
['from'] = 1, ['by'] = 1, ['of'] = 1, ['up'] = 1 }
local res = ''
local s = mw.text.trim( frame.args[1] or "" )
local words = mw.text.split( s, " ")
for i, s in ipairs(words) do
-- {{lc:}} is strip-marker safe, string.lower is not.
s = frame:callParserFunction('lc', s)
if i == 1 or alwayslower[s] ~= 1 then
s = mw.getContentLanguage():ucfirst(s)
end
words[i] = s
end
return table.concat(words, " ")
end
-- findlast finds the last item in a list
-- the first unnamed parameter is the list
-- the second, optional unnamed parameter is the list separator (default = comma space)
-- returns the whole list if separator not found
p.findlast = function(frame)
local s = mw.text.trim( frame.args[1] or "" )
local sep = frame.args[2] or ""
if sep == "" then sep = ", " end
local pattern = ".*" .. sep .. "(.*)"
local a, b, last = s:find(pattern)
if a then
return last
else
return s
end
end
-- stripZeros finds the first number and strips leading zeros (apart from units)
-- e.g "0940" -> "940"; "Year: 0023" -> "Year: 23"; "00.12" -> "0.12"
p.stripZeros = function(frame)
local s = mw.text.trim(frame.args[1] or "")
local n = tonumber( string.match( s, "%d+" ) ) or ""
s = string.gsub( s, "%d+", n, 1 )
return s
end
-- nowiki ensures that a string of text is treated by the MediaWiki software as just a string
-- it takes an unnamed parameter and trims whitespace, then removes any wikicode
p.nowiki = function(frame)
local str = mw.text.trim(frame.args[1] or "")
return mw.text.nowiki(str)
end
-- split splits text at boundaries specified by separator
-- and returns the chunk for the index idx (starting at 1)
-- #invoke:String2 |split |text |separator |index |true/false
-- #invoke:String2 |split |txt=text |sep=separator |idx=index |plain=true/false
-- if plain is false/no/0 then separator is treated as a Lua pattern - defaults to plain=true
p.split = function(frame)
local args = frame.args
if not(args[1] or args.txt) then args = frame:getParent().args end
local txt = args[1] or args.txt or ""
if txt == "" then return nil end
local sep = (args[2] or args.sep or ""):gsub('"', '')
local idx = tonumber(args[3] or args.idx) or 1
local plain = (args[4] or args.plain or "true"):sub(1,1)
plain = (plain ~= "f" and plain ~= "n" and plain ~= "0")
local splittbl = mw.text.split( txt, sep, plain )
if idx < 0 then idx = #splittbl + idx + 1 end
return splittbl[idx]
end
-- val2percent scans through a string, passed as either the first unnamed parameter or |txt=
-- it converts each number it finds into a percentage and returns the resultant string.
p.val2percent = function(frame)
local args = frame.args
if not(args[1] or args.txt) then args = frame:getParent().args end
local txt = mw.text.trim(args[1] or args.txt or "")
if txt == "" then return nil end
local function v2p (x)
x = (tonumber(x) or 0) * 100
if x == math.floor(x) then x = math.floor(x) end
return x .. "%"
end
txt = txt:gsub("%d[%d%.]*", v2p) -- store just the string
return txt
end
-- one2a scans through a string, passed as either the first unnamed parameter or |txt=
-- it converts each occurrence of 'one ' into either 'a ' or 'an ' and returns the resultant string.
p.one2a = function(frame)
local args = frame.args
if not(args[1] or args.txt) then args = frame:getParent().args end
local txt = mw.text.trim(args[1] or args.txt or "")
if txt == "" then return nil end
txt = txt:gsub(" one ", " a "):gsub("^one", "a"):gsub("One ", "A "):gsub("a ([aeiou])", "an %1"):gsub("A ([aeiou])", "An %1")
return txt
end
-- findpagetext returns the position of a piece of text in a page
-- First positional parameter or |text is the search text
-- Optional parameter |title is the page title, defaults to current page
-- Optional parameter |plain is either true for plain search (default) or false for Lua pattern search
-- Optional parameter |nomatch is the return value when no match is found; default is nil
p._findpagetext = function(args)
-- process parameters
local nomatch = args.nomatch or ""
if nomatch == "" then nomatch = nil end
--
local text = mw.text.trim(args[1] or args.text or "")
if text == "" then return nil end
--
local title = args.title or ""
local titleobj
if title == "" then
titleobj = mw.title.getCurrentTitle()
else
titleobj = mw.title.new(title)
end
--
local plain = args.plain or ""
if plain:sub(1, 1) == "f" then plain = false else plain = true end
-- get the page content and look for 'text' - return position or nomatch
local content = titleobj and titleobj:getContent()
return content and mw.ustring.find(content, text, 1, plain) or nomatch
end
p.findpagetext = function(frame)
local args = frame.args
local pargs = frame:getParent().args
for k, v in pairs(pargs) do
args[k] = v
end
if not (args[1] or args.text) then return nil end
-- just the first value
return (p._findpagetext(args))
end
-- returns the decoded url. Inverse of parser function {{urlencode:val|TYPE}}
-- Type is:
-- QUERY decodes + to space (default)
-- PATH does no extra decoding
-- WIKI decodes _ to space
p._urldecode = function(url, type)
url = url or ""
type = (type == "PATH" or type == "WIKI") and type
return mw.uri.decode( url, type )
end
-- {{#invoke:String2|urldecode|url=url|type=type}}
p.urldecode = function(frame)
return mw.uri.decode( frame.args.url, frame.args.type )
end
-- what follows was merged from [[Module:StringFunc]]
-- Argument list helper function, as per [[Module:String]]
function p._getParameters( frame_args, arg_list )
local new_args = {};
local index = 1;
local value;
for i,arg in ipairs( arg_list ) do
value = frame_args[arg]
if value == nil then
value = frame_args[index];
index = index + 1;
end
new_args[arg] = value;
end
return new_args;
end
-- Escape Pattern helper function so that all characters are treated as plain text, as per [[Module:String]]
function p._escapePattern( pattern_str )
return mw.ustring.gsub( pattern_str, "([%(%)%.%%%+%-%*%?%[%^%$%]])", "%%%1" )
end
-- Helper Function to interpret boolean strings, as per [[Module:String]]
function p._getBoolean( boolean_str )
local boolean_value;
if type( boolean_str ) == 'string' then
boolean_str = boolean_str:lower();
if boolean_str == 'false' or boolean_str == 'no' or boolean_str == '0'
or boolean_str == '' then
boolean_value = false;
else
boolean_value = true;
end
elseif type( boolean_str ) == 'boolean' then
boolean_value = boolean_str;
else
error( 'No boolean value found' );
end
return boolean_value
end
--[[
Strip
This function Strips characters from string
Usage:
{{#invoke:String2|strip|source_string|characters_to_strip|plain_flag}}
Parameters
source: The string to strip
chars: The pattern or list of characters to strip from string, replaced with ''
plain: A flag indicating that the chars should be understood as plain text. defaults to true.
Leading and trailing whitespace is also automatically stripped from the string.
]]
function p.strip( frame )
local new_args = p._getParameters( frame.args, {'source', 'chars', 'plain'} )
local source_str = new_args['source'] or ''
local chars = new_args['chars'] or '' or 'characters'
source_str = mw.text.trim(source_str)
if source_str == '' or chars == '' then
return source_str
end
local l_plain = p._getBoolean( new_args['plain'] or true )
if l_plain then
chars = p._escapePattern( chars )
end
local result
result = mw.ustring.gsub(source_str, "["..chars.."]", '')
return result
end
--[[
Match any
Returns the index of the first given pattern to match the input. Patterns must be consecutively numbered.
Returns the empty string if nothing matches for use in {{#if:}}
Usage:
{{#invoke:String2|matchAll|source=123 abc|456|abc}} returns '2'.
Parameters:
source: the string to search
plain: A flag indicating that the patterns should be understood as plain text. defaults to true.
1, 2, 3, ...: the patterns to search for
]]
function p.matchAny(frame)
local source_str = frame.args['source'] or error('The source parameter is mandatory.')
local l_plain = p._getBoolean( frame.args['plain'] or true )
for i = 1, math.huge do
local pattern = frame.args[i]
if not pattern then return '' end
if mw.ustring.find(source_str, pattern, 1, l_plain) then
return tostring(i)
end
end
end
--[[--------------------------< H Y P H E N _ T O _ D A S H >--------------------------------------------------
Converts a hyphen to a dash under certain conditions. The hyphen must separate
like items; unlike items are returned unmodified. These forms are modified:
letter - letter (A - B)
digit - digit (4-5)
digit separator digit - digit separator digit (4.1-4.5 or 4-1-4-5)
letterdigit - letterdigit (A1-A5) (an optional separator between letter and
digit is supported – a.1-a.5 or a-1-a-5)
digitletter - digitletter (5a - 5d) (an optional separator between letter and
digit is supported – 5.a-5.d or 5-a-5-d)
any other forms are returned unmodified.
str may be a comma- or semicolon-separated list
]]
function p.hyphen_to_dash( str, spacing )
if (str == nil or str == '') then
return str
end
local accept
str = mw.text.decode(str, true ) -- replace html entities with their characters; semicolon mucks up the text.split
local out = {}
local list = mw.text.split (str, '%s*[,;]%s*') -- split str at comma or semicolon separators if there are any
for _, item in ipairs (list) do -- for each item in the list
item = mw.text.trim(item) -- trim whitespace
item, accept = item:gsub ('^%(%((.+)%)%)$', '%1')
if accept == 0 and mw.ustring.match (item, '^%w*[%.%-]?%w+%s*[%-–—]%s*%w*[%.%-]?%w+$') then -- if a hyphenated range or has endash or emdash separators
if item:match ('^%a+[%.%-]?%d+%s*%-%s*%a+[%.%-]?%d+$') or -- letterdigit hyphen letterdigit (optional separator between letter and digit)
item:match ('^%d+[%.%-]?%a+%s*%-%s*%d+[%.%-]?%a+$') or -- digitletter hyphen digitletter (optional separator between digit and letter)
item:match ('^%d+[%.%-]%d+%s*%-%s*%d+[%.%-]%d+$') or -- digit separator digit hyphen digit separator digit
item:match ('^%d+%s*%-%s*%d+$') or -- digit hyphen digit
item:match ('^%a+%s*%-%s*%a+$') then -- letter hyphen letter
item = item:gsub ('(%w*[%.%-]?%w+)%s*%-%s*(%w*[%.%-]?%w+)', '%1–%2') -- replace hyphen, remove extraneous space characters
else
item = mw.ustring.gsub (item, '%s*[–—]%s*', '–') -- for endash or emdash separated ranges, replace em with en, remove extraneous whitespace
end
end
table.insert (out, item) -- add the (possibly modified) item to the output table
end
local temp_str = table.concat (out, ',' .. spacing) -- concatenate the output table into a comma separated string
temp_str, accept = temp_str:gsub ('^%(%((.+)%)%)$', '%1') -- remove accept-this-as-written markup when it wraps all of concatenated out
if accept ~= 0 then
temp_str = str:gsub ('^%(%((.+)%)%)$', '%1') -- when global markup removed, return original str; do it this way to suppress boolean second return value
end
return temp_str
end
function p.hyphen2dash( frame )
local str = frame.args[1] or ''
local spacing = frame.args[2] or ' ' -- space is part of the standard separator for normal spacing (but in conjunction with templates r/rp/ran we may need a narrower spacing
return p.hyphen_to_dash(str, spacing)
end
-- Similar to [[Module:String#endswith]]
function p.startswith(frame)
return (frame.args[1]:sub(1, frame.args[2]:len()) == frame.args[2]) and 'yes' or ''
end
-- Implements [[Template:Isnumeric]]
function p.isnumeric(frame)
local s = frame.args[1] or frame:getParent().args[1]
local boolean = (frame.args.boolean or frame:getParent().args.boolean) == 'true'
if type(s) == 'string' and mw.getContentLanguage():parseFormattedNumber( s ) then
return boolean and 1 or s
end
return boolean and 0 or ''
end
-- Checks if a value in a group of numbers is not an interger.
-- Allows usage of an |empty= parameter to allow empty values to be skipped.
function p.isInteger(frame)
local values = frame.args or frame:getParent().args
local allow_empty = frame.args.empty or frame:getParent().args.empty
for _, value in ipairs(values) do
-- Trim spaces
value = value and value:gsub("^%s*(.-)%s*$", "%1")
if value == "" or value == nil then
if not allow_empty then
return false -- Empty values are not allowed
end
else
value = tonumber(value)
if not (type(value) == "number" and value == math.floor(value)) then
return false
end
end
end
return true
end
-- Returns an error found in a string.
function p.getError(frame)
local text = frame.args[1] or frame:getParent().args[1]
local error_message = text:match('(<strong class="error">.-</strong>)')
return error_message or nil
end
return p
ph89g30kzy2uwl0t05s6jtpby1w86b8
Motivation and emotion/Book/2019/Hate crime motivation
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([[c:GR|GR]]) [[c:COM:FR|File renamed]]: [[File:Pauline Hanson 2017 01 (cropped).jpg]] → [[File:Pauline Hanson 2016 01 (cropped).jpg]] [[c:COM:FR#FR3|Criterion 3]] (obvious error) · Photo was taken in December 2016 not 2017
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text/x-wiki
{{title|Hate crime motivation:<br>What motivates people to engage in hate crime?}}
{{MECR3|1=https://youtu.be/_c2d5v6gUQY}}
__TOC__
==Overview==
<blockquote>[[File:Civil Rights March on Washington, D.C. (Dr. Martin Luther King, Jr. and Mathew Ahmann in a crowd.) - NARA - 542015 - Restoration.jpg|thumb|''Figure 1.'' Martin Luther King in Washington, D.C.|alt=|right|300x300px]]
'''''“Darkness cannot drive darkness; Light can do that. Hate cannot drive out hate; Love can do that.”'''''
'''– Martin Luther King (1963)'''
[[wikipedia:Hate_crime|Hate crime]] is one, if not the most important{{gr}} category of crime to agencies such as the [[wikipedia:Federal_Bureau_of_Investigation|FBI]], due to its prevailing and devastating impact on families and surrounding communities.
The history of hate crime dates back before the term "hate crime" was first introduced in the 1980s, where crimes against historically oppressed groups were committed both by the individual and governments. Acts of hate crime are seen as especially heinous and inhumane, leading people to wonder why individuals and certain governments are motivated to participate in such acts. Many aspects of [[wikipedia:Motivation|motivation]] are needed for considering these motivations: including thrill- or [[wikipedia:Sensation_seeking|sensation-seeking]], [[wikipedia:Defence_mechanisms|defensive mechanisms]], mission offenders, or [[wikipedia:Bias|bias]] behaviours. Individuals who participate in hate crimes also vary in characteristics, and there is no one defining factor of a hate crime perpetrator. Certain psychological theories based on motivation and criminal behaviour can help describe why these individuals and groups behave in such ways.
</blockquote>
[[File:Racism in US.jpg|thumb|300x300px|''Figure 3''. The KKK participated in many hate crimes in the US against African Americans ]]
Throughout this chapter, individual case studies and examples of hate crime throughout history will be shown - as well as ones we are all familiar with, the rage of Nazi slaughter against the Jews - [[wikipedia:The_Holocaust|The Holocaust]], (see also [[wikipedia:Final_Solution|The Final Solution]]), and also the ongoing racial hate crimes that was brought into mainstream relevance in the United States in the 1870s, combatting the racially motivated crimes of the [[wikipedia:Ku_Klux_Klan|Klu Klux Klan]]. The term "hate crime" is still a relatively new term, so it is important to highlight relevant information for the purpose of educating people and communities of its dangerous effects, and also ways in which to prevent this type of behaviour arising.
<quiz display="simple">
'''Quiz'''
There is only one defining factor for hate crime motivation
|type="[FALSE]"}
- True
+ False
</quiz>
== Hate Crime ==
In order to understand what a hate crime is and the motivations surrounding such acts, it is important to define how prevalent it is in certain countries and the origins of it. For the purpose of this chapter, two countries will be focused on, the United States and Australia respectively, exploring the terms, statistics, history, and types of motivation. The United States has been an integral country in the history of hate crimes, as the first hate crime laws were passed after the [[wikipedia:American_Civil_War|American Civil War]], beginning with the [[wikipedia:Third_Enforcement_Act|Civil Rights Act of 1871]]. Australia is the second country to focus on, and even though there are very few reported and prosecuted hate crimes within the borders, there are still important examples to draw from.
=== Hate Crime in United States ===
The US FBI Department of Justice defines a hate crime as "a criminal offence against a person or property motivated in whole or in part by an offender's basis against race, religion, disability, sexual orientation, ethnicity, gender, or gender identity," (FBI, n.d). This signifies that hate crime occurs under many sources of motivation, and highlights the major differences between each origin or cause of the crime. There are also acts of non-criminal nature that involve the same factors, which are called [[wikipedia:Bias_incident|"bias-incidents"]]. In 2017, law enforcement agencies in the US identified a total of 7,175 incidents of hate involving 8,437 different offences (FBI, n.d). Hate crimes against race, ethnicity, and ancestry predicted to be the most common form of targeted hate crime.
{| class="wikitable"
|+Hate Crime: Bias Motivation of Single-Biased Incidents in 2017
!Bias Motivation
!Incidents
!Offences
!Victims
!Percentage %
|-
|Total
|7175
|8437
|8828
|100
|-
|Race/Ethnicity/Ancestry
|4131
|4832
|5060
|57.57
|-
|Religion
|1564
|1679
|1794
|21.8
|-
|Sexual Orientation
|1130
|1303
|1338
|15.75
|-
|Gender Identity
|119
|131
|132
|1.65
|-
|Disability
|116
|128
|160
|1.62
|-
|Gender
|46
|53
|54
|0.64
|-
|Multiple-Bias Incidents
|69
|311
|335
|0.96
|}
Criminal acts of hate crime in the United States included aggravated assault, assault and battery, vandalism, rape, threats, arson, trespassing, stalking, and various other crimes, until 1987 where California state legislation included all crimes as possible hate crimes. Each state within the US has varying degrees of prosecution regarding types of hate crimes, however all states recognise that federal prosecution is possible for any type of hate crime committed, particularly if motivation was towards person or person's race, gender, religion, or nation origin, (United States Department of Justice, 2008).
Racism against black African Americans in the United States has been, if not the, most prominent acts of hate crime throughout the countries history. One of the largest and most well-known hate crime case in the United States was in the 1960s, the [[wikipedia:Civil_rights_movement|civil rights movement.]] This was a wave for social justice for African Americans who had been oppressed and discriminated against for several decades. Black men and women had been severely segregated, dividing them from white people by separate toilets to even designating specific bus seating. Civil rights activist [[wikipedia:Martin_Luther_King_Jr.|Martin Luther King Jr.]] became the front and centre leader for civil rights across the United States. The March on Washington, held on August 28th, 1963, led by Luther King as well as other prominent leaders, hosted over 200,000 people, black and white, for the main purpose of forcing legislation for civil rights and job equality. Of the 6370 known hate crime offenders towards race it is important to note that 50.7% were white, 21.3% were African American, and 7.5% were of mixed-racial groups, (FBI, n.d). Hate crime against Hispanics is steadily increasing, as of 2012, violent hate crimes targeted towards Hispanic people had increased 300% (NCJRS, 2014). This rise in hate crimes targeting Hispanics surged due to the reported 758 hate crime incidents in the month of November 2016, coincidentally the same month that [[wikipedia:Donald_Trump|Donald Trump]] won the presidential election against [[wikipedia:Hillary_Clinton|Hillary Clinton]].
'''Quiz''''
<quiz display=simple>
{What was the most frequently reported hate crime in 2017?
|type="()"}
+ Race, ethnicity and ancestry.
- Sexual orientation.
- Robbery.
- Disability.
</quiz>
=== Hate Crime in Australia ===
[[File:Pauline Hanson 2016 01 (cropped).jpg|link=link=Special:FilePath/Pauline Hanson senate.jpg|alt=|thumb|''Figure 4''. Pauline Hanson, leader of the ONE Nation party, has been criticised for mocking the Islamic faith after she entered Australia’s Senate Question Time wearing a burqa]]
History and magnitude of hate crime in Australia is hardly comparable to its prevalence in the United States, which gives good insight into the comparisons of motivation for perpetrators. This does leave however little research and information into data and motivational aspects of hate crime in Australia. The legal history of hate crime in Australia indicates that only 21 people have ever been convicted under hate crime laws. This does not however account for the many offences connected to discrimination and prejudice, noticed by the 4,257 incidents the Victorian Police linked to prejudice within a four-year period, (Cohen and Mitchell, 2019). Media outlets of [https://www.abc.net.au/news/ ABC News] and [https://www.sbs.com.au SBS News], have identified several issues regarding hate crime information and coverage, in particular the absence of: a national hate crime database, relevant statistics of hate crime including the victims, motivations, types of offences, and perpetrators, as well as the little effort taken by Australian law enforcement community to take acts of hate crime seriously. Extensive research from the e-Safety Commissioner (2017) shows that 53% of surveyed 12-17 year olds have witnessed anti-Muslim harmful content online, (Netsafe, 2018). In May 2017, an incident occurred on the campus of [[wikipedia:University_of_Technology_Sydney|University of Technology in Sydney]], where four Muslim women were physically attacked from an unknown suspect, (Cohen and Mitchell, 2019). Each of the four women were wearing a religious scarf. One of the victims, Hanan Merheb, stated that not only was the attack disturbing, but also the reaction from bystanders. She stated that there was only one witness of the attack that came to ask if she was okay, despite it being a busy and occupied street. Islamophobic attacks in Australia are steadily increasing, and reports from the police are not reflective of what is experienced in the Muslim communities. Several small, not-for-profit organisations have risen to combat this form of hate crime in Australia; such as [http://islamophobiawatch.com.au/about-us/ Islamophobia Watch] and [https://www.islamophobia.com.au Islamophobia Register]. Both organisations have services to report any acts of hate crime against the Muslim community, identifying the lack of coherent documentation of Islamophobia across Australia.
== Motivations for and Types of Hate Crime ==
Motivation in psychological terms is defined by the reason's{{gr}} for peoples{{gr}} actions, willingness, and goals. Motivation is our desire to do things that lead us to certain goals and certain needs are met. Motivation occurs on a biological, emotional, cognitive and social level. It is the "why" behind why we do the things that we do. One of the most interesting topics of motivation in psychology is questioning why people engage in criminal behaviour, despite the many consequences that follow such behaviour. This chapter will focus on the motivation of why people choose to engage in hate crime, and the many emotions, anger, fear and indignation that inspire such behaviour.
There are many motivations attached to why hate crime perpetrators choose to partake in such behaviour. These motivations can be broken down into four main categories: [[wikipedia:Sensation_seeking|Thrill-seeking]], [[wikipedia:Military|Defensive]], Retaliatory, and Mission Offenders. Knowing the differences between each motivation is extremely important for both the public and law enforcement agencies to identify predictive behaviours and how to effectively approach each one. by identifying the differences, this increases the available information to the community, enabling them to have better, more inclusive data collections on hate crime.
=== Thrill-seeking ===
Thrill-seeking behaviour is a personality trait defined by the search for experiences and feelings, that are "varied, novel, complex and intense", and by the readiness to "take physical, social, legal, and financial risks for the sake of such experiences." Risks of these behaviours are either ignored, tolerated, or minimised and may even been considered added excitement to the activity. Often there is no real, legitimate reason for some hate crimes, as some are purely attributed to excitement, entertainment, or drama, and many hate crimes like these go unnoticed or unreported. An example of thrill-seeking motivation would be a group of young, white teens verbally assaulting a Muslim girl wearing a hijab on the street, purely due to the fact she is alone and can be identified as Muslim. Victims of thrill-seeking motivated hate crimes are often picked because of their vulnerability or because they are a minority, and they usually differ from their attackers. A study found that 70% of "thrill offences" were assaults, including vicious beatings that put victims in hospital, (Burke, 2017). Victims based on this motivation are picked often at random, usually alone, and because they are perceived as different.
[[wikipedia:Maslow's_hierarchy_of_needs|Maslow's hierarchy of needs theory]] can explain this type of behaviour. Maslow claimed that people have an innate need to feel belonging and acceptance amongst their social groups. These groups do not depend on size, as long as feelings of love and acceptance are felt and reciprocated. Depending on the power and subjective pressure of the group, this can override the physiological and security needs of the individual. Many people are motivated to give into [[wikipedia:Peer_pressure|peer pressure]] in the fear of rejection and isolation from the group, therefore behaving in ways that agree with the group norms that they might not behave in if by themselves or with a different group.
=== Defensive ===
This type of motivation towards hate crimes is driven from the perpetrator feeling "attacked", or "defending" what and who they are; their community, workplace, religion, or country. The main difference is victims are often targeted, unlike thrill-seekers. This helps the perpetrator to justify their crimes, since they are usually acting out as an emotional response to a perceived threat. Where defensive thrill-seeking perpetrators are alike is their lack of remorse for attacks and perceive they are doing so on behalf of the community. An example of this might be an old man refusing to be served by a transgender woman at the supermarket, stating that these people shouldn't be given jobs and are taking employment away from 'normal' people. This prejudice is often triggered from past experiences that might have affected the perpetrator directly or indirectly, perhaps something they saw on the television and experienced an emotional reaction towards it.
[[File:World-Trade-Center 9-11.jpg|alt=|left|thumb|370x370px|''Figure 6.'' September 11 attacks on the World Trade Centre saw a major surge in defensive hate crime against the Muslim community]]
Defensive hate crimes tend to follow an event as an emotional reaction guided by prejudice. This type of motivation is often connected to terrorist attacks. The aftermath of the [[wikipedia:September_11_attacks|September 11 attack]] on America led to a substantial increase in defensive-motivated hate crimes. The Federal Bureau of Investigation (FBI) database reported the number of hate crimes directed towards Muslims and Arabs was 28 in 2000, and surged to 481 in 2001, (Levin and Reichelmann, 2015). Group factors are more important for the purpose of explaining defensive hate crimes. Prejudice against race was explained by Blumer's 1958 theory of group position as a collective perception rather than feelings between the individual members of different groups. Prejudice is an emotion felt by the dominant group and holds a position of superiority over the subordinate group, which is evident in historically White dominant communities who have a sudden surge in minority populations. This surge is interpreted as a threat to the dominant group, and violence is used to combat in order to retain power.
'''Quiz''' <quiz display=simple>
{What is the main difference between thrill-seeking and defensive motivated hate crime
|type="()"}
+ Defensive involves targeted victims.
- There is no difference.
- Defensive hate crime occurs from oppressed groups.
- Thrill-seeking involves targeted victims.
</quiz>
=== Retaliatory ===
Retaliatory-motivated hate crimes share similarities with defensive-motivated hate crimes, both driven by prejudice. The main feature of retaliatory-motivated hate crimes is that it is a response to a previous hate crime, whether real or not, as an act of revenge. They {{missing}} often associated any individual with those that were involved in the original crime, even if they had no involvement at all. These types of motivated hate crimes are also linked to terrorism, (Burke, 2017). A case in 1991 in Brooklyn, New York involving a Jewish school-boy named Yankel Rosenbaum visiting from Australia was randomly selected and killed after several days of racial hostilities, (Pallone and Workowski, 2015). The events prior to his fateful death began with a young black child being accidentally killed by an Orthodox Jewish driver. Rumours began that entailed the ambulance attendants refused to treat the black children in the accident and instead attended to the Jewish passengers. Fuelled by these rumours, black youths marched through the streets shouting "Kill the Jews." Unfortunately, Rosenbaum, who had nothing to do with the prior events or accident, fell victim to fatality and was killed. This case illustrates that complex nature of retaliatory hate crime and the devastation that can occur from public prejudice.
McClelland's {{fact}} three motivators theory describes the need for power through attainment for control over one's own work or the work of others. People who are authority-motivated have a strong need for success and leadership. They also have a strong need to increase personal status and prestige. Certain individuals who are motivated by authority and power often attain this by asserting dominance over group decisions and influence actions in the most extreme form, violence. Retaliatory-motivated offenders are inspired by a desire to assert authority by avenging a perceived assault on groups they belong or identify with.
=== Mission Offenders ===
The last and rarest type of hate crime motivation is mission offenders. These individuals that are committed to create war against members of a rival race or religion are the deadliest type of hate crime perpetrators. They are often considered by society as "crusaders", acting alone or in small groups that are linked to racist groups, (Burke, 2014). Their behaviour prior to their violent crimes often include long memoirs posted publicly of hate speech and violent imagery. They are very calculated in their target audience, dissimilar to retaliatory-motivated hate crime, and heavily plan their hate crime attacks. Often they will choose a very public or well-known place, and sometimes even travel to symbolically significant sites to maximise their coverage. Rather than acting on an emotional response, mission offenders perceive they are riding the world of evil and justify the excessive violent behaviour against innocent people. Organisational groups that fit into this category would be the Ku Klux Klan or the [[wikipedia:National_Alliance_(United_States)|National Alliance]], or they may operate alone, such like the gunman of the [[wikipedia:2014_Sydney_hostage_crisis#Gunman|2014 Sydney Lindt hostage crisis.]]
==== Sydney Lindt Siege ====
[[File:(1)Lindt Cafe siege two days later 013a.jpg|link=link=link=Special:FilePath/Sydney lindt siege.jpg|alt=|thumb|340x340px|''Figure 8''. The Sydney Lindt Cafe in Martin Place 2 days after the terrorist attack]]
The Sydney Lindt Siege, also referred to as the Sydney hostage crisis, occurred on the 15-16 of December 2014, when a lone gunman, Man Haron Monis, held eighteen people hostage in the Lindt chocolate cafe in Martin Place, Sydney. The Coroner concluded after debate of the gunman's motive that it was a terrorist attack. The events prior of Monis' behaviour reflect those similar to mission offenders. 48 hours before the siege, an anonymous tip was made to Australia's anti-terrorism hotline, raising concerns of information published on Monis' website. Monis had denied all the charges against him on his criminal record - including accessory to murder, hate mail offences, and sexual assault charges - calling them politically motivated, and accused the Iranian Ministry of Intelligence and Australia's ASIO of framing him. Terrorist attacks and mission offenders share many similarities, both motivated to act out in terror and hate, and there has been many debates over whether he was classified as a terrorist or not. Prof Greg Barton (from Deakin University) and Dr Clarke Jones (ANU) told the [[wikipedia:Sydney_siege_inquest|inquest]] that "Monis was a loner and had mental health problems, and was desperate to attach himself to something". Roger Shanahan from the Lowy Institute said that if Monis had followed ISIS direction he would have just killed everyone. Other opinions from the chief of ASIO, terrorist experts and researchers of Australian Muslim Centre's believe that Monis was a terrorist.
'''Quiz'''
<quiz display=simple>
{Did Monis act as a lone gunman or was he a member of a terrorist group.
|type="(he was a lone gunman)"}
- He was a member of a larger terrorist group acting on behalf of them
+ He was a lone gunman
</quiz>
== Connecting theory to hate crime ==
Theories and research specific to hate crime motivation and causes is very limited. Similarly, current research on the link between hate crime and motivation theories remains scant. This is primarily due to two factors; the concept of motivated hate crime is a relatively new category of criminal behaviour, and two, national databases and protocol regarding the outcome of hate crime incidents' is very basic, (Walters, 2011).
One of the most common criminological theories used for hate crime is Merton's (1968) strain theory. Merton argues that deviant behaviour is a result of the 'disequilibrium' from culturally prescribed goals and the opportunity to attain these, (Merton, 1968). Individual's{{gr}} sometimes respond to the pressures and expectations of income, education and individual capacities by acting out in violent behaviour or illegitimate avenues in order to try gain materials and respect that accompanies the social status society encourages. Agnew (1992) adapted this theory by including the viewpoint of the effect of relationships. Agnew argued that others who 1. prevent individuals from obtaining socially valued goals, 2. threaten to remove positive valued stimuli (e.g. a death of a family member or loss of romantic relationship), or 3. present negative valued stimuli (e.g. verbal insults), can result in the individual to respond in anger and frustration, and sometimes even violence. To connect it to hate crime, various minority groups become scapegoats and victims to these negative relationships, often viewed as invaders and unstable threats to society. Dominant groups will blame these minorities for problems with unemployment, housing and job loss, which snowballs into unanticipated feelings of animosity, unfairness, anger and frustration.
A theory that can in part explain the certain behaviours hate crime offenders is '''self-control theory''' (Gottfredson and Hirschi, 1990). Self-control is defined by "the ability to forego acts the provide immediate or near-term pleasures, but that also have negative consequences for the actor, and as the ability to act in favour of longer-term interests," (Gottfredson, 2017). According to this theory, people are not inherently criminal, nor is their behaviour formed from socialised crime, rather, people differ in how well they have developed self-control and attend to the types of stimuli in their environment which inhibit crime-type behaviours. It assumes that socialisation differences in childhood rearing produces a continuum among people in their ability to focus on long-term goals. Self-control is a general cause of crime and can't predict all factors such as peers, school, age, family, and opportunities for crime. This theory is the best description for thrill-seeking hate crime. The theory states that most delinquent and criminal acts are highly opportunistic, adventurous, and involve little planning. These types of crimes require little ingenuity (e.g. vandalism) and usually don't offer any success or status to the offender, but often have high cost for the victim.
== Treatments ==
{{expand}}
=== Desistance Theory ===
Treatment programs for hate crime perpetrators and criminals in general are extremely important to integrate them back into society pro-socially. A treatment program that has been adopted to target offenders to cease engaging in these types of behaviours is [https://www.iriss.org.uk/resources/insights/how-why-people-stop-offending-discovering-desistance desistance theory] (Giordano et al, 2002). The theory outlines a four-part 'theory of cognitive transformation' where they argue that the desistance process involves:
# A 'general cognitive openness to change'
# Exposure and reaction to 'hooks for change' or turning points
# The envisioning of an appealing and conventional 'replacement self'
# A transformation in the way the actor views deviant behaviour
Overall, the process involves the offender/s from ceasing to engage in behaviour by maturation, gaining employment, forming pro-social, intimate relationships, gaining a sense of agency over their lives, and changing the schemas of their self-identity, (Iganski, 2008). This theory is based on the relationship between the individual and social structures, and how the elements of their environment and significant life changes can cause anti-social behaviours. The treatment process is 'complete' when old behaviours are no longer perceived as desirable or relevant. Each treatment process is different every individual, some see desistance as a permanent change of behaviour that can take several years, and others see it as more fluid with episodes of violent behaviour reappearing.
=== Good Lives Model ===
A second model that is predominantly used for domestic and sexual violence cases is the [https://www.goodlivesmodel.com Good Lives model,] (Ward, 2002). This model focuses on a more holistic approach, placing emphasis on fundamental human needs of life (healthy living and functioning), knowledge, excellence in work/play, excellence in agency (autonomy of self), inner peace (freedom from stress), friendship, community, spirituality (finding meaning and purpose for life), happiness, and creativity, (Ward, 2002). It argues that criminal behaviour is a result of internal and external obstacles interfering with the acquisition of these primary goods, and individuals who posses many obstacles and few strengths are more susceptible for engagement in problematic and violent behaviours. These individuals are unable to utilise their positive skills or strengths to maintain desired outcomes in prosocial ways, thereby forcing them to engage in maladaptive behaviours. From example, impulsive behaviours may prevent good fulfilment or a loss of attainment for the primary good of agency. Poor or lack of emotional regulation is similar in preventing attainment of inner peace, which can lead to anti-social behaviours such as alcohol abuse.
== Conclusion ==
Hate crime is a new issue for typology of criminal behaviour, and needs to be addressed seriously. The emerging magnitude of these types of crimes, reported and unreported, affect not only the victims but also communities and nations as a whole. From research, it can be concluded that proper databases that report on these crimes needs to be established with coherent framework and guidelines across nations to address these types of behaviours appropriately. There is a major gap on the reporting of these crimes, especially in Australia, which needs to be addressed in order to understand the motivations behind these crimes. Current research that outlines the four motivations: thrill-seeking, defensive, retaliatory, and mission offenders, offer major insight on positions to start tackling this issue, as each hate crime case is different.
==See also==
*[[Motivation and emotion/Book/2011/Criminality|Criminality]] (Book chapter, 2011)
*[[w:Emotion|Emotion]] (Wikipedia)
*[[w:Hate crime|Hate crime]] (Wikipedia)
*[[Motivation and emotion/Book/2016/Ideological motivation and violent crime|Ideological motivation and violent crime]] (Book chapter, 2016)
*[[w:Motivation|Motivation]] (Wikipedia)
*[[Motivation and emotion/Book/2015/Murder motivation|Murder motivation]] (Book chapter, 2015)
*[[Motivation and emotion/Book/2016/Villain motivations|Villain motivations]] (Book chapter, 2016)
*[[Motivation and emotion/Book/2010/Violent crime motivation|Violent crime motivation]] (Book chapter, 2010)
== References ==
{{Hanging indent|1=
Allport, G. W. (1954). The nature of prejudice. Cambridge, MA: Addison-Wesley.
Agnew, R. (1992). Foundation for a general strain theory of crime and delinquency. Criminology, 30, 47–87.
American Psychological Association, (2019). The Psychology of Hate Crimes. https://www.apa.org/advocacy/interpersonal-violence/hate-crimes
Armstrong, T. (2005). Evaluating the competing assumptions of Gottfredson and Hirschi’s (1990) a general theory of crime and psychological explanations of aggression. Western Criminology Review, 6(1), 12–21.
Blumer, Herbert (1958-04). "Race Prejudice as a Sense of Group Position" (in en-US). The Pacific Sociological Review 1 (1): 3–7. doi:10.2307/1388607. ISSN 0030-8919.
Craig, K. M. (2002). Examining hate-motivated aggression: A review of the social psychological literature on hate crimes as a distinct form of aggression. Aggression and Violent Behaviour, 7, 85–101.
Cohen, Hagar; Mitchell, Scott (2019-05-03). "Hate crime laws rarely used by Australian authorities, police figures reveal". ABC News
CNN, Story by Daniel Burke (2017), CNN Religion Editor Graphics and data analysis by Sergio Hernandez. "The four reasons people commit hate crimes".
Federal Bureau of Investigation. (n.d.). Hate Crimes {{!}} Federal Bureau of Investigation. [online] Available at: https://www.fbi.gov/investigate/civil-rights/hate-crimes
Gottfredson, Michael (2017-07-27). Oxford Research Encyclopedia of Criminology and Criminal Justice. Oxford University Press. doi:10.1093/acrefore/9780190264079.013.252. {{ISBN|9780190264079}}
Hamad, R. (2017). Hate Crime: Causes, Motivations and Effective Interventions for Criminal Justice Social Work. Centre for Youth and Criminal Justice, UK.
Iganski, P. (2008) 'Hate crime' and the city. Bristol University Press. (1) pp. 95–114. {{ISBN|9781847423573}}. DOI: 10.2307/j.ctt9qgq3n
Kolb,W. L.(1954-10-01)."THE NATURE OF PREJUDICE. By Gordon W. Allport. Cambridge: Addison-Wesley Publishing Company, Inc., 1954. 537 pp. $5.50".Social Forces33(1): 90–91.doi:10.2307/2573151.ISSN 0037-7732.http://dx.doi.org/10.2307/2573151
Kutner,N. G.(1968-09-01)."ON THEORETICAL SOCIOLOGY: FIVE ESSAYS, OLD AND NEW. By Robert K. Merton. New York: The Free Press, 1967. 171 pp. $2.45".Social Forces47(1): 91–91.doi:10.2307/2574724.ISSN 0037-7732.http://dx.doi.org/10.2307/2574724
Levin, Jack; Reichelmann, Ashley (2015-11). "From Thrill to Defensive Motivation: The Role of Group Threat in the Changing Nature of Hate-Motivated Assaults" (in en). American Behavioral Scientist 59 (12): 1546–1561. doi:10.1177/0002764215588812. ISSN 0002-7642.
Levin, J., & Rabrenovic, G. (2009). Hate as cultural justification for violence. In B. Perry (Ed.), Hate crimes
McDevitt, Jack; Levin, Jack; Bennett, Susan (2002-1). "Hate Crime Offenders: An Expanded Typology" (in en). Journal of Social Issues 58 (2): 303–317. doi:10.1111/1540-4560.00262. ISSN 0022-4537.
Merton, R. K. (1968). Social theory and social structure. New York: Free Press.
National Criminal Justice Reference Service. "NCJRS - National Criminal Justice Reference Service - In the Spotlight". web.archive.org. 2016-12-16.
Organisation for Security and Co-operation in Europe (OSCE), (2010). Understanding Hate Crimes https://www.osce.org/odihr/104165?download=true
PALLONE, NATHANIEL J.; WORKOWSKI, ERIC (2014-01-09). Young Victims, Young Offenders. Routledge. pp. 1–10. {{ISBN|9781315792897}}.
Perry, B. (2009b). The sociology of hate: Theoretical approaches. In B. Perry (Ed.), Hate crimes (Vol. 1).
United States Department Of Justice. Office Of Justice Programs. Bureau Of Justice Statistics (2008), National Crime Victimization Survey, 1999 [Record-Type Files]: Version 1, ICPSR - Interuniversity Consortium for Political and Social Research, doi:10.3886/icpsr22922.vl
Walters, M. (2010). A General Theories of Hate Crime? Strain, Doing Difference and Self Control Critical Criminology, 19 (4). pp. 313-330. Doi: 10.1007/s10612-010-9128-2 | Federal Bureau of Investigation. [online] Available at: https://www.fbi.gov/investigate/civil-rights/hate-crimes
Gottfredson, Michael (2017-07-27). Oxford Research Encyclopedia of Criminology and Criminal Justice. Oxford University Press. doi:10.1093/acrefore/9780190264079.013.252. {{ISBN|9780190264079}}
Hamad, R. (2017). Hate Crime: Causes, Motivations and Effective Interventions for Criminal Justice Social Work. Centre for Youth and Criminal Justice, UK.
Iganski, P. (2008) 'Hate crime' and the city. Bristol University Press. (1) pp. 95–114. {{ISBN|9781847423573}}. DOI: 10.2307/j.ctt9qgq3n
Kolb,W. L.(1954-10-01)."THE NATURE OF PREJUDICE. By Gordon W. Allport. Cambridge: Addison-Wesley Publishing Company, Inc., 1954. 537 pp. $5.50".Social Forces33(1): 90–91.doi:10.2307/2573151.ISSN 0037-7732.http://dx.doi.org/10.2307/2573151
Kutner,N. G.(1968-09-01)."ON THEORETICAL SOCIOLOGY: FIVE ESSAYS, OLD AND NEW. By Robert K. Merton. New York: The Free Press, 1967. 171 pp. $2.45".Social Forces47(1): 91–91.doi:10.2307/2574724.ISSN 0037-7732.http://dx.doi.org/10.2307/2574724
Levin, Jack; Reichelmann, Ashley (2015-11). "From Thrill to Defensive Motivation: The Role of Group Threat in the Changing Nature of Hate-Motivated Assaults" (in en). American Behavioral Scientist 59 (12): 1546–1561. doi:10.1177/0002764215588812. ISSN 0002-7642.
Levin, J., & Rabrenovic, G. (2009). Hate as cultural justification for violence. In B. Perry (Ed.), Hate crimes
McDevitt, Jack; Levin, Jack; Bennett, Susan (2002-1). "Hate Crime Offenders: An Expanded Typology" (in en). Journal of Social Issues 58 (2): 303–317. doi:10.1111/1540-4560.00262. ISSN 0022-4537.
Merton, R. K. (1968). Social theory and social structure. New York: Free Press.
National Criminal Justice Reference Service. "NCJRS - National Criminal Justice Reference Service - In the Spotlight". web.archive.org. 2016-12-16.
Netsafe. (2018). Online hate speech: A survey on personal experiences and exposure among adult New Zealanders. Retrieved from https://www.netsafe.org.nz/wp-content/uploads/2019/11/onlinehatespeech- survey-2018.pdf
Organisation for Security and Co-operation in Europe (OSCE), (2010). Understanding Hate Crimes https://www.osce.org/odihr/104165?download=true
Pallone, J. N., & Workowski, E. (2014). Overview: Crime, Children, and Adolescents. Current Issues in Policy and Treatment, 1, 1-10. DOI: https://doi.org/10.4324/9781315792897
Perry, B. (2009b). The sociology of hate: Theoretical approaches. In B. Perry (Ed.), Hate crimes (Vol. 1).
United States Department Of Justice. Office Of Justice Programs. Bureau Of Justice Statistics (2008), National Crime Victimization Survey, 1999 [Record-Type Files]: Version 1, ICPSR - Interuniversity Consortium for Political and Social Research, doi:10.3886/icpsr22922.vl
Walters, M. (2010). A General Theories of Hate Crime? Strain, Doing Difference and Self Control Critical Criminology, 19 (4). pp. 313-330. Doi: 10.1007/s10612-010-9128-2
}}
== External Links ==
*https://www.crimestoppers.com.au (Crime Stoppers Australia)
*https://www.crimestats.aic.gov.au/facts_figures/ (Crime Statistics)
*http://www.humanrightsfirst.org/sites/default/files/Ten-Point-Plan-english.pdf?id=157 (Human Rights Organisation)
*https://www.maainternational.org.au (Muslim Aid Australia)
[[Category:Motivation and emotion/Book/2019]]
[[Category:Motivation and emotion/Book/Forensic]]
[[Category:Crime]]
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Social Victorians/People/Abercorn
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== Overview ==
The Dukedom of Abercorn is the last non-royal dukedom created. Queen Victoria created it in 1869. This page includes the Earl of Wicklow, the family of which married into this one in
== Also Known As ==
*Family name: Hamilton
*the Duke of Abercorn
**James Hamilton, 1st Duke of Abercorn (10 August 1868 – 31 October 1885)<ref name=":0">"James Hamilton, 1st Duke of Abercorn." {{Cite web|url=http://www.thepeerage.com/p10144.htm#i101433|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
**James Hamilton, 2nd Duke of Abercorn (31 October 1885 – 3 January 1913)<ref name=":12">"James Hamilton, 2nd Duke of Abercorn." {{Cite web|url=http://www.thepeerage.com/p10104.htm#i101033|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
**James Albert Edward Hamilton, 3rd Duke of Abercorn (3 January 1913 – 12 September 1953)<ref name=":13">"James Albert Edward Hamilton, 3rd Duke of Abercorn." {{Cite web|url=http://www.thepeerage.com/p10104.htm#i101031|title=Person Page|website=www.thepeerage.com|access-date=2020-10-09}}</ref>
*the Duchess of Abercorn
**Louisa Russell Hamilton, Duchess of Abercorn (10 August 1868 – 31 October 1885)
**Maria Anna Curzon-Howe Hamilton (31 October 1885 – 3 January 1913)
*Dowager Duchess of Hamilton
**Louisa Russell Hamilton, Duchess of Abercorn (31 October 1885 – March 1905)
**Maria Anna Curzon-Howe Hamilton (3 January 1913 – )
*Subsidiary titles:
**Marquess of Hamilton (courtesy title for the heir apparent)
***James Albert Edward Hamilton, 3rd Duke of Abercorn (31 October 1885 – 12 September 1953)
**Viscount Strabane (courtesy title for the heir apparent of the Marquess of Hamilton)
== Acquaintances, Friends and Enemies ==
=== Friends ===
*The Royal Family, especially [[Social Victorians/People/Albert Edward, Prince of Wales | Albert Edward, Prince]] and [[Social Victorians/People/Alexandra, Princess of Wales | Alexandra, Princess]] of Wales, in the generation of the 2nd duke.
== Timeline ==
'''1832 October 25''', James Hamilton and Louisa Russell married at Gordon Castle, Fochabers, Morayshire, in Scotland.<ref name=":0" />
'''1854 May 23''', Beatrix Frances Hamilton and George Frederick D'Arcy Lambton married.<ref>"Lady Beatrix Frances Hamilton." {{Cite web|url=http://www.thepeerage.com/p1147.htm#i11470|title=Person Page|website=www.thepeerage.com|access-date=2020-10-09}}</ref>
'''1855 April 10''', Harriet Georgiana Louisa Hamilton and Thomas George Anson married.<ref name=":2">"Lady Harriett Georgiana Louisa Hamilton." {{Cite web|url=http://www.thepeerage.com/p1034.htm#i10332|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
'''1858 October 26''', Katherine Elizabeth Hamilton and William Henry Edgcumbe married.<ref>"Lady Katherine Elizabeth Hamilton." {{Cite web|url=http://www.thepeerage.com/p1135.htm#i11344|title=Person Page|website=www.thepeerage.com|access-date=2020-10-09}}</ref>
'''1859 November 22''', Louisa Jane Hamilton and William Montagu Douglass Scott married.<ref>"Lady Louisa Jane Hamilton." {{Cite web|url=http://www.thepeerage.com/p10359.htm#i103583|title=Person Page|website=www.thepeerage.com|access-date=2020-10-09}}</ref>
'''1868''', the title the Duke of Abercorn was created.<ref>{{Cite journal|date=2020-07-06|title=James Hamilton, 1st Duke of Abercorn|url=https://en.wikipedia.org/w/index.php?title=James_Hamilton,_1st_Duke_of_Abercorn&oldid=966293304|journal=Wikipedia|language=en}}</ref>
'''1869 January 7''', James Hamilton (2nd Duke) and Maria Anna Curzon-Howe married at St. George's Church, St. George Street, Hanover Square, in London.<ref name=":3">"Lady Mary Anna Curzon." {{Cite web|url=http://www.thepeerage.com/p10104.htm#i101034|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
'''1869 November 8''', there may have been a double wedding: Albertha Frances Anne Hamilton and George Charles Spencer-Churchill married<ref name=":8">"Lady Albertha Frances Anne Hamilton." {{Cite web|url=http://www.thepeerage.com/p10595.htm#i105942|title=Person Page|website=www.thepeerage.com|access-date=2020-10-09}}</ref>, and Maud Evelyn Hamilton and Henry Petty-Fitzmaurice married<ref name=":1">"Lady Maud Evelyn Hamilton." {{Cite web|url=http://www.thepeerage.com/p1163.htm#i11629|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>.
'''1871 November 28''', George Francis Hamilton and Maud Caroline Lascelles married.<ref name=":6">"Rt. Hon. Lord Sir George Francis Hamilton." {{Cite web|url=http://www.thepeerage.com/p1133.htm#i11323|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
'''1878 July 20''', Claud John Hamilton and Carolina Chandos-Pole married.<ref name=":5">"Lord Claud John Hamilton." {{Cite web|url=http://www.thepeerage.com/p11067.htm#i110662|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
'''1882 March 16''', Georgiana Susan Hamilton and Edward Turnour married.<ref>"Lady Georgiana Susan Hamilton." {{Cite web|url=http://www.thepeerage.com/p1180.htm#i11791|title=Person Page|website=www.thepeerage.com|access-date=2020-10-09}}</ref>
'''1883 November 20''', the marriage between Albertha Frances Anne Hamilton Spencer-Churchill and George Charles Spencer-Churchill was annulled by petition from Albertha Frances Anne Hamilton Spencer-Churchill (married in 1869).<ref name=":8" />
'''1891 June 2''', Ernest William Hamilton and Pamela Campbell married.<ref name=":7">"Pamela Campbell." {{Cite web|url=http://www.thepeerage.com/p2107.htm#i21063|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
'''1894 November 1''', James Albert Edward Hamilton and Rosaline Cecilia Caroline Bingham married at St. Paul's Church, Knightsbridge, in London.<ref name=":14">"Lady Rosalind Cecilia Caroline Bingham." {{Cite web|url=https://www.thepeerage.com/p10104.htm#i101032|title=Person Page|website=www.thepeerage.com|access-date=2021-05-15}}</ref>
'''1897 June 28, Monday''', according to the ''Morning Post'', James Hamilton, 2nd Duke and Maria, Duchess of Abercorn were invited to the [[Social Victorians/Diamond Jubilee Garden Party|Queen's Garden Party]], the official end of the Diamond Jubilee celebrations in London, as were James Albert Edward Hamilton, Marquis and Rosaline, Marchioness of Hamilton.<ref>“The Queen’s Garden Party.” ''Morning Post'' 29 June 1897, Tuesday: 4 [of 12], Cols. 1a–7c [of 7] and 5, Col. 1a–c. ''British Newspaper Archive'' ''<nowiki>https://www.britishnewspaperarchive.co.uk/viewer/BL/0000174/18970629/032/0004</nowiki>'' and ''<nowiki>https://www.britishnewspaperarchive.co.uk/viewer/bl/0000174/18970629/032/0005</nowiki>''.</ref>
'''1897 July 2, Friday''', Alexandra Phyllis Hamilton (#64 on the [[Social Victorians/1897 Fancy Dress Ball#List of People Who Attended|list of people who were present]]) attended the [[Social Victorians/1897 Fancy Dress Ball | Duchess of Devonshire's fancy-dress ball]] at Devonshire House, as did her uncle Lord Frederick Spencer Hamilton (#84), the Marquess of Hamilton (#657), and a Mr. Ronald Hamilton (#105). Besides these, probably, a Mr. and Mrs. Hamilton also attended.
'''1902 January 14''', Gladys Mary Hamilton and Ralph Francis Forward-Howard married.<ref>"Lady Gladys Mary Hamilton." {{Cite web|url=http://www.thepeerage.com/p2107.htm#i21066|title=Person Page|website=www.thepeerage.com|access-date=2020-10-09}}</ref>
'''1933 July 11''', Claud Nigel Hamilton and Violet Ruby Ashton married.<ref name=":4">"Captain Lord Sir Claud Nigel Hamilton." {{Cite web|url=http://www.thepeerage.com/p2109.htm#i21081|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
== Costume at the Duchess of Devonshire's 2 July 1897 Fancy-dress Ball ==
[[File:Helen-Mary-Theresa-ne-Vane-Tempest-Stewart-Countess-of-Ilchester-when-Lady-Helen-Stewart-as-the-Archduchess-Marie-Christine-of-Austria.jpg|thumb|alt=Black-and-white photograph of a seated woman richly dressed in an historical costume with a white feather plume in her hair and a fan|Lady Helen Stewart as Arch-duchess Marie Christine of Austria. ©National Portrait Gallery, London.]]
=== Lady Alexandra Hamilton ===
Lady Alexandra Hamilton was one of the archduchesses — along with with 3 or 4 other young women — in [[Social Victorians/People/Londonderry#The Entourage of Maria Thérèse|the entourage of the Marchioness of Londonderry]], who led the Austrian procession as Marie Thérèse, Empress of the Holy Roman Empire.<ref>“The Ball at Devonshire House. Magnificent Spectacle. Description of the Dresses.” London ''Evening Standard'' 3 July 1897 Saturday: 3 [of 12], Cols. 1a–5b [of 7]. ''British Newspaper Archive'' https://www.britishnewspaperarchive.co.uk/viewer/bl/0000183/18970703/015/0004.</ref>{{rp|p. 3, Col. 3a}} These young women were present at the ball as the daughters of Marie Thérèse, and the young men dressed as archdukes were present as her sons. Lady Alexandra Hamilton went as "Archduchess Marie-Josepha in the Archduchess Marie-Karoline and Emperor Joseph II section of the Austrian Court of Maria Theresa Quadrille."<ref name=":9">"Fancy Dress Ball at Devonshire House." ''Morning Post'' Saturday 3 July 1897: 7 [of 12], Col. 4a–8 Col. 2b. ''British Newspaper Archive'' https://www.britishnewspaperarchive.co.uk/viewer/bl/0000174/18970703/054/0007.</ref>{{rp|p. 7, Col. 6b}} <ref name=":10">"Ball at Devonshire House." The ''Times'' Saturday 3 July 1897: 12, Cols. 1a–4c ''The Times Digital Archive''. Web. 28 Nov. 2015.</ref>
The newspapers report that the archduchesses were all dressed alike, but only one photograph exists of any of these young women in costume — that of [[Social Victorians/People/Londonderry#Helen Mary Theresa Vane-Tempest-Stewart|Helen Mary Theresa Vane-Tempest-Stewart]] (which is shown, right). The newspaper descriptions are on her page, with her portrait in costume, but they apply to all the archduchesses.
=== Lord Frederick Hamilton ===
[[File:Lord Frederick Spencer Hamilton Vanity Fair 1895-02-07.jpg|thumb|left|alt=Colored drawing of a man in a suit, his hands in his pockets, facing to the right|Lord Frederick Hamilton, ''Vanity Fair'', by "Spy," 7 February 1895]]
Lord Frederick Spencer Hamilton was 6th son and 13th child of the 1st Duke of Abercorn. No photograph of him in costume exists.
He is shown (at left) as he looked in 7 February 1895 in a Spy caricature in ''Vanity Fair''. This caricature portrait, by Leslie Ward ("Spy") is called ''The Pall Mall Magazine'' and is Number 647 in Vanity Fair's "Statesmen" series.<ref name=":16">{{Cite journal|date=2024-01-14|title=List of Vanity Fair (British magazine) caricatures (1895–1899)|url=https://en.wikipedia.org/w/index.php?title=List_of_Vanity_Fair_(British_magazine)_caricatures_(1895%E2%80%931899)&oldid=1195518024|journal=Wikipedia|language=en}}</ref> He was editor of the ''Pall Mall Gazette'' 1896–1900.<ref>{{Cite journal|date=2023-09-23|title=Lord Frederick Spencer Hamilton|url=https://en.wikipedia.org/w/index.php?title=Lord_Frederick_Spencer_Hamilton&oldid=1176655264|journal=Wikipedia|language=en}} https://en.wikipedia.org/wiki/Lord_Frederick_Spencer_Hamilton.</ref>
For the ball, Lord Frederick Hamilton was dressed
*as a "gentleman of the Court of Queen Elizabeth," wearing "crimson cloth of gold with jewelled belt."<ref name=":15">“The Duchess of Devonshire’s Ball.” The ''Gentlewoman'' 10 July 1897 Saturday: 32–42 [of 76], Cols. 1a–3c [of 3]. ''British Newspaper Archive'' https://www.britishnewspaperarchive.co.uk/viewer/bl/0003340/18970710/155/0032.</ref>{{rp|p. 36, Col. 3b}}
*as a "Gentleman of the Court of Queen Elizabeth. Costume of crimson and cloth of g [sic] with jewelled belt."<ref name=":9" />{{rp|p. 8, Col. 1b}}
*"in crimson cloth of gold and jeweled belt."<ref>"Duchess of Devonshire's Fancy Ball. A Brilliant Spectacle. Some of the Dresses." London ''Daily News'' Saturday 3 July 1897: 5 [of 10], Col. 6a–6, Col. 1b. ''British Newspaper Archive'' http://www.britishnewspaperarchive.co.uk/viewer/bl/0000051/18970703/024/0005 and http://www.britishnewspaperarchive.co.uk/viewer/BL/0000051/18970703/024/0006.</ref>{{rp|p. 5, Col. 7a}}
*"as a gentleman of the court of Queen Elizabeth, was dressed in a costume of crimson cloth-of-gold, with a jewelled belt."<ref name=":11">“The Devonshire House Ball. A Brilliant Gathering.” The ''Pall Mall Gazette'' 3 July 1897, Saturday: 7 [of 10], Col. 2a–3a. ''British Newspaper Archive'' https://www.britishnewspaperarchive.co.uk/viewer/bl/0000098/18970703/019/0007.</ref>
==== Memoirs ====
* Hamilton, Frederic [sic] Spencer. ''My Yesterdays'' (3 vols.). Hodder and Stoughton, 1920.
*# ''The Days Before Yesterday''. The Internet Archive has this: https://archive.org/details/daysbeforeyester00hamiuoft/page/n5/mode/2up.
*# ''Vanished Pomps of Yesterday''. The Internet Archive has this: https://archive.org/details/vanishedpompsofy028823mbp.
*# ''Here, There and Everywhere''. The Internet Archive has this: https://archive.org/details/herethereeverywh0000hami.
[[File:James Hamilton 3rd Duke of Abercorn.png|thumb|alt=Old colored drawing of a man in a 19th-century officer's uniform of the 1st Life Guards with white gloves, a red stripe down the side of his pants and unbuttoned jacket and a hat, holding a white or silver sword under his left arm, facing 1/4 to his right|"He will be the 3rd Duke" (James Hamilton, Marquis of Hamilton), ''Vanity Fair'' 16 February 1899]]
=== James Hamilton, Marquess of Hamilton ===
James Hamilton, Marquis of Hamilton was dressed in a "black velvet tunic; breeches and cloak trimmed jet; large hat, feathers, wig, sword, &c., of the period" of Charles II.<ref name=":15" />{{rp|34, Col. 3a}} No photograph of him in costume exists.
A caricature portrait (right) called ''He will be the 3rd Duke'' (James Hamilton, Marquess of Hamilton) by "Hadge" appeared in the 16 February 1899 issue of ''Vanity Fair'', as Number 739 in its "Men of the Day" series,<ref name=":16" /> giving a sense of what he looked like at about the time of the ball.
In 1892 Hamilton joined the 1st Life Guards, so the uniform he is wearing in this portrait is likely that of an officer of the 1st Life Guards.<ref>{{Cite journal|date=2024-01-12|title=James Hamilton, 3rd Duke of Abercorn|url=https://en.wikipedia.org/w/index.php?title=James_Hamilton,_3rd_Duke_of_Abercorn&oldid=1195216640|journal=Wikipedia|language=en}} https://en.wikipedia.org/wiki/James_Hamilton,_3rd_Duke_of_Abercorn.</ref>
James Hamilton's wife Lady Rosalind Hamilton is not reported as having been present at the ball, perhaps because she was pregnant with her second child and gave birth in August, five weeks later, so she was around 8 months pregnant.
=== Ronald Hamilton ===
Mr. Ronald Hamilton, possibly Ronald James Hamilton, was dressed as a "Gentleman of the Court of Queen Elizabeth, in black velvet trimmed with jet."<ref name=":9" />{{rp|p. 8, Col. 1c}}
== Demographics ==
*Nationality: the title Duke of Abercorn is in the peerage of Ireland; the Marquess of Hamilton is in the peerage of the U.K.
== Family ==
*James Hamilton, 1st Duke of Abercorn (21 January 1811 – 31 October 1885)<ref name=":0" />
*Louisa Russell Hamilton (– March 1905)
#Lady '''Harriet Georgiana Louisa Hamilton''' Anson (6 July 1834 – 23 April 1913)
#Lady Beatrix Frances Hamilton Lambton (21 July 1835 – 21 January 1871)
#Lady Louisa Jane Hamilton Scott (26 August 1836 – 16 March 1912)
#Lord '''James Hamilton, 2nd Duke of Abercorn''' (24 August 1838 – 3 January 1913)
#Lady Katherine Elizabeth Hamilton Edgcumbe (9 January 1840 – 3 September 1874)
#Lady Georgiana Susan Hamilton Turnour (7 July 1841 – 23 March 1913)
#Lord '''Claud John Hamilton''' (20 February 1843 – 26 January 1925)
#Rt. Hon. Lord Sir '''George Francis Hamilton''' (17 December 1845 – 22 September 1927)
#Lady Albertha Frances Anne Hamilton Spencer-Churchill (29 July 1847 – 7 January 1932)
#Lord Ronald Douglas Hamilton (17 March 1849 – DVP<ref>{{Cite journal|date=2020-07-27|title=James Hamilton, 2nd Duke of Abercorn|url=https://en.wikipedia.org/w/index.php?title=James_Hamilton,_2nd_Duke_of_Abercorn&oldid=969822724|journal=Wikipedia|language=en}}</ref> 6 November 1867)
#Lady Maud Evelyn Hamilton Petty-Fitzmaurice, the [[Social Victorians/People/Lansdowne | Marchioness of Lansdowne]] (17 December 1850 – 21 October 1932)<ref name=":1" />
#Lord Cosmo Hamilton (16 April 1853 – 16 April 1853)
#Lord '''Frederick Spencer Hamilton''' (13 October 1856 – 11 August 1928)
#Lord '''Ernest William Hamilton''' (5 September 1858 – 14 December 1939)
*Harriet Georgiana Louisa Hamilton Anson (6 July 1834 – 23 April 1913)<ref name=":2" />
*Thomas George Anson, 2nd Earl of Lichfield (15 August 1825 – 7 January 1892)
#Lady Evelyn Anson ( – 2 July 1895)
#Thomas Francis Anson, 3rd Earl of Lichfield (31 January 1856 – 29 July 1918)
#Hon. Sir George Augustus Anson (22 December 1857 – 25 May 1947)
#Major Hon. Henry James Anson (29 December 1858 – 26 February 1904)
#Lady Florence Beatrice Anson (1860 – 25 September 1946)
#Hon. Frederic William Anson (4 February 1862 – 2 April 1917)
#Hon. Claud Anson (11 January 1864 – 25 December 1947)
#Lady Beatrice Anson (1865 – 15 December 1919)
#Hon. Francis Anson (7 March 1867 – 13 April 1928)
#Lady Mary Maud Anson (1869 – 22 September 1961)
#Lady Edith Anson (1870 – 8 October 1932)
#Hon. William Anson (19 April 1872 – 22 June 1926)
#Hon. Alfred Anson (15 April 1876 – 25 March 1944)
*James Hamilton, 2nd Duke of Abercorn (24 August 1838 – 3 January 1913)<ref name=":12" />
*Maria Anna Curzon-Howe Hamilton (23 July 1848 – 10 May 1929)<ref name=":3" />
#James Albert Edward Hamilton, 3rd Duke of Abercorn (30 November 1869 – 12 September 1953)
#Claud Penn Alexander Hamilton (18 October 1871 – 18 October 1871)
#Charlie Hamilton (10 April 1874 – 10 April 1874)
#'''Alexandra Phyllis Hamilton''' (23 January 1876 – 10 October 1918)
#Claud Francis Hamilton (25 October 1878 – 25 December 1878)
#Gladys Mary Hamilton Forward-Howard (10 December 1880 – 12 March 1917)
#Arthur John Hamilton (20 August 1883 – 6 November 1914)
#(unnamed son) Hamilton (31 October 1886 – 31 October 1886)
#Claud Nigel Hamilton (10 November 1889 – 22 August 1975)<ref name=":4" />
* '''James Albert Edward Hamilton''', Marquess of Hamilton and 3rd Duke of Abercorn (30 November 1869 – 12 September 1953)<ref name=":13" />
* Lady Rosalind Cecilia Caroline Bingham (26 February 1869 – 18 January 1958)<ref name=":14" />
*# Lady Mary Cecilia Rhodesia Hamilton (21 January 1896 – 5 September 1984)
*# Lady Cynthia Elinor Beatrix Hamilton (16 August 1897 – 4 December 1972)
*# Lady Katharine Hamilton (25 February 1900 – 28 April 1985)
*# James Edward Hamilton, 4th Duke of Abercorn (29 February 1904 – 4 June 1979)
*# Captain Lord Claud David Hamilton (13 February 1907 – 15 February 1968)
*Claud John Hamilton (20 February 1843 – 26 January 1925)<ref name=":5" />
*Carolina Chandos-Pole Hamilton (19 July 1857 – 21 September 1911)<ref>"Carolina Chandos-Pole." {{Cite web|url=http://www.thepeerage.com/p11067.htm#i110663|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
#Colonel Gilbert Claud Hamilton (21 April 1879 – 30 March 1943)
#Ida Hamilton (23 July 1883 – November 1970)
*George Francis Hamilton (17 December 1845 – 22 September 1927)<ref name=":6" />
*Lady Maud Caroline Lascelles Hamilton (1846 – 14 April 1938)
#'''Ronald James Hamilton''' (26 September 1872 – 22 January 1958)
#Anthony George Hamilton (17 December 1874 – 11 July 1936)
#Robert Cecil Hamilton (31 January 1882 – 31 July 1947)
*Ernest William Hamilton (5 September 1858 – 14 December 1939)<ref>"Lord Ernest William Hamilton." {{Cite web|url=http://www.thepeerage.com/p2107.htm#i21062|title=Person Page|website=www.thepeerage.com|access-date=2020-10-08}}</ref>
*Pamela Campbell Hamilton ( – 11 May 1931)<ref name=":7" />
#Guy Ernest Frederick Hamilton (11 November 1894 – 23 November 1914)
#Mary Brenda Hamilton (28 March 1897 – 14 March 1985)
#Jean Barbara Hamilton (6 September 1898 – 2 November 1989)
#John George Peter Hamilton (15 October 1900 – 17 June 1967)
=== Earls of Wicklow ===
* Charles Hamilton (1772 – 29 September 1857)<ref>{{Cite web|url=https://www.thepeerage.com/p2139.htm#i21387|title=Charles Hamilton. Person Page #2139|website=www.thepeerage.com|access-date=2026-06-19}}</ref>
* Marianne '''Caroline Tighe''' ( – 29 July 1861)<ref>{{Cite web|url=https://www.thepeerage.com/p62375.htm#i623745|title=Marianne Caroline Tighe. Person Page #62375|website=www.thepeerage.com|access-date=2026-06-19}}</ref>
*# '''Sarah Hamilton''' ( – 13 March 1892)
*# Caroline Elizabeth Hamilton ( – 31 May 1909)
*# Mary Hamilton
*# Charles William Hamilton (1 April 1802 – 16 February 1880)
*# William Tighe Hamilton (31 March 1807 – )
*# Frederick John Henry Fownes Hamilton (27 July 1816 – 1893)
* Rev. Hon. Francis Howard (12 January 1797 – 16 February 1857)<ref>{{Cite web|url=https://www.thepeerage.com/p2140.htm#i21391|title=Rev. Hon. Francis Howard. Person Page #2140|website=www.thepeerage.com|access-date=2026-06-19}}</ref>
* Frances Beresford ( – 17 November 1833)<ref>{{Cite web|url=https://www.thepeerage.com/p3227.htm#i32266|title=Frances Beresford. Person Page #3227|website=www.thepeerage.com|access-date=2026-06-19}}</ref>
*# William George Howard (25 April 1825 – 12 October 1864)
* '''Sarah Hamilton''' (1805<ref name=":17">{{Cite web|url=https://catalogue.nli.ie/Collection/vtls000572704|title=Tighe, Hamilton and Howard Papers,|date=1737|website=catalogue.nli.ie|language=English|access-date=2026-06-19}}</ref> – 13 March 1892)<ref>{{Cite web|url=https://www.thepeerage.com/p2141.htm#i21405|title=Sarah Hamilton. Person Page #2141|website=www.thepeerage.com|access-date=2026-06-19}}</ref>
*# 4 unnamed daughters [per The Peerage; The NLI has 3 daughters]
*## Lady Alice Howard
*## Lady Louisa 'Loulie' Howard
*## Lady Caroline Howard (1836–1923)<ref name=":17" />
*# Charles Francis Arnold Howard, 5th Earl of Wicklow (5 November 1839 – 20 June 1881)
*# Cecil Ralph Howard, 6th Earl of Wicklow (26 April 1842 – 24 July 1891)
== Memoirs and Archives ==
# The Abercorn Papers: GB 0255 PRONI/D623 (found via https://iar.ie/archive/abercorn-papers). A descriptive list is available to search online at: http://www.proni.gov.uk/. The collection is arranged as follows: D623/A Correspondence D623/B Title deeds and leases D623/C Rentals, accounts and vouchers D623/D Maps, plans, surveys, inventories and valuations D623/E Photographs, illuminations, addresses and albums D623/F Material still at Baronscourt D623/G Miscellaneous
#
== Questions and Notes ==
#DVP = decessit vita patris, died while the father was still living
#Mr. Ronald Hamilton cannot be Frederick Hamilton's brother, who should be Lord Ronald Hamilton rather than Mr. Ronald Hamilton, and he died in 1867. He could be this Ronald Hamilton, who would be a Mr. Hamilton: http://www.thepeerage.com/p2163.htm#i21622. He was Lady Alexandra's cousin and nephew of the 1st Duke of Abercorn.
#A Mr. Hamilton is mentioned in the ''Gentlewoman'' article: "Mr. Hamilton (Elizabethan costume), black velvet, trimmed gold."<ref name=":15" />{{rp|34, Col. 1c}} But a later reference in this same article to Mr. Ronald Hamilton matches the description in the ''Morning Post'' article, saying he wore black velvet with jet, rather than gold trim: "'''Mr. Ronald Hamilton''' (gentleman of the Court of Queen Elizabeth), black velvet with jet."<ref name=":15" /> (36, Col. 3b) I believe the other Mr. Hamilton is Mr. [[Social Victorians/People/Cole-Hamilton|Claud Cole-Hamilton]], particularly since Mrs. Hamilton was dressed as Amy Robsart and thus must be Lucy Charlewood Cole-Hamilton because of the description of her costume in the Album of photographs given to the Duchess of Devonshire later.
#Claud John Hamilton is probably who attended the social events, because the other Claud, of whatever generation either died too young or was born too late.
== Footnotes ==
{{reflist}}
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[[File:Components stress tensor.svg|thumb|right|Components of the Cauchy stress tensor in Cartesian coordinates]]
{{Proposed deletion}}
In mathematics, a tensor is a certain kind of geometrical entity and array concept. It generalizes the concepts of scalar, vector (geometric) and linear operator, in a way that is independent of any chosen frame of reference. For example, doing rotations over axis does not affect at all the properties of tensors, if a transformation law is followed. Tensors are of importance in pure and applied mathematics, physics and engineering.
== Resources ==
* [[Acceleration stress-energy tensor]]
* [[Acceleration tensor]]
* [[Dissipation field tensor]]
* [[Dissipation stress-energy tensor]]
* [[Gravitational stress-energy tensor]]
* [[Gravitational tensor]]
* [[Pressure field tensor]]
* [[Pressure stress-energy tensor]]
== See Also ==
* [[Tensors]]
* [[Wikipedia: Tensor]]
[[Category:Tensors| ]]
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AP United States History/1607-1754
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Introduces the colonies established in the New World by the Spanish, French, Dutch, and British.<ref>[https://apstudents.collegeboard.org/courses/ap-united-states-history College Board: AP United States History]</ref>
== Objectives and Skills ==
Topics may include:<ref>[https://apstudents.collegeboard.org/courses/ap-united-states-history College Board: AP United States History]</ref>
* How different European colonies developed and expanded
* Transatlantic trade
* Interactions between American Indians and Europeans
* Slavery in the British colonies
* Colonial society and culture
==Study Notes==
#John Smith - Leader of Jamestown. Saved them. 1608 he ruled. In 1607 he was kidnapped in December and was forced to be executed by Powhatan but Pocahontas saved him.last Federalist, governor of Connecticut
#John Winthrop - Calvinist religious leader, became governor of Massachusetts Bay Company in 1629; successful attorney and manor lord in England believed he had a calling from God to be governor. Was governor for 19 years and helped Massachusetts prosper said “a city upon a hill”
#King Philip/Metacom - Plymouth colony forced him to give up ammunition and forced him to adhere to English law '''King Philip's War''' - War in 1676 between Metacom and the English. This started due to the death of two chiefs and the English wanted control of the Indians then. Colonists had won and beat Metacom. He was killed and his wife and son were traded into slavery. Plymouth colony forced him to give up ammunition and forced him to adhere to English law
#William Penn - attracted to Quaker faith in 1660, when 16.Penn wanted to get away from the persecution of the Church of England. 1681 he was granted fertile land from the King and he founded Pennsylvania. Best advertised state of the New World. He gave out substantial land holdings to get people to come over. Indian relationships were amazing with Penn. They hired Indians as baby sitters! A representative assembly elected by the landowners. No tax supported state church drained coffers or demanded allegiance. He attracted a mix amount of ethnicity with its liberal laws of generosity.
#Anne Hutchinson - Puritan orthodoxy, exceptionally intelligent, strong-willed, and talkative woman, ultimately the mother of 14 children. Swift and sharp in the theological argument, she carried to logical extremes the Puritan doctrine of predestination. She claimed that a holy life was no sure sign of salvation and that the truly saved need not bother to obey the law of either God or man. Trialed in 1638 she boasted that she had come by her beliefs through a direct revelation from God. Puritans banished her and with her family she set out on foot for Rhode Island. She finally moved to New York where Indians had killed her
#founding of Georgia (year,purpose) - Founded in 1733 last of 13 colonies to be planted 126 years after Virginia and 52 years after the twelfth Pennsylvania. The English crown intended Georgia to serve as a buffer. It would protect the more valuable Carolinas against vengeful Spaniards from Florida and against the hostile French from Louisiana. It did suffer much buffeting, it received monetary subsides from the British government at the outset-the only one of the original 13 to get this. It produced silk and wine and they were determined to carve out a haven for wretched souls imprisoned for debt. They wanted to keep slavery out
#joint-stock company - Virginia company of London received a charter from King James I of England for a settlement in New World. Main attraction was gold, combined with strong desire to find a passage through America to the Indies. It let colonists have same rights as Englishmen if they were living in England. Investors paid for their expedition and their equipment in return of hopefully earning a profit. company in which people invest money in hoping that a settlement in the New World will be profitable
#"The Starving Time" - during winter of 1609-1610, 60 out of 500 colonists died
#second Anglo-Powhatan War (1644) - in effort to drive English colonists away; ended with treaty pushing Natives further west
#first slaves in the colonies - before pilgrims landed in New England, the Dutch brought a ship off the coast of Jamestown with 20 Africans. afterwards American colonists took these moments into consideration for slavery
#tobacco - major crop introduced by Natives, helped colonies strive economically
#House of Burgesses - first representative government; founded in Virginia; established in 1619
#"the elect" - Calvinist idea that God chose to "save" certain people, aka "the elect"
#Henry VIII - founded Anglican church
#Protestant reforms - Little did German friar Martin Luther know, when he nailed his protests against Catholic doctrines to the door of Wittenberg’s cathedral in 1517, that he was shaping the destiny of a yet unknown nation. Denouncing the authority of priests and popes, Luther declared that the Bible alone was the source of God’s word. He ignited a fire of religious reform (the Protestant Reformation) that licked its way across Europe for more than a century, dividing peoples, toppling sovereigns, and kindling the spiritual fervor of millions of men and women-some of whom helped to found America.
#"visible saints" - Gnawing doubts about their eternal life (elects life) fate plagued Calvinists. They constantly sought, in themselves and others, signs of conversion, or the receipt of God’s free gift of savaging grace. Conversion was thought to be an intense, identifiable personal experience in which God revealed to the elect their heavenly destiny. Thereafter they were expected to lead sanctified lives, demonstrating by their holy behavior that they were among the visible saints.
#Mayflower Compact - simple agreement, majority rules in voting, further developed to laws and town meetings
#separatists - aka Pilgrims; believed in separation of church and state; Protestants
#Rhode Island - Roger Williams who spoke against Massachusetts and fled to Rhode Island with the help of Indians in 1636. Built a Baptist church and established complete freedom of religion, even for the Jews and Catholics. Named “Rogue’s Island” due to open religion, by other states. Received permission of rights to the soil in 1644. Independent state
#indentured servants - essentially white slaves, had advantage of being same race as colonists, served 7 years then granted very little land, most went back to servitude
#"The Middle Passage" - Most of the slaves who reached North America came from the west coast of Africa, especially the area stretching from present day Senegal to Angola. They were originally captured by African coastal tribes, who traded them in crude markets on the shimmering tropical beaches to itinerant European-and American- flesh merchants. Usually branded and bound, the captives were herded aboard sweltering ships for the nasty “middle passage” on which death rates ran as high as 20%. Terrified survivors were eventually shoved onto auction blocks in New Worlds ports like Newport, Rhode Island, or Charleston, South Carolina, where a giant slave market traded in human misery for more than a century.
#African-American contributions to American culture - From their earliest presence in North America, African Americans have contributed literature, art, agricultural skills, foods, clothing styles, music, language, social and technological innovation to American culture. The cultivation and use of many agricultural products in the U.S., such as yams, peanuts, rice, okra, sorghum, grits, watermelon, indigo dyes, and cotton, can be traced to African and African-American influences.
#typical New England family - Clean water and cool temperatures added ten years to their lives. They enjoyed a good 70 years of life. They migrated as families and the families were very fertile even if the soil was not. Early marriage made up in booming birth rate. Babies just popped right out of the women. Women had to give up their rights when married.
#women's status in colonies - no suffrage, just worked mostly as housewife
#Lord De La Warr - Ordered Jamestown survivors of Starving Time back to Jamestown and ordered a military regime. He arrived in 1610. He had war with the Indians and they raided villages, burned them and stole their goods. A peace treaty of John Rolfe’s marriage to Pocahontas ended the first Anglo-Powhatan War in 1614. Indians attacked and killed 347 settlers, including John Rolfe and the Virginia Company followed with a second war
== References ==
{{Reflist}}
{{subpage navbar}}
{{CourseCat}}
[[Category:18th century in North America]]
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{{:{{BASEPAGENAME}}/Sidebar}}
Introduces the colonies established in the New World by the Spanish, French, Dutch, and British.<ref>[https://apstudents.collegeboard.org/courses/ap-united-states-history College Board: AP United States History]</ref>
== Objectives and Skills ==
Topics may include:<ref>[https://apstudents.collegeboard.org/courses/ap-united-states-history College Board: AP United States History]</ref>
* How different European colonies developed and expanded
* Transatlantic trade
* Interactions between American Indians and Europeans
* Slavery in the British colonies
* Colonial society and culture
==Study Notes==
#John Smith - Leader of Jamestown. Saved them. 1608 he ruled. In 1607 he was kidnapped in December and was forced to be executed by Powhatan but Pocahontas saved him. Last Federalist, governor of Connecticut
#John Winthrop - Calvinist religious leader, became governor of Massachusetts Bay Company in 1629; successful attorney and manor lord in England believed he had a calling from God to be governor. Was governor for 19 years and helped Massachusetts prosper said “a city upon a hill”
#King Philip/Metacom - Plymouth colony forced him to give up ammunition and forced him to adhere to English law '''King Philip's War''' - War in 1676 between Metacom and the English. This started due to the death of two chiefs and the English wanted control of the Indians then. Colonists had won and beat Metacom. He was killed and his wife and son were traded into slavery. Plymouth colony forced him to give up ammunition and forced him to adhere to English law
#William Penn - attracted to Quaker faith in 1660, when 16. Penn wanted to get away from the persecution of the Church of England. 1681 he was granted fertile land from the King and he founded Pennsylvania. Best advertised state of the New World. He gave out substantial land holdings to get people to come over. Indian relationships were amazing with Penn. They hired Indians as baby sitters! A representative assembly elected by the landowners. No tax supported state church drained coffers or demanded allegiance. He attracted a mix amount of ethnicity with its liberal laws of generosity.
#Anne Hutchinson - Puritan orthodoxy, exceptionally intelligent, strong-willed, and talkative woman, ultimately the mother of 14 children. Swift and sharp in the theological argument, she carried to logical extremes the Puritan doctrine of predestination. She claimed that a holy life was no sure sign of salvation and that the truly saved need not bother to obey the law of either God or man. Trialed in 1638 she boasted that she had come by her beliefs through a direct revelation from God. Puritans banished her and with her family she set out on foot for Rhode Island. She finally moved to New York where Indians had killed her
#founding of Georgia (year,purpose) - Founded in 1733 last of 13 colonies to be planted 126 years after Virginia and 52 years after the twelfth Pennsylvania. The English crown intended Georgia to serve as a buffer. It would protect the more valuable Carolinas against vengeful Spaniards from Florida and against the hostile French from Louisiana. It did suffer much buffeting, it received monetary subsides from the British government at the outset-the only one of the original 13 to get this. It produced silk and wine and they were determined to carve out a haven for wretched souls imprisoned for debt. They wanted to keep slavery out
#joint-stock company - Virginia company of London received a charter from King James I of England for a settlement in New World. Main attraction was gold, combined with strong desire to find a passage through America to the Indies. It let colonists have same rights as Englishmen if they were living in England. Investors paid for their expedition and their equipment in return of hopefully earning a profit. company in which people invest money in hoping that a settlement in the New World will be profitable
#"The Starving Time" - during winter of 1609-1610, 60 out of 500 colonists died
#second Anglo-Powhatan War (1644) - in effort to drive English colonists away; ended with treaty pushing Natives further west
#first slaves in the colonies - before pilgrims landed in New England, the Dutch brought a ship off the coast of Jamestown with 20 Africans. afterwards American colonists took these moments into consideration for slavery
#tobacco - major crop introduced by Natives, helped colonies strive economically
#House of Burgesses - first representative government; founded in Virginia; established in 1619
#"the elect" - Calvinist idea that God chose to "save" certain people, aka "the elect"
#Henry VIII - founded Anglican church
#Protestant reforms - Little did German friar Martin Luther know, when he nailed his protests against Catholic doctrines to the door of Wittenberg’s cathedral in 1517, that he was shaping the destiny of a yet unknown nation. Denouncing the authority of priests and popes, Luther declared that the Bible alone was the source of God’s word. He ignited a fire of religious reform (the Protestant Reformation) that licked its way across Europe for more than a century, dividing peoples, toppling sovereigns, and kindling the spiritual fervor of millions of men and women-some of whom helped to found America.
#"visible saints" - Gnawing doubts about their eternal life (elects life) fate plagued Calvinists. They constantly sought, in themselves and others, signs of conversion, or the receipt of God’s free gift of savaging grace. Conversion was thought to be an intense, identifiable personal experience in which God revealed to the elect their heavenly destiny. Thereafter they were expected to lead sanctified lives, demonstrating by their holy behavior that they were among the visible saints.
#Mayflower Compact - simple agreement, majority rules in voting, further developed to laws and town meetings
#separatists - aka Pilgrims; believed in separation of church and state; Protestants
#Rhode Island - Roger Williams who spoke against Massachusetts and fled to Rhode Island with the help of Indians in 1636. Built a Baptist church and established complete freedom of religion, even for the Jews and Catholics. Named “Rogue’s Island” due to open religion, by other states. Received permission of rights to the soil in 1644. Independent state
#indentured servants - essentially white slaves, had advantage of being same race as colonists, served 7 years then granted very little land, most went back to servitude
#"The Middle Passage" - Most of the slaves who reached North America came from the west coast of Africa, especially the area stretching from present day Senegal to Angola. They were originally captured by African coastal tribes, who traded them in crude markets on the shimmering tropical beaches to itinerant European-and American- flesh merchants. Usually branded and bound, the captives were herded aboard sweltering ships for the nasty “middle passage” on which death rates ran as high as 20%. Terrified survivors were eventually shoved onto auction blocks in New Worlds ports like Newport, Rhode Island, or Charleston, South Carolina, where a giant slave market traded in human misery for more than a century.
#African-American contributions to American culture - From their earliest presence in North America, African Americans have contributed literature, art, agricultural skills, foods, clothing styles, music, language, social and technological innovation to American culture. The cultivation and use of many agricultural products in the U.S., such as yams, peanuts, rice, okra, sorghum, grits, watermelon, indigo dyes, and cotton, can be traced to African and African-American influences.
#typical New England family - Clean water and cool temperatures added ten years to their lives. They enjoyed a good 70 years of life. They migrated as families and the families were very fertile even if the soil was not. Early marriage made up in booming birth rate. Babies just popped right out of the women. Women had to give up their rights when married.
#women's status in colonies - no suffrage, just worked mostly as housewife
#Lord De La Warr - Ordered Jamestown survivors of Starving Time back to Jamestown and ordered a military regime. He arrived in 1610. He had war with the Indians and they raided villages, burned them and stole their goods. A peace treaty of John Rolfe’s marriage to Pocahontas ended the first Anglo-Powhatan War in 1614. Indians attacked and killed 347 settlers, including John Rolfe and the Virginia Company followed with a second war
== References ==
{{Reflist}}
{{subpage navbar}}
{{CourseCat}}
[[Category:18th century in North America]]
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Maritime Health Research and Education-NET
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== '''The John Snow Prediabetes Research Institute.''' ==
[[File:ChatGPT Image 30 may 2026, 11 58 20 a.m.png|thumb|Prediabetes-remission research program]]
[[File:ChatGPT Image 24 abr 2026, 08 16 04 a.m.png|thumb|]]
Millions are at increased risk of developing metabolic syndromes with prediabetes, diabetes type 2, high blood pressure and overweight. All can lower their risks by staying physical active and eating well. For early identification of the risks we propose to register weight and height (BMI) and the fasting blood sugar in the '''Prevalence studies''' at the schools for seafarers, nurses, medical students and the kids schools.(12+ y).The 16-weeks '''intervention studies''' include learnings by short video sequences and self-monitoring of blood sugar with glucometer, and self-evaluation of diet and physical activity. Early diagnosis of prediabetes can provide both health and financial benefits.From a financial perspective, preventing or delaying diabetes can significantly lower healthcare costs. Early diagnosis of prediabetes is a cost-effective preventive strategy that can improve long-term health outcomes while helping individuals and healthcare systems avoid the substantial costs associated with diabetes and its complications.[[File:Lifestyle Medicine Pillars.png|300px|right|The focus of Lifestyle Medicine is on these 6 pillars.]]
[[File:John Snow.jpg|thumb|left| John Snow in the early nineteenth century]]
[[File:Cholera in London 1866.gif|thumb|250px|Map of a later cholera outbreak in London, in 1866]] [[File:Choleramaplondon1866.png|thumb|right|250px|Legend for the map above]]
1. '<nowiki/>'''Prevalence studies''''
1.1 The-International-Maritime-Health-Database <ref>https://www.dropbox.com/scl/fi/z3cq5ciiev06y8v9duw7u/A-International-Maritime-Health-Database.docx?cloud_editor=word&dl=0&rlkey=pt0kdesvmagcxaa2wez3tmza3 </ref>
1.2 The Maritime Officer`s Health-Database <ref>https://www.dropbox.com/t/8LjP7cmulhr2x8Ty </ref>
1.3 Nursing Students Health Database <ref> https://www.dropbox.com/scl/fi/tcznmmd2y3nona5e3h1ro/The-Nursing-students-health-database.docx?cloud_editor=word&dl=0&rlkey=onbjh4o8ko1lzdvgyi8nlrotk </ref>
1.4. Medical student's Health Database <ref>https://www.dropbox.com/scl/fi/f16h9b60u4gxgt56un2jf/The-Medical-students-Health-database.docx?cloud_editor=word&dl=0&rlkey=xyfqen5trdc5lniaovipl548n </ref>
1.5. School childrens Health database <ref> https://www.dropbox.com/scl/fi/u6u50c8bxwhte9t2t6ck8/The-School-children-s-Health-database.docx?cloud_editor=word&dl=0&rlkey=zlyz5wn673wf7owettq3nx3h5 </ref>
2. '''Intervention studies''' Englsh
<ref>https://www.dropbox.com/scl/fi/oi6cx6tlwwvoko3ed37tn/Invitation-to-the-course-English.docx?cloud_editor=word&dl=0&rlkey=7kzg91tqfgjskxf5aji8khicx </ref> Danish
<ref>https://www.dropbox.com/scl/fi/2qahc3q9hmf4skbvk77ab/Invitation-to-the-course-in-Danish.docx?cloud_editor=word&dl=0&rlkey=x63w8oqvarz284zg2btq2johv </ref> Spanish <ref> https://www.dropbox.com/scl/fi/bn71inqeeth4o4mc1fjth/Invitation-to-the-course-Spanish.docx?cloud_editor=word&dl=0&rlkey=popmr1fnodh1v951v9l7k9ezv </ref>
- General research protocol draft
<ref> https://www.dropbox.com/scl/fi/gau25oy5y1s57046icjt2/Research-protocol-draft.docx?cloud_editor=word&dl=0&rlkey=wat63e25ritmujwcpss8s4v0s </ref>
- Health Promoting Schools <ref> https://www.dropbox.com/scl/fi/0rm7honrezbjwrcy3h3yk/Health-promoting-schools.docx?cloud_editor=word&dl=0&rlkey=673jyzcmwbfw7k9ui9nmtp0zh </ref>
- John Snow Institute bylaws <ref> https://www.dropbox.com/scl/fi/lccr7jtnga1u0x75117zn/John-Snow-revision-2-March-11.doc?cloud_editor=word&dl=0&rlkey=lz2gi7mslcoay5dzygg8h6n6r </ref>
3. '''Publications and pptx''' 2016-2026 <ref>https://en.wikiversity.org/wiki/Maritime_Health_Research_and_Education-NET/The_International_Type_2_Diabetes_Mellitus_and_Hypertension_Research_Group#The_John_Snow_Institute </ref><ref name=":0"> https://www.dropbox.com/scl/fi/mw7ft423lkkpjoxywd2bf </ref>
4. '''Strategies for research and implementation'''
For early identification of the risks we propose to register weight and height (Body Mass Index) and the fasting blood sugar in the '''Prevalence studies''' at the schools for seafarers, nurses, medical students and the kids` schools..
A practical strategy for prediabetes remission in low- and middle-income countries (LMICs) must assume that laboratory capacity, workforce, and financing are constrained:
'''5. Minutes from meetings''' <ref> https://www.dropbox.com/t/3ZfLGngkS3pSlAQ3 </ref>
6. '''Prediabetes-Remission Research Network:'''
<small>Prof. Ing. MSc. Nailet Delgado; Dr. Olaf Jensen, MD, MPH, PhD, o147248@gmail.com; MSc.Ph.D. Bishal Gyawali (SDU); MSc.PhD Vivi Just-Nørregaard; Dr. Johan Hviid Andersen MD, PhD. Prof Århus University; Prof. MSc. Agnes Flores, UMECIT, Panama; Dr. Maite, Vacamonte, Panama; Bruno Nørdam, Randers; Dr. Maite Duque, Venezuela; Dr. Indira Santos Panama; Med.Stud. Ashley Lezcano, Panama; Dr. Antonio Roberto Abaya MD Filippines; Dr. Jen Mendoza, MD, Filippines; Dr. Andra Ergle MD, Latvia; Prof. MSc. Ingrid Morató, Tarragona/Cadiz, Spain; MBA Christian Acheampong, Turkey; Dr. Alejandro Martinez, MPH, Costa Rica; Dr. Med. Sci Finn Gyntelberg; NFA.and Bispebj. Hosp. Denmark,</small>
==References==
[[Category:Prediabetes ]]
<references />Education 1: Research Methodology <ref>https://en.wikiversity.org/wiki/Maritime_Health_Research_and_Education-NET/EDUCATION/Education_module_links</ref>
<references />
= Online Meeting , May 11, 2026 =
Prediabetes – Remission in Small - and medium economy countries is the target.
Keeping eyes open for applications for lifestyle medicine, sporadic supplement metformin
Prepare documentation to apply for funding. Clearly define the project title, objectives, scope (countries, communities, ages), strategy (how to collect data, with what equipment, what variables), required materials, and required personnel.
Meeting with Lene Daugaard dir. SIMAC Svendborg.
Periodically search for organizations that could fund our project.
Apply for funding when the opportunity arises.
Obtain those funds.
In parallel, without interruption, continue prevalence data collection and a comparative study between countries can be conducted using this collected data.
Intervention study 16 weeks in one or two of the target populations.
Proposed budget for 5 years: 5 mill Dkr.
The first year could be collect data from two countries, Denmark and Turkey (Istanbul) compare with the data from Panama, UMIP including a short review study on similar data and an 16 week intervention study with the goal to produce a strategic model for prevalence and effectful intervention to be reported in 1-2 international articles.
Possible funding entities:
Innovation Fund Denmark;
EIFO;
DANIDA;
CROWDFOUNDING;
European Commission programs;
SKOV website;
Lundbeckfonden: other
2g4vxv81ec35261wnv7v6nwepxlaki6
C language in plain view
0
285380
2816301
2816219
2026-06-19T14:09:01Z
Young1lim
21186
/* Applications */
2816301
wikitext
text/x-wiki
=== Introduction ===
* Overview ([[Media:C01.Intro1.Overview.1.A.20170925.pdf |A.pdf]], [[Media:C01.Intro1.Overview.1.B.20170901.pdf |B.pdf]], [[Media:C01.Intro1.Overview.1.C.20170904.pdf |C.pdf]])
* Number System ([[Media:C01.Intro2.Number.1.A.20171023.pdf |A.pdf]], [[Media:C01.Intro2.Number.1.B.20170909.pdf |B.pdf]], [[Media:C01.Intro2.Number.1.C.20170914.pdf |C.pdf]])
* Memory System ([[Media:C01.Intro2.Memory.1.A.20170907.pdf |A.pdf]], [[Media:C01.Intro3.Memory.1.B.20170909.pdf |B.pdf]], [[Media:C01.Intro3.Memory.1.C.20170914.pdf |C.pdf]])
=== Handling Repetition ===
* Control ([[Media:C02.Repeat1.Control.1.A.20170925.pdf |A.pdf]], [[Media:C02.Repeat1.Control.1.B.20170918.pdf |B.pdf]], [[Media:C02.Repeat1.Control.1.C.20170926.pdf |C.pdf]])
* Loop ([[Media:C02.Repeat2.Loop.1.A.20170925.pdf |A.pdf]], [[Media:C02.Repeat2.Loop.1.B.20170918.pdf |B.pdf]])
=== Handling a Big Work ===
* Function Overview ([[Media:C03.Func1.Overview.1.A.20171030.pdf |A.pdf]], [[Media:C03.Func1.Oerview.1.B.20161022.pdf |B.pdf]])
* Functions & Variables ([[Media:C03.Func2.Variable.1.A.20161222.pdf |A.pdf]], [[Media:C03.Func2.Variable.1.B.20161222.pdf |B.pdf]])
* Functions & Pointers ([[Media:C03.Func3.Pointer.1.A.20161122.pdf |A.pdf]], [[Media:C03.Func3.Pointer.1.B.20161122.pdf |B.pdf]])
* Functions & Recursions ([[Media:C03.Func4.Recursion.1.A.20161214.pdf |A.pdf]], [[Media:C03.Func4.Recursion.1.B.20161214.pdf |B.pdf]])
=== Handling Series of Data ===
==== Background ====
* Background ([[Media:C04.Series0.Background.1.A.20180727.pdf |A.pdf]])
==== Basics ====
* Pointers ([[Media:C04.S1.Pointer.1A.20240524.pdf |A.pdf]], [[Media:C04.Series2.Pointer.1.B.20161115.pdf |B.pdf]])
* Arrays ([[Media:C04.S2.Array.1A.20240514.pdf |A.pdf]], [[Media:C04.Series1.Array.1.B.20161115.pdf |B.pdf]])
* Array Pointers ([[Media:C04.S3.ArrayPointer.1A.20240208.pdf |A.pdf]], [[Media:C04.Series3.ArrayPointer.1.B.20181203.pdf |B.pdf]])
* Multi-dimensional Arrays ([[Media:C04.Series4.MultiDim.1.A.20221130.pdf |A.pdf]], [[Media:C04.Series4.MultiDim.1.B.1111.pdf |B.pdf]])
* Array Access Methods ([[Media:C04.Series4.ArrayAccess.1.A.20190511.pdf |A.pdf]], [[Media:C04.Series3.ArrayPointer.1.B.20181203.pdf |B.pdf]])
* Structures ([[Media:C04.Series3.Structure.1.A.20171204.pdf |A.pdf]], [[Media:C04.Series2.Structure.1.B.20161130.pdf |B.pdf]])
==== Examples ====
* Spreadsheet Example Programs
:: Example 1 ([[Media:C04.Series7.Example.1.A.20171213.pdf |A.pdf]], [[Media:C04.Series7.Example.1.C.20171213.pdf |C.pdf]])
:: Example 2 ([[Media:C04.Series7.Example.2.A.20171213.pdf |A.pdf]], [[Media:C04.Series7.Example.2.C.20171213.pdf |C.pdf]])
:: Example 3 ([[Media:C04.Series7.Example.3.A.20171213.pdf |A.pdf]], [[Media:C04.Series7.Example.3.C.20171213.pdf |C.pdf]])
:: Bubble Sort ([[Media:C04.Series7.BubbleSort.1.A.20171211.pdf |A.pdf]])
==== Applications ====
* Address-of and de-reference operators ([[Media:C04.SA0.PtrOperator.1A.20260619.pdf |A.pdf]])
* Applications of Pointers ([[Media:C04.SA1.AppPointer.1A.20241121.pdf |A.pdf]])
* Applications of Arrays ([[Media:C04.SA2.AppArray.1A.20240715.pdf |A.pdf]])
* Applications of Array Pointers ([[Media:C04.SA3.AppArrayPointer.1A.20240210.pdf |A.pdf]])
* Applications of Multi-dimensional Arrays ([[Media:C04.Series4App.MultiDim.1.A.20210719.pdf |A.pdf]])
* Applications of Array Access Methods ([[Media:C04.Series9.AppArrAcess.1.A.20190511.pdf |A.pdf]])
* Applications of Structures ([[Media:C04.Series6.AppStruct.1.A.20190423.pdf |A.pdf]])
=== Handling Various Kinds of Data ===
* Types ([[Media:C05.Data1.Type.1.A.20180217.pdf |A.pdf]], [[Media:C05.Data1.Type.1.B.20161212.pdf |B.pdf]])
* Typecasts ([[Media:C05.Data2.TypeCast.1.A.20180217.pdf |A.pdf]], [[Media:C05.Data2.TypeCast.1.B.20161216.pdf |A.pdf]])
* Operators ([[Media:C05.Data3.Operators.1.A.20161219.pdf |A.pdf]], [[Media:C05.Data3.Operators.1.B.20161216.pdf |B.pdf]])
* Files ([[Media:C05.Data4.File.1.A.20161124.pdf |A.pdf]], [[Media:C05.Data4.File.1.B.20161212.pdf |B.pdf]])
=== Handling Low Level Operations ===
* Bitwise Operations ([[Media:BitOp.1.B.20161214.pdf |A.pdf]], [[Media:BitOp.1.B.20161203.pdf |B.pdf]])
* Bit Field ([[Media:BitField.1.A.20161214.pdf |A.pdf]], [[Media:BitField.1.B.20161202.pdf |B.pdf]])
* Union ([[Media:Union.1.A.20161221.pdf |A.pdf]], [[Media:Union.1.B.20161111.pdf |B.pdf]])
* Accessing IO Registers ([[Media:IO.1.A.20141215.pdf |A.pdf]], [[Media:IO.1.B.20161217.pdf |B.pdf]])
=== Declarations ===
* Type Specifiers and Qualifiers ([[Media:C07.Spec1.Type.1.A.20171004.pdf |pdf]])
* Storage Class Specifiers ([[Media:C07.Spec2.Storage.1.A.20171009.pdf |pdf]])
* Scope
=== Class Notes ===
* TOC ([[Media:TOC.20171007.pdf |TOC.pdf]])
* Day01 ([[Media:Day01.A.20171007.pdf |A.pdf]], [[Media:Day01.B.20171209.pdf |B.pdf]], [[Media:Day01.C.20171211.pdf |C.pdf]]) ...... Introduction (1) Standard Library
* Day02 ([[Media:Day02.A.20171007.pdf |A.pdf]], [[Media:Day02.B.20171209.pdf |B.pdf]], [[Media:Day02.C.20171209.pdf |C.pdf]]) ...... Introduction (2) Basic Elements
* Day03 ([[Media:Day03.A.20171007.pdf |A.pdf]], [[Media:Day03.B.20170908.pdf |B.pdf]], [[Media:Day03.C.20171209.pdf |C.pdf]]) ...... Introduction (3) Numbers
* Day04 ([[Media:Day04.A.20171007.pdf |A.pdf]], [[Media:Day04.B.20170915.pdf |B.pdf]], [[Media:Day04.C.20171209.pdf |C.pdf]]) ...... Structured Programming (1) Flowcharts
* Day05 ([[Media:Day05.A.20171007.pdf |A.pdf]], [[Media:Day05.B.20170915.pdf |B.pdf]], [[Media:Day05.C.20171209.pdf |C.pdf]]) ...... Structured Programming (2) Conditions and Loops
* Day06 ([[Media:Day06.A.20171007.pdf |A.pdf]], [[Media:Day06.B.20170923.pdf |B.pdf]], [[Media:Day06.C.20171209.pdf |C.pdf]]) ...... Program Control
* Day07 ([[Media:Day07.A.20171007.pdf |A.pdf]], [[Media:Day07.B.20170926.pdf |B.pdf]], [[Media:Day07.C.20171209.pdf |C.pdf]]) ...... Function (1) Definitions
* Day08 ([[Media:Day08.A.20171028.pdf |A.pdf]], [[Media:Day08.B.20171016.pdf |B.pdf]], [[Media:Day08.C.20171209.pdf |C.pdf]]) ...... Function (2) Storage Class and Scope
* Day09 ([[Media:Day09.A.20171007.pdf |A.pdf]], [[Media:Day09.B.20171017.pdf |B.pdf]], [[Media:Day09.C.20171209.pdf |C.pdf]]) ...... Function (3) Recursion
* Day10 ([[Media:Day10.A.20171209.pdf |A.pdf]], [[Media:Day10.B.20171017.pdf |B.pdf]], [[Media:Day10.C.20171209.pdf |C.pdf]]) ...... Arrays (1) Definitions
* Day11 ([[Media:Day11.A.20171024.pdf |A.pdf]], [[Media:Day11.B.20171017.pdf |B.pdf]], [[Media:Day11.C.20171212.pdf |C.pdf]]) ...... Arrays (2) Applications
* Day12 ([[Media:Day12.A.20171024.pdf |A.pdf]], [[Media:Day12.B.20171020.pdf |B.pdf]], [[Media:Day12.C.20171209.pdf |C.pdf]]) ...... Pointers (1) Definitions
* Day13 ([[Media:Day13.A.20171025.pdf |A.pdf]], [[Media:Day13.B.20171024.pdf |B.pdf]], [[Media:Day13.C.20171209.pdf |C.pdf]]) ...... Pointers (2) Applications
* Day14 ([[Media:Day14.A.20171226.pdf |A.pdf]], [[Media:Day14.B.20171101.pdf |B.pdf]], [[Media:Day14.C.20171209.pdf |C.pdf]]) ...... C String (1)
* Day15 ([[Media:Day15.A.20171209.pdf |A.pdf]], [[Media:Day15.B.20171124.pdf |B.pdf]], [[Media:Day15.C.20171209.pdf |C.pdf]]) ...... C String (2)
* Day16 ([[Media:Day16.A.20171208.pdf |A.pdf]], [[Media:Day16.B.20171114.pdf |B.pdf]], [[Media:Day16.C.20171209.pdf |C.pdf]]) ...... C Formatted IO
* Day17 ([[Media:Day17.A.20171031.pdf |A.pdf]], [[Media:Day17.B.20171111.pdf |B.pdf]], [[Media:Day17.C.20171209.pdf |C.pdf]]) ...... Structure (1) Definitions
* Day18 ([[Media:Day18.A.20171206.pdf |A.pdf]], [[Media:Day18.B.20171128.pdf |B.pdf]], [[Media:Day18.C.20171212.pdf |C.pdf]]) ...... Structure (2) Applications
* Day19 ([[Media:Day19.A.20171205.pdf |A.pdf]], [[Media:Day19.B.20171121.pdf |B.pdf]], [[Media:Day19.C.20171209.pdf |C.pdf]]) ...... Union, Bitwise Operators, Enum
* Day20 ([[Media:Day20.A.20171205.pdf |A.pdf]], [[Media:Day20.B.20171201.pdf |B.pdf]], [[Media:Day20.C.20171212.pdf |C.pdf]]) ...... Linked List
* Day21 ([[Media:Day21.A.20171206.pdf |A.pdf]], [[Media:Day21.B.20171208.pdf |B.pdf]], [[Media:Day21.C.20171212.pdf |C.pdf]]) ...... File Processing
* Day22 ([[Media:Day22.A.20171212.pdf |A.pdf]], [[Media:Day22.B.20171213.pdf |B.pdf]], [[Media:Day22.C.20171212.pdf |C.pdf]]) ...... Preprocessing
<!---------------------------------------------------------------------->
</br>
See also https://cprogramex.wordpress.com/
== '''Old Materials '''==
until 201201
* Intro.Overview.1.A ([[Media:C.Intro.Overview.1.A.20120107.pdf |pdf]])
* Intro.Memory.1.A ([[Media:C.Intro.Memory.1.A.20120107.pdf |pdf]])
* Intro.Number.1.A ([[Media:C.Intro.Number.1.A.20120107.pdf |pdf]])
* Repeat.Control.1.A ([[Media:C.Repeat.Control.1.A.20120109.pdf |pdf]])
* Repeat.Loop.1.A ([[Media:C.Repeat.Loop.1.A.20120113.pdf |pdf]])
* Work.Function.1.A ([[Media:C.Work.Function.1.A.20120117.pdf |pdf]])
* Work.Scope.1.A ([[Media:C.Work.Scope.1.A.20120117.pdf |pdf]])
* Series.Array.1.A ([[Media:Series.Array.1.A.20110718.pdf |pdf]])
* Series.Pointer.1.A ([[Media:Series.Pointer.1.A.20110719.pdf |pdf]])
* Series.Structure.1.A ([[Media:Series.Structure.1.A.20110805.pdf |pdf]])
* Data.Type.1.A ([[Media:C05.Data2.TypeCast.1.A.20130813.pdf |pdf]])
* Data.TypeCast.1.A ([[Media:Data.TypeCast.1.A.pdf |pdf]])
* Data.Operators.1.A ([[Media:Data.Operators.1.A.20110712.pdf |pdf]])
<br>
until 201107
* Intro.1.A ([[Media:Intro.1.A.pdf |pdf]])
* Control.1.A ([[Media:Control.1.A.20110706.pdf |pdf]])
* Iteration.1.A ([[Media:Iteration.1.A.pdf |pdf]])
* Function.1.A ([[Media:Function.1.A.20110705.pdf |pdf]])
* Variable.1.A ([[Media:Variable.1.A.20110708.pdf |pdf]])
* Operators.1.A ([[Media:Operators.1.A.20110712.pdf |pdf]])
* Pointer.1.A ([[Media:Pointer.1.A.pdf |pdf]])
* Pointer.2.A ([[Media:Pointer.2.A.pdf |pdf]])
* Array.1.A ([[Media:Array.1.A.pdf |pdf]])
* Type.1.A ([[Media:Type.1.A.pdf |pdf]])
* Structure.1.A ([[Media:Structure.1.A.pdf |pdf]])
go to [ [[C programming in plain view]] ]
[[Category:C programming language]]
</br>
qmontnta1rj0wge57r9cyr4ozk536xc
User:Tommy Kronkvist
2
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2816093
2026-06-19T22:31:29Z
Tommy Kronkvist
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[[File:Sorbus torminalis Trunk and canopy.jpg|thumb|310px|The intracanopy of a Wild Service Tree, i.e. <small>''Torminalis glaberrima'' (Gand.) Sennikov & Kurtto, ''Memoranda Soc. Fauna Fl. Fenn.'' 93: 32 (2017).</small>]]<br />
Most of my wiki contributions are made to [[:species:Main Page|Wikispecies]] where I'm an administrator, bureaucrat and interface admin,<small><sup>[https://species.wikimedia.org/w/index.php?title=Special:ListUsers&limit=1&username=Tommy_Kronkvist (verify)]</sup></small> to the Swedish Wikimedia Chapter [[WMSE:|Wikimedia Sverige]] (WMSE) where I'm an administrator,<small><sup>(<span class="plainlinks">[https://se.wikimedia.org/w/index.php?title=Special:Användare&limit=1&username=Tommy_Kronkvist verify]</span>)</sup></small> and as administrator and interface administrator at the Swedish version of [[wikivoyage:sv:Huvudsida|Wikivoyage]].<small><sup>(<span class="plainlinks">[https://sv.wikivoyage.org/w/index.php?title=Special:ListUsers&limit=1&username=Tommy_Kronkvist verify]</span>)</sup></small>
So far (June 19, 2026), I've made just over 393,800 edits to 153 of the Wikimedia sister projects – the majority of them to Wikispecies and Wikidata. My global account information for all of Wikimedia can be found [[meta:Special:CentralAuth/Tommy Kronkvist|here]].
Swedish is my mother tongue – even though I was born in Finland – but I feel comfortable speaking and writing English and to some extent in German as well. Odd as it may seem, unfortunately I can't speak any Finnish even though I went to school there for a few years prior to moving to Sweden (see [[w:Swedish-speaking population of Finland|Swedish-speaking population of Finland]] in Wikipedia). I've lived all over Sweden but nowadays reside in Uppsala, the fourth biggest city and former capital of Sweden.
I'm only the fourth generation named "Kronkvist". My family name consists of two parts: ''kron'' – a short form of the Swedish word ''krona'' meaning 'crown', as in coronation crown or tree crown – and ''kvist'', meaning 'bough' or 'twig'. Hence the name ''Kronkvist'' refers to a twig in the canopy of a forest. I'm the fourth generation of Kronkvist's. Prior to that our family name was ''Mattus'': an oeconym meaning "Matthew's Farm", dating back to at least 1637.
{{Clear}}
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2026-06-20T09:43:45Z
Tommy Kronkvist
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<div style="margin: 0 0 1em 0;">{{userpage}}</div>
{{Userboxtop|toptext=Babel:}}
{{#babel:sv|en-4|de-2|la-1}}
{{Userboxbottom}}
[[File:Sorbus torminalis Trunk and canopy.jpg|thumb|310px|The intracanopy of a Wild Service Tree, i.e. <small>''Torminalis glaberrima'' (Gand.) Sennikov & Kurtto, ''Memoranda Soc. Fauna Fl. Fenn.'' 93: 32 (2017).</small>]]<br />
Most of my wiki contributions are made to [[:species:Main Page|Wikispecies]] where I'm an administrator, bureaucrat and interface admin,<small><sup>[https://species.wikimedia.org/w/index.php?title=Special:ListUsers&limit=1&username=Tommy_Kronkvist (verify)]</sup></small> to the Swedish Wikimedia Chapter [[WMSE:|Wikimedia Sverige]] (WMSE) where I'm an administrator,<small><sup>(<span class="plainlinks">[https://se.wikimedia.org/w/index.php?title=Special:Användare&limit=1&username=Tommy_Kronkvist verify]</span>)</sup></small> and as administrator and interface administrator at the Swedish version of [[wikivoyage:sv:Huvudsida|Wikivoyage]].<small><sup>(<span class="plainlinks">[https://sv.wikivoyage.org/w/index.php?title=Special:ListUsers&limit=1&username=Tommy_Kronkvist verify]</span>)</sup></small>
So far (June 20, 2026), I've made just over 393,900 edits to 153 of the Wikimedia sister projects – the majority of them to Wikispecies and Wikidata. My global account information for all of Wikimedia can be found [[meta:Special:CentralAuth/Tommy Kronkvist|here]].
Swedish is my mother tongue – even though I was born in Finland – but I feel comfortable speaking and writing English and to some extent in German as well. Odd as it may seem, unfortunately I can't speak any Finnish even though I went to school there for a few years prior to moving to Sweden (see [[w:Swedish-speaking population of Finland|Swedish-speaking population of Finland]] in Wikipedia). I've lived all over Sweden but nowadays reside in Uppsala, the fourth biggest city and former capital of Sweden.
I'm only the fourth generation named "Kronkvist". My family name consists of two parts: ''kron'' – a short form of the Swedish word ''krona'' meaning 'crown', as in coronation crown or tree crown – and ''kvist'', meaning 'bough' or 'twig'. Hence the name ''Kronkvist'' refers to a twig in the canopy of a forest. I'm the fourth generation of Kronkvist's. Prior to that our family name was ''Mattus'': an oeconym meaning "Matthew's Farm", dating back to at least 1637.
{{Clear}}
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User:Dc.samizdat/Golden chords of the 120-cell
2
326765
2816288
2816279
2026-06-19T12:25:09Z
Dc.samizdat
2856930
/* The 600-cell */
2816288
wikitext
text/x-wiki
= Golden chords of the 120-cell =
{{align|center|David Brooks Christie}}
{{align|center|dc@samizdat.org}}
{{align|center|Draft in progress}}
{{align|center|January 2026 - June 2026}}
<blockquote>Steinbach discovered the formula for the ratios of diagonal to side in the regular polygons. Fontaine and Hurley extended this result, discovering a formula for the reciprocal of a regular polygon chord derived geometrically from the chord's star polygon. We observe that these findings in plane geometry apply more generally, to polytopes of any dimensionality. Fontaine and Hurley's geometric procedure for finding the reciprocals of the chords of a regular polygon from their star polygons also finds the rotational geodesics of any polytope of any dimensionality.</blockquote>
== Introduction ==
Steinbach discovered the Diagonal Product Formula and the Golden Fields family of ratios of diagonal to side in the regular polygons. He showed how this family extends beyond the pentagon {5} with its well-known golden bisection proportional to 𝜙, finding that the heptagon {7} has an analogous trisection, the nonagon {9} has an analogous quadrasection, and the hendecagon {11} has an analogous pentasection, an extended family of golden proportions with quasiperiodic properties.
Kappraff and Adamson extended these findings in plane geometry to a theory of Generalized Fibonacci Sequences, showing that the Golden Fields not only do not end with the hendecagon, they form an infinite number of periodic trajectories when operated on by the Mandelbrot operator. They found a relation between the edges of star polygons and dynamical systems in the state of chaos, revealing a connection between chaos theory, number, and rotations in Coxeter Euclidean geometry.
Fontaine and Hurley examined Steinbach's finding that the length of each chord of a regular polygon is both the product of two chords and the sum of a set of smaller chords, so that in rotations to add is to multiply. They illustrated Steinbach's sets of additive chords lying parallel to each other in the plane (pointing in the same direction), and by applying Steinbach's formula more generally they found another summation relation of signed parallel chords (pointing in opposite directions) which relates each chord length to its reciprocal, and relates the summation to a distinct star polygon rotation.
We examine these remarkable findings (which stem from study of the chords of humble regular polygons) in higher-dimensional spaces, specifically in the chords, polygons and rotations of the [[120-cell]], the largest four-dimensional regular convex polytope.
== Visualizing the 120-cell ==
{| class="wikitable floatright" width="400"
|style="vertical-align:top"|[[File:120-cell.gif|200px]]<br>Orthographic projection of the 600-point 120-cell <small><math>\{5,3,3\}</math></small> performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]].{{Sfn|Hise|2011|loc=File:120-cell.gif|ps=; "Created by Jason Hise with Maya and Macromedia Fireworks. A 3D projection of a 120-cell performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]]."}} In this simplified rendering only the 120-cell's own edges are shown; its 29 interior chords are not rendered. Therefore even though it is translucent, only its outer surface is visible. The complex interior parts of the 120-cell, all its inscribed 5-cells, 16-cells, 8-cells, 24-cells, 600-cells and its much larger inventory of polyhedra, are completely invisible in this view, as none of their edges are rendered at all.
|style="vertical-align:top"|[[File:Ortho solid 016-uniform polychoron p33-t0.png|200px]]<br>Orthographic projection of the 600-point [[W:Great grand stellated 120-cell|great grand stellated 120-cell]] <small><math>\{\tfrac{5}{2},3,3\}</math></small>.{{Sfn|Ruen: Great grand stellated 120-cell|2007}} The 120-cell is its convex hull. The projection to the left renders only the 120-cell's shortest chord, its 1200 edges. The projection above also renders only one of the 120-cell's 30 chords, the edges of its 120 inscribed regular 5-cells. The 120-cell itself (the convex hull) is invisible in this view, as its edges are not rendered.
|}
[[120-cell#Geometry|The 120-cell is the maximally complex regular 4-polytope]], containing inscribed instances of every regular 1-, 2-, 3-, and 4-polytope, except the regular polygons of more than {15} sides.
The 120-cell is the convex hull of a regular [[120-cell#Relationships among interior polytopes|compound of each of the 6 regular convex 4-polytopes]]. They are the [[5-cell|5-point (5-cell) 4-simplex]], the [[16-cell|8-point (16-cell) 4-orthoplex]], the [[W:Tesseract|16-point (8-cell) tesseract]], the [[24-cell|24-point (24-cell)]], the [[600-cell|120-point (600-cell)]], and the [[120-cell|600-point (120-cell)]]. The 120-cell is the convex hull of a compound of 120 disjoint regular 5-cells, of 75 disjoint 16-cells, of 25 disjoint 24-cells, and of 5 disjoint 600-cells.
The 120-cell contains an even larger inventory of irregular polytopes, created by the intersection of multiple instances of these component regular 4-polytopes. Many are quite unexpected, because they do not occur as components of any regular polytope smaller than the 120-cell. As just one example among the [[120-cell#Concentric hulls|sections of the 120-cell]], there is an irregular 24-point polyhedron with 16 triangle faces and 4 nonagon {9} faces.{{Sfn|Moxness|}}
Most renderings of the 120-cell, like the rotating projection here, only illustrate its outer surface, which is a honeycomb of face-bonded dodecahedral cells. Only the objects in its 3-dimensional surface are rendered, namely the 120 dodecahedra, their pentagon faces, and their edges. Although the 120-cell has chords of 30 distinct lengths, in this kind of simplified rendering only the 120-cell's own edges (its shortest chord) are shown. Its 29 interior chords, the edges of objects in the interior of the 120-cell, are not rendered, so interior objects are not visible at all.
Visualizing the complete interior of the 600-vertex 120-cell in a single image is impractical because of its complexity. Only four 120-cell edges are incident at each vertex, but [[120-cell#Chords|600 chords (of all 30 lengths)]] are incident at ''each'' vertex.
== Compounds in the 120-cell ==
The 8-point (16-cell), not the 5-point (5-cell), is the smallest building block; it compounds to every larger regular 4-polytope. The 5-point (5-cell) does compound to the 600-point (120-cell), but it does not fit into any smaller regular 4-polytope.
The 8-point (16-cell) compounds by 2 in the 16-point (8-cell), and by 3 in the 24-point (24-cell). The 16-point (8-cell) compounds in the 24-point (24-cell) by 3 non-disjoint instances of itself, with each of the 24 vertices shared by two 16-point (8-cells). The 24-point (24-cell) compounds by 5 disjoint instances of itself in the 120-point (600-cell), and the 120-point (600-cell) compounds by 5 disjoint instances of itself in the 600-point (120-cell).
The 24-point (24-cell) also compounds by 5<sup>2</sup> non-disjoint instances of itself in the 120-point (600-cell); it compounds in 5 disjoint instances of itself, 10 (not 5) different ways. Whichever set of 5 disjoint 24-point (24-cells) are assembled, the resulting 120-point (600-cell) contains 25 distinct 24-point (24-cells), not just 5 (or 10). This implies that 15 disjoint 8-point (16-cells) will construct a 120-point (600-cell), which will contain 75 distinct 8-point (16-cells).
The 600-point (120-cell) is 5 disjoint 120-point (600-cells), just 2 different ways (not 5 or 10 ways), so it is 10 distinct 120-point (600-cells). This implies that the 8-point (16-cell) compounds by 3 times 5<sup>2</sup> (75) disjoint instances of itself in the 600-point (120-cell), which contains 3<sup>2</sup> times 5<sup>2</sup> (225) distinct instances of the 24-point (24-cell), and 3<sup>3</sup> times 5<sup>2</sup> (675) distinct instances of the 8-point (16-cell).
These facts were discovered painstakingly by various researchers, and no one has found a general rule governing subsumption relations among regular polytopes. The reasons for some of their numeric incidence relations are far from obvious. [[W:Pieter Hendrik Schoute|Schoute]] was the first to see that the 120-point (600-cell) is a compound of 5 24-point (24-cells) ''10 different ways'', and after he saw it a hundred years lapsed until Denney, Hooker, Johnson, Robinson, Butler & Claiborne proved his result, and showed why.{{Sfn|Denney, Hooker, Johnson, Robinson, Butler & Claiborne|2020|loc=''The geometry of H4 polytopes''}}
So much for the compounds of 16-cells. The 120-cell is also the convex hull of the compound of 120 disjoint regular 5-cells. That stellated compound (without its convex hull of 120-cell edges) is the [[w:Great_grand_stellated_120-cell|great grand stellated 120-cell]] illustrated above, the final regular [[W:Stellation|stellation]] of the 120-cell, and the only [[W:Schläfli-Hess polychoron|regular star 4-polytope]] to have the 120-cell for its convex hull. The edges of the great grand stellated 120-cell are <math>\phi^6</math> as long as those of its 120-cell [[W:List of polyhedral stellations#Stellation process|stellation core]] deep inside.
The compound of 120 disjoint 5-point (5-cells) can be seen to be equivalent to the compound of 5 disjoint 120-point (600-cells), as follows. Beginning with a single 120-point (600-cell), expand each vertex into a regular 5-cell, by adding 4 new equidistant vertices, such that the 5 vertices form a regular 5-cell inscribed in the 3-sphere. The 120 5-cells are disjoint, and the 600 vertices form 5 disjoint 120-point (600-cells): a 120-cell.
== Thirty distinguished distances ==
The 30 numbers listed in the table are all-important in Euclidean geometry. A case can be made on symmetry grounds that their squares are the 30 most important numbers between 0 and 4. The 30 rows of the table are the 30 distinct [[120-cell#Geodesic rectangles|chord lengths of the unit-radius 120-cell]], the largest regular convex 4-polytope. Since the 120-cell subsumes all smaller regular polytopes, its 30 chords are the complete chord set of all the regular polytopes that can be constructed in the first four dimensions of Euclidean space, except for regular polygons of more than 15 sides.
{| class="wikitable" style="white-space:nowrap;text-align:center"
!rowspan=2|<math>c_t</math>
!rowspan=2|arc
!rowspan=2|<small><math>\left\{\frac{30}{n}\right\}</math></small>
!rowspan=2|<math>\left\{p\right\}</math>
!rowspan=2|<small><math>m\left\{\frac{k}{d}\right\}</math></small>
!rowspan=2|Steinbach roots
!colspan=7|Chord lengths of the unit 120-cell
|-
!colspan=5|unit-radius length <math>c_t</math>
!colspan=2|unit-edge length <math>c_t/c_1</math><br>in 120-cell of radius <math>c_8=\sqrt{2}\phi^2</math>
|-
|<small><math>c_{1,1}</math></small>
|<small><math>15.5{}^{\circ}</math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math>c_{4,1}-c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7-3 \sqrt{5}}</math></small>
|<small><math>0.270091</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi ^2}</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^4}}</math></small>
|<small><math>\sqrt{0.072949}</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|-
|<small><math>c_{2,1}</math></small>
|<small><math>25.2{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{2}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{15\right\}</math></small>
|<small><math>\frac{1}{2} \left(c_{18,1}-c_{4,1}\right)</math></small>
|<small><math>\frac{\sqrt{3-\sqrt{5}}}{2}</math></small>
|<small><math>0.437016</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi }</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.190983}</math></small>
|<small><math>\phi </math></small>
|<small><math>1.61803</math></small>
|-
|<small><math>c_{3,1}</math></small>
|<small><math>36{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{3}\right\}</math></small>
|<small><math>\left\{10\right\}</math></small>
|<small><math>3 \left\{\frac{10}{3}\right\}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right) c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right)</math></small>
|<small><math>0.618034</math></small>
|<small><math>\frac{1}{\phi }</math></small>
|<small><math>\sqrt{\frac{1}{\phi ^2}}</math></small>
|<small><math>\sqrt{0.381966}</math></small>
|<small><math>\sqrt{2} \phi </math></small>
|<small><math>2.28825</math></small>
|-
|<small><math>c_{4,1}</math></small>
|<small><math>41.4{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{7}\right\}</math></small>
|<small><math>\frac{c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>0.707107</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{1}{2}}</math></small>
|<small><math>\sqrt{0.5}</math></small>
|<small><math>\phi ^2</math></small>
|<small><math>2.61803</math></small>
|-
|<small><math>c_{5,1}</math></small>
|<small><math>44.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{4}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{\frac{15}{2}\right\}</math></small>
|<small><math>\sqrt{3} c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-3 \sqrt{5}}</math></small>
|<small><math>0.756934</math></small>
|<small><math>\frac{\sqrt{\frac{3}{2}}}{\phi }</math></small>
|<small><math>\sqrt{\frac{3}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.572949}</math></small>
|<small><math>\sqrt{3} \phi </math></small>
|<small><math>2.80252</math></small>
|-
|<small><math>c_{6,1}</math></small>
|<small><math>49.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{17}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{5-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{5-\sqrt{5}}}{2}</math></small>
|<small><math>0.831254</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\frac{1}{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5}}{2 \phi }}</math></small>
|<small><math>\sqrt{0.690983}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^3}</math></small>
|<small><math>3.07768</math></small>
|-
|<small><math>c_{7,1}</math></small>
|<small><math>56.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{3}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>0.93913</math></small>
|<small><math>\frac{\sqrt{\frac{\psi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{0.881966}</math></small>
|<small><math>\sqrt{\psi \phi ^3}</math></small>
|<small><math>3.47709</math></small>
|-
|<small><math>c_{8,1}</math></small>
|<small><math>60{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{5}\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>1</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|<small><math>1</math></small>
|<small><math>\sqrt{1}</math></small>
|<small><math>\sqrt{1.}</math></small>
|<small><math>\sqrt{2} \phi ^2</math></small>
|<small><math>3.70246</math></small>
|-
|<small><math>c_{9,1}</math></small>
|<small><math>66.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{7}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{2 \phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.09132</math></small>
|<small><math>\frac{\sqrt{\frac{\chi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\chi }{2 \phi }}</math></small>
|<small><math>\sqrt{1.19098}</math></small>
|<small><math>\sqrt{\chi \phi ^3}</math></small>
|<small><math>4.04057</math></small>
|-
|<small><math>c_{10,1}</math></small>
|<small><math>69.8{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{11}\right\}</math></small>
|<small><math>\phi c_{4,1}</math></small>
|<small><math>\frac{1+\sqrt{5}}{2 \sqrt{2}}</math></small>
|<small><math>1.14412</math></small>
|<small><math>\frac{\phi }{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^2}{2}}</math></small>
|<small><math>\sqrt{1.30902}</math></small>
|<small><math>\phi ^3</math></small>
|<small><math>4.23607</math></small>
|-
|<small><math>c_{11,1}</math></small>
|<small><math>72{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{6}\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.17557</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{1.38197}</math></small>
|<small><math>\sqrt{2} \sqrt{3-\phi } \phi ^2</math></small>
|<small><math>4.3525</math></small>
|-
|<small><math>c_{12,1}</math></small>
|<small><math>75.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{24}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>1.22474</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{1.5}</math></small>
|<small><math>\sqrt{3} \phi ^2</math></small>
|<small><math>4.53457</math></small>
|-
|<small><math>c_{13,1}</math></small>
|<small><math>81.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>1.30038</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(9-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{1.69098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(9-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>4.8146</math></small>
|-
|<small><math>c_{14,1}</math></small>
|<small><math>84.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{9}\right\}</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi } c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{2} \sqrt[4]{5} \sqrt{1+\sqrt{5}}</math></small>
|<small><math>1.345</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi }}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5} \phi }{2}}</math></small>
|<small><math>\sqrt{1.80902}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^5}</math></small>
|<small><math>4.9798</math></small>
|-
|<small><math>c_{15,1}</math></small>
|<small><math>90.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{7}\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>2 c_{4,1}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>1.41421</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2.}</math></small>
|<small><math>2 \phi ^2</math></small>
|<small><math>5.23607</math></small>
|-
|<small><math>c_{16,1}</math></small>
|<small><math>95.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{29}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>1.4802</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.19098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(11-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>5.48037</math></small>
|-
|<small><math>c_{17,1}</math></small>
|<small><math>98.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{31}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>1.51954</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(7+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.30902}</math></small>
|<small><math>\sqrt{\psi \phi ^5}</math></small>
|<small><math>5.62605</math></small>
|-
|<small><math>c_{18,1}</math></small>
|<small><math>104.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{8}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{4}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>1.58114</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{2.5}</math></small>
|<small><math>\sqrt{5} \sqrt{\phi ^4}</math></small>
|<small><math>5.8541</math></small>
|-
|<small><math>c_{19,1}</math></small>
|<small><math>108.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{9}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{10}{3}\right\}</math></small>
|<small><math>c_{3,1}+c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.61803</math></small>
|<small><math>\phi </math></small>
|<small><math>\sqrt{1+\phi }</math></small>
|<small><math>\sqrt{2.61803}</math></small>
|<small><math>\sqrt{2} \phi ^3</math></small>
|<small><math>5.9907</math></small>
|-
|<small><math>c_{20,1}</math></small>
|<small><math>110.2{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>1.64042</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.69098}</math></small>
|<small><math>\phi ^2 \sqrt{8-\phi ^2}</math></small>
|<small><math>6.07359</math></small>
|-
|<small><math>c_{21,1}</math></small>
|<small><math>113.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{19}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.67601</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{2.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\chi }{\phi }}</math></small>
|<small><math>6.20537</math></small>
|-
|<small><math>c_{22,1}</math></small>
|<small><math>120{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{10}\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\sqrt{3} c_{8,1}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>1.73205</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3.}</math></small>
|<small><math>\sqrt{6} \phi ^2</math></small>
|<small><math>6.41285</math></small>
|-
|<small><math>c_{23,1}</math></small>
|<small><math>124.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{41}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{\phi }+\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.7658</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{3.11803}</math></small>
|<small><math>\sqrt{\chi \phi ^5}</math></small>
|<small><math>6.53779</math></small>
|-
|<small><math>c_{24,1}</math></small>
|<small><math>130.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>1.81907</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.30902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\sqrt{5}}{\phi }}</math></small>
|<small><math>6.73503</math></small>
|-
|<small><math>c_{25,1}</math></small>
|<small><math>135.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}}</math></small>
|<small><math>1.85123</math></small>
|<small><math>\frac{\phi ^2}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^4}{2}}</math></small>
|<small><math>\sqrt{3.42705}</math></small>
|<small><math>\phi ^4</math></small>
|<small><math>6.8541</math></small>
|-
|<small><math>c_{26,1}</math></small>
|<small><math>138.6{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{12}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{7}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>1.87083</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{3.5}</math></small>
|<small><math>\sqrt{7} \phi ^2</math></small>
|<small><math>6.92667</math></small>
|-
|<small><math>c_{27,1}</math></small>
|<small><math>144{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{12}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{5}{2}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)}</math></small>
|<small><math>1.90211</math></small>
|<small><math>\sqrt{\phi +2}</math></small>
|<small><math>\sqrt{2+\phi }</math></small>
|<small><math>\sqrt{3.61803}</math></small>
|<small><math>\phi ^2 \sqrt{2 \phi +4}</math></small>
|<small><math>7.0425</math></small>
|-
|<small><math>c_{28,1}</math></small>
|<small><math>154.8{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>1.95167</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{1}{\phi ^2}}</math></small>
|<small><math>7.22598</math></small>
|-
|<small><math>c_{29,1}</math></small>
|<small><math>164.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{14}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{7}\right\}</math></small>
|<small><math>\phi c_{12,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{\frac{3}{2}} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.98168</math></small>
|<small><math>\sqrt{\frac{3}{2}} \phi </math></small>
|<small><math>\sqrt{\frac{3 \phi ^2}{2}}</math></small>
|<small><math>\sqrt{3.92705}</math></small>
|<small><math>\sqrt{3} \phi ^3</math></small>
|<small><math>7.33708</math></small>
|-
|<small><math>c_{30,1}</math></small>
|<small><math>180{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{15}\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>2 c_{8,1}</math></small>
|<small><math>2</math></small>
|<small><math>2.</math></small>
|<small><math>2</math></small>
|<small><math>\sqrt{4}</math></small>
|<small><math>\sqrt{4.}</math></small>
|<small><math>2 \sqrt{2} \phi ^2</math></small>
|<small><math>7.40492</math></small>
|-
|rowspan=4 colspan=6|
|rowspan=4 colspan=4|
<small><math>\phi</math></small> is the golden ratio:<br>
<small><math>\phi ^2-\phi -1=0</math></small><br>
<small><math>\frac{1}{\phi }+1=\phi</math></small>, and: <small><math>\phi+1=\phi^2</math></small><br>
<small><math>\frac{1}{\phi }::1::\phi ::\phi ^2</math></small><br>
<small><math>1/\phi</math></small> and <small><math>\phi</math></small> are the golden sections of <small><math>\sqrt{5}</math></small>:<br>
<small><math>\phi +\frac{1}{\phi }=\sqrt{5}</math></small>
|colspan=2|<small><math>\phi = (\sqrt{5} + 1)/2</math></small>
|<small><math>1.618034</math></small>
|-
|colspan=2|<small><math>\chi = (3\sqrt{5} + 1)/2</math></small>
|<small><math>3.854102</math></small>
|-
|colspan=2|<small><math>\psi = (3\sqrt{5} - 1)/2</math></small>
|<small><math>2.854102</math></small>
|-
|colspan=2|<small><math>\psi = 11/\chi = 22/(3\sqrt{5} + 1)</math></small>
|<small><math>2.854102</math></small>
|}
== The 5-cell 4-simplex ==
...
== The 16-cell 4-orthoplex ==
In 2-space we have the regular 8-point octagon, in 3-space the regular 8-point cube, and in 4-space the regular 8-point [[16-cell]].
A planar octagon with rigid edges of unit length has chords of length:
:<math>r_1=1,r_2=\sqrt{2+\sqrt{2}} \approx 1.848,r_3=\sqrt{2}+1 \approx 2.414,r_4=\sqrt{4 + \sqrt{8}} \approx 2.613</math>
The chord ratio <math>r_3=\sqrt{2}+1</math> is a geometrical proportion, the [[W:Silver ratio|silver ratio]]. Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_3-r_1-r_1=1/r_3 \approx 0.414</math>
Note that <math>r_3-2=1/r_3=\sqrt{2}-1</math>. The procedure rotates counterclockwise over three <math>r_3</math> chords of an {8/3} octagram. Over the first <math>r_3</math> chord the displacement is <math>\sqrt{2}+r_1</math>. Over the second <math>r_3</math> chord it moves in the opposite direction a distance of <math>-r_1</math> . Over the third <math>r_3</math> chord it moves a distance of <math>-r_1</math>.
If we embed the planar octagon in 3-space, we can make it skew, repositioning its vertices so that each is one unit-edge length distant from three others instead of two others, at the vertices of a unit-edge cube with chords of length:
:<math>r_1=1, r_2=\sqrt{2}, r_3=\sqrt{3}, r_4=\sqrt{2}</math>
If we embed this cube in 4-space, we can skew it some more, repositioning its vertices so that each is one unit-edge length distant from six others instead of three others, at the vertices of a unit-edge 4-polytope with chords of length:
:<math>r_1=1,r_2=1,r_3=1,r_4=\sqrt{2}</math>
All of its chords except its long diameters are the same unit length as its edge. In fact they are its 24 edges, and it is a 16-cell of radius <math>1/\sqrt{2}</math>.
[[File:octagon16cell.png|thumb|Orthogonal projection of a regular 16-cell to the [[16-cell#Projections|B<sub>4</sub> Coxeter plane]]. Only its edges are shown; its long diameter chords are not drawn. All 24 edges are the same length and none lie parallel to the projection plane. The octagon circumference is a Petrie polygon. The two disjoint squares lie in completely orthogonal central planes. The blue octagram is a Clifford polygon. ]]
The [[16-cell]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{3,3,4\}</math></small>. It has 8 vertices, 24 edges, 32 equilateral triangle faces, and 16 regular tetrahedron cells. It is the [[16-cell#Octahedral dipyramid|four-dimensional analogue of the octahedron]], and each of its four orthogonal central hyperplanes is an octahedron.
The only planar regular polygons found in the 16-cell are face triangles and central plane squares, but the 16-cell also contains a skew regular octagon, its [[W:Petrie polygon|Petrie polygon]].{{Efn|name=Petrie polygon of a honeycomb}} The chords of this regular octagon, which lies skew in 4-space, are those given above for the 16-cell, as opposed to those for the cube or the regular octagon in the plane. The 16-cell is a construct of 3 Petrie octagons which share the same 8 vertices but have disjoint sets of 8 edges each.
The regular octad has higher symmetry in 4-space than it does in 2-space. The 16-cell is the 4-[[w:Cross-polytope|orthoplex]], the simplest regular 4-polytope after the [[5-cell|4-simplex]]. All the larger regular convex 4-polytopes are compounds of the 16-cell. The regular octagon exhibits this high symmetry only when embedded in 4-space at the vertices of the 16-cell.
The 16-cell constitutes an [[W:Orthonormal basis|orthonormal basis]] for the choice of a 4-dimensional Cartesian reference frame, because its vertices define four orthogonal axes. The eight vertices of a unit-radius 16-cell are (±1, 0, 0, 0), (0, ±1, 0, 0), (0, 0, ±1, 0), (0, 0, 0, ±1). All vertices are connected by <math>\sqrt{2}</math> edges except opposite pairs.
The vertex coordinates of the 16-cell form 6 central squares lying in 6 pairwise [[W:Orthogonal|orthogonal]] coordinate planes. Great squares in opposite planes that do not share an axis (e.g. in the ''xy'' and ''wz'' planes) are completely disjoint (they do not intersect at any vertices). These planes are [[W:Completely orthogonal|completely orthogonal]].{{Efn|name=Six orthogonal planes of the Cartesian basis}}
Since the unit-radius coordinate system is convenient, let us derive the unit-radius 16-cell by skewing a unit-radius planar octagon, which has chords of length:
:<math>r_1=\sqrt{2-\sqrt{2}} \approx 0.765,r_2=\sqrt{2},r_3=\sqrt{2+\sqrt{2}} \approx 1.848,r_4=2</math>
We will need a planar octagon with rigid <math>r_2</math> chords, rather than one with rigid <math>r_1</math> edges. The octagon's <math>r_2</math> chords form two disjoint great squares, visible in the orthogonal projection, which we can reposition in 3-space to form a cube by making them parallel, and in 4-space to form a 16-cell by making them completely orthogonal.
Since the edges of the 16-cell are all the same length <math>r_1=\sqrt{2},r_2=\sqrt{2},r_3=\sqrt{2}</math>, those chords are distinct only in the context of a rotation. Each chord is a 4-vector with a length and a direction. The rotational curve over each <math>r_i</math> chord makes <math>i</math> 45° turns.
[[File:16-cell-orig.gif|thumb|Orthographic projection of the 8-point 16-cell <small><math>\{3,3,4\}</math></small> performing a double rotation.{{Sfn|Hise|2007}}]]
[[W:Rotations in 4-dimensional Euclidean space|Rotations in 4-dimensional Euclidean space]] can be seen as the composition of two 2-dimensional rotations in completely orthogonal planes. The general rotation in 4-space is a [[W:SO(4)#Double rotations|double rotation]] in pairs of completely orthogonal planes. Two completely orthogonal planes are called invariant planes of the rotation when all points in the plane rotate on circles that remain in the plane, even as the whole plane tilts sideways (like a coin flipping) into another plane. The two completely orthogonal rotations of each plane (like a wheel, and like a coin flipping) are simultaneous but independent, in that they are not geometrically constrained to turn at the same rate. However, the most circular kind of rotation (as opposed to an elliptical double rotation of a rigid spherical object) occurs when the completely orthogonal planes do rotate through the same angle in the same time interval. Such equi-angled double rotations are called [[w:SO(4)#Isoclinic_rotations|isoclinic]], also [[w:William_Kingdon_Clifford|Clifford]] displacements.
The <math>r_1</math> chords of the 16-cell form a Petrie polygon which zig-zags back and forth, in the left and right rotational directions, between two completely orthogonal great squares formed by <math>r_2</math> chords.
The <math>r_2</math> chords of two completely orthogonal great squares lie parallel and perpendicular to each other. A ''simple'' rotation of the 16-cell in ''one'' of those two square central planes rotates that square like a wheel, while the other square does not move.{{Efn|name=simple rotations}} The four vertices of the rotating square orbit on a great circle in the plane.
The <math>r_3</math> chords of the 16-cell form a circular helix, visible as a blue {8/3} octagram in the orthogonal projection. A ''double'' rotation of the 16-cell, in both of two completely orthogonal invariant <math>r_2</math> square planes at once by equal angles, moves the eight vertices along the circular helix over the <math>r_3</math> chords. The vertex motion is a [[w:Geodesic|geodesic]] circle orbit on the 3-sphere of a special kind: it does not lie in a central plane, its [[w:Winding_number|winding number]] is not 1 (it is 3 in this case), its circumference is not <math>2\pi</math>, and it moves in either a left or right handed circular spiral. We shall refer to such a chiral circle orbit as an ''isocline'', and to the skew polygram of its rotational chords as a ''Clifford polygon''.
The 16-cell is the simplest possible frame in which to [[16-cell#Rotations|observe 4-dimensional rotations]] because its characteristic rotations feature a single pair of invariant rotation planes. In the 16-cell an isoclinic rotation by 90° in any pair of invariant completely orthogonal square central planes takes every great square to its completely orthogonal great square in a twisting displacement, as the invariant planes tilt sideways 90° into each other's plane while rotating 90° internally. All the vertices move at once along the same circular helix geodesic isocline of <math>r_3</math> chords, displaced 90° in 8 orthogonal directions, and the rigid 16-cell assumes a new orientation in 4-space. When the 90° isoclinic rotation is continued in the same rotational direction through an additional 90°, each vertex is again displaced 90°, but from the new orientation in a direction orthogonal to its first 90° displacement. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. In 360° of isoclinic rotation over four <math>r_3</math> chords, each vertex makes six 90° turns and reaches its antipodal position.
The trajectory of each vertex over each 90° isoclinic rotational displacement is a one-eighth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>6\pi</math> over eight <math>r_3</math> chords, and also traces an ordinary great circle in the plane twice, over the four <math>r_2</math> edges of a great square in one of the two moving invariant rotation planes. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions just once and returns to its original position, and the 16-cell returns to its original orientation.
Because this is the isoclinic rotation of the 16-cell in its invariant edge planes we shall refer to it as the ''characteristic rotation of the 16-cell'', and note once again that it is Fontaine and Hurley's rotation over the <math>r_3</math> star polygon which constructs <math>1/r_3</math>.
== The 8-cell tesseract ==
The long diameter of the unit-edge [[W:Hypercube|hypercube]] of dimension <math>n</math> is <math>\sqrt{n}</math>, so the unit-edge [[w:Tesseract|4-hypercube, the 16-point (8-cell) tesseract,]] has chords:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
Uniquely in its 4-dimensional case, the hypercube's edge length equals its radius, like the hexagon. We call such polytopes ''radially equilateral'', because they can be constructed from equilateral triangles which meet at their center, each contributing two radii and an edge. The [[w:Cuboctahedron|cuboctahedron]] and the 24-cell are also radially equilateral.
[[File:8-cell.gif|thumb|Orthographic projection of the 16-point (8-cell) tesseract <small><math>\{4,3,3\}</math></small> performing a simple rotation about a plane in 4-space.{{Sfn|Hise|2007}} The stationary plane bisects the figure from front-left to back-right and top to bottom.]]
The [[W:Tesseract|tesseract]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{4,3,3\}</math></small>. It has 16 vertices, 32 edges, 24 square faces, and 8 cube cells. It is the four-dimensional analogue of the cube.
The 16-point tesseract is the convex hull of a compound of two 8-point 16-cells, in exact dimensional analogy to the way the 8-point cube is the convex hull of a [[W:Stellated octahedron|compound of two 4-point regular tetrahedra]]. The [[W:Demihypercube|demihypercubes]] occupy alternate vertices of the hypercubes. The diagonals of the square faces of the unit-edge, unit-radius tesseract are the <math>\sqrt{2}</math> edges of two unit-radius 16-cells, also the edges of the square central planes.
We can rotate the tesseract isoclinically the way we rotated the 16-cell, by 90° in completely orthogonal invariant square central planes, with the same effect on both alternate-position 16-cells. In the course of a 720° isoclinic rotation in invariant square central planes each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cell. The two skew {8/3} octagram Clifford polygons lie on two disjoint parallel isoclines of the same chirality, of circumference <math>6\pi</math> over <math>\sqrt{2}</math> chords. They form a circular double helix which intersects each vertex of the tesseract once.
The tesseract is the [[W:Dual polytope|dual polytope]] of the 16-cell. They have the same Petrie polygon, the regular skew octagon, but the tesseract is a construct of 4 Petrie octagons with disjoint sets of 8 tesseract edges each. We can construct the tesseract by skewing two planar octagons. Because the tesseract is radially equilateral (unlike the 16-cell), we use two octagons of unit-edge length to build the unit-radius tesseract. To start we embed the planar octagons in 4-space at the same point and make them completely orthogonal. Then we skew each planar octagon into a cube, so we have a compound of two completely orthogonal cubes, provided we skewed them both in the same direction. The 16 vertices will be the vertices of a tesseract with half its 32 edges missing.
Because the tesseract contains two 16-cells in alternate positions it has two sets of 6 orthogonal square central planes. Two angles are required to specify the relationship between two planes in 4-space. Pairs of square central planes within each 16-cell are 90° apart in one angle, and either 0° or 90° apart in the other angle. They are 90° apart in both angles if and only if they are completely orthogonal planes, 90° apart by isoclinic rotation, with no vertices in common. Otherwise they are 0° apart in one of the angles, 90° apart by simple rotation, and they intersect in one axis and lie in a common 3-dimensional hyperplane.{{Efn|A double rotation in which one of the two angles of rotation is 0°, so that one of the completely orthogonal invariant planes does not rotate, is called a simple rotation. Ordinary rotations observed in a 3-dimensional space are simple rotations.|name=simple rotations}}
A pair of square central planes from alternate-position 16-cells are 60° apart by isoclinic rotation, with their corresponding vertices 120° apart. The planes are not orthogonal or parallel, so they intersect in a line somewhere, but they have no vertices in common, they have no 3-dimensional hyperplane in common, and they cannot reach each other by simple rotation. Such pairs of objects are called [[W:Clifford parallel|Clifford parallel]] because all their corresponding pairs of vertices are the same distance apart, although they are not parallel in the usual sense, because they have a common center. Not only the alternate-position 16-cells' corresponding square central planes, but also the 16-cells themselves, are Clifford parallel objects. More generally, multiple disjoint instances of a 4-polytope which compound to make a larger 4-polytope are Clifford parallel objects.
== The 24-cell ==
[[File:24-cell vertex geometry.png|thumb|Planar geometry of the radially equilateral 24-cell, showing its 3 great circle polygons and its 4 chord lengths.]]
In 2-space we have the radially equilateral 6-point hexagon. In 3-space we have the radially equilateral 12-point cuboctahedron, with 4 hexagonal central planes. In 4-space we have the radially equilateral 24-point 24-cell, with 12 cuboctahedron central hyperplanes and 16 hexagonal central planes.
The [[24-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,4,3\}</math></small>. It has 24 vertices, 96 edges, 96 equilateral triangle faces, and 24 octahedron cells. It is the four-dimensional analogue of the cuboctahedron.
The 24-cell has the same chord set as the 4-hypercube tesseract:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
[[Image:24-cell.gif|thumb|Orthographic projection of the 24-point 24-cell <small><math>\{3,4,3\}</math></small> performing a simple rotation.{{Sfn|Hise|2007}} The 3-dimensional surface made of 24 octahedra is visible.]]
The 24-cell is [[W:Dual polytope|self-dual]], like the regular polygons and regular simplexes. It is the maximal regular construct of triangles and squares (with no pentagons). It is the convex hull of a compound of three disjoint 8-point 16-cells, rotated 60° isoclinically with respect to each other. Each of the three pairs of 16-cells is a tesseract. Each 24-cell edge is also a tesseract edge. The corresponding vertices of two 16-cells or two tesseracts are 120° apart by a <math>\sqrt{3}</math> chord. Each tesseract has 8 cube cells, and each cube has four <math>\sqrt{3}</math> long diameters. The <math>\sqrt{3}</math> chords joining the corresponding vertices of two tesseracts belong to the third tesseract as cell long diameters.
The 24-cell's Petrie polygon is the regular dodecagon {12}, which has chords:
:<math>r_1=\tfrac{\sqrt{3}-1}{\sqrt{2}} \approx 0.518,r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\tfrac{\sqrt{3}+1}{\sqrt{2}} \approx 1.932,r_6=\sqrt{4}</math>
Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_5-r_3+r_1+r_1-r_3=1/r_5</math>
when <math>r_1=1</math>. The procedure rotates counterclockwise over five <math>r_5</math> chords of a {12/5} dodecagram. In the system of unit-radius coordinates <math>r_1=1/r_5</math>.
The <math>r_1</math> and <math>r_5</math> chords of the planar dodecagon do not occur in the 24-cell, which is a construct of eight skew dodecagons with disjoint sets of twelve <math>\sqrt{1}</math> edges each. In the skew dodecagons the chord lengths are:
:<math>r_1=\sqrt{1},r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\sqrt{3},r_6=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
[[File:dodecagon24cell.png|thumb|Orthogonal projection of half a 24-cell to the [[24-cell#Geodesics|F<sub>4</sub> Coxeter plane]]. Only one Petrie dodecagon {12} of the 24-cell is shown. In a unit-radius 24-cell, all black lines are 24-cell edges of unit length, also tesseract edges. The two disjoint hexagons lie in Clifford parallel central planes. Blue chords are <math>\sqrt{2}</math> 16-cell edges, also isocline chords in square rotations. Green chords are <math>\sqrt{3}</math> distances between corresponding vertices of two 16-cells, also isocline chords in hexagonal rotations. Note the {12/5} dodecagram.]]
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_3=\sqrt{2}</math></small>]]
We can rotate the 24-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in completely orthogonal invariant great square planes, with the same effect on all three 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cells. The <math>r_3=\sqrt{2}</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Three Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_3</math> chords form a circular triple helix {24/9}=3{8/3} that intersects each 24-cell vertex once.
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_5=\sqrt{3}</math></small> ]]
We can also rotate the 24-cell isoclinically in 4 Clifford parallel invariant great hexagon planes containing its vertices, over <math>r_{5}=\sqrt{3}</math> isocline chords. This is the ''characteristic rotation of the 24-cell'' in its invariant edge planes, also Fontaine and Hurley's rotation over the <math>r_5</math> star polygon which constructs <math>1/r_5</math>. A complete hexagonal isoclinic revolution requires 720° like a complete square isoclinic revolution, but it is completed in 12 isoclinic displacements of 60° each rather than 8 isoclinic displacements of 90° each. The rotational curve over each 120° <math>r_5</math> chord makes five 30° turns. Two Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_5</math> chords form a circular double helix {24/10}=2{12/5} that intersects each 24-cell vertex once.
In the 24-cell the characteristic isoclinic rotation by 60° in any invariant hexagon central plane takes every great hexagon to a Clifford parallel great hexagon in a twisting displacement, as all the central planes tilt sideways 60° while rotating 60° internally. It also takes every great square to a Clifford parallel great square in another 16-cell; it takes every 16-cell to another 16-cell. The 16-cells revolve within the 24-cell as well as rotating within it. All 24 vertices move at once on two Clifford parallel geodesic isoclines, displaced 120° in different directions.
The trajectory of each vertex over each 60° isoclinic rotational displacement is a one-twelfth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>10\pi</math> over twelve <math>\sqrt{3}</math> chords, and also traces an ordinary great circle in the plane twice, over the six <math>\sqrt{1}</math> edges of a great hexagon in a moving invariant rotation plane. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions just once and returns to its original position, and the 24-cell returns to its original orientation.
== The 600-cell ==
[[Image:600-cell.gif|thumb|Orthographic projection of the 120-point 600-cell <small><math>\{3,3,5\}</math></small> performing a simple rotation.{{Sfn|Hise|2011}} The 3-dimensional surface made of 600 tetrahedra is visible. Invisible in this rendering are 25 inscribed instances of the 24-cell (above), which occur in the 600-cell as interior boundary envelopes.]]
The [[600-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,3,5\}</math></small>. It has 120 vertices, 720 edges, 1200 equilateral triangle faces, and 600 tetrahedron cells. It is the four-dimensional analogue of the icosahedron.
The 600-cell rounds out the 24-cell by adding 96 more vertices (four more disjoint 24-cells) between the 24-cell's existing 24 vertices, in effect adding twenty-four more distinct 24-cells inscribed in the 600-cell. The new surface thus formed is a honeycomb of smaller, more numerous cells: tetrahedra of edge length <math>\phi^{-1} \approx 0.618</math> instead of octahedra of edge length <math>\sqrt{1}</math>. It encloses the <math>\sqrt{1}</math> edges of the 24-cells, which become invisible interior chords in the 600-cell, like the <math>\sqrt{2}</math> and <math>\sqrt{3}</math> chords.
Since the tetrahedra are made of shorter triangle edges than the octahedra (by a factor of <math>\phi^{-1}</math>, the inverse golden ratio), the 600-cell is not radially equilateral like the 24-cell and the tesseract. Like them it is radially triangular in a special way, but one in which [[w:Golden_triangle_(mathematics)|golden triangles]] rather than equilateral triangles meet at the center.
In 2-space we have the ''radially golden'' [[W:Decagon#The golden ratio in decagon|regular decagon]]. In 3-space we have the radially golden 30-point [[W:icosidodecahedron|icosidodecahedron]], with 6 decagon central planes. In 4-space we have the radially golden 120-point 600-cell, with 60 icosidodecahedron central hyperplanes and 72 decagon central planes.
The 600-cell's Petrie polygon is the regular [[w:Triacontagon|triacontagon {30}]]. The unit-radius planar {30}-gon has these distinct chords:
:<math>r_1=2 \sin (\tfrac{\pi}{15}/2) \approx 0.209</math>
:<math>r_2=2 \sin (\tfrac{2\pi}{15}/2) \approx 0.416</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{4\pi}{15}/2) \approx 0.813</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{7\pi}{15}/2) \approx 1.338</math>
:<math>r_8=2 \cos (\tfrac{7\pi}{15}/2) \approx 1.486</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{11}=2 \cos (\tfrac{4\pi}{15}/2) \approx 1.827</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \cos (\tfrac{2\pi}{15}/2) \approx 1.956</math>
:<math>r_{14}=2 \cos (\tfrac{\pi}{15}/2) \approx 1.989</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Only the chord lengths <math>r_3</math>, <math>r_5</math>, <math>r_6</math>, <math>\sqrt{2}</math>, <math>r_9</math>, <math>r_{10}</math>, <math>r_{12}</math>, <math>r_{15}</math> occur in the 600-cell, which is a construct of 24 Petrie {30}-gons of edge length <math>r_3</math>, six of which intersect in each icosahedral vertex figure. In the skew {30}-gons the chord lengths are:
[[File:600-cell vertex geometry.png|thumb|Planar geometry of the 600-cell, showing its 5 regular great circle polygons and its 8 chord lengths with angles of arc. The golden ratio governs the fractional roots of every other chord, and the radial golden triangles which meet at the center.|400x400px]]
:<math>r_1=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_2=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}=\text{24-cell-}r_2</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}</math>
:<math>r_8=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}=\text{16-cell-}r_3</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}=\text{24-cell-}r_5</math>
:<math>r_{11}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{14}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="7" |15 chords (4 distinct 180° pairs) make 4 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>r_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>r_{15}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>r_1</math>
|36°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}=2{15/7}
|144°
| rowspan="3" |<math>r_{14}</math>
|- style="background: palegreen;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: palegreen;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>r_2</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|144°
| rowspan="3" |<math>r_{13}</math>
|- style="background: gainsboro;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: gainsboro;" |
|0.618~
|1.902~
|- style="background: yellow;" |
| rowspan="3" |<math>r_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |[[File:V1 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>r_{12}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_4</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|120°
| rowspan="3" |<math>r_{11}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_5</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |[[File:V2 dodecahedron.png|100px]]<br>Dodecahedron
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>r_{10}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: yellow;" |
| rowspan="3" |<math>r_{6}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |[[File:V3 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>r_{9}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>r_{8}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: seashell;" |
| rowspan="3" |<math>r_{7}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |[[File:V4 icosidodecahedron.png|100px]]<br>Icosidodecahedron
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>r_{8}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The list of 600-cell chords <math>r_{i}</math> can be rearranged into a table of 8 rows and 2 columns with a pair of 180° complements in each row. The short chord and long chord each have their characteristic {30}-gon. Each row identifies a discrete isoclinic rotation of the 600-cell in invariant central planes containing the edges of the short chord {30}-gon, over the isocline chords of the long chord {30}-gon, the rotation's Clifford polygon.
Each distinct pair of complementary chord lengths is identified with a distinct [[w:600-cell#Polyhedral sections|polyhedral section of the 600-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 7 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>\phi^{-1}</math> is a icosahedron vertex figure, and the largest section at radial distance <math>\sqrt{2}</math> is an [[W:Icosidodecahedron|icosidodecahedron]] central section bisecting the 600-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>\sqrt{2}</math> the successive complement-radius polyhedra decrease in size, to the antipodal icosahedron vertex figure at distance <math>\sqrt{2+\phi}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 7 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section).
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_8=\sqrt{2}</math></small>]]
We can rotate the 600-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in two completely orthogonal invariant great square planes over <math>r_8=\sqrt{2}</math> isocline chords, with the same effect on 15 disjoint 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_8</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Fifteen Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_8</math> chords form a circular helix of 15 twisted parallel strands 5{24/9}=15{8/3} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_polygon_30-7.svg|thumb|left|150px|{30/7} <small><math>r_7=\sqrt{2}</math></small>]]
In the 600-cell there is another distinct 90° isoclinic rotation in completely orthogonal great square planes, over <math>r_7=\sqrt{2}</math> isocline chords. This rotation has period 30 and visits every vertex of a 600-cell Petrie polygon. Each 90° isoclinic rotational displacement takes every great square plane to a great square plane in another 16-cell. The vertices of the great squares of this rotation each make seven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 90° <math>r_7</math> isocline chord makes seven 12° turns. Four Clifford parallel {30/7} geodesic isoclines of circumference <math>14\pi</math> over <math>r_7</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_{10}=\sqrt{3}</math></small> ]]
We can also rotate the 600-cell isoclinically in the characteristic rotation of the 24-cell, by 60° in great hexagon planes over <math>r_{10}=\sqrt{3}</math> isocline chords, with the same effect on 5 disjoint 24-cells. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions of its 24-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_{10}</math> chord is the 24-cell <math>r_5</math> chord. The rotational curve over each 60° <math>r_5</math> chord makes five 30° turns. Ten Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_{10}</math> chords form a circular helix of 10 twisted parallel strands 5{24/10}=10{12/5} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_figure_2(15,4).svg|thumb|left|150px|{30/8}=2{15/4} <small><math>r_{13}=\sqrt{1}</math></small>]]
We can also rotate the 600-cell isoclinically in 12 Clifford parallel invariant decagon central planes containing its <math>r_{3}</math> edges, over <math>r_{13}=\sqrt{1}</math> isocline chords. This is the ''characteristic rotation of the 600-cell'' in its invariant edge planes. Its Clifford polygon is a skew {15/4} pentadecagram of <math>r_{13}</math> chords. The <math>r_{4}</math> chord is the 24-cell <math>r_2</math> chord. Successive <math>r_{13}</math> chords are edges of different 24-cells. The rotational curve over each <math>r_{13}</math> chord makes two 30° turns. Eight Clifford parallel {15/4} pentadecagon geodesic isoclines of circumference <math>5\pi</math> over <math>r_{13}</math> chords form a circular helix of eight twisted parallel strands 4{30/8}=8{15/4} that intersects each 600-cell vertex once.
In the 600-cell the characteristic isoclinic rotation by 36° in any invariant decagon central plane takes every great decagon to a Clifford parallel great decagon in a twisting displacement, as all the central planes tilt sideways 36° while rotating 36° internally. It also takes every great hexagon to a Clifford parallel great hexagon in another 24-cell, and every great square to a Clifford parallel great square in another 16-cell; it takes 24-cells to a non-disjoint 24-cell and 16-cells to a 16-cell in another 24-cell. The 24-cells revolve within the 600-cell, as the 16-cells revolve within the 24-cells. All 120 vertices move at once on eight Clifford parallel geodesic isoclines, displaced 60° in different directions.
The trajectory of each vertex over each 36° isoclinic rotational displacement is a one-fifteenth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>5\pi</math> over 15 <math>r_5</math> chords, and also traces an ordinary great circle in the plane 3 times, over the 5 edges of a great pentagon in a moving invariant rotation plane. In the course of a complete isoclinic revolution each vertex departs from 15 vertex positions just once and returns to its original position, and the 600-cell returns to its original orientation.
{{Clear}}
[[File:Regular_star_figure_6(5,2).svg|thumb|left|150px|{30/12}=6{5/2} <small><math>r_{12}=\sqrt{3.618\sim}</math></small>]]
In the 600-cell there is another distinct isoclinic rotation taking decagon planes to each other, over 144° <math>r_{12}</math> isocline chords. It also takes disjoint 24-cells to each other. This rotation has period 5 and visits every 12th vertex of a 600-cell Petrie polygon. Its Clifford polygon is a skew {5/2} pentagram of <math>r_{12}</math> chords. The invariant central planes of this rotation each intersect only one vertex of the 600-cell, which makes two orbits of a great pentagon within the moving invariant plane in the course of one complete isoclinic revolution of period 5. The rotational curve over each <math>r_{12}</math> chord makes twelve 12° turns. 24 Clifford parallel {5/2} pentagram geodesic isoclines of circumference <math>4\pi</math> over five <math>r_{12}</math> chords form a circular helix of 24 twisted parallel strands 4{30/12}=24{5/2} that intersects each 600-cell vertex once.
{{Clear}}
== Finally the 120-cell ==
The [[120-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{5,3,3\}</math></small>. It has 600 vertices, 1200 edges, 720 pentagon faces, and 120 dodecahedron cells. It is the four-dimensional analogue of the dodecahedron.
The 120-cell is the [[W:Dual polytope|dual polytope]] of the 600-cell. They have the same Petrie polygon, the regular skew triacontagon {30}, but the 120-cell is a construct of 40 Petrie {30}-gons of edge length <math>c_1</math>, two of which intersect in each tetrahedral vertex figure.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="9" |30 chords (15 180° pairs) make 15 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>c_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>c_{30}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>c_1</math>
|15.5~°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}
|164.5~°
| rowspan="3" |<math>c_{29}</math>
|- style="background: palegreen;" |
|{{radic|0.073~}}
|{{radic|3.927~}}
|- style="background: palegreen;" |
|0.270~
|1.982~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_2</math>
|25.2~°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|154.8~°
| rowspan="3" |<math>c_{28}</math>
|- style="background: gainsboro;" |
|{{radic|0.191~}}
|{{radic|3.809~}}
|- style="background: gainsboro;" |
|0.437~
|1.952~
|- style="background: yellow;" |
| rowspan="3" |<math>c_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>c_{27}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_4</math>
|41.4~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|138.6~°
| rowspan="3" |<math>c_{26}</math>
|- style="background: gainsboro;" |
|{{radic|0.5}}
|{{radic|3.5}}
|- style="background: gainsboro;" |
|0.707~
|1.871~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_5</math>
|44.5~°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|135.5~°
| rowspan="3" |<math>c_{25}</math>
|- style="background: palegreen;" |
|{{radic|0.573~}}
|{{radic|3.427~}}
|- style="background: palegreen;" |
|0.757~
|1.851~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_6</math>
|49.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|130.9~°
| rowspan="3" |<math>c_{24}</math>
|- style="background: gainsboro;" |
|{{radic|0.691~}}
|{{radic|3.309~}}
|- style="background: gainsboro;" |
|0.831~
|1.819~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_7</math>
|56°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|124°
| rowspan="3" |<math>c_{23}</math>
|- style="background: gainsboro;" |
|{{radic|0.882~}}
|{{radic|3.118~}}
|- style="background: gainsboro;" |
|0.939~
|1.766~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_8</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>c_{22}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_9</math>
|66.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|113.9~°
| rowspan="3" |<math>c_{21}</math>
|- style="background: gainsboro;" |
|{{radic|1.191~}}
|{{radic|2.809~}}
|- style="background: gainsboro;" |
|1.091~
|1.676~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{10}</math>
|69.8~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|110.2~°
| rowspan="3" |<math>c_{20}</math>
|- style="background: gainsboro;" |
|{{radic|1.309~}}
|{{radic|2.691~}}
|- style="background: gainsboro;" |
|1.144~
|1.640~
|- style="background: yellow;" |
| rowspan="3" |<math>c_{11}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>c_{19}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>c_{18}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{13}</math>
|81.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|98.9~°
| rowspan="3" |<math>c_{17}</math>
|- style="background: gainsboro;" |
|{{radic|1.691~}}
|{{radic|2.309~}}
|- style="background: gainsboro;" |
|1.300~
|1.520~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{14}</math>
|84.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|95.5~°
| rowspan="3" |<math>c_{16}</math>
|- style="background: gainsboro;" |
|{{radic|0.809~}}
|{{radic|2.191~}}
|- style="background: gainsboro;" |
|1.345~
|1.480~
|- style="background: seashell;" |
| rowspan="3" |<math>c_{15}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>c_{15}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The [[User:Dc.samizdat/Golden chords of the 120-cell#Thirty distinguished distances|table above]] of 30 chords <math>c_{t}</math> can be rearranged into a table of 16 rows and 2 columns with a pair of 180° complements in each row. This table first appears in [[w:Regular_Polytopes_(book)|''Regular Polytopes'']] (1947),{{Sfn|Coxeter|1973|loc=Table V(v): Simplified sections of {5,3,3} beginning with a vertex|pp=300-301}} where Coxeter identified each row with a distinct [[w:120-cell#Concentric_hulls|polyhedral section of the 120-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 29 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>c_1</math> is a tetrahedron vertex figure, and the largest section at radial distance <math>c_{15}</math> is a central section bisecting the 120-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>c_{15}</math> the successive complement-radius polyhedra decrease in size, to the antipodal tetrahedron vertex figure at distance <math>c_{29}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 29 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section). Each section also lies completely orthogonal to a congruent section.
Only 8 of the 30 chords in the table occur in the 600-cell and the planar {30)-gon. The 120-cell's additional chords arise originally from the regular 5-cell, in its interaction with the other regular 4-polytopes that compound to make the 120-cell. Since all those polytopes except the 5-cell occur in the 600-cell, and the 600-cell and the 120-cell have the same symmetry group, the 5-cell's symmetry group is what's new in the 120-cell.
...
{{Clear}}
== Conclusions ==
Fontaine and Hurley's discovery is more than a geometric formula for the reciprocal of a regular ''n''-polygon diagonal. It also yields the discrete sequence of isocline chords of the characteristic isoclinic rotation of a ''d''-dimensional polytope in its invariant edge planes. The characteristic rotational chord sequence of the ''d''-polytope can be represented geometrically in two dimensions on a distinct star polygon, but it lies on a geodesic circle through ''d''-dimensional space. Fontaine and Hurley discovered the geodesic topology of polytopes generally. Their procedure will reveal the geodesics of arbitrary non-uniform polytopes, since it can be applied to a polytope of any dimensionality and irregularity, by first fitting the polytope to the smallest regular polygon whose chords include its chords. [If what is meant by this is its Petrie polygon, it is not quite necessary or possible with respect to the planar polygon chords, e.g. the planar Petrie polygon of the 600-cell does not contain the <math>\sqrt{2}</math> chord. But perhaps it would work if the fit is to the smallest regular skew polygon in the ''d''-space.]
The discovery of a chordal construction for discrete isoclinic rotations generally closes the circuit on Kappraff and Adamson's discovery of a rotational connection between dynamical systems, Steinbach's golden fields, and Coxeter's Euclidean geometry of ''n'' dimensions. Application of the Fontaine and Hurley procedure in the 120-cell demonstrates why the connection exists: because polytope sequences generally, from Steinbach's golden chord sequences in polygons, to sequences of star polygons in isoclinic rotations, to subsumption relations in the sequence of regular 4-polytopes, arise as expressions of the reflections and rotations of distinct Coxeter symmetry groups, when those various groups interact.
== Appendix: Sequence of regular 4-polytopes ==
{{Regular convex 4-polytopes|wiki=W:|columns=7}}
== Notes ==
{{Notelist}}
== Citations ==
{{Reflist}}
== References ==
{{Refbegin}}
* {{Cite journal | last=Steinbach | first=Peter | year=1997 | title=Golden fields: A case for the Heptagon | journal=Mathematics Magazine | volume=70 | issue=Feb 1997 | pages=22–31 | doi=10.1080/0025570X.1997.11996494 | jstor=2691048 | ref={{SfnRef|Steinbach|1997}} }}
* {{Cite journal | last=Steinbach | first=Peter | year=2000 | title=Sections Beyond Golden| journal=Bridges: Mathematical Connections in Art, Music and Science | issue=2000 | pages=35-44 | url=https://archive.bridgesmathart.org/2000/bridges2000-35.pdf | ref={{SfnRef|Steinbach|2000}}}}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Jablan | first2=Slavik | last3=Adamson | first3=Gary | last4=Sazdanovich | first4=Radmila | year=2004 | title=Golden Fields, Generalized Fibonacci Sequences, and Chaotic Matrices | journal=Forma | volume=19 | pages=367-387 | url=https://archive.bridgesmathart.org/2005/bridges2005-369.pdf | ref={{SfnRef|Kappraff, Jablan, Adamson & Sazdanovich|2004}} }}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Adamson | first2=Gary | year=2004 | title=Polygons and Chaos | journal=Dynamical Systems and Geometric Theories | url=https://archive.bridgesmathart.org/2001/bridges2001-67.pdf | ref={{SfnRef|Kappraff & Adamson|2004}} }}
* {{Cite journal | last1=Fontaine | first1=Anne | last2=Hurley | first2=Susan | year=2006 | title=Proof by Picture: Products and Reciprocals of Diagonal Length Ratios in the Regular Polygon | journal=Forum Geometricorum | volume=6 | pages=97-101 | url=https://scispace.com/pdf/proof-by-picture-products-and-reciprocals-of-diagonal-length-1aian8mgp9.pdf }}
{{Refend}}
gonntwqq3bgzxmwn6p4uekx0od4cks3
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Dc.samizdat
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/* The 600-cell */
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text/x-wiki
= Golden chords of the 120-cell =
{{align|center|David Brooks Christie}}
{{align|center|dc@samizdat.org}}
{{align|center|Draft in progress}}
{{align|center|January 2026 - June 2026}}
<blockquote>Steinbach discovered the formula for the ratios of diagonal to side in the regular polygons. Fontaine and Hurley extended this result, discovering a formula for the reciprocal of a regular polygon chord derived geometrically from the chord's star polygon. We observe that these findings in plane geometry apply more generally, to polytopes of any dimensionality. Fontaine and Hurley's geometric procedure for finding the reciprocals of the chords of a regular polygon from their star polygons also finds the rotational geodesics of any polytope of any dimensionality.</blockquote>
== Introduction ==
Steinbach discovered the Diagonal Product Formula and the Golden Fields family of ratios of diagonal to side in the regular polygons. He showed how this family extends beyond the pentagon {5} with its well-known golden bisection proportional to 𝜙, finding that the heptagon {7} has an analogous trisection, the nonagon {9} has an analogous quadrasection, and the hendecagon {11} has an analogous pentasection, an extended family of golden proportions with quasiperiodic properties.
Kappraff and Adamson extended these findings in plane geometry to a theory of Generalized Fibonacci Sequences, showing that the Golden Fields not only do not end with the hendecagon, they form an infinite number of periodic trajectories when operated on by the Mandelbrot operator. They found a relation between the edges of star polygons and dynamical systems in the state of chaos, revealing a connection between chaos theory, number, and rotations in Coxeter Euclidean geometry.
Fontaine and Hurley examined Steinbach's finding that the length of each chord of a regular polygon is both the product of two chords and the sum of a set of smaller chords, so that in rotations to add is to multiply. They illustrated Steinbach's sets of additive chords lying parallel to each other in the plane (pointing in the same direction), and by applying Steinbach's formula more generally they found another summation relation of signed parallel chords (pointing in opposite directions) which relates each chord length to its reciprocal, and relates the summation to a distinct star polygon rotation.
We examine these remarkable findings (which stem from study of the chords of humble regular polygons) in higher-dimensional spaces, specifically in the chords, polygons and rotations of the [[120-cell]], the largest four-dimensional regular convex polytope.
== Visualizing the 120-cell ==
{| class="wikitable floatright" width="400"
|style="vertical-align:top"|[[File:120-cell.gif|200px]]<br>Orthographic projection of the 600-point 120-cell <small><math>\{5,3,3\}</math></small> performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]].{{Sfn|Hise|2011|loc=File:120-cell.gif|ps=; "Created by Jason Hise with Maya and Macromedia Fireworks. A 3D projection of a 120-cell performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]]."}} In this simplified rendering only the 120-cell's own edges are shown; its 29 interior chords are not rendered. Therefore even though it is translucent, only its outer surface is visible. The complex interior parts of the 120-cell, all its inscribed 5-cells, 16-cells, 8-cells, 24-cells, 600-cells and its much larger inventory of polyhedra, are completely invisible in this view, as none of their edges are rendered at all.
|style="vertical-align:top"|[[File:Ortho solid 016-uniform polychoron p33-t0.png|200px]]<br>Orthographic projection of the 600-point [[W:Great grand stellated 120-cell|great grand stellated 120-cell]] <small><math>\{\tfrac{5}{2},3,3\}</math></small>.{{Sfn|Ruen: Great grand stellated 120-cell|2007}} The 120-cell is its convex hull. The projection to the left renders only the 120-cell's shortest chord, its 1200 edges. The projection above also renders only one of the 120-cell's 30 chords, the edges of its 120 inscribed regular 5-cells. The 120-cell itself (the convex hull) is invisible in this view, as its edges are not rendered.
|}
[[120-cell#Geometry|The 120-cell is the maximally complex regular 4-polytope]], containing inscribed instances of every regular 1-, 2-, 3-, and 4-polytope, except the regular polygons of more than {15} sides.
The 120-cell is the convex hull of a regular [[120-cell#Relationships among interior polytopes|compound of each of the 6 regular convex 4-polytopes]]. They are the [[5-cell|5-point (5-cell) 4-simplex]], the [[16-cell|8-point (16-cell) 4-orthoplex]], the [[W:Tesseract|16-point (8-cell) tesseract]], the [[24-cell|24-point (24-cell)]], the [[600-cell|120-point (600-cell)]], and the [[120-cell|600-point (120-cell)]]. The 120-cell is the convex hull of a compound of 120 disjoint regular 5-cells, of 75 disjoint 16-cells, of 25 disjoint 24-cells, and of 5 disjoint 600-cells.
The 120-cell contains an even larger inventory of irregular polytopes, created by the intersection of multiple instances of these component regular 4-polytopes. Many are quite unexpected, because they do not occur as components of any regular polytope smaller than the 120-cell. As just one example among the [[120-cell#Concentric hulls|sections of the 120-cell]], there is an irregular 24-point polyhedron with 16 triangle faces and 4 nonagon {9} faces.{{Sfn|Moxness|}}
Most renderings of the 120-cell, like the rotating projection here, only illustrate its outer surface, which is a honeycomb of face-bonded dodecahedral cells. Only the objects in its 3-dimensional surface are rendered, namely the 120 dodecahedra, their pentagon faces, and their edges. Although the 120-cell has chords of 30 distinct lengths, in this kind of simplified rendering only the 120-cell's own edges (its shortest chord) are shown. Its 29 interior chords, the edges of objects in the interior of the 120-cell, are not rendered, so interior objects are not visible at all.
Visualizing the complete interior of the 600-vertex 120-cell in a single image is impractical because of its complexity. Only four 120-cell edges are incident at each vertex, but [[120-cell#Chords|600 chords (of all 30 lengths)]] are incident at ''each'' vertex.
== Compounds in the 120-cell ==
The 8-point (16-cell), not the 5-point (5-cell), is the smallest building block; it compounds to every larger regular 4-polytope. The 5-point (5-cell) does compound to the 600-point (120-cell), but it does not fit into any smaller regular 4-polytope.
The 8-point (16-cell) compounds by 2 in the 16-point (8-cell), and by 3 in the 24-point (24-cell). The 16-point (8-cell) compounds in the 24-point (24-cell) by 3 non-disjoint instances of itself, with each of the 24 vertices shared by two 16-point (8-cells). The 24-point (24-cell) compounds by 5 disjoint instances of itself in the 120-point (600-cell), and the 120-point (600-cell) compounds by 5 disjoint instances of itself in the 600-point (120-cell).
The 24-point (24-cell) also compounds by 5<sup>2</sup> non-disjoint instances of itself in the 120-point (600-cell); it compounds in 5 disjoint instances of itself, 10 (not 5) different ways. Whichever set of 5 disjoint 24-point (24-cells) are assembled, the resulting 120-point (600-cell) contains 25 distinct 24-point (24-cells), not just 5 (or 10). This implies that 15 disjoint 8-point (16-cells) will construct a 120-point (600-cell), which will contain 75 distinct 8-point (16-cells).
The 600-point (120-cell) is 5 disjoint 120-point (600-cells), just 2 different ways (not 5 or 10 ways), so it is 10 distinct 120-point (600-cells). This implies that the 8-point (16-cell) compounds by 3 times 5<sup>2</sup> (75) disjoint instances of itself in the 600-point (120-cell), which contains 3<sup>2</sup> times 5<sup>2</sup> (225) distinct instances of the 24-point (24-cell), and 3<sup>3</sup> times 5<sup>2</sup> (675) distinct instances of the 8-point (16-cell).
These facts were discovered painstakingly by various researchers, and no one has found a general rule governing subsumption relations among regular polytopes. The reasons for some of their numeric incidence relations are far from obvious. [[W:Pieter Hendrik Schoute|Schoute]] was the first to see that the 120-point (600-cell) is a compound of 5 24-point (24-cells) ''10 different ways'', and after he saw it a hundred years lapsed until Denney, Hooker, Johnson, Robinson, Butler & Claiborne proved his result, and showed why.{{Sfn|Denney, Hooker, Johnson, Robinson, Butler & Claiborne|2020|loc=''The geometry of H4 polytopes''}}
So much for the compounds of 16-cells. The 120-cell is also the convex hull of the compound of 120 disjoint regular 5-cells. That stellated compound (without its convex hull of 120-cell edges) is the [[w:Great_grand_stellated_120-cell|great grand stellated 120-cell]] illustrated above, the final regular [[W:Stellation|stellation]] of the 120-cell, and the only [[W:Schläfli-Hess polychoron|regular star 4-polytope]] to have the 120-cell for its convex hull. The edges of the great grand stellated 120-cell are <math>\phi^6</math> as long as those of its 120-cell [[W:List of polyhedral stellations#Stellation process|stellation core]] deep inside.
The compound of 120 disjoint 5-point (5-cells) can be seen to be equivalent to the compound of 5 disjoint 120-point (600-cells), as follows. Beginning with a single 120-point (600-cell), expand each vertex into a regular 5-cell, by adding 4 new equidistant vertices, such that the 5 vertices form a regular 5-cell inscribed in the 3-sphere. The 120 5-cells are disjoint, and the 600 vertices form 5 disjoint 120-point (600-cells): a 120-cell.
== Thirty distinguished distances ==
The 30 numbers listed in the table are all-important in Euclidean geometry. A case can be made on symmetry grounds that their squares are the 30 most important numbers between 0 and 4. The 30 rows of the table are the 30 distinct [[120-cell#Geodesic rectangles|chord lengths of the unit-radius 120-cell]], the largest regular convex 4-polytope. Since the 120-cell subsumes all smaller regular polytopes, its 30 chords are the complete chord set of all the regular polytopes that can be constructed in the first four dimensions of Euclidean space, except for regular polygons of more than 15 sides.
{| class="wikitable" style="white-space:nowrap;text-align:center"
!rowspan=2|<math>c_t</math>
!rowspan=2|arc
!rowspan=2|<small><math>\left\{\frac{30}{n}\right\}</math></small>
!rowspan=2|<math>\left\{p\right\}</math>
!rowspan=2|<small><math>m\left\{\frac{k}{d}\right\}</math></small>
!rowspan=2|Steinbach roots
!colspan=7|Chord lengths of the unit 120-cell
|-
!colspan=5|unit-radius length <math>c_t</math>
!colspan=2|unit-edge length <math>c_t/c_1</math><br>in 120-cell of radius <math>c_8=\sqrt{2}\phi^2</math>
|-
|<small><math>c_{1,1}</math></small>
|<small><math>15.5{}^{\circ}</math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math>c_{4,1}-c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7-3 \sqrt{5}}</math></small>
|<small><math>0.270091</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi ^2}</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^4}}</math></small>
|<small><math>\sqrt{0.072949}</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|-
|<small><math>c_{2,1}</math></small>
|<small><math>25.2{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{2}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{15\right\}</math></small>
|<small><math>\frac{1}{2} \left(c_{18,1}-c_{4,1}\right)</math></small>
|<small><math>\frac{\sqrt{3-\sqrt{5}}}{2}</math></small>
|<small><math>0.437016</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi }</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.190983}</math></small>
|<small><math>\phi </math></small>
|<small><math>1.61803</math></small>
|-
|<small><math>c_{3,1}</math></small>
|<small><math>36{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{3}\right\}</math></small>
|<small><math>\left\{10\right\}</math></small>
|<small><math>3 \left\{\frac{10}{3}\right\}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right) c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right)</math></small>
|<small><math>0.618034</math></small>
|<small><math>\frac{1}{\phi }</math></small>
|<small><math>\sqrt{\frac{1}{\phi ^2}}</math></small>
|<small><math>\sqrt{0.381966}</math></small>
|<small><math>\sqrt{2} \phi </math></small>
|<small><math>2.28825</math></small>
|-
|<small><math>c_{4,1}</math></small>
|<small><math>41.4{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{7}\right\}</math></small>
|<small><math>\frac{c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>0.707107</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{1}{2}}</math></small>
|<small><math>\sqrt{0.5}</math></small>
|<small><math>\phi ^2</math></small>
|<small><math>2.61803</math></small>
|-
|<small><math>c_{5,1}</math></small>
|<small><math>44.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{4}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{\frac{15}{2}\right\}</math></small>
|<small><math>\sqrt{3} c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-3 \sqrt{5}}</math></small>
|<small><math>0.756934</math></small>
|<small><math>\frac{\sqrt{\frac{3}{2}}}{\phi }</math></small>
|<small><math>\sqrt{\frac{3}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.572949}</math></small>
|<small><math>\sqrt{3} \phi </math></small>
|<small><math>2.80252</math></small>
|-
|<small><math>c_{6,1}</math></small>
|<small><math>49.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{17}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{5-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{5-\sqrt{5}}}{2}</math></small>
|<small><math>0.831254</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\frac{1}{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5}}{2 \phi }}</math></small>
|<small><math>\sqrt{0.690983}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^3}</math></small>
|<small><math>3.07768</math></small>
|-
|<small><math>c_{7,1}</math></small>
|<small><math>56.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{3}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>0.93913</math></small>
|<small><math>\frac{\sqrt{\frac{\psi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{0.881966}</math></small>
|<small><math>\sqrt{\psi \phi ^3}</math></small>
|<small><math>3.47709</math></small>
|-
|<small><math>c_{8,1}</math></small>
|<small><math>60{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{5}\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>1</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|<small><math>1</math></small>
|<small><math>\sqrt{1}</math></small>
|<small><math>\sqrt{1.}</math></small>
|<small><math>\sqrt{2} \phi ^2</math></small>
|<small><math>3.70246</math></small>
|-
|<small><math>c_{9,1}</math></small>
|<small><math>66.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{7}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{2 \phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.09132</math></small>
|<small><math>\frac{\sqrt{\frac{\chi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\chi }{2 \phi }}</math></small>
|<small><math>\sqrt{1.19098}</math></small>
|<small><math>\sqrt{\chi \phi ^3}</math></small>
|<small><math>4.04057</math></small>
|-
|<small><math>c_{10,1}</math></small>
|<small><math>69.8{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{11}\right\}</math></small>
|<small><math>\phi c_{4,1}</math></small>
|<small><math>\frac{1+\sqrt{5}}{2 \sqrt{2}}</math></small>
|<small><math>1.14412</math></small>
|<small><math>\frac{\phi }{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^2}{2}}</math></small>
|<small><math>\sqrt{1.30902}</math></small>
|<small><math>\phi ^3</math></small>
|<small><math>4.23607</math></small>
|-
|<small><math>c_{11,1}</math></small>
|<small><math>72{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{6}\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.17557</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{1.38197}</math></small>
|<small><math>\sqrt{2} \sqrt{3-\phi } \phi ^2</math></small>
|<small><math>4.3525</math></small>
|-
|<small><math>c_{12,1}</math></small>
|<small><math>75.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{24}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>1.22474</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{1.5}</math></small>
|<small><math>\sqrt{3} \phi ^2</math></small>
|<small><math>4.53457</math></small>
|-
|<small><math>c_{13,1}</math></small>
|<small><math>81.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>1.30038</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(9-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{1.69098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(9-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>4.8146</math></small>
|-
|<small><math>c_{14,1}</math></small>
|<small><math>84.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{9}\right\}</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi } c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{2} \sqrt[4]{5} \sqrt{1+\sqrt{5}}</math></small>
|<small><math>1.345</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi }}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5} \phi }{2}}</math></small>
|<small><math>\sqrt{1.80902}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^5}</math></small>
|<small><math>4.9798</math></small>
|-
|<small><math>c_{15,1}</math></small>
|<small><math>90.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{7}\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>2 c_{4,1}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>1.41421</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2.}</math></small>
|<small><math>2 \phi ^2</math></small>
|<small><math>5.23607</math></small>
|-
|<small><math>c_{16,1}</math></small>
|<small><math>95.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{29}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>1.4802</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.19098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(11-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>5.48037</math></small>
|-
|<small><math>c_{17,1}</math></small>
|<small><math>98.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{31}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>1.51954</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(7+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.30902}</math></small>
|<small><math>\sqrt{\psi \phi ^5}</math></small>
|<small><math>5.62605</math></small>
|-
|<small><math>c_{18,1}</math></small>
|<small><math>104.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{8}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{4}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>1.58114</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{2.5}</math></small>
|<small><math>\sqrt{5} \sqrt{\phi ^4}</math></small>
|<small><math>5.8541</math></small>
|-
|<small><math>c_{19,1}</math></small>
|<small><math>108.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{9}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{10}{3}\right\}</math></small>
|<small><math>c_{3,1}+c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.61803</math></small>
|<small><math>\phi </math></small>
|<small><math>\sqrt{1+\phi }</math></small>
|<small><math>\sqrt{2.61803}</math></small>
|<small><math>\sqrt{2} \phi ^3</math></small>
|<small><math>5.9907</math></small>
|-
|<small><math>c_{20,1}</math></small>
|<small><math>110.2{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>1.64042</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.69098}</math></small>
|<small><math>\phi ^2 \sqrt{8-\phi ^2}</math></small>
|<small><math>6.07359</math></small>
|-
|<small><math>c_{21,1}</math></small>
|<small><math>113.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{19}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.67601</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{2.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\chi }{\phi }}</math></small>
|<small><math>6.20537</math></small>
|-
|<small><math>c_{22,1}</math></small>
|<small><math>120{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{10}\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\sqrt{3} c_{8,1}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>1.73205</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3.}</math></small>
|<small><math>\sqrt{6} \phi ^2</math></small>
|<small><math>6.41285</math></small>
|-
|<small><math>c_{23,1}</math></small>
|<small><math>124.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{41}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{\phi }+\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.7658</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{3.11803}</math></small>
|<small><math>\sqrt{\chi \phi ^5}</math></small>
|<small><math>6.53779</math></small>
|-
|<small><math>c_{24,1}</math></small>
|<small><math>130.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>1.81907</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.30902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\sqrt{5}}{\phi }}</math></small>
|<small><math>6.73503</math></small>
|-
|<small><math>c_{25,1}</math></small>
|<small><math>135.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}}</math></small>
|<small><math>1.85123</math></small>
|<small><math>\frac{\phi ^2}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^4}{2}}</math></small>
|<small><math>\sqrt{3.42705}</math></small>
|<small><math>\phi ^4</math></small>
|<small><math>6.8541</math></small>
|-
|<small><math>c_{26,1}</math></small>
|<small><math>138.6{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{12}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{7}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>1.87083</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{3.5}</math></small>
|<small><math>\sqrt{7} \phi ^2</math></small>
|<small><math>6.92667</math></small>
|-
|<small><math>c_{27,1}</math></small>
|<small><math>144{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{12}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{5}{2}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)}</math></small>
|<small><math>1.90211</math></small>
|<small><math>\sqrt{\phi +2}</math></small>
|<small><math>\sqrt{2+\phi }</math></small>
|<small><math>\sqrt{3.61803}</math></small>
|<small><math>\phi ^2 \sqrt{2 \phi +4}</math></small>
|<small><math>7.0425</math></small>
|-
|<small><math>c_{28,1}</math></small>
|<small><math>154.8{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>1.95167</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{1}{\phi ^2}}</math></small>
|<small><math>7.22598</math></small>
|-
|<small><math>c_{29,1}</math></small>
|<small><math>164.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{14}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{7}\right\}</math></small>
|<small><math>\phi c_{12,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{\frac{3}{2}} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.98168</math></small>
|<small><math>\sqrt{\frac{3}{2}} \phi </math></small>
|<small><math>\sqrt{\frac{3 \phi ^2}{2}}</math></small>
|<small><math>\sqrt{3.92705}</math></small>
|<small><math>\sqrt{3} \phi ^3</math></small>
|<small><math>7.33708</math></small>
|-
|<small><math>c_{30,1}</math></small>
|<small><math>180{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{15}\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>2 c_{8,1}</math></small>
|<small><math>2</math></small>
|<small><math>2.</math></small>
|<small><math>2</math></small>
|<small><math>\sqrt{4}</math></small>
|<small><math>\sqrt{4.}</math></small>
|<small><math>2 \sqrt{2} \phi ^2</math></small>
|<small><math>7.40492</math></small>
|-
|rowspan=4 colspan=6|
|rowspan=4 colspan=4|
<small><math>\phi</math></small> is the golden ratio:<br>
<small><math>\phi ^2-\phi -1=0</math></small><br>
<small><math>\frac{1}{\phi }+1=\phi</math></small>, and: <small><math>\phi+1=\phi^2</math></small><br>
<small><math>\frac{1}{\phi }::1::\phi ::\phi ^2</math></small><br>
<small><math>1/\phi</math></small> and <small><math>\phi</math></small> are the golden sections of <small><math>\sqrt{5}</math></small>:<br>
<small><math>\phi +\frac{1}{\phi }=\sqrt{5}</math></small>
|colspan=2|<small><math>\phi = (\sqrt{5} + 1)/2</math></small>
|<small><math>1.618034</math></small>
|-
|colspan=2|<small><math>\chi = (3\sqrt{5} + 1)/2</math></small>
|<small><math>3.854102</math></small>
|-
|colspan=2|<small><math>\psi = (3\sqrt{5} - 1)/2</math></small>
|<small><math>2.854102</math></small>
|-
|colspan=2|<small><math>\psi = 11/\chi = 22/(3\sqrt{5} + 1)</math></small>
|<small><math>2.854102</math></small>
|}
== The 5-cell 4-simplex ==
...
== The 16-cell 4-orthoplex ==
In 2-space we have the regular 8-point octagon, in 3-space the regular 8-point cube, and in 4-space the regular 8-point [[16-cell]].
A planar octagon with rigid edges of unit length has chords of length:
:<math>r_1=1,r_2=\sqrt{2+\sqrt{2}} \approx 1.848,r_3=\sqrt{2}+1 \approx 2.414,r_4=\sqrt{4 + \sqrt{8}} \approx 2.613</math>
The chord ratio <math>r_3=\sqrt{2}+1</math> is a geometrical proportion, the [[W:Silver ratio|silver ratio]]. Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_3-r_1-r_1=1/r_3 \approx 0.414</math>
Note that <math>r_3-2=1/r_3=\sqrt{2}-1</math>. The procedure rotates counterclockwise over three <math>r_3</math> chords of an {8/3} octagram. Over the first <math>r_3</math> chord the displacement is <math>\sqrt{2}+r_1</math>. Over the second <math>r_3</math> chord it moves in the opposite direction a distance of <math>-r_1</math> . Over the third <math>r_3</math> chord it moves a distance of <math>-r_1</math>.
If we embed the planar octagon in 3-space, we can make it skew, repositioning its vertices so that each is one unit-edge length distant from three others instead of two others, at the vertices of a unit-edge cube with chords of length:
:<math>r_1=1, r_2=\sqrt{2}, r_3=\sqrt{3}, r_4=\sqrt{2}</math>
If we embed this cube in 4-space, we can skew it some more, repositioning its vertices so that each is one unit-edge length distant from six others instead of three others, at the vertices of a unit-edge 4-polytope with chords of length:
:<math>r_1=1,r_2=1,r_3=1,r_4=\sqrt{2}</math>
All of its chords except its long diameters are the same unit length as its edge. In fact they are its 24 edges, and it is a 16-cell of radius <math>1/\sqrt{2}</math>.
[[File:octagon16cell.png|thumb|Orthogonal projection of a regular 16-cell to the [[16-cell#Projections|B<sub>4</sub> Coxeter plane]]. Only its edges are shown; its long diameter chords are not drawn. All 24 edges are the same length and none lie parallel to the projection plane. The octagon circumference is a Petrie polygon. The two disjoint squares lie in completely orthogonal central planes. The blue octagram is a Clifford polygon. ]]
The [[16-cell]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{3,3,4\}</math></small>. It has 8 vertices, 24 edges, 32 equilateral triangle faces, and 16 regular tetrahedron cells. It is the [[16-cell#Octahedral dipyramid|four-dimensional analogue of the octahedron]], and each of its four orthogonal central hyperplanes is an octahedron.
The only planar regular polygons found in the 16-cell are face triangles and central plane squares, but the 16-cell also contains a skew regular octagon, its [[W:Petrie polygon|Petrie polygon]].{{Efn|name=Petrie polygon of a honeycomb}} The chords of this regular octagon, which lies skew in 4-space, are those given above for the 16-cell, as opposed to those for the cube or the regular octagon in the plane. The 16-cell is a construct of 3 Petrie octagons which share the same 8 vertices but have disjoint sets of 8 edges each.
The regular octad has higher symmetry in 4-space than it does in 2-space. The 16-cell is the 4-[[w:Cross-polytope|orthoplex]], the simplest regular 4-polytope after the [[5-cell|4-simplex]]. All the larger regular convex 4-polytopes are compounds of the 16-cell. The regular octagon exhibits this high symmetry only when embedded in 4-space at the vertices of the 16-cell.
The 16-cell constitutes an [[W:Orthonormal basis|orthonormal basis]] for the choice of a 4-dimensional Cartesian reference frame, because its vertices define four orthogonal axes. The eight vertices of a unit-radius 16-cell are (±1, 0, 0, 0), (0, ±1, 0, 0), (0, 0, ±1, 0), (0, 0, 0, ±1). All vertices are connected by <math>\sqrt{2}</math> edges except opposite pairs.
The vertex coordinates of the 16-cell form 6 central squares lying in 6 pairwise [[W:Orthogonal|orthogonal]] coordinate planes. Great squares in opposite planes that do not share an axis (e.g. in the ''xy'' and ''wz'' planes) are completely disjoint (they do not intersect at any vertices). These planes are [[W:Completely orthogonal|completely orthogonal]].{{Efn|name=Six orthogonal planes of the Cartesian basis}}
Since the unit-radius coordinate system is convenient, let us derive the unit-radius 16-cell by skewing a unit-radius planar octagon, which has chords of length:
:<math>r_1=\sqrt{2-\sqrt{2}} \approx 0.765,r_2=\sqrt{2},r_3=\sqrt{2+\sqrt{2}} \approx 1.848,r_4=2</math>
We will need a planar octagon with rigid <math>r_2</math> chords, rather than one with rigid <math>r_1</math> edges. The octagon's <math>r_2</math> chords form two disjoint great squares, visible in the orthogonal projection, which we can reposition in 3-space to form a cube by making them parallel, and in 4-space to form a 16-cell by making them completely orthogonal.
Since the edges of the 16-cell are all the same length <math>r_1=\sqrt{2},r_2=\sqrt{2},r_3=\sqrt{2}</math>, those chords are distinct only in the context of a rotation. Each chord is a 4-vector with a length and a direction. The rotational curve over each <math>r_i</math> chord makes <math>i</math> 45° turns.
[[File:16-cell-orig.gif|thumb|Orthographic projection of the 8-point 16-cell <small><math>\{3,3,4\}</math></small> performing a double rotation.{{Sfn|Hise|2007}}]]
[[W:Rotations in 4-dimensional Euclidean space|Rotations in 4-dimensional Euclidean space]] can be seen as the composition of two 2-dimensional rotations in completely orthogonal planes. The general rotation in 4-space is a [[W:SO(4)#Double rotations|double rotation]] in pairs of completely orthogonal planes. Two completely orthogonal planes are called invariant planes of the rotation when all points in the plane rotate on circles that remain in the plane, even as the whole plane tilts sideways (like a coin flipping) into another plane. The two completely orthogonal rotations of each plane (like a wheel, and like a coin flipping) are simultaneous but independent, in that they are not geometrically constrained to turn at the same rate. However, the most circular kind of rotation (as opposed to an elliptical double rotation of a rigid spherical object) occurs when the completely orthogonal planes do rotate through the same angle in the same time interval. Such equi-angled double rotations are called [[w:SO(4)#Isoclinic_rotations|isoclinic]], also [[w:William_Kingdon_Clifford|Clifford]] displacements.
The <math>r_1</math> chords of the 16-cell form a Petrie polygon which zig-zags back and forth, in the left and right rotational directions, between two completely orthogonal great squares formed by <math>r_2</math> chords.
The <math>r_2</math> chords of two completely orthogonal great squares lie parallel and perpendicular to each other. A ''simple'' rotation of the 16-cell in ''one'' of those two square central planes rotates that square like a wheel, while the other square does not move.{{Efn|name=simple rotations}} The four vertices of the rotating square orbit on a great circle in the plane.
The <math>r_3</math> chords of the 16-cell form a circular helix, visible as a blue {8/3} octagram in the orthogonal projection. A ''double'' rotation of the 16-cell, in both of two completely orthogonal invariant <math>r_2</math> square planes at once by equal angles, moves the eight vertices along the circular helix over the <math>r_3</math> chords. The vertex motion is a [[w:Geodesic|geodesic]] circle orbit on the 3-sphere of a special kind: it does not lie in a central plane, its [[w:Winding_number|winding number]] is not 1 (it is 3 in this case), its circumference is not <math>2\pi</math>, and it moves in either a left or right handed circular spiral. We shall refer to such a chiral circle orbit as an ''isocline'', and to the skew polygram of its rotational chords as a ''Clifford polygon''.
The 16-cell is the simplest possible frame in which to [[16-cell#Rotations|observe 4-dimensional rotations]] because its characteristic rotations feature a single pair of invariant rotation planes. In the 16-cell an isoclinic rotation by 90° in any pair of invariant completely orthogonal square central planes takes every great square to its completely orthogonal great square in a twisting displacement, as the invariant planes tilt sideways 90° into each other's plane while rotating 90° internally. All the vertices move at once along the same circular helix geodesic isocline of <math>r_3</math> chords, displaced 90° in 8 orthogonal directions, and the rigid 16-cell assumes a new orientation in 4-space. When the 90° isoclinic rotation is continued in the same rotational direction through an additional 90°, each vertex is again displaced 90°, but from the new orientation in a direction orthogonal to its first 90° displacement. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. In 360° of isoclinic rotation over four <math>r_3</math> chords, each vertex makes six 90° turns and reaches its antipodal position.
The trajectory of each vertex over each 90° isoclinic rotational displacement is a one-eighth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>6\pi</math> over eight <math>r_3</math> chords, and also traces an ordinary great circle in the plane twice, over the four <math>r_2</math> edges of a great square in one of the two moving invariant rotation planes. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions just once and returns to its original position, and the 16-cell returns to its original orientation.
Because this is the isoclinic rotation of the 16-cell in its invariant edge planes we shall refer to it as the ''characteristic rotation of the 16-cell'', and note once again that it is Fontaine and Hurley's rotation over the <math>r_3</math> star polygon which constructs <math>1/r_3</math>.
== The 8-cell tesseract ==
The long diameter of the unit-edge [[W:Hypercube|hypercube]] of dimension <math>n</math> is <math>\sqrt{n}</math>, so the unit-edge [[w:Tesseract|4-hypercube, the 16-point (8-cell) tesseract,]] has chords:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
Uniquely in its 4-dimensional case, the hypercube's edge length equals its radius, like the hexagon. We call such polytopes ''radially equilateral'', because they can be constructed from equilateral triangles which meet at their center, each contributing two radii and an edge. The [[w:Cuboctahedron|cuboctahedron]] and the 24-cell are also radially equilateral.
[[File:8-cell.gif|thumb|Orthographic projection of the 16-point (8-cell) tesseract <small><math>\{4,3,3\}</math></small> performing a simple rotation about a plane in 4-space.{{Sfn|Hise|2007}} The stationary plane bisects the figure from front-left to back-right and top to bottom.]]
The [[W:Tesseract|tesseract]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{4,3,3\}</math></small>. It has 16 vertices, 32 edges, 24 square faces, and 8 cube cells. It is the four-dimensional analogue of the cube.
The 16-point tesseract is the convex hull of a compound of two 8-point 16-cells, in exact dimensional analogy to the way the 8-point cube is the convex hull of a [[W:Stellated octahedron|compound of two 4-point regular tetrahedra]]. The [[W:Demihypercube|demihypercubes]] occupy alternate vertices of the hypercubes. The diagonals of the square faces of the unit-edge, unit-radius tesseract are the <math>\sqrt{2}</math> edges of two unit-radius 16-cells, also the edges of the square central planes.
We can rotate the tesseract isoclinically the way we rotated the 16-cell, by 90° in completely orthogonal invariant square central planes, with the same effect on both alternate-position 16-cells. In the course of a 720° isoclinic rotation in invariant square central planes each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cell. The two skew {8/3} octagram Clifford polygons lie on two disjoint parallel isoclines of the same chirality, of circumference <math>6\pi</math> over <math>\sqrt{2}</math> chords. They form a circular double helix which intersects each vertex of the tesseract once.
The tesseract is the [[W:Dual polytope|dual polytope]] of the 16-cell. They have the same Petrie polygon, the regular skew octagon, but the tesseract is a construct of 4 Petrie octagons with disjoint sets of 8 tesseract edges each. We can construct the tesseract by skewing two planar octagons. Because the tesseract is radially equilateral (unlike the 16-cell), we use two octagons of unit-edge length to build the unit-radius tesseract. To start we embed the planar octagons in 4-space at the same point and make them completely orthogonal. Then we skew each planar octagon into a cube, so we have a compound of two completely orthogonal cubes, provided we skewed them both in the same direction. The 16 vertices will be the vertices of a tesseract with half its 32 edges missing.
Because the tesseract contains two 16-cells in alternate positions it has two sets of 6 orthogonal square central planes. Two angles are required to specify the relationship between two planes in 4-space. Pairs of square central planes within each 16-cell are 90° apart in one angle, and either 0° or 90° apart in the other angle. They are 90° apart in both angles if and only if they are completely orthogonal planes, 90° apart by isoclinic rotation, with no vertices in common. Otherwise they are 0° apart in one of the angles, 90° apart by simple rotation, and they intersect in one axis and lie in a common 3-dimensional hyperplane.{{Efn|A double rotation in which one of the two angles of rotation is 0°, so that one of the completely orthogonal invariant planes does not rotate, is called a simple rotation. Ordinary rotations observed in a 3-dimensional space are simple rotations.|name=simple rotations}}
A pair of square central planes from alternate-position 16-cells are 60° apart by isoclinic rotation, with their corresponding vertices 120° apart. The planes are not orthogonal or parallel, so they intersect in a line somewhere, but they have no vertices in common, they have no 3-dimensional hyperplane in common, and they cannot reach each other by simple rotation. Such pairs of objects are called [[W:Clifford parallel|Clifford parallel]] because all their corresponding pairs of vertices are the same distance apart, although they are not parallel in the usual sense, because they have a common center. Not only the alternate-position 16-cells' corresponding square central planes, but also the 16-cells themselves, are Clifford parallel objects. More generally, multiple disjoint instances of a 4-polytope which compound to make a larger 4-polytope are Clifford parallel objects.
== The 24-cell ==
[[File:24-cell vertex geometry.png|thumb|Planar geometry of the radially equilateral 24-cell, showing its 3 great circle polygons and its 4 chord lengths.]]
In 2-space we have the radially equilateral 6-point hexagon. In 3-space we have the radially equilateral 12-point cuboctahedron, with 4 hexagonal central planes. In 4-space we have the radially equilateral 24-point 24-cell, with 12 cuboctahedron central hyperplanes and 16 hexagonal central planes.
The [[24-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,4,3\}</math></small>. It has 24 vertices, 96 edges, 96 equilateral triangle faces, and 24 octahedron cells. It is the four-dimensional analogue of the cuboctahedron.
The 24-cell has the same chord set as the 4-hypercube tesseract:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
[[Image:24-cell.gif|thumb|Orthographic projection of the 24-point 24-cell <small><math>\{3,4,3\}</math></small> performing a simple rotation.{{Sfn|Hise|2007}} The 3-dimensional surface made of 24 octahedra is visible.]]
The 24-cell is [[W:Dual polytope|self-dual]], like the regular polygons and regular simplexes. It is the maximal regular construct of triangles and squares (with no pentagons). It is the convex hull of a compound of three disjoint 8-point 16-cells, rotated 60° isoclinically with respect to each other. Each of the three pairs of 16-cells is a tesseract. Each 24-cell edge is also a tesseract edge. The corresponding vertices of two 16-cells or two tesseracts are 120° apart by a <math>\sqrt{3}</math> chord. Each tesseract has 8 cube cells, and each cube has four <math>\sqrt{3}</math> long diameters. The <math>\sqrt{3}</math> chords joining the corresponding vertices of two tesseracts belong to the third tesseract as cell long diameters.
The 24-cell's Petrie polygon is the regular dodecagon {12}, which has chords:
:<math>r_1=\tfrac{\sqrt{3}-1}{\sqrt{2}} \approx 0.518,r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\tfrac{\sqrt{3}+1}{\sqrt{2}} \approx 1.932,r_6=\sqrt{4}</math>
Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_5-r_3+r_1+r_1-r_3=1/r_5</math>
when <math>r_1=1</math>. The procedure rotates counterclockwise over five <math>r_5</math> chords of a {12/5} dodecagram. In the system of unit-radius coordinates <math>r_1=1/r_5</math>.
The <math>r_1</math> and <math>r_5</math> chords of the planar dodecagon do not occur in the 24-cell, which is a construct of eight skew dodecagons with disjoint sets of twelve <math>\sqrt{1}</math> edges each. In the skew dodecagons the chord lengths are:
:<math>r_1=\sqrt{1},r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\sqrt{3},r_6=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
[[File:dodecagon24cell.png|thumb|Orthogonal projection of half a 24-cell to the [[24-cell#Geodesics|F<sub>4</sub> Coxeter plane]]. Only one Petrie dodecagon {12} of the 24-cell is shown. In a unit-radius 24-cell, all black lines are 24-cell edges of unit length, also tesseract edges. The two disjoint hexagons lie in Clifford parallel central planes. Blue chords are <math>\sqrt{2}</math> 16-cell edges, also isocline chords in square rotations. Green chords are <math>\sqrt{3}</math> distances between corresponding vertices of two 16-cells, also isocline chords in hexagonal rotations. Note the {12/5} dodecagram.]]
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_3=\sqrt{2}</math></small>]]
We can rotate the 24-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in completely orthogonal invariant great square planes, with the same effect on all three 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cells. The <math>r_3=\sqrt{2}</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Three Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_3</math> chords form a circular triple helix {24/9}=3{8/3} that intersects each 24-cell vertex once.
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_5=\sqrt{3}</math></small> ]]
We can also rotate the 24-cell isoclinically in 4 Clifford parallel invariant great hexagon planes containing its vertices, over <math>r_{5}=\sqrt{3}</math> isocline chords. This is the ''characteristic rotation of the 24-cell'' in its invariant edge planes, also Fontaine and Hurley's rotation over the <math>r_5</math> star polygon which constructs <math>1/r_5</math>. A complete hexagonal isoclinic revolution requires 720° like a complete square isoclinic revolution, but it is completed in 12 isoclinic displacements of 60° each rather than 8 isoclinic displacements of 90° each. The rotational curve over each 120° <math>r_5</math> chord makes five 30° turns. Two Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_5</math> chords form a circular double helix {24/10}=2{12/5} that intersects each 24-cell vertex once.
In the 24-cell the characteristic isoclinic rotation by 60° in any invariant hexagon central plane takes every great hexagon to a Clifford parallel great hexagon in a twisting displacement, as all the central planes tilt sideways 60° while rotating 60° internally. It also takes every great square to a Clifford parallel great square in another 16-cell; it takes every 16-cell to another 16-cell. The 16-cells revolve within the 24-cell as well as rotating within it. All 24 vertices move at once on two Clifford parallel geodesic isoclines, displaced 120° in different directions.
The trajectory of each vertex over each 60° isoclinic rotational displacement is a one-twelfth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>10\pi</math> over twelve <math>\sqrt{3}</math> chords, and also traces an ordinary great circle in the plane twice, over the six <math>\sqrt{1}</math> edges of a great hexagon in a moving invariant rotation plane. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions just once and returns to its original position, and the 24-cell returns to its original orientation.
== The 600-cell ==
[[Image:600-cell.gif|thumb|Orthographic projection of the 120-point 600-cell <small><math>\{3,3,5\}</math></small> performing a simple rotation.{{Sfn|Hise|2011}} The 3-dimensional surface made of 600 tetrahedra is visible. Invisible in this rendering are 25 inscribed instances of the 24-cell (above), which occur in the 600-cell as interior boundary envelopes.]]
The [[600-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,3,5\}</math></small>. It has 120 vertices, 720 edges, 1200 equilateral triangle faces, and 600 tetrahedron cells. It is the four-dimensional analogue of the icosahedron.
The 600-cell rounds out the 24-cell by adding 96 more vertices (four more disjoint 24-cells) between the 24-cell's existing 24 vertices, in effect adding twenty-four more distinct 24-cells inscribed in the 600-cell. The new surface thus formed is a honeycomb of smaller, more numerous cells: tetrahedra of edge length <math>\phi^{-1} \approx 0.618</math> instead of octahedra of edge length <math>\sqrt{1}</math>. It encloses the <math>\sqrt{1}</math> edges of the 24-cells, which become invisible interior chords in the 600-cell, like the <math>\sqrt{2}</math> and <math>\sqrt{3}</math> chords.
Since the tetrahedra are made of shorter triangle edges than the octahedra (by a factor of <math>\phi^{-1}</math>, the inverse golden ratio), the 600-cell is not radially equilateral like the 24-cell and the tesseract. Like them it is radially triangular in a special way, but one in which [[w:Golden_triangle_(mathematics)|golden triangles]] rather than equilateral triangles meet at the center.
In 2-space we have the ''radially golden'' [[W:Decagon#The golden ratio in decagon|regular decagon]]. In 3-space we have the radially golden 30-point [[W:icosidodecahedron|icosidodecahedron]], with 6 decagon central planes. In 4-space we have the radially golden 120-point 600-cell, with 60 icosidodecahedron central hyperplanes and 72 decagon central planes.
The 600-cell's Petrie polygon is the regular [[w:Triacontagon|triacontagon {30}]]. The unit-radius planar {30}-gon has these distinct chords:
:<math>r_1=2 \sin (\tfrac{\pi}{15}/2) \approx 0.209</math>
:<math>r_2=2 \sin (\tfrac{2\pi}{15}/2) \approx 0.416</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{4\pi}{15}/2) \approx 0.813</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{7\pi}{15}/2) \approx 1.338</math>
:<math>r_8=2 \cos (\tfrac{7\pi}{15}/2) \approx 1.486</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{11}=2 \cos (\tfrac{4\pi}{15}/2) \approx 1.827</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \cos (\tfrac{2\pi}{15}/2) \approx 1.956</math>
:<math>r_{14}=2 \cos (\tfrac{\pi}{15}/2) \approx 1.989</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Only the chord lengths <math>r_3</math>, <math>r_5</math>, <math>r_6</math>, <math>\sqrt{2}</math>, <math>r_9</math>, <math>r_{10}</math>, <math>r_{12}</math>, <math>r_{15}</math> occur in the 600-cell, which is a construct of 24 Petrie {30}-gons of edge length <math>r_3</math>, six of which intersect in each icosahedral vertex figure. In the skew {30}-gons the chord lengths are:
[[File:600-cell vertex geometry.png|thumb|Planar geometry of the 600-cell, showing its 5 regular great circle polygons and its 8 chord lengths with angles of arc. The golden ratio governs the fractional roots of every other chord, and the radial golden triangles which meet at the center.|400x400px]]
:<math>r_1=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_2=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}=\text{24-cell-}r_2</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}</math>
:<math>r_8=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}=\text{16-cell-}r_3</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}=\text{24-cell-}r_5</math>
:<math>r_{11}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{14}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="7" |15 chords (4 distinct 180° pairs) make 4 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>r_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>r_{15}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>r_1</math>
|36°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}=2{15/7}
|144°
| rowspan="3" |<math>r_{14}</math>
|- style="background: palegreen;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: palegreen;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>r_2</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|144°
| rowspan="3" |<math>r_{13}</math>
|- style="background: gainsboro;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: gainsboro;" |
|0.618~
|1.902~
|- style="background: yellow;" |
| rowspan="3" |<math>r_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |[[File:V1 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>r_{12}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_4</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|120°
| rowspan="3" |<math>r_{11}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_5</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |[[File:V2 dodecahedron.png|100px]]<br>Dodecahedron
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>r_{10}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: yellow;" |
| rowspan="3" |<math>r_{6}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |[[File:V3 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>r_{9}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>r_{8}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: seashell;" |
| rowspan="3" |<math>r_{7}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |[[File:V4 icosidodecahedron.png|100px]]<br>Icosidodecahedron
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>r_{8}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The list of 600-cell chords <math>r_{i}</math> can be rearranged into a table of 8 rows and 2 columns with a pair of 180° complements in each row. The short chord and long chord each have their characteristic {30}-gon. Each row identifies a discrete isoclinic rotation of the 600-cell in invariant central planes containing the edges of the short chord {30}-gon, over the isocline chords of the long chord {30}-gon, the rotation's Clifford polygon.
Each distinct pair of complementary chord lengths is identified with a distinct [[w:600-cell#Polyhedral sections|polyhedral section of the 600-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 7 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>\phi^{-1}</math> is a icosahedron vertex figure, and the largest section at radial distance <math>\sqrt{2}</math> is an [[W:Icosidodecahedron|icosidodecahedron]] central section bisecting the 600-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>\sqrt{2}</math> the successive complement-radius polyhedra decrease in size, to the antipodal icosahedron vertex figure at distance <math>\sqrt{2+\phi}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 7 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section).
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_8=\sqrt{2}</math></small>]]
We can rotate the 600-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in two completely orthogonal invariant great square planes over <math>r_8=\sqrt{2}</math> isocline chords, with the same effect on 15 disjoint 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_8</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Fifteen Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_8</math> chords form a circular helix of 15 twisted parallel strands 5{24/9}=15{8/3} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_polygon_30-7.svg|thumb|left|150px|{30/7} <small><math>r_7=\sqrt{2}</math></small>]]
In the 600-cell this 90° isoclinic rotation in completely orthogonal great square planes takes place over the <math>r_7=\sqrt{2}</math> chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. ... The vertices of the invariant great squares of this rotation each make seven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 90° <math>r_7</math> isocline chord makes seven 12° turns. Four Clifford parallel {30/7} geodesic isoclines of circumference <math>14\pi</math> over <math>r_7</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_{10}=\sqrt{3}</math></small> ]]
We can also rotate the 600-cell isoclinically in the characteristic rotation of the 24-cell, by 60° in great hexagon planes over <math>r_{10}=\sqrt{3}</math> isocline chords, with the same effect on 5 disjoint 24-cells. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions of its 24-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_{10}</math> chord is the 24-cell <math>r_5</math> chord. The rotational curve over each 60° <math>r_5</math> chord makes five 30° turns. Ten Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_{10}</math> chords form a circular helix of 10 twisted parallel strands 5{24/10}=10{12/5} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_figure_2(15,4).svg|thumb|left|150px|{30/8}=2{15/4} <small><math>r_{13}=\sqrt{1}</math></small>]]
We can also rotate the 600-cell isoclinically in 12 Clifford parallel invariant decagon central planes containing its <math>r_{3}</math> edges, over <math>r_{13}=\sqrt{1}</math> isocline chords. This is the ''characteristic rotation of the 600-cell'' in its invariant edge planes. Its Clifford polygon is a skew {15/4} pentadecagram of <math>r_{13}</math> chords. The <math>r_{4}</math> chord is the 24-cell <math>r_2</math> chord. Successive <math>r_{13}</math> chords are edges of different 24-cells. The rotational curve over each <math>r_{13}</math> chord makes two 30° turns. Eight Clifford parallel {15/4} pentadecagon geodesic isoclines of circumference <math>5\pi</math> over <math>r_{13}</math> chords form a circular helix of eight twisted parallel strands 4{30/8}=8{15/4} that intersects each 600-cell vertex once.
In the 600-cell the characteristic isoclinic rotation by 36° in any invariant decagon central plane takes every great decagon to a Clifford parallel great decagon in a twisting displacement, as all the central planes tilt sideways 36° while rotating 36° internally. It also takes every great hexagon to a Clifford parallel great hexagon in another 24-cell, and every great square to a Clifford parallel great square in another 16-cell; it takes 24-cells to a non-disjoint 24-cell and 16-cells to a 16-cell in another 24-cell. The 24-cells revolve within the 600-cell, as the 16-cells revolve within the 24-cells. All 120 vertices move at once on eight Clifford parallel geodesic isoclines, displaced 60° in different directions.
The trajectory of each vertex over each 36° isoclinic rotational displacement is a one-fifteenth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>5\pi</math> over 15 <math>r_5</math> chords, and also traces an ordinary great circle in the plane 3 times, over the 5 edges of a great pentagon in a moving invariant rotation plane. In the course of a complete isoclinic revolution each vertex departs from 15 vertex positions just once and returns to its original position, and the 600-cell returns to its original orientation.
{{Clear}}
[[File:Regular_star_figure_6(5,2).svg|thumb|left|150px|{30/12}=6{5/2} <small><math>r_{12}=\sqrt{3.618\sim}</math></small>]]
In the 600-cell there is another distinct isoclinic rotation taking decagon planes to each other, over 144° <math>r_{12}</math> isocline chords. It also takes disjoint 24-cells to each other. This rotation has period 5 and visits every 12th vertex of a 600-cell Petrie polygon. Its Clifford polygon is a skew {5/2} pentagram of <math>r_{12}</math> chords. The invariant central planes of this rotation each intersect only one vertex of the 600-cell, which makes two orbits of a great pentagon within the moving invariant plane in the course of one complete isoclinic revolution of period 5. The rotational curve over each <math>r_{12}</math> chord makes twelve 12° turns. 24 Clifford parallel {5/2} pentagram geodesic isoclines of circumference <math>4\pi</math> over five <math>r_{12}</math> chords form a circular helix of 24 twisted parallel strands 4{30/12}=24{5/2} that intersects each 600-cell vertex once.
{{Clear}}
== Finally the 120-cell ==
The [[120-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{5,3,3\}</math></small>. It has 600 vertices, 1200 edges, 720 pentagon faces, and 120 dodecahedron cells. It is the four-dimensional analogue of the dodecahedron.
The 120-cell is the [[W:Dual polytope|dual polytope]] of the 600-cell. They have the same Petrie polygon, the regular skew triacontagon {30}, but the 120-cell is a construct of 40 Petrie {30}-gons of edge length <math>c_1</math>, two of which intersect in each tetrahedral vertex figure.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="9" |30 chords (15 180° pairs) make 15 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>c_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>c_{30}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>c_1</math>
|15.5~°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}
|164.5~°
| rowspan="3" |<math>c_{29}</math>
|- style="background: palegreen;" |
|{{radic|0.073~}}
|{{radic|3.927~}}
|- style="background: palegreen;" |
|0.270~
|1.982~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_2</math>
|25.2~°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|154.8~°
| rowspan="3" |<math>c_{28}</math>
|- style="background: gainsboro;" |
|{{radic|0.191~}}
|{{radic|3.809~}}
|- style="background: gainsboro;" |
|0.437~
|1.952~
|- style="background: yellow;" |
| rowspan="3" |<math>c_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>c_{27}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_4</math>
|41.4~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|138.6~°
| rowspan="3" |<math>c_{26}</math>
|- style="background: gainsboro;" |
|{{radic|0.5}}
|{{radic|3.5}}
|- style="background: gainsboro;" |
|0.707~
|1.871~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_5</math>
|44.5~°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|135.5~°
| rowspan="3" |<math>c_{25}</math>
|- style="background: palegreen;" |
|{{radic|0.573~}}
|{{radic|3.427~}}
|- style="background: palegreen;" |
|0.757~
|1.851~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_6</math>
|49.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|130.9~°
| rowspan="3" |<math>c_{24}</math>
|- style="background: gainsboro;" |
|{{radic|0.691~}}
|{{radic|3.309~}}
|- style="background: gainsboro;" |
|0.831~
|1.819~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_7</math>
|56°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|124°
| rowspan="3" |<math>c_{23}</math>
|- style="background: gainsboro;" |
|{{radic|0.882~}}
|{{radic|3.118~}}
|- style="background: gainsboro;" |
|0.939~
|1.766~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_8</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>c_{22}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_9</math>
|66.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|113.9~°
| rowspan="3" |<math>c_{21}</math>
|- style="background: gainsboro;" |
|{{radic|1.191~}}
|{{radic|2.809~}}
|- style="background: gainsboro;" |
|1.091~
|1.676~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{10}</math>
|69.8~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|110.2~°
| rowspan="3" |<math>c_{20}</math>
|- style="background: gainsboro;" |
|{{radic|1.309~}}
|{{radic|2.691~}}
|- style="background: gainsboro;" |
|1.144~
|1.640~
|- style="background: yellow;" |
| rowspan="3" |<math>c_{11}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>c_{19}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>c_{18}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{13}</math>
|81.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|98.9~°
| rowspan="3" |<math>c_{17}</math>
|- style="background: gainsboro;" |
|{{radic|1.691~}}
|{{radic|2.309~}}
|- style="background: gainsboro;" |
|1.300~
|1.520~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{14}</math>
|84.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|95.5~°
| rowspan="3" |<math>c_{16}</math>
|- style="background: gainsboro;" |
|{{radic|0.809~}}
|{{radic|2.191~}}
|- style="background: gainsboro;" |
|1.345~
|1.480~
|- style="background: seashell;" |
| rowspan="3" |<math>c_{15}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>c_{15}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The [[User:Dc.samizdat/Golden chords of the 120-cell#Thirty distinguished distances|table above]] of 30 chords <math>c_{t}</math> can be rearranged into a table of 16 rows and 2 columns with a pair of 180° complements in each row. This table first appears in [[w:Regular_Polytopes_(book)|''Regular Polytopes'']] (1947),{{Sfn|Coxeter|1973|loc=Table V(v): Simplified sections of {5,3,3} beginning with a vertex|pp=300-301}} where Coxeter identified each row with a distinct [[w:120-cell#Concentric_hulls|polyhedral section of the 120-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 29 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>c_1</math> is a tetrahedron vertex figure, and the largest section at radial distance <math>c_{15}</math> is a central section bisecting the 120-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>c_{15}</math> the successive complement-radius polyhedra decrease in size, to the antipodal tetrahedron vertex figure at distance <math>c_{29}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 29 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section). Each section also lies completely orthogonal to a congruent section.
Only 8 of the 30 chords in the table occur in the 600-cell and the planar {30)-gon. The 120-cell's additional chords arise originally from the regular 5-cell, in its interaction with the other regular 4-polytopes that compound to make the 120-cell. Since all those polytopes except the 5-cell occur in the 600-cell, and the 600-cell and the 120-cell have the same symmetry group, the 5-cell's symmetry group is what's new in the 120-cell.
...
{{Clear}}
== Conclusions ==
Fontaine and Hurley's discovery is more than a geometric formula for the reciprocal of a regular ''n''-polygon diagonal. It also yields the discrete sequence of isocline chords of the characteristic isoclinic rotation of a ''d''-dimensional polytope in its invariant edge planes. The characteristic rotational chord sequence of the ''d''-polytope can be represented geometrically in two dimensions on a distinct star polygon, but it lies on a geodesic circle through ''d''-dimensional space. Fontaine and Hurley discovered the geodesic topology of polytopes generally. Their procedure will reveal the geodesics of arbitrary non-uniform polytopes, since it can be applied to a polytope of any dimensionality and irregularity, by first fitting the polytope to the smallest regular polygon whose chords include its chords. [If what is meant by this is its Petrie polygon, it is not quite necessary or possible with respect to the planar polygon chords, e.g. the planar Petrie polygon of the 600-cell does not contain the <math>\sqrt{2}</math> chord. But perhaps it would work if the fit is to the smallest regular skew polygon in the ''d''-space.]
The discovery of a chordal construction for discrete isoclinic rotations generally closes the circuit on Kappraff and Adamson's discovery of a rotational connection between dynamical systems, Steinbach's golden fields, and Coxeter's Euclidean geometry of ''n'' dimensions. Application of the Fontaine and Hurley procedure in the 120-cell demonstrates why the connection exists: because polytope sequences generally, from Steinbach's golden chord sequences in polygons, to sequences of star polygons in isoclinic rotations, to subsumption relations in the sequence of regular 4-polytopes, arise as expressions of the reflections and rotations of distinct Coxeter symmetry groups, when those various groups interact.
== Appendix: Sequence of regular 4-polytopes ==
{{Regular convex 4-polytopes|wiki=W:|columns=7}}
== Notes ==
{{Notelist}}
== Citations ==
{{Reflist}}
== References ==
{{Refbegin}}
* {{Cite journal | last=Steinbach | first=Peter | year=1997 | title=Golden fields: A case for the Heptagon | journal=Mathematics Magazine | volume=70 | issue=Feb 1997 | pages=22–31 | doi=10.1080/0025570X.1997.11996494 | jstor=2691048 | ref={{SfnRef|Steinbach|1997}} }}
* {{Cite journal | last=Steinbach | first=Peter | year=2000 | title=Sections Beyond Golden| journal=Bridges: Mathematical Connections in Art, Music and Science | issue=2000 | pages=35-44 | url=https://archive.bridgesmathart.org/2000/bridges2000-35.pdf | ref={{SfnRef|Steinbach|2000}}}}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Jablan | first2=Slavik | last3=Adamson | first3=Gary | last4=Sazdanovich | first4=Radmila | year=2004 | title=Golden Fields, Generalized Fibonacci Sequences, and Chaotic Matrices | journal=Forma | volume=19 | pages=367-387 | url=https://archive.bridgesmathart.org/2005/bridges2005-369.pdf | ref={{SfnRef|Kappraff, Jablan, Adamson & Sazdanovich|2004}} }}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Adamson | first2=Gary | year=2004 | title=Polygons and Chaos | journal=Dynamical Systems and Geometric Theories | url=https://archive.bridgesmathart.org/2001/bridges2001-67.pdf | ref={{SfnRef|Kappraff & Adamson|2004}} }}
* {{Cite journal | last1=Fontaine | first1=Anne | last2=Hurley | first2=Susan | year=2006 | title=Proof by Picture: Products and Reciprocals of Diagonal Length Ratios in the Regular Polygon | journal=Forum Geometricorum | volume=6 | pages=97-101 | url=https://scispace.com/pdf/proof-by-picture-products-and-reciprocals-of-diagonal-length-1aian8mgp9.pdf }}
{{Refend}}
nmwnnz0rbhv6pz8t37rnnpstra6r4ph
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2026-06-19T12:59:52Z
Dc.samizdat
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/* The 600-cell */
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text/x-wiki
= Golden chords of the 120-cell =
{{align|center|David Brooks Christie}}
{{align|center|dc@samizdat.org}}
{{align|center|Draft in progress}}
{{align|center|January 2026 - June 2026}}
<blockquote>Steinbach discovered the formula for the ratios of diagonal to side in the regular polygons. Fontaine and Hurley extended this result, discovering a formula for the reciprocal of a regular polygon chord derived geometrically from the chord's star polygon. We observe that these findings in plane geometry apply more generally, to polytopes of any dimensionality. Fontaine and Hurley's geometric procedure for finding the reciprocals of the chords of a regular polygon from their star polygons also finds the rotational geodesics of any polytope of any dimensionality.</blockquote>
== Introduction ==
Steinbach discovered the Diagonal Product Formula and the Golden Fields family of ratios of diagonal to side in the regular polygons. He showed how this family extends beyond the pentagon {5} with its well-known golden bisection proportional to 𝜙, finding that the heptagon {7} has an analogous trisection, the nonagon {9} has an analogous quadrasection, and the hendecagon {11} has an analogous pentasection, an extended family of golden proportions with quasiperiodic properties.
Kappraff and Adamson extended these findings in plane geometry to a theory of Generalized Fibonacci Sequences, showing that the Golden Fields not only do not end with the hendecagon, they form an infinite number of periodic trajectories when operated on by the Mandelbrot operator. They found a relation between the edges of star polygons and dynamical systems in the state of chaos, revealing a connection between chaos theory, number, and rotations in Coxeter Euclidean geometry.
Fontaine and Hurley examined Steinbach's finding that the length of each chord of a regular polygon is both the product of two chords and the sum of a set of smaller chords, so that in rotations to add is to multiply. They illustrated Steinbach's sets of additive chords lying parallel to each other in the plane (pointing in the same direction), and by applying Steinbach's formula more generally they found another summation relation of signed parallel chords (pointing in opposite directions) which relates each chord length to its reciprocal, and relates the summation to a distinct star polygon rotation.
We examine these remarkable findings (which stem from study of the chords of humble regular polygons) in higher-dimensional spaces, specifically in the chords, polygons and rotations of the [[120-cell]], the largest four-dimensional regular convex polytope.
== Visualizing the 120-cell ==
{| class="wikitable floatright" width="400"
|style="vertical-align:top"|[[File:120-cell.gif|200px]]<br>Orthographic projection of the 600-point 120-cell <small><math>\{5,3,3\}</math></small> performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]].{{Sfn|Hise|2011|loc=File:120-cell.gif|ps=; "Created by Jason Hise with Maya and Macromedia Fireworks. A 3D projection of a 120-cell performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]]."}} In this simplified rendering only the 120-cell's own edges are shown; its 29 interior chords are not rendered. Therefore even though it is translucent, only its outer surface is visible. The complex interior parts of the 120-cell, all its inscribed 5-cells, 16-cells, 8-cells, 24-cells, 600-cells and its much larger inventory of polyhedra, are completely invisible in this view, as none of their edges are rendered at all.
|style="vertical-align:top"|[[File:Ortho solid 016-uniform polychoron p33-t0.png|200px]]<br>Orthographic projection of the 600-point [[W:Great grand stellated 120-cell|great grand stellated 120-cell]] <small><math>\{\tfrac{5}{2},3,3\}</math></small>.{{Sfn|Ruen: Great grand stellated 120-cell|2007}} The 120-cell is its convex hull. The projection to the left renders only the 120-cell's shortest chord, its 1200 edges. The projection above also renders only one of the 120-cell's 30 chords, the edges of its 120 inscribed regular 5-cells. The 120-cell itself (the convex hull) is invisible in this view, as its edges are not rendered.
|}
[[120-cell#Geometry|The 120-cell is the maximally complex regular 4-polytope]], containing inscribed instances of every regular 1-, 2-, 3-, and 4-polytope, except the regular polygons of more than {15} sides.
The 120-cell is the convex hull of a regular [[120-cell#Relationships among interior polytopes|compound of each of the 6 regular convex 4-polytopes]]. They are the [[5-cell|5-point (5-cell) 4-simplex]], the [[16-cell|8-point (16-cell) 4-orthoplex]], the [[W:Tesseract|16-point (8-cell) tesseract]], the [[24-cell|24-point (24-cell)]], the [[600-cell|120-point (600-cell)]], and the [[120-cell|600-point (120-cell)]]. The 120-cell is the convex hull of a compound of 120 disjoint regular 5-cells, of 75 disjoint 16-cells, of 25 disjoint 24-cells, and of 5 disjoint 600-cells.
The 120-cell contains an even larger inventory of irregular polytopes, created by the intersection of multiple instances of these component regular 4-polytopes. Many are quite unexpected, because they do not occur as components of any regular polytope smaller than the 120-cell. As just one example among the [[120-cell#Concentric hulls|sections of the 120-cell]], there is an irregular 24-point polyhedron with 16 triangle faces and 4 nonagon {9} faces.{{Sfn|Moxness|}}
Most renderings of the 120-cell, like the rotating projection here, only illustrate its outer surface, which is a honeycomb of face-bonded dodecahedral cells. Only the objects in its 3-dimensional surface are rendered, namely the 120 dodecahedra, their pentagon faces, and their edges. Although the 120-cell has chords of 30 distinct lengths, in this kind of simplified rendering only the 120-cell's own edges (its shortest chord) are shown. Its 29 interior chords, the edges of objects in the interior of the 120-cell, are not rendered, so interior objects are not visible at all.
Visualizing the complete interior of the 600-vertex 120-cell in a single image is impractical because of its complexity. Only four 120-cell edges are incident at each vertex, but [[120-cell#Chords|600 chords (of all 30 lengths)]] are incident at ''each'' vertex.
== Compounds in the 120-cell ==
The 8-point (16-cell), not the 5-point (5-cell), is the smallest building block; it compounds to every larger regular 4-polytope. The 5-point (5-cell) does compound to the 600-point (120-cell), but it does not fit into any smaller regular 4-polytope.
The 8-point (16-cell) compounds by 2 in the 16-point (8-cell), and by 3 in the 24-point (24-cell). The 16-point (8-cell) compounds in the 24-point (24-cell) by 3 non-disjoint instances of itself, with each of the 24 vertices shared by two 16-point (8-cells). The 24-point (24-cell) compounds by 5 disjoint instances of itself in the 120-point (600-cell), and the 120-point (600-cell) compounds by 5 disjoint instances of itself in the 600-point (120-cell).
The 24-point (24-cell) also compounds by 5<sup>2</sup> non-disjoint instances of itself in the 120-point (600-cell); it compounds in 5 disjoint instances of itself, 10 (not 5) different ways. Whichever set of 5 disjoint 24-point (24-cells) are assembled, the resulting 120-point (600-cell) contains 25 distinct 24-point (24-cells), not just 5 (or 10). This implies that 15 disjoint 8-point (16-cells) will construct a 120-point (600-cell), which will contain 75 distinct 8-point (16-cells).
The 600-point (120-cell) is 5 disjoint 120-point (600-cells), just 2 different ways (not 5 or 10 ways), so it is 10 distinct 120-point (600-cells). This implies that the 8-point (16-cell) compounds by 3 times 5<sup>2</sup> (75) disjoint instances of itself in the 600-point (120-cell), which contains 3<sup>2</sup> times 5<sup>2</sup> (225) distinct instances of the 24-point (24-cell), and 3<sup>3</sup> times 5<sup>2</sup> (675) distinct instances of the 8-point (16-cell).
These facts were discovered painstakingly by various researchers, and no one has found a general rule governing subsumption relations among regular polytopes. The reasons for some of their numeric incidence relations are far from obvious. [[W:Pieter Hendrik Schoute|Schoute]] was the first to see that the 120-point (600-cell) is a compound of 5 24-point (24-cells) ''10 different ways'', and after he saw it a hundred years lapsed until Denney, Hooker, Johnson, Robinson, Butler & Claiborne proved his result, and showed why.{{Sfn|Denney, Hooker, Johnson, Robinson, Butler & Claiborne|2020|loc=''The geometry of H4 polytopes''}}
So much for the compounds of 16-cells. The 120-cell is also the convex hull of the compound of 120 disjoint regular 5-cells. That stellated compound (without its convex hull of 120-cell edges) is the [[w:Great_grand_stellated_120-cell|great grand stellated 120-cell]] illustrated above, the final regular [[W:Stellation|stellation]] of the 120-cell, and the only [[W:Schläfli-Hess polychoron|regular star 4-polytope]] to have the 120-cell for its convex hull. The edges of the great grand stellated 120-cell are <math>\phi^6</math> as long as those of its 120-cell [[W:List of polyhedral stellations#Stellation process|stellation core]] deep inside.
The compound of 120 disjoint 5-point (5-cells) can be seen to be equivalent to the compound of 5 disjoint 120-point (600-cells), as follows. Beginning with a single 120-point (600-cell), expand each vertex into a regular 5-cell, by adding 4 new equidistant vertices, such that the 5 vertices form a regular 5-cell inscribed in the 3-sphere. The 120 5-cells are disjoint, and the 600 vertices form 5 disjoint 120-point (600-cells): a 120-cell.
== Thirty distinguished distances ==
The 30 numbers listed in the table are all-important in Euclidean geometry. A case can be made on symmetry grounds that their squares are the 30 most important numbers between 0 and 4. The 30 rows of the table are the 30 distinct [[120-cell#Geodesic rectangles|chord lengths of the unit-radius 120-cell]], the largest regular convex 4-polytope. Since the 120-cell subsumes all smaller regular polytopes, its 30 chords are the complete chord set of all the regular polytopes that can be constructed in the first four dimensions of Euclidean space, except for regular polygons of more than 15 sides.
{| class="wikitable" style="white-space:nowrap;text-align:center"
!rowspan=2|<math>c_t</math>
!rowspan=2|arc
!rowspan=2|<small><math>\left\{\frac{30}{n}\right\}</math></small>
!rowspan=2|<math>\left\{p\right\}</math>
!rowspan=2|<small><math>m\left\{\frac{k}{d}\right\}</math></small>
!rowspan=2|Steinbach roots
!colspan=7|Chord lengths of the unit 120-cell
|-
!colspan=5|unit-radius length <math>c_t</math>
!colspan=2|unit-edge length <math>c_t/c_1</math><br>in 120-cell of radius <math>c_8=\sqrt{2}\phi^2</math>
|-
|<small><math>c_{1,1}</math></small>
|<small><math>15.5{}^{\circ}</math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math>c_{4,1}-c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7-3 \sqrt{5}}</math></small>
|<small><math>0.270091</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi ^2}</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^4}}</math></small>
|<small><math>\sqrt{0.072949}</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|-
|<small><math>c_{2,1}</math></small>
|<small><math>25.2{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{2}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{15\right\}</math></small>
|<small><math>\frac{1}{2} \left(c_{18,1}-c_{4,1}\right)</math></small>
|<small><math>\frac{\sqrt{3-\sqrt{5}}}{2}</math></small>
|<small><math>0.437016</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi }</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.190983}</math></small>
|<small><math>\phi </math></small>
|<small><math>1.61803</math></small>
|-
|<small><math>c_{3,1}</math></small>
|<small><math>36{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{3}\right\}</math></small>
|<small><math>\left\{10\right\}</math></small>
|<small><math>3 \left\{\frac{10}{3}\right\}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right) c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right)</math></small>
|<small><math>0.618034</math></small>
|<small><math>\frac{1}{\phi }</math></small>
|<small><math>\sqrt{\frac{1}{\phi ^2}}</math></small>
|<small><math>\sqrt{0.381966}</math></small>
|<small><math>\sqrt{2} \phi </math></small>
|<small><math>2.28825</math></small>
|-
|<small><math>c_{4,1}</math></small>
|<small><math>41.4{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{7}\right\}</math></small>
|<small><math>\frac{c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>0.707107</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{1}{2}}</math></small>
|<small><math>\sqrt{0.5}</math></small>
|<small><math>\phi ^2</math></small>
|<small><math>2.61803</math></small>
|-
|<small><math>c_{5,1}</math></small>
|<small><math>44.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{4}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{\frac{15}{2}\right\}</math></small>
|<small><math>\sqrt{3} c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-3 \sqrt{5}}</math></small>
|<small><math>0.756934</math></small>
|<small><math>\frac{\sqrt{\frac{3}{2}}}{\phi }</math></small>
|<small><math>\sqrt{\frac{3}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.572949}</math></small>
|<small><math>\sqrt{3} \phi </math></small>
|<small><math>2.80252</math></small>
|-
|<small><math>c_{6,1}</math></small>
|<small><math>49.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{17}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{5-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{5-\sqrt{5}}}{2}</math></small>
|<small><math>0.831254</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\frac{1}{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5}}{2 \phi }}</math></small>
|<small><math>\sqrt{0.690983}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^3}</math></small>
|<small><math>3.07768</math></small>
|-
|<small><math>c_{7,1}</math></small>
|<small><math>56.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{3}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>0.93913</math></small>
|<small><math>\frac{\sqrt{\frac{\psi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{0.881966}</math></small>
|<small><math>\sqrt{\psi \phi ^3}</math></small>
|<small><math>3.47709</math></small>
|-
|<small><math>c_{8,1}</math></small>
|<small><math>60{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{5}\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>1</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|<small><math>1</math></small>
|<small><math>\sqrt{1}</math></small>
|<small><math>\sqrt{1.}</math></small>
|<small><math>\sqrt{2} \phi ^2</math></small>
|<small><math>3.70246</math></small>
|-
|<small><math>c_{9,1}</math></small>
|<small><math>66.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{7}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{2 \phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.09132</math></small>
|<small><math>\frac{\sqrt{\frac{\chi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\chi }{2 \phi }}</math></small>
|<small><math>\sqrt{1.19098}</math></small>
|<small><math>\sqrt{\chi \phi ^3}</math></small>
|<small><math>4.04057</math></small>
|-
|<small><math>c_{10,1}</math></small>
|<small><math>69.8{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{11}\right\}</math></small>
|<small><math>\phi c_{4,1}</math></small>
|<small><math>\frac{1+\sqrt{5}}{2 \sqrt{2}}</math></small>
|<small><math>1.14412</math></small>
|<small><math>\frac{\phi }{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^2}{2}}</math></small>
|<small><math>\sqrt{1.30902}</math></small>
|<small><math>\phi ^3</math></small>
|<small><math>4.23607</math></small>
|-
|<small><math>c_{11,1}</math></small>
|<small><math>72{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{6}\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.17557</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{1.38197}</math></small>
|<small><math>\sqrt{2} \sqrt{3-\phi } \phi ^2</math></small>
|<small><math>4.3525</math></small>
|-
|<small><math>c_{12,1}</math></small>
|<small><math>75.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{24}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>1.22474</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{1.5}</math></small>
|<small><math>\sqrt{3} \phi ^2</math></small>
|<small><math>4.53457</math></small>
|-
|<small><math>c_{13,1}</math></small>
|<small><math>81.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>1.30038</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(9-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{1.69098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(9-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>4.8146</math></small>
|-
|<small><math>c_{14,1}</math></small>
|<small><math>84.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{9}\right\}</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi } c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{2} \sqrt[4]{5} \sqrt{1+\sqrt{5}}</math></small>
|<small><math>1.345</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi }}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5} \phi }{2}}</math></small>
|<small><math>\sqrt{1.80902}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^5}</math></small>
|<small><math>4.9798</math></small>
|-
|<small><math>c_{15,1}</math></small>
|<small><math>90.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{7}\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>2 c_{4,1}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>1.41421</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2.}</math></small>
|<small><math>2 \phi ^2</math></small>
|<small><math>5.23607</math></small>
|-
|<small><math>c_{16,1}</math></small>
|<small><math>95.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{29}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>1.4802</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.19098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(11-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>5.48037</math></small>
|-
|<small><math>c_{17,1}</math></small>
|<small><math>98.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{31}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>1.51954</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(7+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.30902}</math></small>
|<small><math>\sqrt{\psi \phi ^5}</math></small>
|<small><math>5.62605</math></small>
|-
|<small><math>c_{18,1}</math></small>
|<small><math>104.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{8}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{4}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>1.58114</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{2.5}</math></small>
|<small><math>\sqrt{5} \sqrt{\phi ^4}</math></small>
|<small><math>5.8541</math></small>
|-
|<small><math>c_{19,1}</math></small>
|<small><math>108.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{9}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{10}{3}\right\}</math></small>
|<small><math>c_{3,1}+c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.61803</math></small>
|<small><math>\phi </math></small>
|<small><math>\sqrt{1+\phi }</math></small>
|<small><math>\sqrt{2.61803}</math></small>
|<small><math>\sqrt{2} \phi ^3</math></small>
|<small><math>5.9907</math></small>
|-
|<small><math>c_{20,1}</math></small>
|<small><math>110.2{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>1.64042</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.69098}</math></small>
|<small><math>\phi ^2 \sqrt{8-\phi ^2}</math></small>
|<small><math>6.07359</math></small>
|-
|<small><math>c_{21,1}</math></small>
|<small><math>113.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{19}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.67601</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{2.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\chi }{\phi }}</math></small>
|<small><math>6.20537</math></small>
|-
|<small><math>c_{22,1}</math></small>
|<small><math>120{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{10}\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\sqrt{3} c_{8,1}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>1.73205</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3.}</math></small>
|<small><math>\sqrt{6} \phi ^2</math></small>
|<small><math>6.41285</math></small>
|-
|<small><math>c_{23,1}</math></small>
|<small><math>124.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{41}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{\phi }+\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.7658</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{3.11803}</math></small>
|<small><math>\sqrt{\chi \phi ^5}</math></small>
|<small><math>6.53779</math></small>
|-
|<small><math>c_{24,1}</math></small>
|<small><math>130.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>1.81907</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.30902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\sqrt{5}}{\phi }}</math></small>
|<small><math>6.73503</math></small>
|-
|<small><math>c_{25,1}</math></small>
|<small><math>135.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}}</math></small>
|<small><math>1.85123</math></small>
|<small><math>\frac{\phi ^2}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^4}{2}}</math></small>
|<small><math>\sqrt{3.42705}</math></small>
|<small><math>\phi ^4</math></small>
|<small><math>6.8541</math></small>
|-
|<small><math>c_{26,1}</math></small>
|<small><math>138.6{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{12}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{7}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>1.87083</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{3.5}</math></small>
|<small><math>\sqrt{7} \phi ^2</math></small>
|<small><math>6.92667</math></small>
|-
|<small><math>c_{27,1}</math></small>
|<small><math>144{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{12}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{5}{2}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)}</math></small>
|<small><math>1.90211</math></small>
|<small><math>\sqrt{\phi +2}</math></small>
|<small><math>\sqrt{2+\phi }</math></small>
|<small><math>\sqrt{3.61803}</math></small>
|<small><math>\phi ^2 \sqrt{2 \phi +4}</math></small>
|<small><math>7.0425</math></small>
|-
|<small><math>c_{28,1}</math></small>
|<small><math>154.8{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>1.95167</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{1}{\phi ^2}}</math></small>
|<small><math>7.22598</math></small>
|-
|<small><math>c_{29,1}</math></small>
|<small><math>164.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{14}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{7}\right\}</math></small>
|<small><math>\phi c_{12,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{\frac{3}{2}} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.98168</math></small>
|<small><math>\sqrt{\frac{3}{2}} \phi </math></small>
|<small><math>\sqrt{\frac{3 \phi ^2}{2}}</math></small>
|<small><math>\sqrt{3.92705}</math></small>
|<small><math>\sqrt{3} \phi ^3</math></small>
|<small><math>7.33708</math></small>
|-
|<small><math>c_{30,1}</math></small>
|<small><math>180{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{15}\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>2 c_{8,1}</math></small>
|<small><math>2</math></small>
|<small><math>2.</math></small>
|<small><math>2</math></small>
|<small><math>\sqrt{4}</math></small>
|<small><math>\sqrt{4.}</math></small>
|<small><math>2 \sqrt{2} \phi ^2</math></small>
|<small><math>7.40492</math></small>
|-
|rowspan=4 colspan=6|
|rowspan=4 colspan=4|
<small><math>\phi</math></small> is the golden ratio:<br>
<small><math>\phi ^2-\phi -1=0</math></small><br>
<small><math>\frac{1}{\phi }+1=\phi</math></small>, and: <small><math>\phi+1=\phi^2</math></small><br>
<small><math>\frac{1}{\phi }::1::\phi ::\phi ^2</math></small><br>
<small><math>1/\phi</math></small> and <small><math>\phi</math></small> are the golden sections of <small><math>\sqrt{5}</math></small>:<br>
<small><math>\phi +\frac{1}{\phi }=\sqrt{5}</math></small>
|colspan=2|<small><math>\phi = (\sqrt{5} + 1)/2</math></small>
|<small><math>1.618034</math></small>
|-
|colspan=2|<small><math>\chi = (3\sqrt{5} + 1)/2</math></small>
|<small><math>3.854102</math></small>
|-
|colspan=2|<small><math>\psi = (3\sqrt{5} - 1)/2</math></small>
|<small><math>2.854102</math></small>
|-
|colspan=2|<small><math>\psi = 11/\chi = 22/(3\sqrt{5} + 1)</math></small>
|<small><math>2.854102</math></small>
|}
== The 5-cell 4-simplex ==
...
== The 16-cell 4-orthoplex ==
In 2-space we have the regular 8-point octagon, in 3-space the regular 8-point cube, and in 4-space the regular 8-point [[16-cell]].
A planar octagon with rigid edges of unit length has chords of length:
:<math>r_1=1,r_2=\sqrt{2+\sqrt{2}} \approx 1.848,r_3=\sqrt{2}+1 \approx 2.414,r_4=\sqrt{4 + \sqrt{8}} \approx 2.613</math>
The chord ratio <math>r_3=\sqrt{2}+1</math> is a geometrical proportion, the [[W:Silver ratio|silver ratio]]. Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_3-r_1-r_1=1/r_3 \approx 0.414</math>
Note that <math>r_3-2=1/r_3=\sqrt{2}-1</math>. The procedure rotates counterclockwise over three <math>r_3</math> chords of an {8/3} octagram. Over the first <math>r_3</math> chord the displacement is <math>\sqrt{2}+r_1</math>. Over the second <math>r_3</math> chord it moves in the opposite direction a distance of <math>-r_1</math> . Over the third <math>r_3</math> chord it moves a distance of <math>-r_1</math>.
If we embed the planar octagon in 3-space, we can make it skew, repositioning its vertices so that each is one unit-edge length distant from three others instead of two others, at the vertices of a unit-edge cube with chords of length:
:<math>r_1=1, r_2=\sqrt{2}, r_3=\sqrt{3}, r_4=\sqrt{2}</math>
If we embed this cube in 4-space, we can skew it some more, repositioning its vertices so that each is one unit-edge length distant from six others instead of three others, at the vertices of a unit-edge 4-polytope with chords of length:
:<math>r_1=1,r_2=1,r_3=1,r_4=\sqrt{2}</math>
All of its chords except its long diameters are the same unit length as its edge. In fact they are its 24 edges, and it is a 16-cell of radius <math>1/\sqrt{2}</math>.
[[File:octagon16cell.png|thumb|Orthogonal projection of a regular 16-cell to the [[16-cell#Projections|B<sub>4</sub> Coxeter plane]]. Only its edges are shown; its long diameter chords are not drawn. All 24 edges are the same length and none lie parallel to the projection plane. The octagon circumference is a Petrie polygon. The two disjoint squares lie in completely orthogonal central planes. The blue octagram is a Clifford polygon. ]]
The [[16-cell]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{3,3,4\}</math></small>. It has 8 vertices, 24 edges, 32 equilateral triangle faces, and 16 regular tetrahedron cells. It is the [[16-cell#Octahedral dipyramid|four-dimensional analogue of the octahedron]], and each of its four orthogonal central hyperplanes is an octahedron.
The only planar regular polygons found in the 16-cell are face triangles and central plane squares, but the 16-cell also contains a skew regular octagon, its [[W:Petrie polygon|Petrie polygon]].{{Efn|name=Petrie polygon of a honeycomb}} The chords of this regular octagon, which lies skew in 4-space, are those given above for the 16-cell, as opposed to those for the cube or the regular octagon in the plane. The 16-cell is a construct of 3 Petrie octagons which share the same 8 vertices but have disjoint sets of 8 edges each.
The regular octad has higher symmetry in 4-space than it does in 2-space. The 16-cell is the 4-[[w:Cross-polytope|orthoplex]], the simplest regular 4-polytope after the [[5-cell|4-simplex]]. All the larger regular convex 4-polytopes are compounds of the 16-cell. The regular octagon exhibits this high symmetry only when embedded in 4-space at the vertices of the 16-cell.
The 16-cell constitutes an [[W:Orthonormal basis|orthonormal basis]] for the choice of a 4-dimensional Cartesian reference frame, because its vertices define four orthogonal axes. The eight vertices of a unit-radius 16-cell are (±1, 0, 0, 0), (0, ±1, 0, 0), (0, 0, ±1, 0), (0, 0, 0, ±1). All vertices are connected by <math>\sqrt{2}</math> edges except opposite pairs.
The vertex coordinates of the 16-cell form 6 central squares lying in 6 pairwise [[W:Orthogonal|orthogonal]] coordinate planes. Great squares in opposite planes that do not share an axis (e.g. in the ''xy'' and ''wz'' planes) are completely disjoint (they do not intersect at any vertices). These planes are [[W:Completely orthogonal|completely orthogonal]].{{Efn|name=Six orthogonal planes of the Cartesian basis}}
Since the unit-radius coordinate system is convenient, let us derive the unit-radius 16-cell by skewing a unit-radius planar octagon, which has chords of length:
:<math>r_1=\sqrt{2-\sqrt{2}} \approx 0.765,r_2=\sqrt{2},r_3=\sqrt{2+\sqrt{2}} \approx 1.848,r_4=2</math>
We will need a planar octagon with rigid <math>r_2</math> chords, rather than one with rigid <math>r_1</math> edges. The octagon's <math>r_2</math> chords form two disjoint great squares, visible in the orthogonal projection, which we can reposition in 3-space to form a cube by making them parallel, and in 4-space to form a 16-cell by making them completely orthogonal.
Since the edges of the 16-cell are all the same length <math>r_1=\sqrt{2},r_2=\sqrt{2},r_3=\sqrt{2}</math>, those chords are distinct only in the context of a rotation. Each chord is a 4-vector with a length and a direction. The rotational curve over each <math>r_i</math> chord makes <math>i</math> 45° turns.
[[File:16-cell-orig.gif|thumb|Orthographic projection of the 8-point 16-cell <small><math>\{3,3,4\}</math></small> performing a double rotation.{{Sfn|Hise|2007}}]]
[[W:Rotations in 4-dimensional Euclidean space|Rotations in 4-dimensional Euclidean space]] can be seen as the composition of two 2-dimensional rotations in completely orthogonal planes. The general rotation in 4-space is a [[W:SO(4)#Double rotations|double rotation]] in pairs of completely orthogonal planes. Two completely orthogonal planes are called invariant planes of the rotation when all points in the plane rotate on circles that remain in the plane, even as the whole plane tilts sideways (like a coin flipping) into another plane. The two completely orthogonal rotations of each plane (like a wheel, and like a coin flipping) are simultaneous but independent, in that they are not geometrically constrained to turn at the same rate. However, the most circular kind of rotation (as opposed to an elliptical double rotation of a rigid spherical object) occurs when the completely orthogonal planes do rotate through the same angle in the same time interval. Such equi-angled double rotations are called [[w:SO(4)#Isoclinic_rotations|isoclinic]], also [[w:William_Kingdon_Clifford|Clifford]] displacements.
The <math>r_1</math> chords of the 16-cell form a Petrie polygon which zig-zags back and forth, in the left and right rotational directions, between two completely orthogonal great squares formed by <math>r_2</math> chords.
The <math>r_2</math> chords of two completely orthogonal great squares lie parallel and perpendicular to each other. A ''simple'' rotation of the 16-cell in ''one'' of those two square central planes rotates that square like a wheel, while the other square does not move.{{Efn|name=simple rotations}} The four vertices of the rotating square orbit on a great circle in the plane.
The <math>r_3</math> chords of the 16-cell form a circular helix, visible as a blue {8/3} octagram in the orthogonal projection. A ''double'' rotation of the 16-cell, in both of two completely orthogonal invariant <math>r_2</math> square planes at once by equal angles, moves the eight vertices along the circular helix over the <math>r_3</math> chords. The vertex motion is a [[w:Geodesic|geodesic]] circle orbit on the 3-sphere of a special kind: it does not lie in a central plane, its [[w:Winding_number|winding number]] is not 1 (it is 3 in this case), its circumference is not <math>2\pi</math>, and it moves in either a left or right handed circular spiral. We shall refer to such a chiral circle orbit as an ''isocline'', and to the skew polygram of its rotational chords as a ''Clifford polygon''.
The 16-cell is the simplest possible frame in which to [[16-cell#Rotations|observe 4-dimensional rotations]] because its characteristic rotations feature a single pair of invariant rotation planes. In the 16-cell an isoclinic rotation by 90° in any pair of invariant completely orthogonal square central planes takes every great square to its completely orthogonal great square in a twisting displacement, as the invariant planes tilt sideways 90° into each other's plane while rotating 90° internally. All the vertices move at once along the same circular helix geodesic isocline of <math>r_3</math> chords, displaced 90° in 8 orthogonal directions, and the rigid 16-cell assumes a new orientation in 4-space. When the 90° isoclinic rotation is continued in the same rotational direction through an additional 90°, each vertex is again displaced 90°, but from the new orientation in a direction orthogonal to its first 90° displacement. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. In 360° of isoclinic rotation over four <math>r_3</math> chords, each vertex makes six 90° turns and reaches its antipodal position.
The trajectory of each vertex over each 90° isoclinic rotational displacement is a one-eighth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>6\pi</math> over eight <math>r_3</math> chords, and also traces an ordinary great circle in the plane twice, over the four <math>r_2</math> edges of a great square in one of the two moving invariant rotation planes. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions just once and returns to its original position, and the 16-cell returns to its original orientation.
Because this is the isoclinic rotation of the 16-cell in its invariant edge planes we shall refer to it as the ''characteristic rotation of the 16-cell'', and note once again that it is Fontaine and Hurley's rotation over the <math>r_3</math> star polygon which constructs <math>1/r_3</math>.
== The 8-cell tesseract ==
The long diameter of the unit-edge [[W:Hypercube|hypercube]] of dimension <math>n</math> is <math>\sqrt{n}</math>, so the unit-edge [[w:Tesseract|4-hypercube, the 16-point (8-cell) tesseract,]] has chords:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
Uniquely in its 4-dimensional case, the hypercube's edge length equals its radius, like the hexagon. We call such polytopes ''radially equilateral'', because they can be constructed from equilateral triangles which meet at their center, each contributing two radii and an edge. The [[w:Cuboctahedron|cuboctahedron]] and the 24-cell are also radially equilateral.
[[File:8-cell.gif|thumb|Orthographic projection of the 16-point (8-cell) tesseract <small><math>\{4,3,3\}</math></small> performing a simple rotation about a plane in 4-space.{{Sfn|Hise|2007}} The stationary plane bisects the figure from front-left to back-right and top to bottom.]]
The [[W:Tesseract|tesseract]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{4,3,3\}</math></small>. It has 16 vertices, 32 edges, 24 square faces, and 8 cube cells. It is the four-dimensional analogue of the cube.
The 16-point tesseract is the convex hull of a compound of two 8-point 16-cells, in exact dimensional analogy to the way the 8-point cube is the convex hull of a [[W:Stellated octahedron|compound of two 4-point regular tetrahedra]]. The [[W:Demihypercube|demihypercubes]] occupy alternate vertices of the hypercubes. The diagonals of the square faces of the unit-edge, unit-radius tesseract are the <math>\sqrt{2}</math> edges of two unit-radius 16-cells, also the edges of the square central planes.
We can rotate the tesseract isoclinically the way we rotated the 16-cell, by 90° in completely orthogonal invariant square central planes, with the same effect on both alternate-position 16-cells. In the course of a 720° isoclinic rotation in invariant square central planes each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cell. The two skew {8/3} octagram Clifford polygons lie on two disjoint parallel isoclines of the same chirality, of circumference <math>6\pi</math> over <math>\sqrt{2}</math> chords. They form a circular double helix which intersects each vertex of the tesseract once.
The tesseract is the [[W:Dual polytope|dual polytope]] of the 16-cell. They have the same Petrie polygon, the regular skew octagon, but the tesseract is a construct of 4 Petrie octagons with disjoint sets of 8 tesseract edges each. We can construct the tesseract by skewing two planar octagons. Because the tesseract is radially equilateral (unlike the 16-cell), we use two octagons of unit-edge length to build the unit-radius tesseract. To start we embed the planar octagons in 4-space at the same point and make them completely orthogonal. Then we skew each planar octagon into a cube, so we have a compound of two completely orthogonal cubes, provided we skewed them both in the same direction. The 16 vertices will be the vertices of a tesseract with half its 32 edges missing.
Because the tesseract contains two 16-cells in alternate positions it has two sets of 6 orthogonal square central planes. Two angles are required to specify the relationship between two planes in 4-space. Pairs of square central planes within each 16-cell are 90° apart in one angle, and either 0° or 90° apart in the other angle. They are 90° apart in both angles if and only if they are completely orthogonal planes, 90° apart by isoclinic rotation, with no vertices in common. Otherwise they are 0° apart in one of the angles, 90° apart by simple rotation, and they intersect in one axis and lie in a common 3-dimensional hyperplane.{{Efn|A double rotation in which one of the two angles of rotation is 0°, so that one of the completely orthogonal invariant planes does not rotate, is called a simple rotation. Ordinary rotations observed in a 3-dimensional space are simple rotations.|name=simple rotations}}
A pair of square central planes from alternate-position 16-cells are 60° apart by isoclinic rotation, with their corresponding vertices 120° apart. The planes are not orthogonal or parallel, so they intersect in a line somewhere, but they have no vertices in common, they have no 3-dimensional hyperplane in common, and they cannot reach each other by simple rotation. Such pairs of objects are called [[W:Clifford parallel|Clifford parallel]] because all their corresponding pairs of vertices are the same distance apart, although they are not parallel in the usual sense, because they have a common center. Not only the alternate-position 16-cells' corresponding square central planes, but also the 16-cells themselves, are Clifford parallel objects. More generally, multiple disjoint instances of a 4-polytope which compound to make a larger 4-polytope are Clifford parallel objects.
== The 24-cell ==
[[File:24-cell vertex geometry.png|thumb|Planar geometry of the radially equilateral 24-cell, showing its 3 great circle polygons and its 4 chord lengths.]]
In 2-space we have the radially equilateral 6-point hexagon. In 3-space we have the radially equilateral 12-point cuboctahedron, with 4 hexagonal central planes. In 4-space we have the radially equilateral 24-point 24-cell, with 12 cuboctahedron central hyperplanes and 16 hexagonal central planes.
The [[24-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,4,3\}</math></small>. It has 24 vertices, 96 edges, 96 equilateral triangle faces, and 24 octahedron cells. It is the four-dimensional analogue of the cuboctahedron.
The 24-cell has the same chord set as the 4-hypercube tesseract:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
[[Image:24-cell.gif|thumb|Orthographic projection of the 24-point 24-cell <small><math>\{3,4,3\}</math></small> performing a simple rotation.{{Sfn|Hise|2007}} The 3-dimensional surface made of 24 octahedra is visible.]]
The 24-cell is [[W:Dual polytope|self-dual]], like the regular polygons and regular simplexes. It is the maximal regular construct of triangles and squares (with no pentagons). It is the convex hull of a compound of three disjoint 8-point 16-cells, rotated 60° isoclinically with respect to each other. Each of the three pairs of 16-cells is a tesseract. Each 24-cell edge is also a tesseract edge. The corresponding vertices of two 16-cells or two tesseracts are 120° apart by a <math>\sqrt{3}</math> chord. Each tesseract has 8 cube cells, and each cube has four <math>\sqrt{3}</math> long diameters. The <math>\sqrt{3}</math> chords joining the corresponding vertices of two tesseracts belong to the third tesseract as cell long diameters.
The 24-cell's Petrie polygon is the regular dodecagon {12}, which has chords:
:<math>r_1=\tfrac{\sqrt{3}-1}{\sqrt{2}} \approx 0.518,r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\tfrac{\sqrt{3}+1}{\sqrt{2}} \approx 1.932,r_6=\sqrt{4}</math>
Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_5-r_3+r_1+r_1-r_3=1/r_5</math>
when <math>r_1=1</math>. The procedure rotates counterclockwise over five <math>r_5</math> chords of a {12/5} dodecagram. In the system of unit-radius coordinates <math>r_1=1/r_5</math>.
The <math>r_1</math> and <math>r_5</math> chords of the planar dodecagon do not occur in the 24-cell, which is a construct of eight skew dodecagons with disjoint sets of twelve <math>\sqrt{1}</math> edges each. In the skew dodecagons the chord lengths are:
:<math>r_1=\sqrt{1},r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\sqrt{3},r_6=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
[[File:dodecagon24cell.png|thumb|Orthogonal projection of half a 24-cell to the [[24-cell#Geodesics|F<sub>4</sub> Coxeter plane]]. Only one Petrie dodecagon {12} of the 24-cell is shown. In a unit-radius 24-cell, all black lines are 24-cell edges of unit length, also tesseract edges. The two disjoint hexagons lie in Clifford parallel central planes. Blue chords are <math>\sqrt{2}</math> 16-cell edges, also isocline chords in square rotations. Green chords are <math>\sqrt{3}</math> distances between corresponding vertices of two 16-cells, also isocline chords in hexagonal rotations. Note the {12/5} dodecagram.]]
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_3=\sqrt{2}</math></small>]]
We can rotate the 24-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in completely orthogonal invariant great square planes, with the same effect on all three 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cells. The <math>r_3=\sqrt{2}</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Three Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_3</math> chords form a circular triple helix {24/9}=3{8/3} that intersects each 24-cell vertex once.
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_5=\sqrt{3}</math></small> ]]
We can also rotate the 24-cell isoclinically in 4 Clifford parallel invariant great hexagon planes containing its vertices, over <math>r_{5}=\sqrt{3}</math> isocline chords. This is the ''characteristic rotation of the 24-cell'' in its invariant edge planes, also Fontaine and Hurley's rotation over the <math>r_5</math> star polygon which constructs <math>1/r_5</math>. A complete hexagonal isoclinic revolution requires 720° like a complete square isoclinic revolution, but it is completed in 12 isoclinic displacements of 60° each rather than 8 isoclinic displacements of 90° each. The rotational curve over each 120° <math>r_5</math> chord makes five 30° turns. Two Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_5</math> chords form a circular double helix {24/10}=2{12/5} that intersects each 24-cell vertex once.
In the 24-cell the characteristic isoclinic rotation by 60° in any invariant hexagon central plane takes every great hexagon to a Clifford parallel great hexagon in a twisting displacement, as all the central planes tilt sideways 60° while rotating 60° internally. It also takes every great square to a Clifford parallel great square in another 16-cell; it takes every 16-cell to another 16-cell. The 16-cells revolve within the 24-cell as well as rotating within it. All 24 vertices move at once on two Clifford parallel geodesic isoclines, displaced 120° in different directions.
The trajectory of each vertex over each 60° isoclinic rotational displacement is a one-twelfth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>10\pi</math> over twelve <math>\sqrt{3}</math> chords, and also traces an ordinary great circle in the plane twice, over the six <math>\sqrt{1}</math> edges of a great hexagon in a moving invariant rotation plane. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions just once and returns to its original position, and the 24-cell returns to its original orientation.
== The 600-cell ==
[[Image:600-cell.gif|thumb|Orthographic projection of the 120-point 600-cell <small><math>\{3,3,5\}</math></small> performing a simple rotation.{{Sfn|Hise|2011}} The 3-dimensional surface made of 600 tetrahedra is visible. Invisible in this rendering are 25 inscribed instances of the 24-cell (above), which occur in the 600-cell as interior boundary envelopes.]]
The [[600-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,3,5\}</math></small>. It has 120 vertices, 720 edges, 1200 equilateral triangle faces, and 600 tetrahedron cells. It is the four-dimensional analogue of the icosahedron.
The 600-cell rounds out the 24-cell by adding 96 more vertices (four more disjoint 24-cells) between the 24-cell's existing 24 vertices, in effect adding twenty-four more distinct 24-cells inscribed in the 600-cell. The new surface thus formed is a honeycomb of smaller, more numerous cells: tetrahedra of edge length <math>\phi^{-1} \approx 0.618</math> instead of octahedra of edge length <math>\sqrt{1}</math>. It encloses the <math>\sqrt{1}</math> edges of the 24-cells, which become invisible interior chords in the 600-cell, like the <math>\sqrt{2}</math> and <math>\sqrt{3}</math> chords.
Since the tetrahedra are made of shorter triangle edges than the octahedra (by a factor of <math>\phi^{-1}</math>, the inverse golden ratio), the 600-cell is not radially equilateral like the 24-cell and the tesseract. Like them it is radially triangular in a special way, but one in which [[w:Golden_triangle_(mathematics)|golden triangles]] rather than equilateral triangles meet at the center.
In 2-space we have the ''radially golden'' [[W:Decagon#The golden ratio in decagon|regular decagon]]. In 3-space we have the radially golden 30-point [[W:icosidodecahedron|icosidodecahedron]], with 6 decagon central planes. In 4-space we have the radially golden 120-point 600-cell, with 60 icosidodecahedron central hyperplanes and 72 decagon central planes.
The 600-cell's Petrie polygon is the regular [[w:Triacontagon|triacontagon {30}]]. The unit-radius planar {30}-gon has these distinct chords:
:<math>r_1=2 \sin (\tfrac{\pi}{15}/2) \approx 0.209</math>
:<math>r_2=2 \sin (\tfrac{2\pi}{15}/2) \approx 0.416</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{4\pi}{15}/2) \approx 0.813</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{7\pi}{15}/2) \approx 1.338</math>
:<math>r_8=2 \cos (\tfrac{7\pi}{15}/2) \approx 1.486</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{11}=2 \cos (\tfrac{4\pi}{15}/2) \approx 1.827</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \cos (\tfrac{2\pi}{15}/2) \approx 1.956</math>
:<math>r_{14}=2 \cos (\tfrac{\pi}{15}/2) \approx 1.989</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Only the chord lengths <math>r_3</math>, <math>r_5</math>, <math>r_6</math>, <math>\sqrt{2}</math>, <math>r_9</math>, <math>r_{10}</math>, <math>r_{12}</math>, <math>r_{15}</math> occur in the 600-cell, which is a construct of 24 Petrie {30}-gons of edge length <math>r_3</math>, six of which intersect in each icosahedral vertex figure. In the skew {30}-gons the chord lengths are:
[[File:600-cell vertex geometry.png|thumb|Planar geometry of the 600-cell, showing its 5 regular great circle polygons and its 8 chord lengths with angles of arc. The golden ratio governs the fractional roots of every other chord, and the radial golden triangles which meet at the center.|400x400px]]
:<math>r_1=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_2=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}=\text{24-cell-}r_2</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}</math>
:<math>r_8=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}=\text{16-cell-}r_3</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}=\text{24-cell-}r_5</math>
:<math>r_{11}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{14}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="7" |15 chords (4 distinct 180° pairs) make 4 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>r_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>r_{15}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>r_1</math>
|36°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}=2{15/7}
|144°
| rowspan="3" |<math>r_{14}</math>
|- style="background: palegreen;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: palegreen;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>r_2</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|144°
| rowspan="3" |<math>r_{13}</math>
|- style="background: gainsboro;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: gainsboro;" |
|0.618~
|1.902~
|- style="background: yellow;" |
| rowspan="3" |<math>r_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |[[File:V1 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>r_{12}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_4</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|120°
| rowspan="3" |<math>r_{11}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_5</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |[[File:V2 dodecahedron.png|100px]]<br>Dodecahedron
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>r_{10}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: yellow;" |
| rowspan="3" |<math>r_{6}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |[[File:V3 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>r_{9}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>r_{8}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: seashell;" |
| rowspan="3" |<math>r_{7}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |[[File:V4 icosidodecahedron.png|100px]]<br>Icosidodecahedron
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>r_{8}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The list of 600-cell chords <math>r_{i}</math> can be rearranged into a table of 8 rows and 2 columns with a pair of 180° complements in each row. The short chord and long chord each have their characteristic {30}-gon. Each row identifies a discrete isoclinic rotation of the 600-cell in invariant central planes containing the edges of the short chord {30}-gon, over the isocline chords of the long chord {30}-gon, the rotation's Clifford polygon.
Each distinct pair of complementary chord lengths is identified with a distinct [[w:600-cell#Polyhedral sections|polyhedral section of the 600-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 7 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>\phi^{-1}</math> is a icosahedron vertex figure, and the largest section at radial distance <math>\sqrt{2}</math> is an [[W:Icosidodecahedron|icosidodecahedron]] central section bisecting the 600-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>\sqrt{2}</math> the successive complement-radius polyhedra decrease in size, to the antipodal icosahedron vertex figure at distance <math>\sqrt{2+\phi}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 7 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section).
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_8=\sqrt{2}</math></small>]]
We can rotate the 600-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in two completely orthogonal invariant great square planes over <math>r_8=\sqrt{2}</math> isocline chords, with the same effect on 15 disjoint 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_8</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Fifteen Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_8</math> chords form a circular helix of 15 twisted parallel strands 5{24/9}=15{8/3} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_polygon_30-7.svg|thumb|left|150px|{30/7} <small><math>r_7=\sqrt{2}</math></small>]]
In the 600-cell this 90° isoclinic rotation in completely orthogonal great square planes takes place over the <math>r_7=\sqrt{2}</math> chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/7} polygon is a skew helix with each <math>r_7</math> edge belonging to a distinct great square. The vertices of the invariant great squares of this rotation each make seven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 90° <math>r_7</math> isocline chord makes seven 12° turns. Four Clifford parallel {30/7} geodesic isoclines of circumference <math>14\pi</math> over <math>r_7</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_{10}=\sqrt{3}</math></small> ]]
We can also rotate the 600-cell isoclinically in the characteristic rotation of the 24-cell, by 60° in great hexagon planes over <math>r_{10}=\sqrt{3}</math> isocline chords, with the same effect on 5 disjoint 24-cells. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions of its 24-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_{10}</math> chord is the 24-cell <math>r_5</math> chord. The rotational curve over each 60° <math>r_5</math> chord makes five 30° turns. Ten Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_{10}</math> chords form a circular helix of 10 twisted parallel strands 5{24/10}=10{12/5} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_figure_2(15,4).svg|thumb|left|150px|{30/8}=2{15/4} <small><math>r_{13}=\sqrt{1}</math></small>]]
We can also rotate the 600-cell isoclinically in 12 Clifford parallel invariant decagon central planes containing its <math>r_{3}</math> edges, over <math>r_{13}=\sqrt{1}</math> isocline chords. This is the ''characteristic rotation of the 600-cell'' in its invariant edge planes. Its Clifford polygon is a skew {15/4} pentadecagram of <math>r_{13}</math> chords. The <math>r_{4}</math> chord is the 24-cell <math>r_2</math> chord. Successive <math>r_{13}</math> chords are edges of different 24-cells. The rotational curve over each <math>r_{13}</math> chord makes two 30° turns. Eight Clifford parallel {15/4} pentadecagon geodesic isoclines of circumference <math>5\pi</math> over <math>r_{13}</math> chords form a circular helix of eight twisted parallel strands 4{30/8}=8{15/4} that intersects each 600-cell vertex once.
In the 600-cell the characteristic isoclinic rotation by 36° in any invariant decagon central plane takes every great decagon to a Clifford parallel great decagon in a twisting displacement, as all the central planes tilt sideways 36° while rotating 36° internally. It also takes every great hexagon to a Clifford parallel great hexagon in another 24-cell, and every great square to a Clifford parallel great square in another 16-cell; it takes 24-cells to a non-disjoint 24-cell and 16-cells to a 16-cell in another 24-cell. The 24-cells revolve within the 600-cell, as the 16-cells revolve within the 24-cells. All 120 vertices move at once on eight Clifford parallel geodesic isoclines, displaced 60° in different directions.
The trajectory of each vertex over each 36° isoclinic rotational displacement is a one-fifteenth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>5\pi</math> over 15 <math>r_5</math> chords, and also traces an ordinary great circle in the plane 3 times, over the 5 edges of a great pentagon in a moving invariant rotation plane. In the course of a complete isoclinic revolution each vertex departs from 15 vertex positions just once and returns to its original position, and the 600-cell returns to its original orientation.
{{Clear}}
[[File:Regular_star_figure_6(5,2).svg|thumb|left|150px|{30/12}=6{5/2} <small><math>r_{12}=\sqrt{3.618\sim}</math></small>]]
In the 600-cell there is another distinct isoclinic rotation taking decagon planes to each other, over 144° <math>r_{12}</math> isocline chords. It also takes disjoint 24-cells to each other. This rotation has period 5 and visits every 12th vertex of a 600-cell Petrie polygon. Its Clifford polygon is a skew {5/2} pentagram of <math>r_{12}</math> chords. The invariant central planes of this rotation each intersect only one vertex of the 600-cell, which makes two orbits of a great pentagon within the moving invariant plane in the course of one complete isoclinic revolution of period 5. The rotational curve over each <math>r_{12}</math> chord makes twelve 12° turns. 24 Clifford parallel {5/2} pentagram geodesic isoclines of circumference <math>4\pi</math> over five <math>r_{12}</math> chords form a circular helix of 24 twisted parallel strands 4{30/12}=24{5/2} that intersects each 600-cell vertex once.
{{Clear}}
== Finally the 120-cell ==
The [[120-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{5,3,3\}</math></small>. It has 600 vertices, 1200 edges, 720 pentagon faces, and 120 dodecahedron cells. It is the four-dimensional analogue of the dodecahedron.
The 120-cell is the [[W:Dual polytope|dual polytope]] of the 600-cell. They have the same Petrie polygon, the regular skew triacontagon {30}, but the 120-cell is a construct of 40 Petrie {30}-gons of edge length <math>c_1</math>, two of which intersect in each tetrahedral vertex figure.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="9" |30 chords (15 180° pairs) make 15 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>c_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>c_{30}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>c_1</math>
|15.5~°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}
|164.5~°
| rowspan="3" |<math>c_{29}</math>
|- style="background: palegreen;" |
|{{radic|0.073~}}
|{{radic|3.927~}}
|- style="background: palegreen;" |
|0.270~
|1.982~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_2</math>
|25.2~°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|154.8~°
| rowspan="3" |<math>c_{28}</math>
|- style="background: gainsboro;" |
|{{radic|0.191~}}
|{{radic|3.809~}}
|- style="background: gainsboro;" |
|0.437~
|1.952~
|- style="background: yellow;" |
| rowspan="3" |<math>c_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>c_{27}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_4</math>
|41.4~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|138.6~°
| rowspan="3" |<math>c_{26}</math>
|- style="background: gainsboro;" |
|{{radic|0.5}}
|{{radic|3.5}}
|- style="background: gainsboro;" |
|0.707~
|1.871~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_5</math>
|44.5~°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|135.5~°
| rowspan="3" |<math>c_{25}</math>
|- style="background: palegreen;" |
|{{radic|0.573~}}
|{{radic|3.427~}}
|- style="background: palegreen;" |
|0.757~
|1.851~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_6</math>
|49.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|130.9~°
| rowspan="3" |<math>c_{24}</math>
|- style="background: gainsboro;" |
|{{radic|0.691~}}
|{{radic|3.309~}}
|- style="background: gainsboro;" |
|0.831~
|1.819~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_7</math>
|56°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|124°
| rowspan="3" |<math>c_{23}</math>
|- style="background: gainsboro;" |
|{{radic|0.882~}}
|{{radic|3.118~}}
|- style="background: gainsboro;" |
|0.939~
|1.766~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_8</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>c_{22}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_9</math>
|66.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|113.9~°
| rowspan="3" |<math>c_{21}</math>
|- style="background: gainsboro;" |
|{{radic|1.191~}}
|{{radic|2.809~}}
|- style="background: gainsboro;" |
|1.091~
|1.676~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{10}</math>
|69.8~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|110.2~°
| rowspan="3" |<math>c_{20}</math>
|- style="background: gainsboro;" |
|{{radic|1.309~}}
|{{radic|2.691~}}
|- style="background: gainsboro;" |
|1.144~
|1.640~
|- style="background: yellow;" |
| rowspan="3" |<math>c_{11}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>c_{19}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>c_{18}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{13}</math>
|81.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|98.9~°
| rowspan="3" |<math>c_{17}</math>
|- style="background: gainsboro;" |
|{{radic|1.691~}}
|{{radic|2.309~}}
|- style="background: gainsboro;" |
|1.300~
|1.520~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{14}</math>
|84.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|95.5~°
| rowspan="3" |<math>c_{16}</math>
|- style="background: gainsboro;" |
|{{radic|0.809~}}
|{{radic|2.191~}}
|- style="background: gainsboro;" |
|1.345~
|1.480~
|- style="background: seashell;" |
| rowspan="3" |<math>c_{15}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>c_{15}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The [[User:Dc.samizdat/Golden chords of the 120-cell#Thirty distinguished distances|table above]] of 30 chords <math>c_{t}</math> can be rearranged into a table of 16 rows and 2 columns with a pair of 180° complements in each row. This table first appears in [[w:Regular_Polytopes_(book)|''Regular Polytopes'']] (1947),{{Sfn|Coxeter|1973|loc=Table V(v): Simplified sections of {5,3,3} beginning with a vertex|pp=300-301}} where Coxeter identified each row with a distinct [[w:120-cell#Concentric_hulls|polyhedral section of the 120-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 29 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>c_1</math> is a tetrahedron vertex figure, and the largest section at radial distance <math>c_{15}</math> is a central section bisecting the 120-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>c_{15}</math> the successive complement-radius polyhedra decrease in size, to the antipodal tetrahedron vertex figure at distance <math>c_{29}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 29 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section). Each section also lies completely orthogonal to a congruent section.
Only 8 of the 30 chords in the table occur in the 600-cell and the planar {30)-gon. The 120-cell's additional chords arise originally from the regular 5-cell, in its interaction with the other regular 4-polytopes that compound to make the 120-cell. Since all those polytopes except the 5-cell occur in the 600-cell, and the 600-cell and the 120-cell have the same symmetry group, the 5-cell's symmetry group is what's new in the 120-cell.
...
{{Clear}}
== Conclusions ==
Fontaine and Hurley's discovery is more than a geometric formula for the reciprocal of a regular ''n''-polygon diagonal. It also yields the discrete sequence of isocline chords of the characteristic isoclinic rotation of a ''d''-dimensional polytope in its invariant edge planes. The characteristic rotational chord sequence of the ''d''-polytope can be represented geometrically in two dimensions on a distinct star polygon, but it lies on a geodesic circle through ''d''-dimensional space. Fontaine and Hurley discovered the geodesic topology of polytopes generally. Their procedure will reveal the geodesics of arbitrary non-uniform polytopes, since it can be applied to a polytope of any dimensionality and irregularity, by first fitting the polytope to the smallest regular polygon whose chords include its chords. [If what is meant by this is its Petrie polygon, it is not quite necessary or possible with respect to the planar polygon chords, e.g. the planar Petrie polygon of the 600-cell does not contain the <math>\sqrt{2}</math> chord. But perhaps it would work if the fit is to the smallest regular skew polygon in the ''d''-space.]
The discovery of a chordal construction for discrete isoclinic rotations generally closes the circuit on Kappraff and Adamson's discovery of a rotational connection between dynamical systems, Steinbach's golden fields, and Coxeter's Euclidean geometry of ''n'' dimensions. Application of the Fontaine and Hurley procedure in the 120-cell demonstrates why the connection exists: because polytope sequences generally, from Steinbach's golden chord sequences in polygons, to sequences of star polygons in isoclinic rotations, to subsumption relations in the sequence of regular 4-polytopes, arise as expressions of the reflections and rotations of distinct Coxeter symmetry groups, when those various groups interact.
== Appendix: Sequence of regular 4-polytopes ==
{{Regular convex 4-polytopes|wiki=W:|columns=7}}
== Notes ==
{{Notelist}}
== Citations ==
{{Reflist}}
== References ==
{{Refbegin}}
* {{Cite journal | last=Steinbach | first=Peter | year=1997 | title=Golden fields: A case for the Heptagon | journal=Mathematics Magazine | volume=70 | issue=Feb 1997 | pages=22–31 | doi=10.1080/0025570X.1997.11996494 | jstor=2691048 | ref={{SfnRef|Steinbach|1997}} }}
* {{Cite journal | last=Steinbach | first=Peter | year=2000 | title=Sections Beyond Golden| journal=Bridges: Mathematical Connections in Art, Music and Science | issue=2000 | pages=35-44 | url=https://archive.bridgesmathart.org/2000/bridges2000-35.pdf | ref={{SfnRef|Steinbach|2000}}}}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Jablan | first2=Slavik | last3=Adamson | first3=Gary | last4=Sazdanovich | first4=Radmila | year=2004 | title=Golden Fields, Generalized Fibonacci Sequences, and Chaotic Matrices | journal=Forma | volume=19 | pages=367-387 | url=https://archive.bridgesmathart.org/2005/bridges2005-369.pdf | ref={{SfnRef|Kappraff, Jablan, Adamson & Sazdanovich|2004}} }}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Adamson | first2=Gary | year=2004 | title=Polygons and Chaos | journal=Dynamical Systems and Geometric Theories | url=https://archive.bridgesmathart.org/2001/bridges2001-67.pdf | ref={{SfnRef|Kappraff & Adamson|2004}} }}
* {{Cite journal | last1=Fontaine | first1=Anne | last2=Hurley | first2=Susan | year=2006 | title=Proof by Picture: Products and Reciprocals of Diagonal Length Ratios in the Regular Polygon | journal=Forum Geometricorum | volume=6 | pages=97-101 | url=https://scispace.com/pdf/proof-by-picture-products-and-reciprocals-of-diagonal-length-1aian8mgp9.pdf }}
{{Refend}}
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/* The 600-cell */
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= Golden chords of the 120-cell =
{{align|center|David Brooks Christie}}
{{align|center|dc@samizdat.org}}
{{align|center|Draft in progress}}
{{align|center|January 2026 - June 2026}}
<blockquote>Steinbach discovered the formula for the ratios of diagonal to side in the regular polygons. Fontaine and Hurley extended this result, discovering a formula for the reciprocal of a regular polygon chord derived geometrically from the chord's star polygon. We observe that these findings in plane geometry apply more generally, to polytopes of any dimensionality. Fontaine and Hurley's geometric procedure for finding the reciprocals of the chords of a regular polygon from their star polygons also finds the rotational geodesics of any polytope of any dimensionality.</blockquote>
== Introduction ==
Steinbach discovered the Diagonal Product Formula and the Golden Fields family of ratios of diagonal to side in the regular polygons. He showed how this family extends beyond the pentagon {5} with its well-known golden bisection proportional to 𝜙, finding that the heptagon {7} has an analogous trisection, the nonagon {9} has an analogous quadrasection, and the hendecagon {11} has an analogous pentasection, an extended family of golden proportions with quasiperiodic properties.
Kappraff and Adamson extended these findings in plane geometry to a theory of Generalized Fibonacci Sequences, showing that the Golden Fields not only do not end with the hendecagon, they form an infinite number of periodic trajectories when operated on by the Mandelbrot operator. They found a relation between the edges of star polygons and dynamical systems in the state of chaos, revealing a connection between chaos theory, number, and rotations in Coxeter Euclidean geometry.
Fontaine and Hurley examined Steinbach's finding that the length of each chord of a regular polygon is both the product of two chords and the sum of a set of smaller chords, so that in rotations to add is to multiply. They illustrated Steinbach's sets of additive chords lying parallel to each other in the plane (pointing in the same direction), and by applying Steinbach's formula more generally they found another summation relation of signed parallel chords (pointing in opposite directions) which relates each chord length to its reciprocal, and relates the summation to a distinct star polygon rotation.
We examine these remarkable findings (which stem from study of the chords of humble regular polygons) in higher-dimensional spaces, specifically in the chords, polygons and rotations of the [[120-cell]], the largest four-dimensional regular convex polytope.
== Visualizing the 120-cell ==
{| class="wikitable floatright" width="400"
|style="vertical-align:top"|[[File:120-cell.gif|200px]]<br>Orthographic projection of the 600-point 120-cell <small><math>\{5,3,3\}</math></small> performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]].{{Sfn|Hise|2011|loc=File:120-cell.gif|ps=; "Created by Jason Hise with Maya and Macromedia Fireworks. A 3D projection of a 120-cell performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]]."}} In this simplified rendering only the 120-cell's own edges are shown; its 29 interior chords are not rendered. Therefore even though it is translucent, only its outer surface is visible. The complex interior parts of the 120-cell, all its inscribed 5-cells, 16-cells, 8-cells, 24-cells, 600-cells and its much larger inventory of polyhedra, are completely invisible in this view, as none of their edges are rendered at all.
|style="vertical-align:top"|[[File:Ortho solid 016-uniform polychoron p33-t0.png|200px]]<br>Orthographic projection of the 600-point [[W:Great grand stellated 120-cell|great grand stellated 120-cell]] <small><math>\{\tfrac{5}{2},3,3\}</math></small>.{{Sfn|Ruen: Great grand stellated 120-cell|2007}} The 120-cell is its convex hull. The projection to the left renders only the 120-cell's shortest chord, its 1200 edges. The projection above also renders only one of the 120-cell's 30 chords, the edges of its 120 inscribed regular 5-cells. The 120-cell itself (the convex hull) is invisible in this view, as its edges are not rendered.
|}
[[120-cell#Geometry|The 120-cell is the maximally complex regular 4-polytope]], containing inscribed instances of every regular 1-, 2-, 3-, and 4-polytope, except the regular polygons of more than {15} sides.
The 120-cell is the convex hull of a regular [[120-cell#Relationships among interior polytopes|compound of each of the 6 regular convex 4-polytopes]]. They are the [[5-cell|5-point (5-cell) 4-simplex]], the [[16-cell|8-point (16-cell) 4-orthoplex]], the [[W:Tesseract|16-point (8-cell) tesseract]], the [[24-cell|24-point (24-cell)]], the [[600-cell|120-point (600-cell)]], and the [[120-cell|600-point (120-cell)]]. The 120-cell is the convex hull of a compound of 120 disjoint regular 5-cells, of 75 disjoint 16-cells, of 25 disjoint 24-cells, and of 5 disjoint 600-cells.
The 120-cell contains an even larger inventory of irregular polytopes, created by the intersection of multiple instances of these component regular 4-polytopes. Many are quite unexpected, because they do not occur as components of any regular polytope smaller than the 120-cell. As just one example among the [[120-cell#Concentric hulls|sections of the 120-cell]], there is an irregular 24-point polyhedron with 16 triangle faces and 4 nonagon {9} faces.{{Sfn|Moxness|}}
Most renderings of the 120-cell, like the rotating projection here, only illustrate its outer surface, which is a honeycomb of face-bonded dodecahedral cells. Only the objects in its 3-dimensional surface are rendered, namely the 120 dodecahedra, their pentagon faces, and their edges. Although the 120-cell has chords of 30 distinct lengths, in this kind of simplified rendering only the 120-cell's own edges (its shortest chord) are shown. Its 29 interior chords, the edges of objects in the interior of the 120-cell, are not rendered, so interior objects are not visible at all.
Visualizing the complete interior of the 600-vertex 120-cell in a single image is impractical because of its complexity. Only four 120-cell edges are incident at each vertex, but [[120-cell#Chords|600 chords (of all 30 lengths)]] are incident at ''each'' vertex.
== Compounds in the 120-cell ==
The 8-point (16-cell), not the 5-point (5-cell), is the smallest building block; it compounds to every larger regular 4-polytope. The 5-point (5-cell) does compound to the 600-point (120-cell), but it does not fit into any smaller regular 4-polytope.
The 8-point (16-cell) compounds by 2 in the 16-point (8-cell), and by 3 in the 24-point (24-cell). The 16-point (8-cell) compounds in the 24-point (24-cell) by 3 non-disjoint instances of itself, with each of the 24 vertices shared by two 16-point (8-cells). The 24-point (24-cell) compounds by 5 disjoint instances of itself in the 120-point (600-cell), and the 120-point (600-cell) compounds by 5 disjoint instances of itself in the 600-point (120-cell).
The 24-point (24-cell) also compounds by 5<sup>2</sup> non-disjoint instances of itself in the 120-point (600-cell); it compounds in 5 disjoint instances of itself, 10 (not 5) different ways. Whichever set of 5 disjoint 24-point (24-cells) are assembled, the resulting 120-point (600-cell) contains 25 distinct 24-point (24-cells), not just 5 (or 10). This implies that 15 disjoint 8-point (16-cells) will construct a 120-point (600-cell), which will contain 75 distinct 8-point (16-cells).
The 600-point (120-cell) is 5 disjoint 120-point (600-cells), just 2 different ways (not 5 or 10 ways), so it is 10 distinct 120-point (600-cells). This implies that the 8-point (16-cell) compounds by 3 times 5<sup>2</sup> (75) disjoint instances of itself in the 600-point (120-cell), which contains 3<sup>2</sup> times 5<sup>2</sup> (225) distinct instances of the 24-point (24-cell), and 3<sup>3</sup> times 5<sup>2</sup> (675) distinct instances of the 8-point (16-cell).
These facts were discovered painstakingly by various researchers, and no one has found a general rule governing subsumption relations among regular polytopes. The reasons for some of their numeric incidence relations are far from obvious. [[W:Pieter Hendrik Schoute|Schoute]] was the first to see that the 120-point (600-cell) is a compound of 5 24-point (24-cells) ''10 different ways'', and after he saw it a hundred years lapsed until Denney, Hooker, Johnson, Robinson, Butler & Claiborne proved his result, and showed why.{{Sfn|Denney, Hooker, Johnson, Robinson, Butler & Claiborne|2020|loc=''The geometry of H4 polytopes''}}
So much for the compounds of 16-cells. The 120-cell is also the convex hull of the compound of 120 disjoint regular 5-cells. That stellated compound (without its convex hull of 120-cell edges) is the [[w:Great_grand_stellated_120-cell|great grand stellated 120-cell]] illustrated above, the final regular [[W:Stellation|stellation]] of the 120-cell, and the only [[W:Schläfli-Hess polychoron|regular star 4-polytope]] to have the 120-cell for its convex hull. The edges of the great grand stellated 120-cell are <math>\phi^6</math> as long as those of its 120-cell [[W:List of polyhedral stellations#Stellation process|stellation core]] deep inside.
The compound of 120 disjoint 5-point (5-cells) can be seen to be equivalent to the compound of 5 disjoint 120-point (600-cells), as follows. Beginning with a single 120-point (600-cell), expand each vertex into a regular 5-cell, by adding 4 new equidistant vertices, such that the 5 vertices form a regular 5-cell inscribed in the 3-sphere. The 120 5-cells are disjoint, and the 600 vertices form 5 disjoint 120-point (600-cells): a 120-cell.
== Thirty distinguished distances ==
The 30 numbers listed in the table are all-important in Euclidean geometry. A case can be made on symmetry grounds that their squares are the 30 most important numbers between 0 and 4. The 30 rows of the table are the 30 distinct [[120-cell#Geodesic rectangles|chord lengths of the unit-radius 120-cell]], the largest regular convex 4-polytope. Since the 120-cell subsumes all smaller regular polytopes, its 30 chords are the complete chord set of all the regular polytopes that can be constructed in the first four dimensions of Euclidean space, except for regular polygons of more than 15 sides.
{| class="wikitable" style="white-space:nowrap;text-align:center"
!rowspan=2|<math>c_t</math>
!rowspan=2|arc
!rowspan=2|<small><math>\left\{\frac{30}{n}\right\}</math></small>
!rowspan=2|<math>\left\{p\right\}</math>
!rowspan=2|<small><math>m\left\{\frac{k}{d}\right\}</math></small>
!rowspan=2|Steinbach roots
!colspan=7|Chord lengths of the unit 120-cell
|-
!colspan=5|unit-radius length <math>c_t</math>
!colspan=2|unit-edge length <math>c_t/c_1</math><br>in 120-cell of radius <math>c_8=\sqrt{2}\phi^2</math>
|-
|<small><math>c_{1,1}</math></small>
|<small><math>15.5{}^{\circ}</math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math>c_{4,1}-c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7-3 \sqrt{5}}</math></small>
|<small><math>0.270091</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi ^2}</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^4}}</math></small>
|<small><math>\sqrt{0.072949}</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|-
|<small><math>c_{2,1}</math></small>
|<small><math>25.2{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{2}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{15\right\}</math></small>
|<small><math>\frac{1}{2} \left(c_{18,1}-c_{4,1}\right)</math></small>
|<small><math>\frac{\sqrt{3-\sqrt{5}}}{2}</math></small>
|<small><math>0.437016</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi }</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.190983}</math></small>
|<small><math>\phi </math></small>
|<small><math>1.61803</math></small>
|-
|<small><math>c_{3,1}</math></small>
|<small><math>36{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{3}\right\}</math></small>
|<small><math>\left\{10\right\}</math></small>
|<small><math>3 \left\{\frac{10}{3}\right\}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right) c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right)</math></small>
|<small><math>0.618034</math></small>
|<small><math>\frac{1}{\phi }</math></small>
|<small><math>\sqrt{\frac{1}{\phi ^2}}</math></small>
|<small><math>\sqrt{0.381966}</math></small>
|<small><math>\sqrt{2} \phi </math></small>
|<small><math>2.28825</math></small>
|-
|<small><math>c_{4,1}</math></small>
|<small><math>41.4{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{7}\right\}</math></small>
|<small><math>\frac{c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>0.707107</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{1}{2}}</math></small>
|<small><math>\sqrt{0.5}</math></small>
|<small><math>\phi ^2</math></small>
|<small><math>2.61803</math></small>
|-
|<small><math>c_{5,1}</math></small>
|<small><math>44.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{4}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{\frac{15}{2}\right\}</math></small>
|<small><math>\sqrt{3} c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-3 \sqrt{5}}</math></small>
|<small><math>0.756934</math></small>
|<small><math>\frac{\sqrt{\frac{3}{2}}}{\phi }</math></small>
|<small><math>\sqrt{\frac{3}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.572949}</math></small>
|<small><math>\sqrt{3} \phi </math></small>
|<small><math>2.80252</math></small>
|-
|<small><math>c_{6,1}</math></small>
|<small><math>49.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{17}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{5-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{5-\sqrt{5}}}{2}</math></small>
|<small><math>0.831254</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\frac{1}{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5}}{2 \phi }}</math></small>
|<small><math>\sqrt{0.690983}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^3}</math></small>
|<small><math>3.07768</math></small>
|-
|<small><math>c_{7,1}</math></small>
|<small><math>56.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{3}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>0.93913</math></small>
|<small><math>\frac{\sqrt{\frac{\psi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{0.881966}</math></small>
|<small><math>\sqrt{\psi \phi ^3}</math></small>
|<small><math>3.47709</math></small>
|-
|<small><math>c_{8,1}</math></small>
|<small><math>60{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{5}\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>1</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|<small><math>1</math></small>
|<small><math>\sqrt{1}</math></small>
|<small><math>\sqrt{1.}</math></small>
|<small><math>\sqrt{2} \phi ^2</math></small>
|<small><math>3.70246</math></small>
|-
|<small><math>c_{9,1}</math></small>
|<small><math>66.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{7}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{2 \phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.09132</math></small>
|<small><math>\frac{\sqrt{\frac{\chi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\chi }{2 \phi }}</math></small>
|<small><math>\sqrt{1.19098}</math></small>
|<small><math>\sqrt{\chi \phi ^3}</math></small>
|<small><math>4.04057</math></small>
|-
|<small><math>c_{10,1}</math></small>
|<small><math>69.8{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{11}\right\}</math></small>
|<small><math>\phi c_{4,1}</math></small>
|<small><math>\frac{1+\sqrt{5}}{2 \sqrt{2}}</math></small>
|<small><math>1.14412</math></small>
|<small><math>\frac{\phi }{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^2}{2}}</math></small>
|<small><math>\sqrt{1.30902}</math></small>
|<small><math>\phi ^3</math></small>
|<small><math>4.23607</math></small>
|-
|<small><math>c_{11,1}</math></small>
|<small><math>72{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{6}\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.17557</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{1.38197}</math></small>
|<small><math>\sqrt{2} \sqrt{3-\phi } \phi ^2</math></small>
|<small><math>4.3525</math></small>
|-
|<small><math>c_{12,1}</math></small>
|<small><math>75.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{24}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>1.22474</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{1.5}</math></small>
|<small><math>\sqrt{3} \phi ^2</math></small>
|<small><math>4.53457</math></small>
|-
|<small><math>c_{13,1}</math></small>
|<small><math>81.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>1.30038</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(9-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{1.69098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(9-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>4.8146</math></small>
|-
|<small><math>c_{14,1}</math></small>
|<small><math>84.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{9}\right\}</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi } c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{2} \sqrt[4]{5} \sqrt{1+\sqrt{5}}</math></small>
|<small><math>1.345</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi }}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5} \phi }{2}}</math></small>
|<small><math>\sqrt{1.80902}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^5}</math></small>
|<small><math>4.9798</math></small>
|-
|<small><math>c_{15,1}</math></small>
|<small><math>90.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{7}\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>2 c_{4,1}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>1.41421</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2.}</math></small>
|<small><math>2 \phi ^2</math></small>
|<small><math>5.23607</math></small>
|-
|<small><math>c_{16,1}</math></small>
|<small><math>95.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{29}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>1.4802</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.19098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(11-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>5.48037</math></small>
|-
|<small><math>c_{17,1}</math></small>
|<small><math>98.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{31}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>1.51954</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(7+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.30902}</math></small>
|<small><math>\sqrt{\psi \phi ^5}</math></small>
|<small><math>5.62605</math></small>
|-
|<small><math>c_{18,1}</math></small>
|<small><math>104.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{8}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{4}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>1.58114</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{2.5}</math></small>
|<small><math>\sqrt{5} \sqrt{\phi ^4}</math></small>
|<small><math>5.8541</math></small>
|-
|<small><math>c_{19,1}</math></small>
|<small><math>108.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{9}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{10}{3}\right\}</math></small>
|<small><math>c_{3,1}+c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.61803</math></small>
|<small><math>\phi </math></small>
|<small><math>\sqrt{1+\phi }</math></small>
|<small><math>\sqrt{2.61803}</math></small>
|<small><math>\sqrt{2} \phi ^3</math></small>
|<small><math>5.9907</math></small>
|-
|<small><math>c_{20,1}</math></small>
|<small><math>110.2{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>1.64042</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.69098}</math></small>
|<small><math>\phi ^2 \sqrt{8-\phi ^2}</math></small>
|<small><math>6.07359</math></small>
|-
|<small><math>c_{21,1}</math></small>
|<small><math>113.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{19}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.67601</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{2.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\chi }{\phi }}</math></small>
|<small><math>6.20537</math></small>
|-
|<small><math>c_{22,1}</math></small>
|<small><math>120{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{10}\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\sqrt{3} c_{8,1}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>1.73205</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3.}</math></small>
|<small><math>\sqrt{6} \phi ^2</math></small>
|<small><math>6.41285</math></small>
|-
|<small><math>c_{23,1}</math></small>
|<small><math>124.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{41}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{\phi }+\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.7658</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{3.11803}</math></small>
|<small><math>\sqrt{\chi \phi ^5}</math></small>
|<small><math>6.53779</math></small>
|-
|<small><math>c_{24,1}</math></small>
|<small><math>130.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>1.81907</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.30902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\sqrt{5}}{\phi }}</math></small>
|<small><math>6.73503</math></small>
|-
|<small><math>c_{25,1}</math></small>
|<small><math>135.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}}</math></small>
|<small><math>1.85123</math></small>
|<small><math>\frac{\phi ^2}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^4}{2}}</math></small>
|<small><math>\sqrt{3.42705}</math></small>
|<small><math>\phi ^4</math></small>
|<small><math>6.8541</math></small>
|-
|<small><math>c_{26,1}</math></small>
|<small><math>138.6{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{12}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{7}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>1.87083</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{3.5}</math></small>
|<small><math>\sqrt{7} \phi ^2</math></small>
|<small><math>6.92667</math></small>
|-
|<small><math>c_{27,1}</math></small>
|<small><math>144{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{12}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{5}{2}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)}</math></small>
|<small><math>1.90211</math></small>
|<small><math>\sqrt{\phi +2}</math></small>
|<small><math>\sqrt{2+\phi }</math></small>
|<small><math>\sqrt{3.61803}</math></small>
|<small><math>\phi ^2 \sqrt{2 \phi +4}</math></small>
|<small><math>7.0425</math></small>
|-
|<small><math>c_{28,1}</math></small>
|<small><math>154.8{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>1.95167</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{1}{\phi ^2}}</math></small>
|<small><math>7.22598</math></small>
|-
|<small><math>c_{29,1}</math></small>
|<small><math>164.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{14}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{7}\right\}</math></small>
|<small><math>\phi c_{12,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{\frac{3}{2}} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.98168</math></small>
|<small><math>\sqrt{\frac{3}{2}} \phi </math></small>
|<small><math>\sqrt{\frac{3 \phi ^2}{2}}</math></small>
|<small><math>\sqrt{3.92705}</math></small>
|<small><math>\sqrt{3} \phi ^3</math></small>
|<small><math>7.33708</math></small>
|-
|<small><math>c_{30,1}</math></small>
|<small><math>180{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{15}\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>2 c_{8,1}</math></small>
|<small><math>2</math></small>
|<small><math>2.</math></small>
|<small><math>2</math></small>
|<small><math>\sqrt{4}</math></small>
|<small><math>\sqrt{4.}</math></small>
|<small><math>2 \sqrt{2} \phi ^2</math></small>
|<small><math>7.40492</math></small>
|-
|rowspan=4 colspan=6|
|rowspan=4 colspan=4|
<small><math>\phi</math></small> is the golden ratio:<br>
<small><math>\phi ^2-\phi -1=0</math></small><br>
<small><math>\frac{1}{\phi }+1=\phi</math></small>, and: <small><math>\phi+1=\phi^2</math></small><br>
<small><math>\frac{1}{\phi }::1::\phi ::\phi ^2</math></small><br>
<small><math>1/\phi</math></small> and <small><math>\phi</math></small> are the golden sections of <small><math>\sqrt{5}</math></small>:<br>
<small><math>\phi +\frac{1}{\phi }=\sqrt{5}</math></small>
|colspan=2|<small><math>\phi = (\sqrt{5} + 1)/2</math></small>
|<small><math>1.618034</math></small>
|-
|colspan=2|<small><math>\chi = (3\sqrt{5} + 1)/2</math></small>
|<small><math>3.854102</math></small>
|-
|colspan=2|<small><math>\psi = (3\sqrt{5} - 1)/2</math></small>
|<small><math>2.854102</math></small>
|-
|colspan=2|<small><math>\psi = 11/\chi = 22/(3\sqrt{5} + 1)</math></small>
|<small><math>2.854102</math></small>
|}
== The 5-cell 4-simplex ==
...
== The 16-cell 4-orthoplex ==
In 2-space we have the regular 8-point octagon, in 3-space the regular 8-point cube, and in 4-space the regular 8-point [[16-cell]].
A planar octagon with rigid edges of unit length has chords of length:
:<math>r_1=1,r_2=\sqrt{2+\sqrt{2}} \approx 1.848,r_3=\sqrt{2}+1 \approx 2.414,r_4=\sqrt{4 + \sqrt{8}} \approx 2.613</math>
The chord ratio <math>r_3=\sqrt{2}+1</math> is a geometrical proportion, the [[W:Silver ratio|silver ratio]]. Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_3-r_1-r_1=1/r_3 \approx 0.414</math>
Note that <math>r_3-2=1/r_3=\sqrt{2}-1</math>. The procedure rotates counterclockwise over three <math>r_3</math> chords of an {8/3} octagram. Over the first <math>r_3</math> chord the displacement is <math>\sqrt{2}+r_1</math>. Over the second <math>r_3</math> chord it moves in the opposite direction a distance of <math>-r_1</math> . Over the third <math>r_3</math> chord it moves a distance of <math>-r_1</math>.
If we embed the planar octagon in 3-space, we can make it skew, repositioning its vertices so that each is one unit-edge length distant from three others instead of two others, at the vertices of a unit-edge cube with chords of length:
:<math>r_1=1, r_2=\sqrt{2}, r_3=\sqrt{3}, r_4=\sqrt{2}</math>
If we embed this cube in 4-space, we can skew it some more, repositioning its vertices so that each is one unit-edge length distant from six others instead of three others, at the vertices of a unit-edge 4-polytope with chords of length:
:<math>r_1=1,r_2=1,r_3=1,r_4=\sqrt{2}</math>
All of its chords except its long diameters are the same unit length as its edge. In fact they are its 24 edges, and it is a 16-cell of radius <math>1/\sqrt{2}</math>.
[[File:octagon16cell.png|thumb|Orthogonal projection of a regular 16-cell to the [[16-cell#Projections|B<sub>4</sub> Coxeter plane]]. Only its edges are shown; its long diameter chords are not drawn. All 24 edges are the same length and none lie parallel to the projection plane. The octagon circumference is a Petrie polygon. The two disjoint squares lie in completely orthogonal central planes. The blue octagram is a Clifford polygon. ]]
The [[16-cell]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{3,3,4\}</math></small>. It has 8 vertices, 24 edges, 32 equilateral triangle faces, and 16 regular tetrahedron cells. It is the [[16-cell#Octahedral dipyramid|four-dimensional analogue of the octahedron]], and each of its four orthogonal central hyperplanes is an octahedron.
The only planar regular polygons found in the 16-cell are face triangles and central plane squares, but the 16-cell also contains a skew regular octagon, its [[W:Petrie polygon|Petrie polygon]].{{Efn|name=Petrie polygon of a honeycomb}} The chords of this regular octagon, which lies skew in 4-space, are those given above for the 16-cell, as opposed to those for the cube or the regular octagon in the plane. The 16-cell is a construct of 3 Petrie octagons which share the same 8 vertices but have disjoint sets of 8 edges each.
The regular octad has higher symmetry in 4-space than it does in 2-space. The 16-cell is the 4-[[w:Cross-polytope|orthoplex]], the simplest regular 4-polytope after the [[5-cell|4-simplex]]. All the larger regular convex 4-polytopes are compounds of the 16-cell. The regular octagon exhibits this high symmetry only when embedded in 4-space at the vertices of the 16-cell.
The 16-cell constitutes an [[W:Orthonormal basis|orthonormal basis]] for the choice of a 4-dimensional Cartesian reference frame, because its vertices define four orthogonal axes. The eight vertices of a unit-radius 16-cell are (±1, 0, 0, 0), (0, ±1, 0, 0), (0, 0, ±1, 0), (0, 0, 0, ±1). All vertices are connected by <math>\sqrt{2}</math> edges except opposite pairs.
The vertex coordinates of the 16-cell form 6 central squares lying in 6 pairwise [[W:Orthogonal|orthogonal]] coordinate planes. Great squares in opposite planes that do not share an axis (e.g. in the ''xy'' and ''wz'' planes) are completely disjoint (they do not intersect at any vertices). These planes are [[W:Completely orthogonal|completely orthogonal]].{{Efn|name=Six orthogonal planes of the Cartesian basis}}
Since the unit-radius coordinate system is convenient, let us derive the unit-radius 16-cell by skewing a unit-radius planar octagon, which has chords of length:
:<math>r_1=\sqrt{2-\sqrt{2}} \approx 0.765,r_2=\sqrt{2},r_3=\sqrt{2+\sqrt{2}} \approx 1.848,r_4=2</math>
We will need a planar octagon with rigid <math>r_2</math> chords, rather than one with rigid <math>r_1</math> edges. The octagon's <math>r_2</math> chords form two disjoint great squares, visible in the orthogonal projection, which we can reposition in 3-space to form a cube by making them parallel, and in 4-space to form a 16-cell by making them completely orthogonal.
Since the edges of the 16-cell are all the same length <math>r_1=\sqrt{2},r_2=\sqrt{2},r_3=\sqrt{2}</math>, those chords are distinct only in the context of a rotation. Each chord is a 4-vector with a length and a direction. The rotational curve over each <math>r_i</math> chord makes <math>i</math> 45° turns.
[[File:16-cell-orig.gif|thumb|Orthographic projection of the 8-point 16-cell <small><math>\{3,3,4\}</math></small> performing a double rotation.{{Sfn|Hise|2007}}]]
[[W:Rotations in 4-dimensional Euclidean space|Rotations in 4-dimensional Euclidean space]] can be seen as the composition of two 2-dimensional rotations in completely orthogonal planes. The general rotation in 4-space is a [[W:SO(4)#Double rotations|double rotation]] in pairs of completely orthogonal planes. Two completely orthogonal planes are called invariant planes of the rotation when all points in the plane rotate on circles that remain in the plane, even as the whole plane tilts sideways (like a coin flipping) into another plane. The two completely orthogonal rotations of each plane (like a wheel, and like a coin flipping) are simultaneous but independent, in that they are not geometrically constrained to turn at the same rate. However, the most circular kind of rotation (as opposed to an elliptical double rotation of a rigid spherical object) occurs when the completely orthogonal planes do rotate through the same angle in the same time interval. Such equi-angled double rotations are called [[w:SO(4)#Isoclinic_rotations|isoclinic]], also [[w:William_Kingdon_Clifford|Clifford]] displacements.
The <math>r_1</math> chords of the 16-cell form a Petrie polygon which zig-zags back and forth, in the left and right rotational directions, between two completely orthogonal great squares formed by <math>r_2</math> chords.
The <math>r_2</math> chords of two completely orthogonal great squares lie parallel and perpendicular to each other. A ''simple'' rotation of the 16-cell in ''one'' of those two square central planes rotates that square like a wheel, while the other square does not move.{{Efn|name=simple rotations}} The four vertices of the rotating square orbit on a great circle in the plane.
The <math>r_3</math> chords of the 16-cell form a circular helix, visible as a blue {8/3} octagram in the orthogonal projection. A ''double'' rotation of the 16-cell, in both of two completely orthogonal invariant <math>r_2</math> square planes at once by equal angles, moves the eight vertices along the circular helix over the <math>r_3</math> chords. The vertex motion is a [[w:Geodesic|geodesic]] circle orbit on the 3-sphere of a special kind: it does not lie in a central plane, its [[w:Winding_number|winding number]] is not 1 (it is 3 in this case), its circumference is not <math>2\pi</math>, and it moves in either a left or right handed circular spiral. We shall refer to such a chiral circle orbit as an ''isocline'', and to the skew polygram of its rotational chords as a ''Clifford polygon''.
The 16-cell is the simplest possible frame in which to [[16-cell#Rotations|observe 4-dimensional rotations]] because its characteristic rotations feature a single pair of invariant rotation planes. In the 16-cell an isoclinic rotation by 90° in any pair of invariant completely orthogonal square central planes takes every great square to its completely orthogonal great square in a twisting displacement, as the invariant planes tilt sideways 90° into each other's plane while rotating 90° internally. All the vertices move at once along the same circular helix geodesic isocline of <math>r_3</math> chords, displaced 90° in 8 orthogonal directions, and the rigid 16-cell assumes a new orientation in 4-space. When the 90° isoclinic rotation is continued in the same rotational direction through an additional 90°, each vertex is again displaced 90°, but from the new orientation in a direction orthogonal to its first 90° displacement. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. In 360° of isoclinic rotation over four <math>r_3</math> chords, each vertex makes six 90° turns and reaches its antipodal position.
The trajectory of each vertex over each 90° isoclinic rotational displacement is a one-eighth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>6\pi</math> over eight <math>r_3</math> chords, and also traces an ordinary great circle in the plane twice, over the four <math>r_2</math> edges of a great square in one of the two moving invariant rotation planes. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions just once and returns to its original position, and the 16-cell returns to its original orientation.
Because this is the isoclinic rotation of the 16-cell in its invariant edge planes we shall refer to it as the ''characteristic rotation of the 16-cell'', and note once again that it is Fontaine and Hurley's rotation over the <math>r_3</math> star polygon which constructs <math>1/r_3</math>.
== The 8-cell tesseract ==
The long diameter of the unit-edge [[W:Hypercube|hypercube]] of dimension <math>n</math> is <math>\sqrt{n}</math>, so the unit-edge [[w:Tesseract|4-hypercube, the 16-point (8-cell) tesseract,]] has chords:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
Uniquely in its 4-dimensional case, the hypercube's edge length equals its radius, like the hexagon. We call such polytopes ''radially equilateral'', because they can be constructed from equilateral triangles which meet at their center, each contributing two radii and an edge. The [[w:Cuboctahedron|cuboctahedron]] and the 24-cell are also radially equilateral.
[[File:8-cell.gif|thumb|Orthographic projection of the 16-point (8-cell) tesseract <small><math>\{4,3,3\}</math></small> performing a simple rotation about a plane in 4-space.{{Sfn|Hise|2007}} The stationary plane bisects the figure from front-left to back-right and top to bottom.]]
The [[W:Tesseract|tesseract]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{4,3,3\}</math></small>. It has 16 vertices, 32 edges, 24 square faces, and 8 cube cells. It is the four-dimensional analogue of the cube.
The 16-point tesseract is the convex hull of a compound of two 8-point 16-cells, in exact dimensional analogy to the way the 8-point cube is the convex hull of a [[W:Stellated octahedron|compound of two 4-point regular tetrahedra]]. The [[W:Demihypercube|demihypercubes]] occupy alternate vertices of the hypercubes. The diagonals of the square faces of the unit-edge, unit-radius tesseract are the <math>\sqrt{2}</math> edges of two unit-radius 16-cells, also the edges of the square central planes.
We can rotate the tesseract isoclinically the way we rotated the 16-cell, by 90° in completely orthogonal invariant square central planes, with the same effect on both alternate-position 16-cells. In the course of a 720° isoclinic rotation in invariant square central planes each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cell. The two skew {8/3} octagram Clifford polygons lie on two disjoint parallel isoclines of the same chirality, of circumference <math>6\pi</math> over <math>\sqrt{2}</math> chords. They form a circular double helix which intersects each vertex of the tesseract once.
The tesseract is the [[W:Dual polytope|dual polytope]] of the 16-cell. They have the same Petrie polygon, the regular skew octagon, but the tesseract is a construct of 4 Petrie octagons with disjoint sets of 8 tesseract edges each. We can construct the tesseract by skewing two planar octagons. Because the tesseract is radially equilateral (unlike the 16-cell), we use two octagons of unit-edge length to build the unit-radius tesseract. To start we embed the planar octagons in 4-space at the same point and make them completely orthogonal. Then we skew each planar octagon into a cube, so we have a compound of two completely orthogonal cubes, provided we skewed them both in the same direction. The 16 vertices will be the vertices of a tesseract with half its 32 edges missing.
Because the tesseract contains two 16-cells in alternate positions it has two sets of 6 orthogonal square central planes. Two angles are required to specify the relationship between two planes in 4-space. Pairs of square central planes within each 16-cell are 90° apart in one angle, and either 0° or 90° apart in the other angle. They are 90° apart in both angles if and only if they are completely orthogonal planes, 90° apart by isoclinic rotation, with no vertices in common. Otherwise they are 0° apart in one of the angles, 90° apart by simple rotation, and they intersect in one axis and lie in a common 3-dimensional hyperplane.{{Efn|A double rotation in which one of the two angles of rotation is 0°, so that one of the completely orthogonal invariant planes does not rotate, is called a simple rotation. Ordinary rotations observed in a 3-dimensional space are simple rotations.|name=simple rotations}}
A pair of square central planes from alternate-position 16-cells are 60° apart by isoclinic rotation, with their corresponding vertices 120° apart. The planes are not orthogonal or parallel, so they intersect in a line somewhere, but they have no vertices in common, they have no 3-dimensional hyperplane in common, and they cannot reach each other by simple rotation. Such pairs of objects are called [[W:Clifford parallel|Clifford parallel]] because all their corresponding pairs of vertices are the same distance apart, although they are not parallel in the usual sense, because they have a common center. Not only the alternate-position 16-cells' corresponding square central planes, but also the 16-cells themselves, are Clifford parallel objects. More generally, multiple disjoint instances of a 4-polytope which compound to make a larger 4-polytope are Clifford parallel objects.
== The 24-cell ==
[[File:24-cell vertex geometry.png|thumb|Planar geometry of the radially equilateral 24-cell, showing its 3 great circle polygons and its 4 chord lengths.]]
In 2-space we have the radially equilateral 6-point hexagon. In 3-space we have the radially equilateral 12-point cuboctahedron, with 4 hexagonal central planes. In 4-space we have the radially equilateral 24-point 24-cell, with 12 cuboctahedron central hyperplanes and 16 hexagonal central planes.
The [[24-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,4,3\}</math></small>. It has 24 vertices, 96 edges, 96 equilateral triangle faces, and 24 octahedron cells. It is the four-dimensional analogue of the cuboctahedron.
The 24-cell has the same chord set as the 4-hypercube tesseract:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
[[Image:24-cell.gif|thumb|Orthographic projection of the 24-point 24-cell <small><math>\{3,4,3\}</math></small> performing a simple rotation.{{Sfn|Hise|2007}} The 3-dimensional surface made of 24 octahedra is visible.]]
The 24-cell is [[W:Dual polytope|self-dual]], like the regular polygons and regular simplexes. It is the maximal regular construct of triangles and squares (with no pentagons). It is the convex hull of a compound of three disjoint 8-point 16-cells, rotated 60° isoclinically with respect to each other. Each of the three pairs of 16-cells is a tesseract. Each 24-cell edge is also a tesseract edge. The corresponding vertices of two 16-cells or two tesseracts are 120° apart by a <math>\sqrt{3}</math> chord. Each tesseract has 8 cube cells, and each cube has four <math>\sqrt{3}</math> long diameters. The <math>\sqrt{3}</math> chords joining the corresponding vertices of two tesseracts belong to the third tesseract as cell long diameters.
The 24-cell's Petrie polygon is the regular dodecagon {12}, which has chords:
:<math>r_1=\tfrac{\sqrt{3}-1}{\sqrt{2}} \approx 0.518,r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\tfrac{\sqrt{3}+1}{\sqrt{2}} \approx 1.932,r_6=\sqrt{4}</math>
Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_5-r_3+r_1+r_1-r_3=1/r_5</math>
when <math>r_1=1</math>. The procedure rotates counterclockwise over five <math>r_5</math> chords of a {12/5} dodecagram. In the system of unit-radius coordinates <math>r_1=1/r_5</math>.
The <math>r_1</math> and <math>r_5</math> chords of the planar dodecagon do not occur in the 24-cell, which is a construct of eight skew dodecagons with disjoint sets of twelve <math>\sqrt{1}</math> edges each. In the skew dodecagons the chord lengths are:
:<math>r_1=\sqrt{1},r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\sqrt{3},r_6=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
[[File:dodecagon24cell.png|thumb|Orthogonal projection of half a 24-cell to the [[24-cell#Geodesics|F<sub>4</sub> Coxeter plane]]. Only one Petrie dodecagon {12} of the 24-cell is shown. In a unit-radius 24-cell, all black lines are 24-cell edges of unit length, also tesseract edges. The two disjoint hexagons lie in Clifford parallel central planes. Blue chords are <math>\sqrt{2}</math> 16-cell edges, also isocline chords in square rotations. Green chords are <math>\sqrt{3}</math> distances between corresponding vertices of two 16-cells, also isocline chords in hexagonal rotations. Note the {12/5} dodecagram.]]
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_3=\sqrt{2}</math></small>]]
We can rotate the 24-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in completely orthogonal invariant great square planes, with the same effect on all three 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cells. The <math>r_3=\sqrt{2}</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Three Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_3</math> chords form a circular triple helix {24/9}=3{8/3} that intersects each 24-cell vertex once.
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_5=\sqrt{3}</math></small> ]]
We can also rotate the 24-cell isoclinically in 4 Clifford parallel invariant great hexagon planes containing its vertices, over <math>r_{5}=\sqrt{3}</math> isocline chords. This is the ''characteristic rotation of the 24-cell'' in its invariant edge planes, also Fontaine and Hurley's rotation over the <math>r_5</math> star polygon which constructs <math>1/r_5</math>. A complete hexagonal isoclinic revolution requires 720° like a complete square isoclinic revolution, but it is completed in 12 isoclinic displacements of 60° each rather than 8 isoclinic displacements of 90° each. The rotational curve over each 120° <math>r_5</math> chord makes five 30° turns. Two Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_5</math> chords form a circular double helix {24/10}=2{12/5} that intersects each 24-cell vertex once.
In the 24-cell the characteristic isoclinic rotation by 60° in any invariant hexagon central plane takes every great hexagon to a Clifford parallel great hexagon in a twisting displacement, as all the central planes tilt sideways 60° while rotating 60° internally. It also takes every great square to a Clifford parallel great square in another 16-cell; it takes every 16-cell to another 16-cell. The 16-cells revolve within the 24-cell as well as rotating within it. All 24 vertices move at once on two Clifford parallel geodesic isoclines, displaced 120° in different directions.
The trajectory of each vertex over each 60° isoclinic rotational displacement is a one-twelfth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>10\pi</math> over twelve <math>\sqrt{3}</math> chords, and also traces an ordinary great circle in the plane twice, over the six <math>\sqrt{1}</math> edges of a great hexagon in a moving invariant rotation plane. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions just once and returns to its original position, and the 24-cell returns to its original orientation.
== The 600-cell ==
[[Image:600-cell.gif|thumb|Orthographic projection of the 120-point 600-cell <small><math>\{3,3,5\}</math></small> performing a simple rotation.{{Sfn|Hise|2011}} The 3-dimensional surface made of 600 tetrahedra is visible. Invisible in this rendering are 25 inscribed instances of the 24-cell (above), which occur in the 600-cell as interior boundary envelopes.]]
The [[600-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,3,5\}</math></small>. It has 120 vertices, 720 edges, 1200 equilateral triangle faces, and 600 tetrahedron cells. It is the four-dimensional analogue of the icosahedron.
The 600-cell rounds out the 24-cell by adding 96 more vertices (four more disjoint 24-cells) between the 24-cell's existing 24 vertices, in effect adding twenty-four more distinct 24-cells inscribed in the 600-cell. The new surface thus formed is a honeycomb of smaller, more numerous cells: tetrahedra of edge length <math>\phi^{-1} \approx 0.618</math> instead of octahedra of edge length <math>\sqrt{1}</math>. It encloses the <math>\sqrt{1}</math> edges of the 24-cells, which become invisible interior chords in the 600-cell, like the <math>\sqrt{2}</math> and <math>\sqrt{3}</math> chords.
Since the tetrahedra are made of shorter triangle edges than the octahedra (by a factor of <math>\phi^{-1}</math>, the inverse golden ratio), the 600-cell is not radially equilateral like the 24-cell and the tesseract. Like them it is radially triangular in a special way, but one in which [[w:Golden_triangle_(mathematics)|golden triangles]] rather than equilateral triangles meet at the center.
In 2-space we have the ''radially golden'' [[W:Decagon#The golden ratio in decagon|regular decagon]]. In 3-space we have the radially golden 30-point [[W:icosidodecahedron|icosidodecahedron]], with 6 decagon central planes. In 4-space we have the radially golden 120-point 600-cell, with 60 icosidodecahedron central hyperplanes and 72 decagon central planes.
The 600-cell's Petrie polygon is the regular [[w:Triacontagon|triacontagon {30}]]. The unit-radius planar {30}-gon has these distinct chords:
:<math>r_1=2 \sin (\tfrac{\pi}{15}/2) \approx 0.209</math>
:<math>r_2=2 \sin (\tfrac{2\pi}{15}/2) \approx 0.416</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{4\pi}{15}/2) \approx 0.813</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{7\pi}{15}/2) \approx 1.338</math>
:<math>r_8=2 \cos (\tfrac{7\pi}{15}/2) \approx 1.486</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{11}=2 \cos (\tfrac{4\pi}{15}/2) \approx 1.827</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \cos (\tfrac{2\pi}{15}/2) \approx 1.956</math>
:<math>r_{14}=2 \cos (\tfrac{\pi}{15}/2) \approx 1.989</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Only the chord lengths <math>r_3</math>, <math>r_5</math>, <math>r_6</math>, <math>\sqrt{2}</math>, <math>r_9</math>, <math>r_{10}</math>, <math>r_{12}</math>, <math>r_{15}</math> occur in the 600-cell, which is a construct of 24 Petrie {30}-gons of edge length <math>r_3</math>, six of which intersect in each icosahedral vertex figure. In the skew {30}-gons the chord lengths are:
[[File:600-cell vertex geometry.png|thumb|Planar geometry of the 600-cell, showing its 5 regular great circle polygons and its 8 chord lengths with angles of arc. The golden ratio governs the fractional roots of every other chord, and the radial golden triangles which meet at the center.|400x400px]]
:<math>r_1=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_2=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}=\text{24-cell-}r_2</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}</math>
:<math>r_8=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}=\text{16-cell-}r_3</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}=\text{24-cell-}r_5</math>
:<math>r_{11}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{14}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="7" |15 chords (4 distinct 180° pairs) make 4 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>r_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>r_{15}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>r_1</math>
|36°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}=2{15/7}
|144°
| rowspan="3" |<math>r_{14}</math>
|- style="background: palegreen;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: palegreen;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>r_2</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|144°
| rowspan="3" |<math>r_{13}</math>
|- style="background: gainsboro;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: gainsboro;" |
|0.618~
|1.902~
|- style="background: yellow;" |
| rowspan="3" |<math>r_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |[[File:V1 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>r_{12}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_4</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|120°
| rowspan="3" |<math>r_{11}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_5</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |[[File:V2 dodecahedron.png|100px]]<br>Dodecahedron
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>r_{10}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: yellow;" |
| rowspan="3" |<math>r_{6}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |[[File:V3 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>r_{9}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>r_{8}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: seashell;" |
| rowspan="3" |<math>r_{7}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |[[File:V4 icosidodecahedron.png|100px]]<br>Icosidodecahedron
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>r_{8}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The list of 600-cell chords <math>r_{i}</math> can be rearranged into a table of 8 rows and 2 columns with a pair of 180° complements in each row. The short chord and long chord each have their characteristic {30}-gon. Each row identifies a discrete isoclinic rotation of the 600-cell in invariant central planes containing the edges of the short chord {30}-gon, over the isocline chords of the long chord {30}-gon, the rotation's Clifford polygon.
Each distinct pair of complementary chord lengths is identified with a distinct [[w:600-cell#Polyhedral sections|polyhedral section of the 600-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 7 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>\phi^{-1}</math> is a icosahedron vertex figure, and the largest section at radial distance <math>\sqrt{2}</math> is an [[W:Icosidodecahedron|icosidodecahedron]] central section bisecting the 600-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>\sqrt{2}</math> the successive complement-radius polyhedra decrease in size, to the antipodal icosahedron vertex figure at distance <math>\sqrt{2+\phi}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 7 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section).
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_8=\sqrt{2}</math></small>]]
We can rotate the 600-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in two completely orthogonal invariant great square planes over <math>r_8=\sqrt{2}</math> isocline chords, with the same effect on 15 disjoint 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_8</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Fifteen Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_8</math> chords form a circular helix of 15 twisted parallel strands 5{24/9}=15{8/3} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_polygon_30-7.svg|thumb|left|150px|{30/7} <small><math>r_7=\sqrt{2}</math></small>]]
In the 600-cell this 90° isoclinic rotation in completely orthogonal great square planes takes place over the <math>r_7=\sqrt{2}</math> chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/7} polygon is a skew helix with each <math>r_7</math> edge belonging to a distinct great square. The vertices of the invariant great squares of this rotation each make seven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 90° <math>r_7</math> isocline chord makes seven 12° turns. Four Clifford parallel {30/7} geodesic isoclines of circumference <math>14\pi</math> over <math>r_7</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_{11}=\sqrt{3}</math></small> ]]
We can also rotate the 600-cell isoclinically in the characteristic rotation of the 24-cell, by 60° in great hexagon planes, with the same effect on 5 disjoint 24-cells. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions of its 24-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_{5}</math> chord is the 24-cell <math>r_2</math> chord, and the <math>r_{10}</math> chord is the 24-cell <math>r_5</math> chord. The rotational curve over each <math>r_{10}</math> chord makes five 30° turns. Ten Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_{10}</math> chords form a circular helix of 10 twisted parallel strands 5{24/10}=10{12/5} that intersects each 600-cell vertex once.
In the 600-cell this 60° isoclinic rotation in great hexagon planes takes place over <math>r_{4}=\sqrt{1}</math> edge chords and <math>r_{11}=\sqrt{3}</math> isocline chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/11} polygon is a skew helix with each <math>r_{11}</math> chord the <math>\sqrt{3}</math> diagonal of a distinct great hexagon. The vertices of the invariant great hexagons of this rotation each make eleven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 120° <math>r_{11}</math> isocline chord makes eleven 12° turns. Four Clifford parallel {30/11} geodesic isoclines of circumference <math>22\pi</math> over <math>r_{11}</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_figure_2(15,4).svg|thumb|left|150px|{30/8}=2{15/4} <small><math>r_{13}=\sqrt{1}</math></small>]]
We can also rotate the 600-cell isoclinically in 12 Clifford parallel invariant decagon central planes containing its <math>r_{3}</math> edges, over <math>r_{13}=\sqrt{1}</math> isocline chords. This is the ''characteristic rotation of the 600-cell'' in its invariant edge planes. Its Clifford polygon is a skew {15/4} pentadecagram of <math>r_{13}</math> chords. The <math>r_{4}</math> chord is the 24-cell <math>r_2</math> chord. Successive <math>r_{13}</math> chords are edges of different 24-cells. The rotational curve over each <math>r_{13}</math> chord makes two 30° turns. Eight Clifford parallel {15/4} pentadecagon geodesic isoclines of circumference <math>5\pi</math> over <math>r_{13}</math> chords form a circular helix of eight twisted parallel strands 4{30/8}=8{15/4} that intersects each 600-cell vertex once.
In the 600-cell the characteristic isoclinic rotation by 36° in any invariant decagon central plane takes every great decagon to a Clifford parallel great decagon in a twisting displacement, as all the central planes tilt sideways 36° while rotating 36° internally. It also takes every great hexagon to a Clifford parallel great hexagon in another 24-cell, and every great square to a Clifford parallel great square in another 16-cell; it takes 24-cells to a non-disjoint 24-cell and 16-cells to a 16-cell in another 24-cell. The 24-cells revolve within the 600-cell, as the 16-cells revolve within the 24-cells. All 120 vertices move at once on eight Clifford parallel geodesic isoclines, displaced 60° in different directions.
The trajectory of each vertex over each 36° isoclinic rotational displacement is a one-fifteenth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>5\pi</math> over 15 <math>r_5</math> chords, and also traces an ordinary great circle in the plane 3 times, over the 5 edges of a great pentagon in a moving invariant rotation plane. In the course of a complete isoclinic revolution each vertex departs from 15 vertex positions just once and returns to its original position, and the 600-cell returns to its original orientation.
{{Clear}}
[[File:Regular_star_figure_6(5,2).svg|thumb|left|150px|{30/12}=6{5/2} <small><math>r_{12}=\sqrt{3.618\sim}</math></small>]]
In the 600-cell there is another distinct isoclinic rotation taking decagon planes to each other, over 144° <math>r_{12}</math> isocline chords. It also takes disjoint 24-cells to each other. This rotation has period 5 and visits every 12th vertex of a 600-cell Petrie polygon. Its Clifford polygon is a skew {5/2} pentagram of <math>r_{12}</math> chords. The invariant central planes of this rotation each intersect only one vertex of the 600-cell, which makes two orbits of a great pentagon within the moving invariant plane in the course of one complete isoclinic revolution of period 5. The rotational curve over each <math>r_{12}</math> chord makes twelve 12° turns. 24 Clifford parallel {5/2} pentagram geodesic isoclines of circumference <math>4\pi</math> over five <math>r_{12}</math> chords form a circular helix of 24 twisted parallel strands 4{30/12}=24{5/2} that intersects each 600-cell vertex once.
{{Clear}}
== Finally the 120-cell ==
The [[120-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{5,3,3\}</math></small>. It has 600 vertices, 1200 edges, 720 pentagon faces, and 120 dodecahedron cells. It is the four-dimensional analogue of the dodecahedron.
The 120-cell is the [[W:Dual polytope|dual polytope]] of the 600-cell. They have the same Petrie polygon, the regular skew triacontagon {30}, but the 120-cell is a construct of 40 Petrie {30}-gons of edge length <math>c_1</math>, two of which intersect in each tetrahedral vertex figure.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="9" |30 chords (15 180° pairs) make 15 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>c_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>c_{30}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>c_1</math>
|15.5~°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}
|164.5~°
| rowspan="3" |<math>c_{29}</math>
|- style="background: palegreen;" |
|{{radic|0.073~}}
|{{radic|3.927~}}
|- style="background: palegreen;" |
|0.270~
|1.982~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_2</math>
|25.2~°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|154.8~°
| rowspan="3" |<math>c_{28}</math>
|- style="background: gainsboro;" |
|{{radic|0.191~}}
|{{radic|3.809~}}
|- style="background: gainsboro;" |
|0.437~
|1.952~
|- style="background: yellow;" |
| rowspan="3" |<math>c_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>c_{27}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_4</math>
|41.4~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|138.6~°
| rowspan="3" |<math>c_{26}</math>
|- style="background: gainsboro;" |
|{{radic|0.5}}
|{{radic|3.5}}
|- style="background: gainsboro;" |
|0.707~
|1.871~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_5</math>
|44.5~°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|135.5~°
| rowspan="3" |<math>c_{25}</math>
|- style="background: palegreen;" |
|{{radic|0.573~}}
|{{radic|3.427~}}
|- style="background: palegreen;" |
|0.757~
|1.851~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_6</math>
|49.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|130.9~°
| rowspan="3" |<math>c_{24}</math>
|- style="background: gainsboro;" |
|{{radic|0.691~}}
|{{radic|3.309~}}
|- style="background: gainsboro;" |
|0.831~
|1.819~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_7</math>
|56°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|124°
| rowspan="3" |<math>c_{23}</math>
|- style="background: gainsboro;" |
|{{radic|0.882~}}
|{{radic|3.118~}}
|- style="background: gainsboro;" |
|0.939~
|1.766~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_8</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>c_{22}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_9</math>
|66.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|113.9~°
| rowspan="3" |<math>c_{21}</math>
|- style="background: gainsboro;" |
|{{radic|1.191~}}
|{{radic|2.809~}}
|- style="background: gainsboro;" |
|1.091~
|1.676~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{10}</math>
|69.8~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|110.2~°
| rowspan="3" |<math>c_{20}</math>
|- style="background: gainsboro;" |
|{{radic|1.309~}}
|{{radic|2.691~}}
|- style="background: gainsboro;" |
|1.144~
|1.640~
|- style="background: yellow;" |
| rowspan="3" |<math>c_{11}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>c_{19}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>c_{18}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{13}</math>
|81.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|98.9~°
| rowspan="3" |<math>c_{17}</math>
|- style="background: gainsboro;" |
|{{radic|1.691~}}
|{{radic|2.309~}}
|- style="background: gainsboro;" |
|1.300~
|1.520~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{14}</math>
|84.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|95.5~°
| rowspan="3" |<math>c_{16}</math>
|- style="background: gainsboro;" |
|{{radic|0.809~}}
|{{radic|2.191~}}
|- style="background: gainsboro;" |
|1.345~
|1.480~
|- style="background: seashell;" |
| rowspan="3" |<math>c_{15}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>c_{15}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The [[User:Dc.samizdat/Golden chords of the 120-cell#Thirty distinguished distances|table above]] of 30 chords <math>c_{t}</math> can be rearranged into a table of 16 rows and 2 columns with a pair of 180° complements in each row. This table first appears in [[w:Regular_Polytopes_(book)|''Regular Polytopes'']] (1947),{{Sfn|Coxeter|1973|loc=Table V(v): Simplified sections of {5,3,3} beginning with a vertex|pp=300-301}} where Coxeter identified each row with a distinct [[w:120-cell#Concentric_hulls|polyhedral section of the 120-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 29 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>c_1</math> is a tetrahedron vertex figure, and the largest section at radial distance <math>c_{15}</math> is a central section bisecting the 120-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>c_{15}</math> the successive complement-radius polyhedra decrease in size, to the antipodal tetrahedron vertex figure at distance <math>c_{29}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 29 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section). Each section also lies completely orthogonal to a congruent section.
Only 8 of the 30 chords in the table occur in the 600-cell and the planar {30)-gon. The 120-cell's additional chords arise originally from the regular 5-cell, in its interaction with the other regular 4-polytopes that compound to make the 120-cell. Since all those polytopes except the 5-cell occur in the 600-cell, and the 600-cell and the 120-cell have the same symmetry group, the 5-cell's symmetry group is what's new in the 120-cell.
...
{{Clear}}
== Conclusions ==
Fontaine and Hurley's discovery is more than a geometric formula for the reciprocal of a regular ''n''-polygon diagonal. It also yields the discrete sequence of isocline chords of the characteristic isoclinic rotation of a ''d''-dimensional polytope in its invariant edge planes. The characteristic rotational chord sequence of the ''d''-polytope can be represented geometrically in two dimensions on a distinct star polygon, but it lies on a geodesic circle through ''d''-dimensional space. Fontaine and Hurley discovered the geodesic topology of polytopes generally. Their procedure will reveal the geodesics of arbitrary non-uniform polytopes, since it can be applied to a polytope of any dimensionality and irregularity, by first fitting the polytope to the smallest regular polygon whose chords include its chords. [If what is meant by this is its Petrie polygon, it is not quite necessary or possible with respect to the planar polygon chords, e.g. the planar Petrie polygon of the 600-cell does not contain the <math>\sqrt{2}</math> chord. But perhaps it would work if the fit is to the smallest regular skew polygon in the ''d''-space.]
The discovery of a chordal construction for discrete isoclinic rotations generally closes the circuit on Kappraff and Adamson's discovery of a rotational connection between dynamical systems, Steinbach's golden fields, and Coxeter's Euclidean geometry of ''n'' dimensions. Application of the Fontaine and Hurley procedure in the 120-cell demonstrates why the connection exists: because polytope sequences generally, from Steinbach's golden chord sequences in polygons, to sequences of star polygons in isoclinic rotations, to subsumption relations in the sequence of regular 4-polytopes, arise as expressions of the reflections and rotations of distinct Coxeter symmetry groups, when those various groups interact.
== Appendix: Sequence of regular 4-polytopes ==
{{Regular convex 4-polytopes|wiki=W:|columns=7}}
== Notes ==
{{Notelist}}
== Citations ==
{{Reflist}}
== References ==
{{Refbegin}}
* {{Cite journal | last=Steinbach | first=Peter | year=1997 | title=Golden fields: A case for the Heptagon | journal=Mathematics Magazine | volume=70 | issue=Feb 1997 | pages=22–31 | doi=10.1080/0025570X.1997.11996494 | jstor=2691048 | ref={{SfnRef|Steinbach|1997}} }}
* {{Cite journal | last=Steinbach | first=Peter | year=2000 | title=Sections Beyond Golden| journal=Bridges: Mathematical Connections in Art, Music and Science | issue=2000 | pages=35-44 | url=https://archive.bridgesmathart.org/2000/bridges2000-35.pdf | ref={{SfnRef|Steinbach|2000}}}}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Jablan | first2=Slavik | last3=Adamson | first3=Gary | last4=Sazdanovich | first4=Radmila | year=2004 | title=Golden Fields, Generalized Fibonacci Sequences, and Chaotic Matrices | journal=Forma | volume=19 | pages=367-387 | url=https://archive.bridgesmathart.org/2005/bridges2005-369.pdf | ref={{SfnRef|Kappraff, Jablan, Adamson & Sazdanovich|2004}} }}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Adamson | first2=Gary | year=2004 | title=Polygons and Chaos | journal=Dynamical Systems and Geometric Theories | url=https://archive.bridgesmathart.org/2001/bridges2001-67.pdf | ref={{SfnRef|Kappraff & Adamson|2004}} }}
* {{Cite journal | last1=Fontaine | first1=Anne | last2=Hurley | first2=Susan | year=2006 | title=Proof by Picture: Products and Reciprocals of Diagonal Length Ratios in the Regular Polygon | journal=Forum Geometricorum | volume=6 | pages=97-101 | url=https://scispace.com/pdf/proof-by-picture-products-and-reciprocals-of-diagonal-length-1aian8mgp9.pdf }}
{{Refend}}
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/* The 600-cell */
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= Golden chords of the 120-cell =
{{align|center|David Brooks Christie}}
{{align|center|dc@samizdat.org}}
{{align|center|Draft in progress}}
{{align|center|January 2026 - June 2026}}
<blockquote>Steinbach discovered the formula for the ratios of diagonal to side in the regular polygons. Fontaine and Hurley extended this result, discovering a formula for the reciprocal of a regular polygon chord derived geometrically from the chord's star polygon. We observe that these findings in plane geometry apply more generally, to polytopes of any dimensionality. Fontaine and Hurley's geometric procedure for finding the reciprocals of the chords of a regular polygon from their star polygons also finds the rotational geodesics of any polytope of any dimensionality.</blockquote>
== Introduction ==
Steinbach discovered the Diagonal Product Formula and the Golden Fields family of ratios of diagonal to side in the regular polygons. He showed how this family extends beyond the pentagon {5} with its well-known golden bisection proportional to 𝜙, finding that the heptagon {7} has an analogous trisection, the nonagon {9} has an analogous quadrasection, and the hendecagon {11} has an analogous pentasection, an extended family of golden proportions with quasiperiodic properties.
Kappraff and Adamson extended these findings in plane geometry to a theory of Generalized Fibonacci Sequences, showing that the Golden Fields not only do not end with the hendecagon, they form an infinite number of periodic trajectories when operated on by the Mandelbrot operator. They found a relation between the edges of star polygons and dynamical systems in the state of chaos, revealing a connection between chaos theory, number, and rotations in Coxeter Euclidean geometry.
Fontaine and Hurley examined Steinbach's finding that the length of each chord of a regular polygon is both the product of two chords and the sum of a set of smaller chords, so that in rotations to add is to multiply. They illustrated Steinbach's sets of additive chords lying parallel to each other in the plane (pointing in the same direction), and by applying Steinbach's formula more generally they found another summation relation of signed parallel chords (pointing in opposite directions) which relates each chord length to its reciprocal, and relates the summation to a distinct star polygon rotation.
We examine these remarkable findings (which stem from study of the chords of humble regular polygons) in higher-dimensional spaces, specifically in the chords, polygons and rotations of the [[120-cell]], the largest four-dimensional regular convex polytope.
== Visualizing the 120-cell ==
{| class="wikitable floatright" width="400"
|style="vertical-align:top"|[[File:120-cell.gif|200px]]<br>Orthographic projection of the 600-point 120-cell <small><math>\{5,3,3\}</math></small> performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]].{{Sfn|Hise|2011|loc=File:120-cell.gif|ps=; "Created by Jason Hise with Maya and Macromedia Fireworks. A 3D projection of a 120-cell performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]]."}} In this simplified rendering only the 120-cell's own edges are shown; its 29 interior chords are not rendered. Therefore even though it is translucent, only its outer surface is visible. The complex interior parts of the 120-cell, all its inscribed 5-cells, 16-cells, 8-cells, 24-cells, 600-cells and its much larger inventory of polyhedra, are completely invisible in this view, as none of their edges are rendered at all.
|style="vertical-align:top"|[[File:Ortho solid 016-uniform polychoron p33-t0.png|200px]]<br>Orthographic projection of the 600-point [[W:Great grand stellated 120-cell|great grand stellated 120-cell]] <small><math>\{\tfrac{5}{2},3,3\}</math></small>.{{Sfn|Ruen: Great grand stellated 120-cell|2007}} The 120-cell is its convex hull. The projection to the left renders only the 120-cell's shortest chord, its 1200 edges. The projection above also renders only one of the 120-cell's 30 chords, the edges of its 120 inscribed regular 5-cells. The 120-cell itself (the convex hull) is invisible in this view, as its edges are not rendered.
|}
[[120-cell#Geometry|The 120-cell is the maximally complex regular 4-polytope]], containing inscribed instances of every regular 1-, 2-, 3-, and 4-polytope, except the regular polygons of more than {15} sides.
The 120-cell is the convex hull of a regular [[120-cell#Relationships among interior polytopes|compound of each of the 6 regular convex 4-polytopes]]. They are the [[5-cell|5-point (5-cell) 4-simplex]], the [[16-cell|8-point (16-cell) 4-orthoplex]], the [[W:Tesseract|16-point (8-cell) tesseract]], the [[24-cell|24-point (24-cell)]], the [[600-cell|120-point (600-cell)]], and the [[120-cell|600-point (120-cell)]]. The 120-cell is the convex hull of a compound of 120 disjoint regular 5-cells, of 75 disjoint 16-cells, of 25 disjoint 24-cells, and of 5 disjoint 600-cells.
The 120-cell contains an even larger inventory of irregular polytopes, created by the intersection of multiple instances of these component regular 4-polytopes. Many are quite unexpected, because they do not occur as components of any regular polytope smaller than the 120-cell. As just one example among the [[120-cell#Concentric hulls|sections of the 120-cell]], there is an irregular 24-point polyhedron with 16 triangle faces and 4 nonagon {9} faces.{{Sfn|Moxness|}}
Most renderings of the 120-cell, like the rotating projection here, only illustrate its outer surface, which is a honeycomb of face-bonded dodecahedral cells. Only the objects in its 3-dimensional surface are rendered, namely the 120 dodecahedra, their pentagon faces, and their edges. Although the 120-cell has chords of 30 distinct lengths, in this kind of simplified rendering only the 120-cell's own edges (its shortest chord) are shown. Its 29 interior chords, the edges of objects in the interior of the 120-cell, are not rendered, so interior objects are not visible at all.
Visualizing the complete interior of the 600-vertex 120-cell in a single image is impractical because of its complexity. Only four 120-cell edges are incident at each vertex, but [[120-cell#Chords|600 chords (of all 30 lengths)]] are incident at ''each'' vertex.
== Compounds in the 120-cell ==
The 8-point (16-cell), not the 5-point (5-cell), is the smallest building block; it compounds to every larger regular 4-polytope. The 5-point (5-cell) does compound to the 600-point (120-cell), but it does not fit into any smaller regular 4-polytope.
The 8-point (16-cell) compounds by 2 in the 16-point (8-cell), and by 3 in the 24-point (24-cell). The 16-point (8-cell) compounds in the 24-point (24-cell) by 3 non-disjoint instances of itself, with each of the 24 vertices shared by two 16-point (8-cells). The 24-point (24-cell) compounds by 5 disjoint instances of itself in the 120-point (600-cell), and the 120-point (600-cell) compounds by 5 disjoint instances of itself in the 600-point (120-cell).
The 24-point (24-cell) also compounds by 5<sup>2</sup> non-disjoint instances of itself in the 120-point (600-cell); it compounds in 5 disjoint instances of itself, 10 (not 5) different ways. Whichever set of 5 disjoint 24-point (24-cells) are assembled, the resulting 120-point (600-cell) contains 25 distinct 24-point (24-cells), not just 5 (or 10). This implies that 15 disjoint 8-point (16-cells) will construct a 120-point (600-cell), which will contain 75 distinct 8-point (16-cells).
The 600-point (120-cell) is 5 disjoint 120-point (600-cells), just 2 different ways (not 5 or 10 ways), so it is 10 distinct 120-point (600-cells). This implies that the 8-point (16-cell) compounds by 3 times 5<sup>2</sup> (75) disjoint instances of itself in the 600-point (120-cell), which contains 3<sup>2</sup> times 5<sup>2</sup> (225) distinct instances of the 24-point (24-cell), and 3<sup>3</sup> times 5<sup>2</sup> (675) distinct instances of the 8-point (16-cell).
These facts were discovered painstakingly by various researchers, and no one has found a general rule governing subsumption relations among regular polytopes. The reasons for some of their numeric incidence relations are far from obvious. [[W:Pieter Hendrik Schoute|Schoute]] was the first to see that the 120-point (600-cell) is a compound of 5 24-point (24-cells) ''10 different ways'', and after he saw it a hundred years lapsed until Denney, Hooker, Johnson, Robinson, Butler & Claiborne proved his result, and showed why.{{Sfn|Denney, Hooker, Johnson, Robinson, Butler & Claiborne|2020|loc=''The geometry of H4 polytopes''}}
So much for the compounds of 16-cells. The 120-cell is also the convex hull of the compound of 120 disjoint regular 5-cells. That stellated compound (without its convex hull of 120-cell edges) is the [[w:Great_grand_stellated_120-cell|great grand stellated 120-cell]] illustrated above, the final regular [[W:Stellation|stellation]] of the 120-cell, and the only [[W:Schläfli-Hess polychoron|regular star 4-polytope]] to have the 120-cell for its convex hull. The edges of the great grand stellated 120-cell are <math>\phi^6</math> as long as those of its 120-cell [[W:List of polyhedral stellations#Stellation process|stellation core]] deep inside.
The compound of 120 disjoint 5-point (5-cells) can be seen to be equivalent to the compound of 5 disjoint 120-point (600-cells), as follows. Beginning with a single 120-point (600-cell), expand each vertex into a regular 5-cell, by adding 4 new equidistant vertices, such that the 5 vertices form a regular 5-cell inscribed in the 3-sphere. The 120 5-cells are disjoint, and the 600 vertices form 5 disjoint 120-point (600-cells): a 120-cell.
== Thirty distinguished distances ==
The 30 numbers listed in the table are all-important in Euclidean geometry. A case can be made on symmetry grounds that their squares are the 30 most important numbers between 0 and 4. The 30 rows of the table are the 30 distinct [[120-cell#Geodesic rectangles|chord lengths of the unit-radius 120-cell]], the largest regular convex 4-polytope. Since the 120-cell subsumes all smaller regular polytopes, its 30 chords are the complete chord set of all the regular polytopes that can be constructed in the first four dimensions of Euclidean space, except for regular polygons of more than 15 sides.
{| class="wikitable" style="white-space:nowrap;text-align:center"
!rowspan=2|<math>c_t</math>
!rowspan=2|arc
!rowspan=2|<small><math>\left\{\frac{30}{n}\right\}</math></small>
!rowspan=2|<math>\left\{p\right\}</math>
!rowspan=2|<small><math>m\left\{\frac{k}{d}\right\}</math></small>
!rowspan=2|Steinbach roots
!colspan=7|Chord lengths of the unit 120-cell
|-
!colspan=5|unit-radius length <math>c_t</math>
!colspan=2|unit-edge length <math>c_t/c_1</math><br>in 120-cell of radius <math>c_8=\sqrt{2}\phi^2</math>
|-
|<small><math>c_{1,1}</math></small>
|<small><math>15.5{}^{\circ}</math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math>c_{4,1}-c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7-3 \sqrt{5}}</math></small>
|<small><math>0.270091</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi ^2}</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^4}}</math></small>
|<small><math>\sqrt{0.072949}</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|-
|<small><math>c_{2,1}</math></small>
|<small><math>25.2{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{2}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{15\right\}</math></small>
|<small><math>\frac{1}{2} \left(c_{18,1}-c_{4,1}\right)</math></small>
|<small><math>\frac{\sqrt{3-\sqrt{5}}}{2}</math></small>
|<small><math>0.437016</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi }</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.190983}</math></small>
|<small><math>\phi </math></small>
|<small><math>1.61803</math></small>
|-
|<small><math>c_{3,1}</math></small>
|<small><math>36{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{3}\right\}</math></small>
|<small><math>\left\{10\right\}</math></small>
|<small><math>3 \left\{\frac{10}{3}\right\}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right) c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right)</math></small>
|<small><math>0.618034</math></small>
|<small><math>\frac{1}{\phi }</math></small>
|<small><math>\sqrt{\frac{1}{\phi ^2}}</math></small>
|<small><math>\sqrt{0.381966}</math></small>
|<small><math>\sqrt{2} \phi </math></small>
|<small><math>2.28825</math></small>
|-
|<small><math>c_{4,1}</math></small>
|<small><math>41.4{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{7}\right\}</math></small>
|<small><math>\frac{c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>0.707107</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{1}{2}}</math></small>
|<small><math>\sqrt{0.5}</math></small>
|<small><math>\phi ^2</math></small>
|<small><math>2.61803</math></small>
|-
|<small><math>c_{5,1}</math></small>
|<small><math>44.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{4}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{\frac{15}{2}\right\}</math></small>
|<small><math>\sqrt{3} c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-3 \sqrt{5}}</math></small>
|<small><math>0.756934</math></small>
|<small><math>\frac{\sqrt{\frac{3}{2}}}{\phi }</math></small>
|<small><math>\sqrt{\frac{3}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.572949}</math></small>
|<small><math>\sqrt{3} \phi </math></small>
|<small><math>2.80252</math></small>
|-
|<small><math>c_{6,1}</math></small>
|<small><math>49.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{17}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{5-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{5-\sqrt{5}}}{2}</math></small>
|<small><math>0.831254</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\frac{1}{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5}}{2 \phi }}</math></small>
|<small><math>\sqrt{0.690983}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^3}</math></small>
|<small><math>3.07768</math></small>
|-
|<small><math>c_{7,1}</math></small>
|<small><math>56.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{3}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>0.93913</math></small>
|<small><math>\frac{\sqrt{\frac{\psi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{0.881966}</math></small>
|<small><math>\sqrt{\psi \phi ^3}</math></small>
|<small><math>3.47709</math></small>
|-
|<small><math>c_{8,1}</math></small>
|<small><math>60{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{5}\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>1</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|<small><math>1</math></small>
|<small><math>\sqrt{1}</math></small>
|<small><math>\sqrt{1.}</math></small>
|<small><math>\sqrt{2} \phi ^2</math></small>
|<small><math>3.70246</math></small>
|-
|<small><math>c_{9,1}</math></small>
|<small><math>66.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{7}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{2 \phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.09132</math></small>
|<small><math>\frac{\sqrt{\frac{\chi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\chi }{2 \phi }}</math></small>
|<small><math>\sqrt{1.19098}</math></small>
|<small><math>\sqrt{\chi \phi ^3}</math></small>
|<small><math>4.04057</math></small>
|-
|<small><math>c_{10,1}</math></small>
|<small><math>69.8{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{11}\right\}</math></small>
|<small><math>\phi c_{4,1}</math></small>
|<small><math>\frac{1+\sqrt{5}}{2 \sqrt{2}}</math></small>
|<small><math>1.14412</math></small>
|<small><math>\frac{\phi }{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^2}{2}}</math></small>
|<small><math>\sqrt{1.30902}</math></small>
|<small><math>\phi ^3</math></small>
|<small><math>4.23607</math></small>
|-
|<small><math>c_{11,1}</math></small>
|<small><math>72{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{6}\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.17557</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{1.38197}</math></small>
|<small><math>\sqrt{2} \sqrt{3-\phi } \phi ^2</math></small>
|<small><math>4.3525</math></small>
|-
|<small><math>c_{12,1}</math></small>
|<small><math>75.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{24}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>1.22474</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{1.5}</math></small>
|<small><math>\sqrt{3} \phi ^2</math></small>
|<small><math>4.53457</math></small>
|-
|<small><math>c_{13,1}</math></small>
|<small><math>81.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>1.30038</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(9-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{1.69098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(9-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>4.8146</math></small>
|-
|<small><math>c_{14,1}</math></small>
|<small><math>84.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{9}\right\}</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi } c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{2} \sqrt[4]{5} \sqrt{1+\sqrt{5}}</math></small>
|<small><math>1.345</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi }}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5} \phi }{2}}</math></small>
|<small><math>\sqrt{1.80902}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^5}</math></small>
|<small><math>4.9798</math></small>
|-
|<small><math>c_{15,1}</math></small>
|<small><math>90.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{7}\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>2 c_{4,1}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>1.41421</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2.}</math></small>
|<small><math>2 \phi ^2</math></small>
|<small><math>5.23607</math></small>
|-
|<small><math>c_{16,1}</math></small>
|<small><math>95.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{29}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>1.4802</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.19098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(11-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>5.48037</math></small>
|-
|<small><math>c_{17,1}</math></small>
|<small><math>98.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{31}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>1.51954</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(7+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.30902}</math></small>
|<small><math>\sqrt{\psi \phi ^5}</math></small>
|<small><math>5.62605</math></small>
|-
|<small><math>c_{18,1}</math></small>
|<small><math>104.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{8}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{4}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>1.58114</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{2.5}</math></small>
|<small><math>\sqrt{5} \sqrt{\phi ^4}</math></small>
|<small><math>5.8541</math></small>
|-
|<small><math>c_{19,1}</math></small>
|<small><math>108.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{9}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{10}{3}\right\}</math></small>
|<small><math>c_{3,1}+c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.61803</math></small>
|<small><math>\phi </math></small>
|<small><math>\sqrt{1+\phi }</math></small>
|<small><math>\sqrt{2.61803}</math></small>
|<small><math>\sqrt{2} \phi ^3</math></small>
|<small><math>5.9907</math></small>
|-
|<small><math>c_{20,1}</math></small>
|<small><math>110.2{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>1.64042</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.69098}</math></small>
|<small><math>\phi ^2 \sqrt{8-\phi ^2}</math></small>
|<small><math>6.07359</math></small>
|-
|<small><math>c_{21,1}</math></small>
|<small><math>113.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{19}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.67601</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{2.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\chi }{\phi }}</math></small>
|<small><math>6.20537</math></small>
|-
|<small><math>c_{22,1}</math></small>
|<small><math>120{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{10}\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\sqrt{3} c_{8,1}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>1.73205</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3.}</math></small>
|<small><math>\sqrt{6} \phi ^2</math></small>
|<small><math>6.41285</math></small>
|-
|<small><math>c_{23,1}</math></small>
|<small><math>124.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{41}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{\phi }+\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.7658</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{3.11803}</math></small>
|<small><math>\sqrt{\chi \phi ^5}</math></small>
|<small><math>6.53779</math></small>
|-
|<small><math>c_{24,1}</math></small>
|<small><math>130.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>1.81907</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.30902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\sqrt{5}}{\phi }}</math></small>
|<small><math>6.73503</math></small>
|-
|<small><math>c_{25,1}</math></small>
|<small><math>135.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}}</math></small>
|<small><math>1.85123</math></small>
|<small><math>\frac{\phi ^2}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^4}{2}}</math></small>
|<small><math>\sqrt{3.42705}</math></small>
|<small><math>\phi ^4</math></small>
|<small><math>6.8541</math></small>
|-
|<small><math>c_{26,1}</math></small>
|<small><math>138.6{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{12}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{7}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>1.87083</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{3.5}</math></small>
|<small><math>\sqrt{7} \phi ^2</math></small>
|<small><math>6.92667</math></small>
|-
|<small><math>c_{27,1}</math></small>
|<small><math>144{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{12}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{5}{2}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)}</math></small>
|<small><math>1.90211</math></small>
|<small><math>\sqrt{\phi +2}</math></small>
|<small><math>\sqrt{2+\phi }</math></small>
|<small><math>\sqrt{3.61803}</math></small>
|<small><math>\phi ^2 \sqrt{2 \phi +4}</math></small>
|<small><math>7.0425</math></small>
|-
|<small><math>c_{28,1}</math></small>
|<small><math>154.8{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>1.95167</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{1}{\phi ^2}}</math></small>
|<small><math>7.22598</math></small>
|-
|<small><math>c_{29,1}</math></small>
|<small><math>164.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{14}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{7}\right\}</math></small>
|<small><math>\phi c_{12,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{\frac{3}{2}} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.98168</math></small>
|<small><math>\sqrt{\frac{3}{2}} \phi </math></small>
|<small><math>\sqrt{\frac{3 \phi ^2}{2}}</math></small>
|<small><math>\sqrt{3.92705}</math></small>
|<small><math>\sqrt{3} \phi ^3</math></small>
|<small><math>7.33708</math></small>
|-
|<small><math>c_{30,1}</math></small>
|<small><math>180{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{15}\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>2 c_{8,1}</math></small>
|<small><math>2</math></small>
|<small><math>2.</math></small>
|<small><math>2</math></small>
|<small><math>\sqrt{4}</math></small>
|<small><math>\sqrt{4.}</math></small>
|<small><math>2 \sqrt{2} \phi ^2</math></small>
|<small><math>7.40492</math></small>
|-
|rowspan=4 colspan=6|
|rowspan=4 colspan=4|
<small><math>\phi</math></small> is the golden ratio:<br>
<small><math>\phi ^2-\phi -1=0</math></small><br>
<small><math>\frac{1}{\phi }+1=\phi</math></small>, and: <small><math>\phi+1=\phi^2</math></small><br>
<small><math>\frac{1}{\phi }::1::\phi ::\phi ^2</math></small><br>
<small><math>1/\phi</math></small> and <small><math>\phi</math></small> are the golden sections of <small><math>\sqrt{5}</math></small>:<br>
<small><math>\phi +\frac{1}{\phi }=\sqrt{5}</math></small>
|colspan=2|<small><math>\phi = (\sqrt{5} + 1)/2</math></small>
|<small><math>1.618034</math></small>
|-
|colspan=2|<small><math>\chi = (3\sqrt{5} + 1)/2</math></small>
|<small><math>3.854102</math></small>
|-
|colspan=2|<small><math>\psi = (3\sqrt{5} - 1)/2</math></small>
|<small><math>2.854102</math></small>
|-
|colspan=2|<small><math>\psi = 11/\chi = 22/(3\sqrt{5} + 1)</math></small>
|<small><math>2.854102</math></small>
|}
== The 5-cell 4-simplex ==
...
== The 16-cell 4-orthoplex ==
In 2-space we have the regular 8-point octagon, in 3-space the regular 8-point cube, and in 4-space the regular 8-point [[16-cell]].
A planar octagon with rigid edges of unit length has chords of length:
:<math>r_1=1,r_2=\sqrt{2+\sqrt{2}} \approx 1.848,r_3=\sqrt{2}+1 \approx 2.414,r_4=\sqrt{4 + \sqrt{8}} \approx 2.613</math>
The chord ratio <math>r_3=\sqrt{2}+1</math> is a geometrical proportion, the [[W:Silver ratio|silver ratio]]. Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_3-r_1-r_1=1/r_3 \approx 0.414</math>
Note that <math>r_3-2=1/r_3=\sqrt{2}-1</math>. The procedure rotates counterclockwise over three <math>r_3</math> chords of an {8/3} octagram. Over the first <math>r_3</math> chord the displacement is <math>\sqrt{2}+r_1</math>. Over the second <math>r_3</math> chord it moves in the opposite direction a distance of <math>-r_1</math> . Over the third <math>r_3</math> chord it moves a distance of <math>-r_1</math>.
If we embed the planar octagon in 3-space, we can make it skew, repositioning its vertices so that each is one unit-edge length distant from three others instead of two others, at the vertices of a unit-edge cube with chords of length:
:<math>r_1=1, r_2=\sqrt{2}, r_3=\sqrt{3}, r_4=\sqrt{2}</math>
If we embed this cube in 4-space, we can skew it some more, repositioning its vertices so that each is one unit-edge length distant from six others instead of three others, at the vertices of a unit-edge 4-polytope with chords of length:
:<math>r_1=1,r_2=1,r_3=1,r_4=\sqrt{2}</math>
All of its chords except its long diameters are the same unit length as its edge. In fact they are its 24 edges, and it is a 16-cell of radius <math>1/\sqrt{2}</math>.
[[File:octagon16cell.png|thumb|Orthogonal projection of a regular 16-cell to the [[16-cell#Projections|B<sub>4</sub> Coxeter plane]]. Only its edges are shown; its long diameter chords are not drawn. All 24 edges are the same length and none lie parallel to the projection plane. The octagon circumference is a Petrie polygon. The two disjoint squares lie in completely orthogonal central planes. The blue octagram is a Clifford polygon. ]]
The [[16-cell]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{3,3,4\}</math></small>. It has 8 vertices, 24 edges, 32 equilateral triangle faces, and 16 regular tetrahedron cells. It is the [[16-cell#Octahedral dipyramid|four-dimensional analogue of the octahedron]], and each of its four orthogonal central hyperplanes is an octahedron.
The only planar regular polygons found in the 16-cell are face triangles and central plane squares, but the 16-cell also contains a skew regular octagon, its [[W:Petrie polygon|Petrie polygon]].{{Efn|name=Petrie polygon of a honeycomb}} The chords of this regular octagon, which lies skew in 4-space, are those given above for the 16-cell, as opposed to those for the cube or the regular octagon in the plane. The 16-cell is a construct of 3 Petrie octagons which share the same 8 vertices but have disjoint sets of 8 edges each.
The regular octad has higher symmetry in 4-space than it does in 2-space. The 16-cell is the 4-[[w:Cross-polytope|orthoplex]], the simplest regular 4-polytope after the [[5-cell|4-simplex]]. All the larger regular convex 4-polytopes are compounds of the 16-cell. The regular octagon exhibits this high symmetry only when embedded in 4-space at the vertices of the 16-cell.
The 16-cell constitutes an [[W:Orthonormal basis|orthonormal basis]] for the choice of a 4-dimensional Cartesian reference frame, because its vertices define four orthogonal axes. The eight vertices of a unit-radius 16-cell are (±1, 0, 0, 0), (0, ±1, 0, 0), (0, 0, ±1, 0), (0, 0, 0, ±1). All vertices are connected by <math>\sqrt{2}</math> edges except opposite pairs.
The vertex coordinates of the 16-cell form 6 central squares lying in 6 pairwise [[W:Orthogonal|orthogonal]] coordinate planes. Great squares in opposite planes that do not share an axis (e.g. in the ''xy'' and ''wz'' planes) are completely disjoint (they do not intersect at any vertices). These planes are [[W:Completely orthogonal|completely orthogonal]].{{Efn|name=Six orthogonal planes of the Cartesian basis}}
Since the unit-radius coordinate system is convenient, let us derive the unit-radius 16-cell by skewing a unit-radius planar octagon, which has chords of length:
:<math>r_1=\sqrt{2-\sqrt{2}} \approx 0.765,r_2=\sqrt{2},r_3=\sqrt{2+\sqrt{2}} \approx 1.848,r_4=2</math>
We will need a planar octagon with rigid <math>r_2</math> chords, rather than one with rigid <math>r_1</math> edges. The octagon's <math>r_2</math> chords form two disjoint great squares, visible in the orthogonal projection, which we can reposition in 3-space to form a cube by making them parallel, and in 4-space to form a 16-cell by making them completely orthogonal.
Since the edges of the 16-cell are all the same length <math>r_1=\sqrt{2},r_2=\sqrt{2},r_3=\sqrt{2}</math>, those chords are distinct only in the context of a rotation. Each chord is a 4-vector with a length and a direction. The rotational curve over each <math>r_i</math> chord makes <math>i</math> 45° turns.
[[File:16-cell-orig.gif|thumb|Orthographic projection of the 8-point 16-cell <small><math>\{3,3,4\}</math></small> performing a double rotation.{{Sfn|Hise|2007}}]]
[[W:Rotations in 4-dimensional Euclidean space|Rotations in 4-dimensional Euclidean space]] can be seen as the composition of two 2-dimensional rotations in completely orthogonal planes. The general rotation in 4-space is a [[W:SO(4)#Double rotations|double rotation]] in pairs of completely orthogonal planes. Two completely orthogonal planes are called invariant planes of the rotation when all points in the plane rotate on circles that remain in the plane, even as the whole plane tilts sideways (like a coin flipping) into another plane. The two completely orthogonal rotations of each plane (like a wheel, and like a coin flipping) are simultaneous but independent, in that they are not geometrically constrained to turn at the same rate. However, the most circular kind of rotation (as opposed to an elliptical double rotation of a rigid spherical object) occurs when the completely orthogonal planes do rotate through the same angle in the same time interval. Such equi-angled double rotations are called [[w:SO(4)#Isoclinic_rotations|isoclinic]], also [[w:William_Kingdon_Clifford|Clifford]] displacements.
The <math>r_1</math> chords of the 16-cell form a Petrie polygon which zig-zags back and forth, in the left and right rotational directions, between two completely orthogonal great squares formed by <math>r_2</math> chords.
The <math>r_2</math> chords of two completely orthogonal great squares lie parallel and perpendicular to each other. A ''simple'' rotation of the 16-cell in ''one'' of those two square central planes rotates that square like a wheel, while the other square does not move.{{Efn|name=simple rotations}} The four vertices of the rotating square orbit on a great circle in the plane.
The <math>r_3</math> chords of the 16-cell form a circular helix, visible as a blue {8/3} octagram in the orthogonal projection. A ''double'' rotation of the 16-cell, in both of two completely orthogonal invariant <math>r_2</math> square planes at once by equal angles, moves the eight vertices along the circular helix over the <math>r_3</math> chords. The vertex motion is a [[w:Geodesic|geodesic]] circle orbit on the 3-sphere of a special kind: it does not lie in a central plane, its [[w:Winding_number|winding number]] is not 1 (it is 3 in this case), its circumference is not <math>2\pi</math>, and it moves in either a left or right handed circular spiral. We shall refer to such a chiral circle orbit as an ''isocline'', and to the skew polygram of its rotational chords as a ''Clifford polygon''.
The 16-cell is the simplest possible frame in which to [[16-cell#Rotations|observe 4-dimensional rotations]] because its characteristic rotations feature a single pair of invariant rotation planes. In the 16-cell an isoclinic rotation by 90° in any pair of invariant completely orthogonal square central planes takes every great square to its completely orthogonal great square in a twisting displacement, as the invariant planes tilt sideways 90° into each other's plane while rotating 90° internally. All the vertices move at once along the same circular helix geodesic isocline of <math>r_3</math> chords, displaced 90° in 8 orthogonal directions, and the rigid 16-cell assumes a new orientation in 4-space. When the 90° isoclinic rotation is continued in the same rotational direction through an additional 90°, each vertex is again displaced 90°, but from the new orientation in a direction orthogonal to its first 90° displacement. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. In 360° of isoclinic rotation over four <math>r_3</math> chords, each vertex makes six 90° turns and reaches its antipodal position.
The trajectory of each vertex over each 90° isoclinic rotational displacement is a one-eighth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>6\pi</math> over eight <math>r_3</math> chords, and also traces an ordinary great circle in the plane twice, over the four <math>r_2</math> edges of a great square in one of the two moving invariant rotation planes. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions just once and returns to its original position, and the 16-cell returns to its original orientation.
Because this is the isoclinic rotation of the 16-cell in its invariant edge planes we shall refer to it as the ''characteristic rotation of the 16-cell'', and note once again that it is Fontaine and Hurley's rotation over the <math>r_3</math> star polygon which constructs <math>1/r_3</math>.
== The 8-cell tesseract ==
The long diameter of the unit-edge [[W:Hypercube|hypercube]] of dimension <math>n</math> is <math>\sqrt{n}</math>, so the unit-edge [[w:Tesseract|4-hypercube, the 16-point (8-cell) tesseract,]] has chords:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
Uniquely in its 4-dimensional case, the hypercube's edge length equals its radius, like the hexagon. We call such polytopes ''radially equilateral'', because they can be constructed from equilateral triangles which meet at their center, each contributing two radii and an edge. The [[w:Cuboctahedron|cuboctahedron]] and the 24-cell are also radially equilateral.
[[File:8-cell.gif|thumb|Orthographic projection of the 16-point (8-cell) tesseract <small><math>\{4,3,3\}</math></small> performing a simple rotation about a plane in 4-space.{{Sfn|Hise|2007}} The stationary plane bisects the figure from front-left to back-right and top to bottom.]]
The [[W:Tesseract|tesseract]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{4,3,3\}</math></small>. It has 16 vertices, 32 edges, 24 square faces, and 8 cube cells. It is the four-dimensional analogue of the cube.
The 16-point tesseract is the convex hull of a compound of two 8-point 16-cells, in exact dimensional analogy to the way the 8-point cube is the convex hull of a [[W:Stellated octahedron|compound of two 4-point regular tetrahedra]]. The [[W:Demihypercube|demihypercubes]] occupy alternate vertices of the hypercubes. The diagonals of the square faces of the unit-edge, unit-radius tesseract are the <math>\sqrt{2}</math> edges of two unit-radius 16-cells, also the edges of the square central planes.
We can rotate the tesseract isoclinically the way we rotated the 16-cell, by 90° in completely orthogonal invariant square central planes, with the same effect on both alternate-position 16-cells. In the course of a 720° isoclinic rotation in invariant square central planes each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cell. The two skew {8/3} octagram Clifford polygons lie on two disjoint parallel isoclines of the same chirality, of circumference <math>6\pi</math> over <math>\sqrt{2}</math> chords. They form a circular double helix which intersects each vertex of the tesseract once.
The tesseract is the [[W:Dual polytope|dual polytope]] of the 16-cell. They have the same Petrie polygon, the regular skew octagon, but the tesseract is a construct of 4 Petrie octagons with disjoint sets of 8 tesseract edges each. We can construct the tesseract by skewing two planar octagons. Because the tesseract is radially equilateral (unlike the 16-cell), we use two octagons of unit-edge length to build the unit-radius tesseract. To start we embed the planar octagons in 4-space at the same point and make them completely orthogonal. Then we skew each planar octagon into a cube, so we have a compound of two completely orthogonal cubes, provided we skewed them both in the same direction. The 16 vertices will be the vertices of a tesseract with half its 32 edges missing.
Because the tesseract contains two 16-cells in alternate positions it has two sets of 6 orthogonal square central planes. Two angles are required to specify the relationship between two planes in 4-space. Pairs of square central planes within each 16-cell are 90° apart in one angle, and either 0° or 90° apart in the other angle. They are 90° apart in both angles if and only if they are completely orthogonal planes, 90° apart by isoclinic rotation, with no vertices in common. Otherwise they are 0° apart in one of the angles, 90° apart by simple rotation, and they intersect in one axis and lie in a common 3-dimensional hyperplane.{{Efn|A double rotation in which one of the two angles of rotation is 0°, so that one of the completely orthogonal invariant planes does not rotate, is called a simple rotation. Ordinary rotations observed in a 3-dimensional space are simple rotations.|name=simple rotations}}
A pair of square central planes from alternate-position 16-cells are 60° apart by isoclinic rotation, with their corresponding vertices 120° apart. The planes are not orthogonal or parallel, so they intersect in a line somewhere, but they have no vertices in common, they have no 3-dimensional hyperplane in common, and they cannot reach each other by simple rotation. Such pairs of objects are called [[W:Clifford parallel|Clifford parallel]] because all their corresponding pairs of vertices are the same distance apart, although they are not parallel in the usual sense, because they have a common center. Not only the alternate-position 16-cells' corresponding square central planes, but also the 16-cells themselves, are Clifford parallel objects. More generally, multiple disjoint instances of a 4-polytope which compound to make a larger 4-polytope are Clifford parallel objects.
== The 24-cell ==
[[File:24-cell vertex geometry.png|thumb|Planar geometry of the radially equilateral 24-cell, showing its 3 great circle polygons and its 4 chord lengths.]]
In 2-space we have the radially equilateral 6-point hexagon. In 3-space we have the radially equilateral 12-point cuboctahedron, with 4 hexagonal central planes. In 4-space we have the radially equilateral 24-point 24-cell, with 12 cuboctahedron central hyperplanes and 16 hexagonal central planes.
The [[24-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,4,3\}</math></small>. It has 24 vertices, 96 edges, 96 equilateral triangle faces, and 24 octahedron cells. It is the four-dimensional analogue of the cuboctahedron.
The 24-cell has the same chord set as the 4-hypercube tesseract:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
[[Image:24-cell.gif|thumb|Orthographic projection of the 24-point 24-cell <small><math>\{3,4,3\}</math></small> performing a simple rotation.{{Sfn|Hise|2007}} The 3-dimensional surface made of 24 octahedra is visible.]]
The 24-cell is [[W:Dual polytope|self-dual]], like the regular polygons and regular simplexes. It is the maximal regular construct of triangles and squares (with no pentagons). It is the convex hull of a compound of three disjoint 8-point 16-cells, rotated 60° isoclinically with respect to each other. Each of the three pairs of 16-cells is a tesseract. Each 24-cell edge is also a tesseract edge. The corresponding vertices of two 16-cells or two tesseracts are 120° apart by a <math>\sqrt{3}</math> chord. Each tesseract has 8 cube cells, and each cube has four <math>\sqrt{3}</math> long diameters. The <math>\sqrt{3}</math> chords joining the corresponding vertices of two tesseracts belong to the third tesseract as cell long diameters.
The 24-cell's Petrie polygon is the regular dodecagon {12}, which has chords:
:<math>r_1=\tfrac{\sqrt{3}-1}{\sqrt{2}} \approx 0.518,r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\tfrac{\sqrt{3}+1}{\sqrt{2}} \approx 1.932,r_6=\sqrt{4}</math>
Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_5-r_3+r_1+r_1-r_3=1/r_5</math>
when <math>r_1=1</math>. The procedure rotates counterclockwise over five <math>r_5</math> chords of a {12/5} dodecagram. In the system of unit-radius coordinates <math>r_1=1/r_5</math>.
The <math>r_1</math> and <math>r_5</math> chords of the planar dodecagon do not occur in the 24-cell, which is a construct of eight skew dodecagons with disjoint sets of twelve <math>\sqrt{1}</math> edges each. In the skew dodecagons the chord lengths are:
:<math>r_1=\sqrt{1},r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\sqrt{3},r_6=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
[[File:dodecagon24cell.png|thumb|Orthogonal projection of half a 24-cell to the [[24-cell#Geodesics|F<sub>4</sub> Coxeter plane]]. Only one Petrie dodecagon {12} of the 24-cell is shown. In a unit-radius 24-cell, all black lines are 24-cell edges of unit length, also tesseract edges. The two disjoint hexagons lie in Clifford parallel central planes. Blue chords are <math>\sqrt{2}</math> 16-cell edges, also isocline chords in square rotations. Green chords are <math>\sqrt{3}</math> distances between corresponding vertices of two 16-cells, also isocline chords in hexagonal rotations. Note the {12/5} dodecagram.]]
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_3=\sqrt{2}</math></small>]]
We can rotate the 24-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in completely orthogonal invariant great square planes, with the same effect on all three 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cells. The <math>r_3=\sqrt{2}</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Three Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_3</math> chords form a circular triple helix {24/9}=3{8/3} that intersects each 24-cell vertex once.
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_5=\sqrt{3}</math></small> ]]
We can also rotate the 24-cell isoclinically in 4 Clifford parallel invariant great hexagon planes containing its vertices, over <math>r_{5}=\sqrt{3}</math> isocline chords. This is the ''characteristic rotation of the 24-cell'' in its invariant edge planes, also Fontaine and Hurley's rotation over the <math>r_5</math> star polygon which constructs <math>1/r_5</math>. A complete hexagonal isoclinic revolution requires 720° like a complete square isoclinic revolution, but it is completed in 12 isoclinic displacements of 60° each rather than 8 isoclinic displacements of 90° each. The rotational curve over each 120° <math>r_5</math> chord makes five 30° turns. Two Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_5</math> chords form a circular double helix {24/10}=2{12/5} that intersects each 24-cell vertex once.
In the 24-cell the characteristic isoclinic rotation by 60° in any invariant hexagon central plane takes every great hexagon to a Clifford parallel great hexagon in a twisting displacement, as all the central planes tilt sideways 60° while rotating 60° internally. It also takes every great square to a Clifford parallel great square in another 16-cell; it takes every 16-cell to another 16-cell. The 16-cells revolve within the 24-cell as well as rotating within it. All 24 vertices move at once on two Clifford parallel geodesic isoclines, displaced 120° in different directions.
The trajectory of each vertex over each 60° isoclinic rotational displacement is a one-twelfth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>10\pi</math> over twelve <math>\sqrt{3}</math> chords, and also traces an ordinary great circle in the plane twice, over the six <math>\sqrt{1}</math> edges of a great hexagon in a moving invariant rotation plane. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions just once and returns to its original position, and the 24-cell returns to its original orientation.
== The 600-cell ==
[[Image:600-cell.gif|thumb|Orthographic projection of the 120-point 600-cell <small><math>\{3,3,5\}</math></small> performing a simple rotation.{{Sfn|Hise|2011}} The 3-dimensional surface made of 600 tetrahedra is visible. Invisible in this rendering are 25 inscribed instances of the 24-cell (above), which occur in the 600-cell as interior boundary envelopes.]]
The [[600-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,3,5\}</math></small>. It has 120 vertices, 720 edges, 1200 equilateral triangle faces, and 600 tetrahedron cells. It is the four-dimensional analogue of the icosahedron.
The 600-cell rounds out the 24-cell by adding 96 more vertices (four more disjoint 24-cells) between the 24-cell's existing 24 vertices, in effect adding twenty-four more distinct 24-cells inscribed in the 600-cell. The new surface thus formed is a honeycomb of smaller, more numerous cells: tetrahedra of edge length <math>\phi^{-1} \approx 0.618</math> instead of octahedra of edge length <math>\sqrt{1}</math>. It encloses the <math>\sqrt{1}</math> edges of the 24-cells, which become invisible interior chords in the 600-cell, like the <math>\sqrt{2}</math> and <math>\sqrt{3}</math> chords.
Since the tetrahedra are made of shorter triangle edges than the octahedra (by a factor of <math>\phi^{-1}</math>, the inverse golden ratio), the 600-cell is not radially equilateral like the 24-cell and the tesseract. Like them it is radially triangular in a special way, but one in which [[w:Golden_triangle_(mathematics)|golden triangles]] rather than equilateral triangles meet at the center.
In 2-space we have the ''radially golden'' [[W:Decagon#The golden ratio in decagon|regular decagon]]. In 3-space we have the radially golden 30-point [[W:icosidodecahedron|icosidodecahedron]], with 6 decagon central planes. In 4-space we have the radially golden 120-point 600-cell, with 60 icosidodecahedron central hyperplanes and 72 decagon central planes.
The 600-cell's Petrie polygon is the regular [[w:Triacontagon|triacontagon {30}]]. The unit-radius planar {30}-gon has these distinct chords:
:<math>r_1=2 \sin (\tfrac{\pi}{15}/2) \approx 0.209</math>
:<math>r_2=2 \sin (\tfrac{2\pi}{15}/2) \approx 0.416</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{4\pi}{15}/2) \approx 0.813</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{7\pi}{15}/2) \approx 1.338</math>
:<math>r_8=2 \cos (\tfrac{7\pi}{15}/2) \approx 1.486</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{11}=2 \cos (\tfrac{4\pi}{15}/2) \approx 1.827</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \cos (\tfrac{2\pi}{15}/2) \approx 1.956</math>
:<math>r_{14}=2 \cos (\tfrac{\pi}{15}/2) \approx 1.989</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Only the chord lengths <math>r_3</math>, <math>r_5</math>, <math>r_6</math>, <math>\sqrt{2}</math>, <math>r_9</math>, <math>r_{10}</math>, <math>r_{12}</math>, <math>r_{15}</math> occur in the 600-cell, which is a construct of 24 Petrie {30}-gons of edge length <math>r_3</math>, six of which intersect in each icosahedral vertex figure. In the skew {30}-gons the chord lengths are:
[[File:600-cell vertex geometry.png|thumb|Planar geometry of the 600-cell, showing its 5 regular great circle polygons and its 8 chord lengths with angles of arc. The golden ratio governs the fractional roots of every other chord, and the radial golden triangles which meet at the center.|400x400px]]
:<math>r_1=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_2=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}=\text{24-cell-}r_2</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}</math>
:<math>r_8=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}=\text{16-cell-}r_3</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}=\text{24-cell-}r_5</math>
:<math>r_{11}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{14}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="7" |15 chords (4 distinct 180° pairs) make 4 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>r_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>r_{15}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>r_1</math>
|36°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}=2{15/7}
|144°
| rowspan="3" |<math>r_{14}</math>
|- style="background: palegreen;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: palegreen;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>r_2</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|144°
| rowspan="3" |<math>r_{13}</math>
|- style="background: gainsboro;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: gainsboro;" |
|0.618~
|1.902~
|- style="background: yellow;" |
| rowspan="3" |<math>r_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |[[File:V1 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>r_{12}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_4</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|120°
| rowspan="3" |<math>r_{11}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_5</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |[[File:V2 dodecahedron.png|100px]]<br>Dodecahedron
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>r_{10}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: yellow;" |
| rowspan="3" |<math>r_{6}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |[[File:V3 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>r_{9}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: seashell;" |
| rowspan="3" |<math>r_{7}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |[[File:V4 icosidodecahedron.png|100px]]<br>Icosidodecahedron
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>r_{8}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The list of 600-cell chords <math>r_{i}</math> can be rearranged into a table of 8 rows and 2 columns with a pair of 180° complements in each row. The short chord and long chord each have their characteristic {30}-gon. Each row identifies a discrete isoclinic rotation of the 600-cell in invariant central planes containing the edges of the short chord {30}-gon, over the isocline chords of the long chord {30}-gon, the rotation's Clifford polygon.
Each distinct pair of complementary chord lengths is identified with a distinct [[w:600-cell#Polyhedral sections|polyhedral section of the 600-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 7 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>\phi^{-1}</math> is a icosahedron vertex figure, and the largest section at radial distance <math>\sqrt{2}</math> is an [[W:Icosidodecahedron|icosidodecahedron]] central section bisecting the 600-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>\sqrt{2}</math> the successive complement-radius polyhedra decrease in size, to the antipodal icosahedron vertex figure at distance <math>\sqrt{2+\phi}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 7 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section).
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_8=\sqrt{2}</math></small>]]
We can rotate the 600-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in two completely orthogonal invariant great square planes over <math>r_8=\sqrt{2}</math> isocline chords, with the same effect on 15 disjoint 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_8</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Fifteen Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_8</math> chords form a circular helix of 15 twisted parallel strands 5{24/9}=15{8/3} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_polygon_30-7.svg|thumb|left|150px|{30/7} <small><math>r_7=\sqrt{2}</math></small>]]
In the 600-cell this 90° isoclinic rotation in completely orthogonal great square planes takes place over the <math>r_7=\sqrt{2}</math> chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/7} polygon is a skew helix with each <math>r_7</math> edge belonging to a distinct great square. The vertices of the invariant great squares of this rotation each make seven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 90° <math>r_7</math> isocline chord makes seven 12° turns. Four Clifford parallel {30/7} geodesic isoclines of circumference <math>14\pi</math> over <math>r_7</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_{11}=\sqrt{3}</math></small> ]]
We can also rotate the 600-cell isoclinically in the characteristic rotation of the 24-cell, by 60° in great hexagon planes, with the same effect on 5 disjoint 24-cells. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions of its 24-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_{5}</math> chord is the 24-cell <math>r_2</math> chord, and the <math>r_{10}</math> chord is the 24-cell <math>r_5</math> chord. The rotational curve over each <math>r_{10}</math> chord makes five 30° turns. Ten Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_{10}</math> chords form a circular helix of 10 twisted parallel strands 5{24/10}=10{12/5} that intersects each 600-cell vertex once.
In the 600-cell this 60° isoclinic rotation in great hexagon planes takes place over <math>r_{4}=\sqrt{1}</math> edge chords and <math>r_{11}=\sqrt{3}</math> isocline chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/11} polygon is a skew helix with each <math>r_{11}</math> chord the <math>\sqrt{3}</math> diagonal of a distinct great hexagon. The vertices of the invariant great hexagons of this rotation each make eleven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 120° <math>r_{11}</math> isocline chord makes eleven 12° turns. Four Clifford parallel {30/11} geodesic isoclines of circumference <math>22\pi</math> over <math>r_{11}</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_figure_2(15,4).svg|thumb|left|150px|{30/8}=2{15/4} <small><math>r_{13}=\sqrt{1}</math></small>]]
We can also rotate the 600-cell isoclinically in 12 Clifford parallel invariant decagon central planes containing its <math>r_{3}</math> edges, over <math>r_{13}=\sqrt{1}</math> isocline chords. This is the ''characteristic rotation of the 600-cell'' in its invariant edge planes. Its Clifford polygon is a skew {15/4} pentadecagram of <math>r_{13}</math> chords. The <math>r_{4}</math> chord is the 24-cell <math>r_2</math> chord. Successive <math>r_{13}</math> chords are edges of different 24-cells. The rotational curve over each <math>r_{13}</math> chord makes two 30° turns. Eight Clifford parallel {15/4} pentadecagon geodesic isoclines of circumference <math>5\pi</math> over <math>r_{13}</math> chords form a circular helix of eight twisted parallel strands 4{30/8}=8{15/4} that intersects each 600-cell vertex once.
In the 600-cell the characteristic isoclinic rotation by 36° in any invariant decagon central plane takes every great decagon to a Clifford parallel great decagon in a twisting displacement, as all the central planes tilt sideways 36° while rotating 36° internally. It also takes every great hexagon to a Clifford parallel great hexagon in another 24-cell, and every great square to a Clifford parallel great square in another 16-cell; it takes 24-cells to a non-disjoint 24-cell and 16-cells to a 16-cell in another 24-cell. The 24-cells revolve within the 600-cell, as the 16-cells revolve within the 24-cells. All 120 vertices move at once on eight Clifford parallel geodesic isoclines, displaced 60° in different directions.
The trajectory of each vertex over each 36° isoclinic rotational displacement is a one-fifteenth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>5\pi</math> over 15 <math>r_5</math> chords, and also traces an ordinary great circle in the plane 3 times, over the 5 edges of a great pentagon in a moving invariant rotation plane. In the course of a complete isoclinic revolution each vertex departs from 15 vertex positions just once and returns to its original position, and the 600-cell returns to its original orientation.
{{Clear}}
[[File:Regular_star_figure_6(5,2).svg|thumb|left|150px|{30/12}=6{5/2} <small><math>r_{12}=\sqrt{3.618\sim}</math></small>]]
In the 600-cell there is another distinct isoclinic rotation taking decagon planes to each other, over 144° <math>r_{12}</math> isocline chords. It also takes disjoint 24-cells to each other. This rotation has period 5 and visits every 12th vertex of a 600-cell Petrie polygon. Its Clifford polygon is a skew {5/2} pentagram of <math>r_{12}</math> chords. The invariant central planes of this rotation each intersect only one vertex of the 600-cell, which makes two orbits of a great pentagon within the moving invariant plane in the course of one complete isoclinic revolution of period 5. The rotational curve over each <math>r_{12}</math> chord makes twelve 12° turns. 24 Clifford parallel {5/2} pentagram geodesic isoclines of circumference <math>4\pi</math> over five <math>r_{12}</math> chords form a circular helix of 24 twisted parallel strands 4{30/12}=24{5/2} that intersects each 600-cell vertex once.
{{Clear}}
== Finally the 120-cell ==
The [[120-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{5,3,3\}</math></small>. It has 600 vertices, 1200 edges, 720 pentagon faces, and 120 dodecahedron cells. It is the four-dimensional analogue of the dodecahedron.
The 120-cell is the [[W:Dual polytope|dual polytope]] of the 600-cell. They have the same Petrie polygon, the regular skew triacontagon {30}, but the 120-cell is a construct of 40 Petrie {30}-gons of edge length <math>c_1</math>, two of which intersect in each tetrahedral vertex figure.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="9" |30 chords (15 180° pairs) make 15 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>c_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>c_{30}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>c_1</math>
|15.5~°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}
|164.5~°
| rowspan="3" |<math>c_{29}</math>
|- style="background: palegreen;" |
|{{radic|0.073~}}
|{{radic|3.927~}}
|- style="background: palegreen;" |
|0.270~
|1.982~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_2</math>
|25.2~°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|154.8~°
| rowspan="3" |<math>c_{28}</math>
|- style="background: gainsboro;" |
|{{radic|0.191~}}
|{{radic|3.809~}}
|- style="background: gainsboro;" |
|0.437~
|1.952~
|- style="background: yellow;" |
| rowspan="3" |<math>c_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>c_{27}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_4</math>
|41.4~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|138.6~°
| rowspan="3" |<math>c_{26}</math>
|- style="background: gainsboro;" |
|{{radic|0.5}}
|{{radic|3.5}}
|- style="background: gainsboro;" |
|0.707~
|1.871~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_5</math>
|44.5~°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|135.5~°
| rowspan="3" |<math>c_{25}</math>
|- style="background: palegreen;" |
|{{radic|0.573~}}
|{{radic|3.427~}}
|- style="background: palegreen;" |
|0.757~
|1.851~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_6</math>
|49.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|130.9~°
| rowspan="3" |<math>c_{24}</math>
|- style="background: gainsboro;" |
|{{radic|0.691~}}
|{{radic|3.309~}}
|- style="background: gainsboro;" |
|0.831~
|1.819~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_7</math>
|56°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|124°
| rowspan="3" |<math>c_{23}</math>
|- style="background: gainsboro;" |
|{{radic|0.882~}}
|{{radic|3.118~}}
|- style="background: gainsboro;" |
|0.939~
|1.766~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_8</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>c_{22}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_9</math>
|66.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|113.9~°
| rowspan="3" |<math>c_{21}</math>
|- style="background: gainsboro;" |
|{{radic|1.191~}}
|{{radic|2.809~}}
|- style="background: gainsboro;" |
|1.091~
|1.676~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{10}</math>
|69.8~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|110.2~°
| rowspan="3" |<math>c_{20}</math>
|- style="background: gainsboro;" |
|{{radic|1.309~}}
|{{radic|2.691~}}
|- style="background: gainsboro;" |
|1.144~
|1.640~
|- style="background: yellow;" |
| rowspan="3" |<math>c_{11}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>c_{19}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>c_{18}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{13}</math>
|81.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|98.9~°
| rowspan="3" |<math>c_{17}</math>
|- style="background: gainsboro;" |
|{{radic|1.691~}}
|{{radic|2.309~}}
|- style="background: gainsboro;" |
|1.300~
|1.520~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{14}</math>
|84.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|95.5~°
| rowspan="3" |<math>c_{16}</math>
|- style="background: gainsboro;" |
|{{radic|0.809~}}
|{{radic|2.191~}}
|- style="background: gainsboro;" |
|1.345~
|1.480~
|- style="background: seashell;" |
| rowspan="3" |<math>c_{15}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>c_{15}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The [[User:Dc.samizdat/Golden chords of the 120-cell#Thirty distinguished distances|table above]] of 30 chords <math>c_{t}</math> can be rearranged into a table of 16 rows and 2 columns with a pair of 180° complements in each row. This table first appears in [[w:Regular_Polytopes_(book)|''Regular Polytopes'']] (1947),{{Sfn|Coxeter|1973|loc=Table V(v): Simplified sections of {5,3,3} beginning with a vertex|pp=300-301}} where Coxeter identified each row with a distinct [[w:120-cell#Concentric_hulls|polyhedral section of the 120-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 29 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>c_1</math> is a tetrahedron vertex figure, and the largest section at radial distance <math>c_{15}</math> is a central section bisecting the 120-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>c_{15}</math> the successive complement-radius polyhedra decrease in size, to the antipodal tetrahedron vertex figure at distance <math>c_{29}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 29 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section). Each section also lies completely orthogonal to a congruent section.
Only 8 of the 30 chords in the table occur in the 600-cell and the planar {30)-gon. The 120-cell's additional chords arise originally from the regular 5-cell, in its interaction with the other regular 4-polytopes that compound to make the 120-cell. Since all those polytopes except the 5-cell occur in the 600-cell, and the 600-cell and the 120-cell have the same symmetry group, the 5-cell's symmetry group is what's new in the 120-cell.
...
{{Clear}}
== Conclusions ==
Fontaine and Hurley's discovery is more than a geometric formula for the reciprocal of a regular ''n''-polygon diagonal. It also yields the discrete sequence of isocline chords of the characteristic isoclinic rotation of a ''d''-dimensional polytope in its invariant edge planes. The characteristic rotational chord sequence of the ''d''-polytope can be represented geometrically in two dimensions on a distinct star polygon, but it lies on a geodesic circle through ''d''-dimensional space. Fontaine and Hurley discovered the geodesic topology of polytopes generally. Their procedure will reveal the geodesics of arbitrary non-uniform polytopes, since it can be applied to a polytope of any dimensionality and irregularity, by first fitting the polytope to the smallest regular polygon whose chords include its chords. [If what is meant by this is its Petrie polygon, it is not quite necessary or possible with respect to the planar polygon chords, e.g. the planar Petrie polygon of the 600-cell does not contain the <math>\sqrt{2}</math> chord. But perhaps it would work if the fit is to the smallest regular skew polygon in the ''d''-space.]
The discovery of a chordal construction for discrete isoclinic rotations generally closes the circuit on Kappraff and Adamson's discovery of a rotational connection between dynamical systems, Steinbach's golden fields, and Coxeter's Euclidean geometry of ''n'' dimensions. Application of the Fontaine and Hurley procedure in the 120-cell demonstrates why the connection exists: because polytope sequences generally, from Steinbach's golden chord sequences in polygons, to sequences of star polygons in isoclinic rotations, to subsumption relations in the sequence of regular 4-polytopes, arise as expressions of the reflections and rotations of distinct Coxeter symmetry groups, when those various groups interact.
== Appendix: Sequence of regular 4-polytopes ==
{{Regular convex 4-polytopes|wiki=W:|columns=7}}
== Notes ==
{{Notelist}}
== Citations ==
{{Reflist}}
== References ==
{{Refbegin}}
* {{Cite journal | last=Steinbach | first=Peter | year=1997 | title=Golden fields: A case for the Heptagon | journal=Mathematics Magazine | volume=70 | issue=Feb 1997 | pages=22–31 | doi=10.1080/0025570X.1997.11996494 | jstor=2691048 | ref={{SfnRef|Steinbach|1997}} }}
* {{Cite journal | last=Steinbach | first=Peter | year=2000 | title=Sections Beyond Golden| journal=Bridges: Mathematical Connections in Art, Music and Science | issue=2000 | pages=35-44 | url=https://archive.bridgesmathart.org/2000/bridges2000-35.pdf | ref={{SfnRef|Steinbach|2000}}}}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Jablan | first2=Slavik | last3=Adamson | first3=Gary | last4=Sazdanovich | first4=Radmila | year=2004 | title=Golden Fields, Generalized Fibonacci Sequences, and Chaotic Matrices | journal=Forma | volume=19 | pages=367-387 | url=https://archive.bridgesmathart.org/2005/bridges2005-369.pdf | ref={{SfnRef|Kappraff, Jablan, Adamson & Sazdanovich|2004}} }}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Adamson | first2=Gary | year=2004 | title=Polygons and Chaos | journal=Dynamical Systems and Geometric Theories | url=https://archive.bridgesmathart.org/2001/bridges2001-67.pdf | ref={{SfnRef|Kappraff & Adamson|2004}} }}
* {{Cite journal | last1=Fontaine | first1=Anne | last2=Hurley | first2=Susan | year=2006 | title=Proof by Picture: Products and Reciprocals of Diagonal Length Ratios in the Regular Polygon | journal=Forum Geometricorum | volume=6 | pages=97-101 | url=https://scispace.com/pdf/proof-by-picture-products-and-reciprocals-of-diagonal-length-1aian8mgp9.pdf }}
{{Refend}}
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/* The 600-cell */
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= Golden chords of the 120-cell =
{{align|center|David Brooks Christie}}
{{align|center|dc@samizdat.org}}
{{align|center|Draft in progress}}
{{align|center|January 2026 - June 2026}}
<blockquote>Steinbach discovered the formula for the ratios of diagonal to side in the regular polygons. Fontaine and Hurley extended this result, discovering a formula for the reciprocal of a regular polygon chord derived geometrically from the chord's star polygon. We observe that these findings in plane geometry apply more generally, to polytopes of any dimensionality. Fontaine and Hurley's geometric procedure for finding the reciprocals of the chords of a regular polygon from their star polygons also finds the rotational geodesics of any polytope of any dimensionality.</blockquote>
== Introduction ==
Steinbach discovered the Diagonal Product Formula and the Golden Fields family of ratios of diagonal to side in the regular polygons. He showed how this family extends beyond the pentagon {5} with its well-known golden bisection proportional to 𝜙, finding that the heptagon {7} has an analogous trisection, the nonagon {9} has an analogous quadrasection, and the hendecagon {11} has an analogous pentasection, an extended family of golden proportions with quasiperiodic properties.
Kappraff and Adamson extended these findings in plane geometry to a theory of Generalized Fibonacci Sequences, showing that the Golden Fields not only do not end with the hendecagon, they form an infinite number of periodic trajectories when operated on by the Mandelbrot operator. They found a relation between the edges of star polygons and dynamical systems in the state of chaos, revealing a connection between chaos theory, number, and rotations in Coxeter Euclidean geometry.
Fontaine and Hurley examined Steinbach's finding that the length of each chord of a regular polygon is both the product of two chords and the sum of a set of smaller chords, so that in rotations to add is to multiply. They illustrated Steinbach's sets of additive chords lying parallel to each other in the plane (pointing in the same direction), and by applying Steinbach's formula more generally they found another summation relation of signed parallel chords (pointing in opposite directions) which relates each chord length to its reciprocal, and relates the summation to a distinct star polygon rotation.
We examine these remarkable findings (which stem from study of the chords of humble regular polygons) in higher-dimensional spaces, specifically in the chords, polygons and rotations of the [[120-cell]], the largest four-dimensional regular convex polytope.
== Visualizing the 120-cell ==
{| class="wikitable floatright" width="400"
|style="vertical-align:top"|[[File:120-cell.gif|200px]]<br>Orthographic projection of the 600-point 120-cell <small><math>\{5,3,3\}</math></small> performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]].{{Sfn|Hise|2011|loc=File:120-cell.gif|ps=; "Created by Jason Hise with Maya and Macromedia Fireworks. A 3D projection of a 120-cell performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]]."}} In this simplified rendering only the 120-cell's own edges are shown; its 29 interior chords are not rendered. Therefore even though it is translucent, only its outer surface is visible. The complex interior parts of the 120-cell, all its inscribed 5-cells, 16-cells, 8-cells, 24-cells, 600-cells and its much larger inventory of polyhedra, are completely invisible in this view, as none of their edges are rendered at all.
|style="vertical-align:top"|[[File:Ortho solid 016-uniform polychoron p33-t0.png|200px]]<br>Orthographic projection of the 600-point [[W:Great grand stellated 120-cell|great grand stellated 120-cell]] <small><math>\{\tfrac{5}{2},3,3\}</math></small>.{{Sfn|Ruen: Great grand stellated 120-cell|2007}} The 120-cell is its convex hull. The projection to the left renders only the 120-cell's shortest chord, its 1200 edges. The projection above also renders only one of the 120-cell's 30 chords, the edges of its 120 inscribed regular 5-cells. The 120-cell itself (the convex hull) is invisible in this view, as its edges are not rendered.
|}
[[120-cell#Geometry|The 120-cell is the maximally complex regular 4-polytope]], containing inscribed instances of every regular 1-, 2-, 3-, and 4-polytope, except the regular polygons of more than {15} sides.
The 120-cell is the convex hull of a regular [[120-cell#Relationships among interior polytopes|compound of each of the 6 regular convex 4-polytopes]]. They are the [[5-cell|5-point (5-cell) 4-simplex]], the [[16-cell|8-point (16-cell) 4-orthoplex]], the [[W:Tesseract|16-point (8-cell) tesseract]], the [[24-cell|24-point (24-cell)]], the [[600-cell|120-point (600-cell)]], and the [[120-cell|600-point (120-cell)]]. The 120-cell is the convex hull of a compound of 120 disjoint regular 5-cells, of 75 disjoint 16-cells, of 25 disjoint 24-cells, and of 5 disjoint 600-cells.
The 120-cell contains an even larger inventory of irregular polytopes, created by the intersection of multiple instances of these component regular 4-polytopes. Many are quite unexpected, because they do not occur as components of any regular polytope smaller than the 120-cell. As just one example among the [[120-cell#Concentric hulls|sections of the 120-cell]], there is an irregular 24-point polyhedron with 16 triangle faces and 4 nonagon {9} faces.{{Sfn|Moxness|}}
Most renderings of the 120-cell, like the rotating projection here, only illustrate its outer surface, which is a honeycomb of face-bonded dodecahedral cells. Only the objects in its 3-dimensional surface are rendered, namely the 120 dodecahedra, their pentagon faces, and their edges. Although the 120-cell has chords of 30 distinct lengths, in this kind of simplified rendering only the 120-cell's own edges (its shortest chord) are shown. Its 29 interior chords, the edges of objects in the interior of the 120-cell, are not rendered, so interior objects are not visible at all.
Visualizing the complete interior of the 600-vertex 120-cell in a single image is impractical because of its complexity. Only four 120-cell edges are incident at each vertex, but [[120-cell#Chords|600 chords (of all 30 lengths)]] are incident at ''each'' vertex.
== Compounds in the 120-cell ==
The 8-point (16-cell), not the 5-point (5-cell), is the smallest building block; it compounds to every larger regular 4-polytope. The 5-point (5-cell) does compound to the 600-point (120-cell), but it does not fit into any smaller regular 4-polytope.
The 8-point (16-cell) compounds by 2 in the 16-point (8-cell), and by 3 in the 24-point (24-cell). The 16-point (8-cell) compounds in the 24-point (24-cell) by 3 non-disjoint instances of itself, with each of the 24 vertices shared by two 16-point (8-cells). The 24-point (24-cell) compounds by 5 disjoint instances of itself in the 120-point (600-cell), and the 120-point (600-cell) compounds by 5 disjoint instances of itself in the 600-point (120-cell).
The 24-point (24-cell) also compounds by 5<sup>2</sup> non-disjoint instances of itself in the 120-point (600-cell); it compounds in 5 disjoint instances of itself, 10 (not 5) different ways. Whichever set of 5 disjoint 24-point (24-cells) are assembled, the resulting 120-point (600-cell) contains 25 distinct 24-point (24-cells), not just 5 (or 10). This implies that 15 disjoint 8-point (16-cells) will construct a 120-point (600-cell), which will contain 75 distinct 8-point (16-cells).
The 600-point (120-cell) is 5 disjoint 120-point (600-cells), just 2 different ways (not 5 or 10 ways), so it is 10 distinct 120-point (600-cells). This implies that the 8-point (16-cell) compounds by 3 times 5<sup>2</sup> (75) disjoint instances of itself in the 600-point (120-cell), which contains 3<sup>2</sup> times 5<sup>2</sup> (225) distinct instances of the 24-point (24-cell), and 3<sup>3</sup> times 5<sup>2</sup> (675) distinct instances of the 8-point (16-cell).
These facts were discovered painstakingly by various researchers, and no one has found a general rule governing subsumption relations among regular polytopes. The reasons for some of their numeric incidence relations are far from obvious. [[W:Pieter Hendrik Schoute|Schoute]] was the first to see that the 120-point (600-cell) is a compound of 5 24-point (24-cells) ''10 different ways'', and after he saw it a hundred years lapsed until Denney, Hooker, Johnson, Robinson, Butler & Claiborne proved his result, and showed why.{{Sfn|Denney, Hooker, Johnson, Robinson, Butler & Claiborne|2020|loc=''The geometry of H4 polytopes''}}
So much for the compounds of 16-cells. The 120-cell is also the convex hull of the compound of 120 disjoint regular 5-cells. That stellated compound (without its convex hull of 120-cell edges) is the [[w:Great_grand_stellated_120-cell|great grand stellated 120-cell]] illustrated above, the final regular [[W:Stellation|stellation]] of the 120-cell, and the only [[W:Schläfli-Hess polychoron|regular star 4-polytope]] to have the 120-cell for its convex hull. The edges of the great grand stellated 120-cell are <math>\phi^6</math> as long as those of its 120-cell [[W:List of polyhedral stellations#Stellation process|stellation core]] deep inside.
The compound of 120 disjoint 5-point (5-cells) can be seen to be equivalent to the compound of 5 disjoint 120-point (600-cells), as follows. Beginning with a single 120-point (600-cell), expand each vertex into a regular 5-cell, by adding 4 new equidistant vertices, such that the 5 vertices form a regular 5-cell inscribed in the 3-sphere. The 120 5-cells are disjoint, and the 600 vertices form 5 disjoint 120-point (600-cells): a 120-cell.
== Thirty distinguished distances ==
The 30 numbers listed in the table are all-important in Euclidean geometry. A case can be made on symmetry grounds that their squares are the 30 most important numbers between 0 and 4. The 30 rows of the table are the 30 distinct [[120-cell#Geodesic rectangles|chord lengths of the unit-radius 120-cell]], the largest regular convex 4-polytope. Since the 120-cell subsumes all smaller regular polytopes, its 30 chords are the complete chord set of all the regular polytopes that can be constructed in the first four dimensions of Euclidean space, except for regular polygons of more than 15 sides.
{| class="wikitable" style="white-space:nowrap;text-align:center"
!rowspan=2|<math>c_t</math>
!rowspan=2|arc
!rowspan=2|<small><math>\left\{\frac{30}{n}\right\}</math></small>
!rowspan=2|<math>\left\{p\right\}</math>
!rowspan=2|<small><math>m\left\{\frac{k}{d}\right\}</math></small>
!rowspan=2|Steinbach roots
!colspan=7|Chord lengths of the unit 120-cell
|-
!colspan=5|unit-radius length <math>c_t</math>
!colspan=2|unit-edge length <math>c_t/c_1</math><br>in 120-cell of radius <math>c_8=\sqrt{2}\phi^2</math>
|-
|<small><math>c_{1,1}</math></small>
|<small><math>15.5{}^{\circ}</math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math>c_{4,1}-c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7-3 \sqrt{5}}</math></small>
|<small><math>0.270091</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi ^2}</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^4}}</math></small>
|<small><math>\sqrt{0.072949}</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|-
|<small><math>c_{2,1}</math></small>
|<small><math>25.2{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{2}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{15\right\}</math></small>
|<small><math>\frac{1}{2} \left(c_{18,1}-c_{4,1}\right)</math></small>
|<small><math>\frac{\sqrt{3-\sqrt{5}}}{2}</math></small>
|<small><math>0.437016</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi }</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.190983}</math></small>
|<small><math>\phi </math></small>
|<small><math>1.61803</math></small>
|-
|<small><math>c_{3,1}</math></small>
|<small><math>36{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{3}\right\}</math></small>
|<small><math>\left\{10\right\}</math></small>
|<small><math>3 \left\{\frac{10}{3}\right\}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right) c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right)</math></small>
|<small><math>0.618034</math></small>
|<small><math>\frac{1}{\phi }</math></small>
|<small><math>\sqrt{\frac{1}{\phi ^2}}</math></small>
|<small><math>\sqrt{0.381966}</math></small>
|<small><math>\sqrt{2} \phi </math></small>
|<small><math>2.28825</math></small>
|-
|<small><math>c_{4,1}</math></small>
|<small><math>41.4{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{7}\right\}</math></small>
|<small><math>\frac{c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>0.707107</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{1}{2}}</math></small>
|<small><math>\sqrt{0.5}</math></small>
|<small><math>\phi ^2</math></small>
|<small><math>2.61803</math></small>
|-
|<small><math>c_{5,1}</math></small>
|<small><math>44.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{4}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{\frac{15}{2}\right\}</math></small>
|<small><math>\sqrt{3} c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-3 \sqrt{5}}</math></small>
|<small><math>0.756934</math></small>
|<small><math>\frac{\sqrt{\frac{3}{2}}}{\phi }</math></small>
|<small><math>\sqrt{\frac{3}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.572949}</math></small>
|<small><math>\sqrt{3} \phi </math></small>
|<small><math>2.80252</math></small>
|-
|<small><math>c_{6,1}</math></small>
|<small><math>49.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{17}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{5-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{5-\sqrt{5}}}{2}</math></small>
|<small><math>0.831254</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\frac{1}{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5}}{2 \phi }}</math></small>
|<small><math>\sqrt{0.690983}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^3}</math></small>
|<small><math>3.07768</math></small>
|-
|<small><math>c_{7,1}</math></small>
|<small><math>56.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{3}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>0.93913</math></small>
|<small><math>\frac{\sqrt{\frac{\psi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{0.881966}</math></small>
|<small><math>\sqrt{\psi \phi ^3}</math></small>
|<small><math>3.47709</math></small>
|-
|<small><math>c_{8,1}</math></small>
|<small><math>60{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{5}\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>1</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|<small><math>1</math></small>
|<small><math>\sqrt{1}</math></small>
|<small><math>\sqrt{1.}</math></small>
|<small><math>\sqrt{2} \phi ^2</math></small>
|<small><math>3.70246</math></small>
|-
|<small><math>c_{9,1}</math></small>
|<small><math>66.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{7}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{2 \phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.09132</math></small>
|<small><math>\frac{\sqrt{\frac{\chi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\chi }{2 \phi }}</math></small>
|<small><math>\sqrt{1.19098}</math></small>
|<small><math>\sqrt{\chi \phi ^3}</math></small>
|<small><math>4.04057</math></small>
|-
|<small><math>c_{10,1}</math></small>
|<small><math>69.8{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{11}\right\}</math></small>
|<small><math>\phi c_{4,1}</math></small>
|<small><math>\frac{1+\sqrt{5}}{2 \sqrt{2}}</math></small>
|<small><math>1.14412</math></small>
|<small><math>\frac{\phi }{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^2}{2}}</math></small>
|<small><math>\sqrt{1.30902}</math></small>
|<small><math>\phi ^3</math></small>
|<small><math>4.23607</math></small>
|-
|<small><math>c_{11,1}</math></small>
|<small><math>72{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{6}\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.17557</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{1.38197}</math></small>
|<small><math>\sqrt{2} \sqrt{3-\phi } \phi ^2</math></small>
|<small><math>4.3525</math></small>
|-
|<small><math>c_{12,1}</math></small>
|<small><math>75.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{24}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>1.22474</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{1.5}</math></small>
|<small><math>\sqrt{3} \phi ^2</math></small>
|<small><math>4.53457</math></small>
|-
|<small><math>c_{13,1}</math></small>
|<small><math>81.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>1.30038</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(9-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{1.69098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(9-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>4.8146</math></small>
|-
|<small><math>c_{14,1}</math></small>
|<small><math>84.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{9}\right\}</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi } c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{2} \sqrt[4]{5} \sqrt{1+\sqrt{5}}</math></small>
|<small><math>1.345</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi }}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5} \phi }{2}}</math></small>
|<small><math>\sqrt{1.80902}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^5}</math></small>
|<small><math>4.9798</math></small>
|-
|<small><math>c_{15,1}</math></small>
|<small><math>90.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{7}\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>2 c_{4,1}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>1.41421</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2.}</math></small>
|<small><math>2 \phi ^2</math></small>
|<small><math>5.23607</math></small>
|-
|<small><math>c_{16,1}</math></small>
|<small><math>95.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{29}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>1.4802</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.19098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(11-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>5.48037</math></small>
|-
|<small><math>c_{17,1}</math></small>
|<small><math>98.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{31}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>1.51954</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(7+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.30902}</math></small>
|<small><math>\sqrt{\psi \phi ^5}</math></small>
|<small><math>5.62605</math></small>
|-
|<small><math>c_{18,1}</math></small>
|<small><math>104.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{8}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{4}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>1.58114</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{2.5}</math></small>
|<small><math>\sqrt{5} \sqrt{\phi ^4}</math></small>
|<small><math>5.8541</math></small>
|-
|<small><math>c_{19,1}</math></small>
|<small><math>108.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{9}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{10}{3}\right\}</math></small>
|<small><math>c_{3,1}+c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.61803</math></small>
|<small><math>\phi </math></small>
|<small><math>\sqrt{1+\phi }</math></small>
|<small><math>\sqrt{2.61803}</math></small>
|<small><math>\sqrt{2} \phi ^3</math></small>
|<small><math>5.9907</math></small>
|-
|<small><math>c_{20,1}</math></small>
|<small><math>110.2{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>1.64042</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.69098}</math></small>
|<small><math>\phi ^2 \sqrt{8-\phi ^2}</math></small>
|<small><math>6.07359</math></small>
|-
|<small><math>c_{21,1}</math></small>
|<small><math>113.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{19}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.67601</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{2.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\chi }{\phi }}</math></small>
|<small><math>6.20537</math></small>
|-
|<small><math>c_{22,1}</math></small>
|<small><math>120{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{10}\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\sqrt{3} c_{8,1}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>1.73205</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3.}</math></small>
|<small><math>\sqrt{6} \phi ^2</math></small>
|<small><math>6.41285</math></small>
|-
|<small><math>c_{23,1}</math></small>
|<small><math>124.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{41}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{\phi }+\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.7658</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{3.11803}</math></small>
|<small><math>\sqrt{\chi \phi ^5}</math></small>
|<small><math>6.53779</math></small>
|-
|<small><math>c_{24,1}</math></small>
|<small><math>130.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>1.81907</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.30902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\sqrt{5}}{\phi }}</math></small>
|<small><math>6.73503</math></small>
|-
|<small><math>c_{25,1}</math></small>
|<small><math>135.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}}</math></small>
|<small><math>1.85123</math></small>
|<small><math>\frac{\phi ^2}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^4}{2}}</math></small>
|<small><math>\sqrt{3.42705}</math></small>
|<small><math>\phi ^4</math></small>
|<small><math>6.8541</math></small>
|-
|<small><math>c_{26,1}</math></small>
|<small><math>138.6{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{12}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{7}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>1.87083</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{3.5}</math></small>
|<small><math>\sqrt{7} \phi ^2</math></small>
|<small><math>6.92667</math></small>
|-
|<small><math>c_{27,1}</math></small>
|<small><math>144{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{12}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{5}{2}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)}</math></small>
|<small><math>1.90211</math></small>
|<small><math>\sqrt{\phi +2}</math></small>
|<small><math>\sqrt{2+\phi }</math></small>
|<small><math>\sqrt{3.61803}</math></small>
|<small><math>\phi ^2 \sqrt{2 \phi +4}</math></small>
|<small><math>7.0425</math></small>
|-
|<small><math>c_{28,1}</math></small>
|<small><math>154.8{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>1.95167</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{1}{\phi ^2}}</math></small>
|<small><math>7.22598</math></small>
|-
|<small><math>c_{29,1}</math></small>
|<small><math>164.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{14}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{7}\right\}</math></small>
|<small><math>\phi c_{12,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{\frac{3}{2}} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.98168</math></small>
|<small><math>\sqrt{\frac{3}{2}} \phi </math></small>
|<small><math>\sqrt{\frac{3 \phi ^2}{2}}</math></small>
|<small><math>\sqrt{3.92705}</math></small>
|<small><math>\sqrt{3} \phi ^3</math></small>
|<small><math>7.33708</math></small>
|-
|<small><math>c_{30,1}</math></small>
|<small><math>180{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{15}\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>2 c_{8,1}</math></small>
|<small><math>2</math></small>
|<small><math>2.</math></small>
|<small><math>2</math></small>
|<small><math>\sqrt{4}</math></small>
|<small><math>\sqrt{4.}</math></small>
|<small><math>2 \sqrt{2} \phi ^2</math></small>
|<small><math>7.40492</math></small>
|-
|rowspan=4 colspan=6|
|rowspan=4 colspan=4|
<small><math>\phi</math></small> is the golden ratio:<br>
<small><math>\phi ^2-\phi -1=0</math></small><br>
<small><math>\frac{1}{\phi }+1=\phi</math></small>, and: <small><math>\phi+1=\phi^2</math></small><br>
<small><math>\frac{1}{\phi }::1::\phi ::\phi ^2</math></small><br>
<small><math>1/\phi</math></small> and <small><math>\phi</math></small> are the golden sections of <small><math>\sqrt{5}</math></small>:<br>
<small><math>\phi +\frac{1}{\phi }=\sqrt{5}</math></small>
|colspan=2|<small><math>\phi = (\sqrt{5} + 1)/2</math></small>
|<small><math>1.618034</math></small>
|-
|colspan=2|<small><math>\chi = (3\sqrt{5} + 1)/2</math></small>
|<small><math>3.854102</math></small>
|-
|colspan=2|<small><math>\psi = (3\sqrt{5} - 1)/2</math></small>
|<small><math>2.854102</math></small>
|-
|colspan=2|<small><math>\psi = 11/\chi = 22/(3\sqrt{5} + 1)</math></small>
|<small><math>2.854102</math></small>
|}
== The 5-cell 4-simplex ==
...
== The 16-cell 4-orthoplex ==
In 2-space we have the regular 8-point octagon, in 3-space the regular 8-point cube, and in 4-space the regular 8-point [[16-cell]].
A planar octagon with rigid edges of unit length has chords of length:
:<math>r_1=1,r_2=\sqrt{2+\sqrt{2}} \approx 1.848,r_3=\sqrt{2}+1 \approx 2.414,r_4=\sqrt{4 + \sqrt{8}} \approx 2.613</math>
The chord ratio <math>r_3=\sqrt{2}+1</math> is a geometrical proportion, the [[W:Silver ratio|silver ratio]]. Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_3-r_1-r_1=1/r_3 \approx 0.414</math>
Note that <math>r_3-2=1/r_3=\sqrt{2}-1</math>. The procedure rotates counterclockwise over three <math>r_3</math> chords of an {8/3} octagram. Over the first <math>r_3</math> chord the displacement is <math>\sqrt{2}+r_1</math>. Over the second <math>r_3</math> chord it moves in the opposite direction a distance of <math>-r_1</math> . Over the third <math>r_3</math> chord it moves a distance of <math>-r_1</math>.
If we embed the planar octagon in 3-space, we can make it skew, repositioning its vertices so that each is one unit-edge length distant from three others instead of two others, at the vertices of a unit-edge cube with chords of length:
:<math>r_1=1, r_2=\sqrt{2}, r_3=\sqrt{3}, r_4=\sqrt{2}</math>
If we embed this cube in 4-space, we can skew it some more, repositioning its vertices so that each is one unit-edge length distant from six others instead of three others, at the vertices of a unit-edge 4-polytope with chords of length:
:<math>r_1=1,r_2=1,r_3=1,r_4=\sqrt{2}</math>
All of its chords except its long diameters are the same unit length as its edge. In fact they are its 24 edges, and it is a 16-cell of radius <math>1/\sqrt{2}</math>.
[[File:octagon16cell.png|thumb|Orthogonal projection of a regular 16-cell to the [[16-cell#Projections|B<sub>4</sub> Coxeter plane]]. Only its edges are shown; its long diameter chords are not drawn. All 24 edges are the same length and none lie parallel to the projection plane. The octagon circumference is a Petrie polygon. The two disjoint squares lie in completely orthogonal central planes. The blue octagram is a Clifford polygon. ]]
The [[16-cell]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{3,3,4\}</math></small>. It has 8 vertices, 24 edges, 32 equilateral triangle faces, and 16 regular tetrahedron cells. It is the [[16-cell#Octahedral dipyramid|four-dimensional analogue of the octahedron]], and each of its four orthogonal central hyperplanes is an octahedron.
The only planar regular polygons found in the 16-cell are face triangles and central plane squares, but the 16-cell also contains a skew regular octagon, its [[W:Petrie polygon|Petrie polygon]].{{Efn|name=Petrie polygon of a honeycomb}} The chords of this regular octagon, which lies skew in 4-space, are those given above for the 16-cell, as opposed to those for the cube or the regular octagon in the plane. The 16-cell is a construct of 3 Petrie octagons which share the same 8 vertices but have disjoint sets of 8 edges each.
The regular octad has higher symmetry in 4-space than it does in 2-space. The 16-cell is the 4-[[w:Cross-polytope|orthoplex]], the simplest regular 4-polytope after the [[5-cell|4-simplex]]. All the larger regular convex 4-polytopes are compounds of the 16-cell. The regular octagon exhibits this high symmetry only when embedded in 4-space at the vertices of the 16-cell.
The 16-cell constitutes an [[W:Orthonormal basis|orthonormal basis]] for the choice of a 4-dimensional Cartesian reference frame, because its vertices define four orthogonal axes. The eight vertices of a unit-radius 16-cell are (±1, 0, 0, 0), (0, ±1, 0, 0), (0, 0, ±1, 0), (0, 0, 0, ±1). All vertices are connected by <math>\sqrt{2}</math> edges except opposite pairs.
The vertex coordinates of the 16-cell form 6 central squares lying in 6 pairwise [[W:Orthogonal|orthogonal]] coordinate planes. Great squares in opposite planes that do not share an axis (e.g. in the ''xy'' and ''wz'' planes) are completely disjoint (they do not intersect at any vertices). These planes are [[W:Completely orthogonal|completely orthogonal]].{{Efn|name=Six orthogonal planes of the Cartesian basis}}
Since the unit-radius coordinate system is convenient, let us derive the unit-radius 16-cell by skewing a unit-radius planar octagon, which has chords of length:
:<math>r_1=\sqrt{2-\sqrt{2}} \approx 0.765,r_2=\sqrt{2},r_3=\sqrt{2+\sqrt{2}} \approx 1.848,r_4=2</math>
We will need a planar octagon with rigid <math>r_2</math> chords, rather than one with rigid <math>r_1</math> edges. The octagon's <math>r_2</math> chords form two disjoint great squares, visible in the orthogonal projection, which we can reposition in 3-space to form a cube by making them parallel, and in 4-space to form a 16-cell by making them completely orthogonal.
Since the edges of the 16-cell are all the same length <math>r_1=\sqrt{2},r_2=\sqrt{2},r_3=\sqrt{2}</math>, those chords are distinct only in the context of a rotation. Each chord is a 4-vector with a length and a direction. The rotational curve over each <math>r_i</math> chord makes <math>i</math> 45° turns.
[[File:16-cell-orig.gif|thumb|Orthographic projection of the 8-point 16-cell <small><math>\{3,3,4\}</math></small> performing a double rotation.{{Sfn|Hise|2007}}]]
[[W:Rotations in 4-dimensional Euclidean space|Rotations in 4-dimensional Euclidean space]] can be seen as the composition of two 2-dimensional rotations in completely orthogonal planes. The general rotation in 4-space is a [[W:SO(4)#Double rotations|double rotation]] in pairs of completely orthogonal planes. Two completely orthogonal planes are called invariant planes of the rotation when all points in the plane rotate on circles that remain in the plane, even as the whole plane tilts sideways (like a coin flipping) into another plane. The two completely orthogonal rotations of each plane (like a wheel, and like a coin flipping) are simultaneous but independent, in that they are not geometrically constrained to turn at the same rate. However, the most circular kind of rotation (as opposed to an elliptical double rotation of a rigid spherical object) occurs when the completely orthogonal planes do rotate through the same angle in the same time interval. Such equi-angled double rotations are called [[w:SO(4)#Isoclinic_rotations|isoclinic]], also [[w:William_Kingdon_Clifford|Clifford]] displacements.
The <math>r_1</math> chords of the 16-cell form a Petrie polygon which zig-zags back and forth, in the left and right rotational directions, between two completely orthogonal great squares formed by <math>r_2</math> chords.
The <math>r_2</math> chords of two completely orthogonal great squares lie parallel and perpendicular to each other. A ''simple'' rotation of the 16-cell in ''one'' of those two square central planes rotates that square like a wheel, while the other square does not move.{{Efn|name=simple rotations}} The four vertices of the rotating square orbit on a great circle in the plane.
The <math>r_3</math> chords of the 16-cell form a circular helix, visible as a blue {8/3} octagram in the orthogonal projection. A ''double'' rotation of the 16-cell, in both of two completely orthogonal invariant <math>r_2</math> square planes at once by equal angles, moves the eight vertices along the circular helix over the <math>r_3</math> chords. The vertex motion is a [[w:Geodesic|geodesic]] circle orbit on the 3-sphere of a special kind: it does not lie in a central plane, its [[w:Winding_number|winding number]] is not 1 (it is 3 in this case), its circumference is not <math>2\pi</math>, and it moves in either a left or right handed circular spiral. We shall refer to such a chiral circle orbit as an ''isocline'', and to the skew polygram of its rotational chords as a ''Clifford polygon''.
The 16-cell is the simplest possible frame in which to [[16-cell#Rotations|observe 4-dimensional rotations]] because its characteristic rotations feature a single pair of invariant rotation planes. In the 16-cell an isoclinic rotation by 90° in any pair of invariant completely orthogonal square central planes takes every great square to its completely orthogonal great square in a twisting displacement, as the invariant planes tilt sideways 90° into each other's plane while rotating 90° internally. All the vertices move at once along the same circular helix geodesic isocline of <math>r_3</math> chords, displaced 90° in 8 orthogonal directions, and the rigid 16-cell assumes a new orientation in 4-space. When the 90° isoclinic rotation is continued in the same rotational direction through an additional 90°, each vertex is again displaced 90°, but from the new orientation in a direction orthogonal to its first 90° displacement. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. In 360° of isoclinic rotation over four <math>r_3</math> chords, each vertex makes six 90° turns and reaches its antipodal position.
The trajectory of each vertex over each 90° isoclinic rotational displacement is a one-eighth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>6\pi</math> over eight <math>r_3</math> chords, and also traces an ordinary great circle in the plane twice, over the four <math>r_2</math> edges of a great square in one of the two moving invariant rotation planes. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions just once and returns to its original position, and the 16-cell returns to its original orientation.
Because this is the isoclinic rotation of the 16-cell in its invariant edge planes we shall refer to it as the ''characteristic rotation of the 16-cell'', and note once again that it is Fontaine and Hurley's rotation over the <math>r_3</math> star polygon which constructs <math>1/r_3</math>.
== The 8-cell tesseract ==
The long diameter of the unit-edge [[W:Hypercube|hypercube]] of dimension <math>n</math> is <math>\sqrt{n}</math>, so the unit-edge [[w:Tesseract|4-hypercube, the 16-point (8-cell) tesseract,]] has chords:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
Uniquely in its 4-dimensional case, the hypercube's edge length equals its radius, like the hexagon. We call such polytopes ''radially equilateral'', because they can be constructed from equilateral triangles which meet at their center, each contributing two radii and an edge. The [[w:Cuboctahedron|cuboctahedron]] and the 24-cell are also radially equilateral.
[[File:8-cell.gif|thumb|Orthographic projection of the 16-point (8-cell) tesseract <small><math>\{4,3,3\}</math></small> performing a simple rotation about a plane in 4-space.{{Sfn|Hise|2007}} The stationary plane bisects the figure from front-left to back-right and top to bottom.]]
The [[W:Tesseract|tesseract]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{4,3,3\}</math></small>. It has 16 vertices, 32 edges, 24 square faces, and 8 cube cells. It is the four-dimensional analogue of the cube.
The 16-point tesseract is the convex hull of a compound of two 8-point 16-cells, in exact dimensional analogy to the way the 8-point cube is the convex hull of a [[W:Stellated octahedron|compound of two 4-point regular tetrahedra]]. The [[W:Demihypercube|demihypercubes]] occupy alternate vertices of the hypercubes. The diagonals of the square faces of the unit-edge, unit-radius tesseract are the <math>\sqrt{2}</math> edges of two unit-radius 16-cells, also the edges of the square central planes.
We can rotate the tesseract isoclinically the way we rotated the 16-cell, by 90° in completely orthogonal invariant square central planes, with the same effect on both alternate-position 16-cells. In the course of a 720° isoclinic rotation in invariant square central planes each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cell. The two skew {8/3} octagram Clifford polygons lie on two disjoint parallel isoclines of the same chirality, of circumference <math>6\pi</math> over <math>\sqrt{2}</math> chords. They form a circular double helix which intersects each vertex of the tesseract once.
The tesseract is the [[W:Dual polytope|dual polytope]] of the 16-cell. They have the same Petrie polygon, the regular skew octagon, but the tesseract is a construct of 4 Petrie octagons with disjoint sets of 8 tesseract edges each. We can construct the tesseract by skewing two planar octagons. Because the tesseract is radially equilateral (unlike the 16-cell), we use two octagons of unit-edge length to build the unit-radius tesseract. To start we embed the planar octagons in 4-space at the same point and make them completely orthogonal. Then we skew each planar octagon into a cube, so we have a compound of two completely orthogonal cubes, provided we skewed them both in the same direction. The 16 vertices will be the vertices of a tesseract with half its 32 edges missing.
Because the tesseract contains two 16-cells in alternate positions it has two sets of 6 orthogonal square central planes. Two angles are required to specify the relationship between two planes in 4-space. Pairs of square central planes within each 16-cell are 90° apart in one angle, and either 0° or 90° apart in the other angle. They are 90° apart in both angles if and only if they are completely orthogonal planes, 90° apart by isoclinic rotation, with no vertices in common. Otherwise they are 0° apart in one of the angles, 90° apart by simple rotation, and they intersect in one axis and lie in a common 3-dimensional hyperplane.{{Efn|A double rotation in which one of the two angles of rotation is 0°, so that one of the completely orthogonal invariant planes does not rotate, is called a simple rotation. Ordinary rotations observed in a 3-dimensional space are simple rotations.|name=simple rotations}}
A pair of square central planes from alternate-position 16-cells are 60° apart by isoclinic rotation, with their corresponding vertices 120° apart. The planes are not orthogonal or parallel, so they intersect in a line somewhere, but they have no vertices in common, they have no 3-dimensional hyperplane in common, and they cannot reach each other by simple rotation. Such pairs of objects are called [[W:Clifford parallel|Clifford parallel]] because all their corresponding pairs of vertices are the same distance apart, although they are not parallel in the usual sense, because they have a common center. Not only the alternate-position 16-cells' corresponding square central planes, but also the 16-cells themselves, are Clifford parallel objects. More generally, multiple disjoint instances of a 4-polytope which compound to make a larger 4-polytope are Clifford parallel objects.
== The 24-cell ==
[[File:24-cell vertex geometry.png|thumb|Planar geometry of the radially equilateral 24-cell, showing its 3 great circle polygons and its 4 chord lengths.]]
In 2-space we have the radially equilateral 6-point hexagon. In 3-space we have the radially equilateral 12-point cuboctahedron, with 4 hexagonal central planes. In 4-space we have the radially equilateral 24-point 24-cell, with 12 cuboctahedron central hyperplanes and 16 hexagonal central planes.
The [[24-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,4,3\}</math></small>. It has 24 vertices, 96 edges, 96 equilateral triangle faces, and 24 octahedron cells. It is the four-dimensional analogue of the cuboctahedron.
The 24-cell has the same chord set as the 4-hypercube tesseract:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
[[Image:24-cell.gif|thumb|Orthographic projection of the 24-point 24-cell <small><math>\{3,4,3\}</math></small> performing a simple rotation.{{Sfn|Hise|2007}} The 3-dimensional surface made of 24 octahedra is visible.]]
The 24-cell is [[W:Dual polytope|self-dual]], like the regular polygons and regular simplexes. It is the maximal regular construct of triangles and squares (with no pentagons). It is the convex hull of a compound of three disjoint 8-point 16-cells, rotated 60° isoclinically with respect to each other. Each of the three pairs of 16-cells is a tesseract. Each 24-cell edge is also a tesseract edge. The corresponding vertices of two 16-cells or two tesseracts are 120° apart by a <math>\sqrt{3}</math> chord. Each tesseract has 8 cube cells, and each cube has four <math>\sqrt{3}</math> long diameters. The <math>\sqrt{3}</math> chords joining the corresponding vertices of two tesseracts belong to the third tesseract as cell long diameters.
The 24-cell's Petrie polygon is the regular dodecagon {12}, which has chords:
:<math>r_1=\tfrac{\sqrt{3}-1}{\sqrt{2}} \approx 0.518,r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\tfrac{\sqrt{3}+1}{\sqrt{2}} \approx 1.932,r_6=\sqrt{4}</math>
Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_5-r_3+r_1+r_1-r_3=1/r_5</math>
when <math>r_1=1</math>. The procedure rotates counterclockwise over five <math>r_5</math> chords of a {12/5} dodecagram. In the system of unit-radius coordinates <math>r_1=1/r_5</math>.
The <math>r_1</math> and <math>r_5</math> chords of the planar dodecagon do not occur in the 24-cell, which is a construct of eight skew dodecagons with disjoint sets of twelve <math>\sqrt{1}</math> edges each. In the skew dodecagons the chord lengths are:
:<math>r_1=\sqrt{1},r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\sqrt{3},r_6=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
[[File:dodecagon24cell.png|thumb|Orthogonal projection of half a 24-cell to the [[24-cell#Geodesics|F<sub>4</sub> Coxeter plane]]. Only one Petrie dodecagon {12} of the 24-cell is shown. In a unit-radius 24-cell, all black lines are 24-cell edges of unit length, also tesseract edges. The two disjoint hexagons lie in Clifford parallel central planes. Blue chords are <math>\sqrt{2}</math> 16-cell edges, also isocline chords in square rotations. Green chords are <math>\sqrt{3}</math> distances between corresponding vertices of two 16-cells, also isocline chords in hexagonal rotations. Note the {12/5} dodecagram.]]
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_3=\sqrt{2}</math></small>]]
We can rotate the 24-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in completely orthogonal invariant great square planes, with the same effect on all three 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cells. The <math>r_3=\sqrt{2}</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Three Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_3</math> chords form a circular triple helix {24/9}=3{8/3} that intersects each 24-cell vertex once.
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_5=\sqrt{3}</math></small> ]]
We can also rotate the 24-cell isoclinically in 4 Clifford parallel invariant great hexagon planes containing its vertices, over <math>r_{5}=\sqrt{3}</math> isocline chords. This is the ''characteristic rotation of the 24-cell'' in its invariant edge planes, also Fontaine and Hurley's rotation over the <math>r_5</math> star polygon which constructs <math>1/r_5</math>. A complete hexagonal isoclinic revolution requires 720° like a complete square isoclinic revolution, but it is completed in 12 isoclinic displacements of 60° each rather than 8 isoclinic displacements of 90° each. The rotational curve over each 120° <math>r_5</math> chord makes five 30° turns. Two Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_5</math> chords form a circular double helix {24/10}=2{12/5} that intersects each 24-cell vertex once.
In the 24-cell the characteristic isoclinic rotation by 60° in any invariant hexagon central plane takes every great hexagon to a Clifford parallel great hexagon in a twisting displacement, as all the central planes tilt sideways 60° while rotating 60° internally. It also takes every great square to a Clifford parallel great square in another 16-cell; it takes every 16-cell to another 16-cell. The 16-cells revolve within the 24-cell as well as rotating within it. All 24 vertices move at once on two Clifford parallel geodesic isoclines, displaced 120° in different directions.
The trajectory of each vertex over each 60° isoclinic rotational displacement is a one-twelfth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>10\pi</math> over twelve <math>\sqrt{3}</math> chords, and also traces an ordinary great circle in the plane twice, over the six <math>\sqrt{1}</math> edges of a great hexagon in a moving invariant rotation plane. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions just once and returns to its original position, and the 24-cell returns to its original orientation.
== The 600-cell ==
[[Image:600-cell.gif|thumb|Orthographic projection of the 120-point 600-cell <small><math>\{3,3,5\}</math></small> performing a simple rotation.{{Sfn|Hise|2011}} The 3-dimensional surface made of 600 tetrahedra is visible. Invisible in this rendering are 25 inscribed instances of the 24-cell (above), which occur in the 600-cell as interior boundary envelopes.]]
The [[600-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,3,5\}</math></small>. It has 120 vertices, 720 edges, 1200 equilateral triangle faces, and 600 tetrahedron cells. It is the four-dimensional analogue of the icosahedron.
The 600-cell rounds out the 24-cell by adding 96 more vertices (four more disjoint 24-cells) between the 24-cell's existing 24 vertices, in effect adding twenty-four more distinct 24-cells inscribed in the 600-cell. The new surface thus formed is a honeycomb of smaller, more numerous cells: tetrahedra of edge length <math>\phi^{-1} \approx 0.618</math> instead of octahedra of edge length <math>\sqrt{1}</math>. It encloses the <math>\sqrt{1}</math> edges of the 24-cells, which become invisible interior chords in the 600-cell, like the <math>\sqrt{2}</math> and <math>\sqrt{3}</math> chords.
Since the tetrahedra are made of shorter triangle edges than the octahedra (by a factor of <math>\phi^{-1}</math>, the inverse golden ratio), the 600-cell is not radially equilateral like the 24-cell and the tesseract. Like them it is radially triangular in a special way, but one in which [[w:Golden_triangle_(mathematics)|golden triangles]] rather than equilateral triangles meet at the center.
In 2-space we have the ''radially golden'' [[W:Decagon#The golden ratio in decagon|regular decagon]]. In 3-space we have the radially golden 30-point [[W:icosidodecahedron|icosidodecahedron]], with 6 decagon central planes. In 4-space we have the radially golden 120-point 600-cell, with 60 icosidodecahedron central hyperplanes and 72 decagon central planes.
The 600-cell's Petrie polygon is the regular [[w:Triacontagon|triacontagon {30}]]. The unit-radius planar {30}-gon has these distinct chords:
:<math>r_1=2 \sin (\tfrac{\pi}{15}/2) \approx 0.209</math>
:<math>r_2=2 \sin (\tfrac{2\pi}{15}/2) \approx 0.416</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{4\pi}{15}/2) \approx 0.813</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{7\pi}{15}/2) \approx 1.338</math>
:<math>r_8=2 \cos (\tfrac{7\pi}{15}/2) \approx 1.486</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{11}=2 \cos (\tfrac{4\pi}{15}/2) \approx 1.827</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \cos (\tfrac{2\pi}{15}/2) \approx 1.956</math>
:<math>r_{14}=2 \cos (\tfrac{\pi}{15}/2) \approx 1.989</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Only the chord lengths <math>r_3</math>, <math>r_5</math>, <math>r_6</math>, <math>\sqrt{2}</math>, <math>r_9</math>, <math>r_{10}</math>, <math>r_{12}</math>, <math>r_{15}</math> occur in the 600-cell, which is a construct of 24 Petrie {30}-gons of edge length <math>r_3</math>, six of which intersect in each icosahedral vertex figure. In the skew {30}-gons the chord lengths are:
[[File:600-cell vertex geometry.png|thumb|Planar geometry of the 600-cell, showing its 5 regular great circle polygons and its 8 chord lengths with angles of arc. The golden ratio governs the fractional roots of every other chord, and the radial golden triangles which meet at the center.|400x400px]]
:<math>r_1=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_2=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}=\text{24-cell-}r_2</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}</math>
:<math>r_8=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}=\text{16-cell-}r_3</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}=\text{24-cell-}r_5</math>
:<math>r_{11}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{14}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="7" |15 chords (4 distinct 180° pairs) make 4 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>r_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>r_{15}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>r_1</math>
|36°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}=2{15/7}
|144°
| rowspan="3" |<math>r_{14}</math>
|- style="background: palegreen;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: palegreen;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>r_2</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|144°
| rowspan="3" |<math>r_{13}</math>
|- style="background: gainsboro;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: gainsboro;" |
|0.618~
|1.902~
|- style="background: yellow;" |
| rowspan="3" |<math>r_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |[[File:V1 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>r_{12}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_4</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|120°
| rowspan="3" |<math>r_{11}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_5</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |[[File:V2 dodecahedron.png|100px]]<br>Dodecahedron
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>r_{10}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: yellow;" |
| rowspan="3" |<math>r_{6}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |[[File:V3 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>r_{9}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: seashell;" |
| rowspan="3" |<math>r_{7}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |[[File:V4 icosidodecahedron.png|100px]]<br>Icosidodecahedron
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>r_{8}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The list of 600-cell chords <math>r_{i}</math> can be rearranged into a table of 8 rows and 2 columns with a pair of 180° complements in each row. The short chord and long chord each have their characteristic {30}-gon. Each row identifies a discrete isoclinic rotation of the 600-cell in invariant central planes containing the edges of the short chord {30}-gon, over the isocline chords of the long chord {30}-gon, the rotation's Clifford polygon.
Each distinct pair of complementary chord lengths is identified with a distinct [[w:600-cell#Polyhedral sections|polyhedral section of the 600-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 7 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>\phi^{-1}</math> is a icosahedron vertex figure, and the largest section at radial distance <math>\sqrt{2}</math> is an [[W:Icosidodecahedron|icosidodecahedron]] central section bisecting the 600-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>\sqrt{2}</math> the successive complement-radius polyhedra decrease in size, to the antipodal icosahedron vertex figure at distance <math>\sqrt{2+\phi}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 7 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section).
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_8=\sqrt{2}</math></small>]]
We can rotate the 600-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in two completely orthogonal invariant great square planes over <math>r_8=\sqrt{2}</math> isocline chords, with the same effect on 15 disjoint 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_8</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Fifteen Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_8</math> chords form a circular helix of 15 twisted parallel strands 5{24/9}=15{8/3} that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_polygon_30-7.svg|thumb|left|150px|{30/7} <small><math>r_7=\sqrt{2}</math></small>]]
In the 600-cell this 90° isoclinic rotation in completely orthogonal great square planes takes place over the <math>r_7=r_8=\sqrt{2}</math> chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/7} polygon is a skew helix with each edge belonging to a distinct great square. The vertices of the invariant great squares of this rotation each make seven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 90° {30/7} isocline chord makes seven 12° turns. Four Clifford parallel {30/7} geodesic isoclines of circumference <math>14\pi</math> form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_{11}=\sqrt{3}</math></small> ]]
We can also rotate the 600-cell isoclinically in the characteristic rotation of the 24-cell, by 60° in great hexagon planes, with the same effect on 5 disjoint 24-cells. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions of its 24-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_{5}</math> chord is the 24-cell <math>r_2</math> chord, and the <math>r_{10}</math> chord is the 24-cell <math>r_5</math> chord. The rotational curve over each <math>r_{10}</math> chord makes five 30° turns. Ten Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_{10}</math> chords form a circular helix of 10 twisted parallel strands 5{24/10}=10{12/5} that intersects each 600-cell vertex once.
In the 600-cell this 60° isoclinic rotation in great hexagon planes takes place over <math>r_{4}=\sqrt{1}</math> edge chords and <math>r_{11}=\sqrt{3}</math> isocline chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/11} polygon is a skew helix with each <math>r_{11}</math> chord the <math>\sqrt{3}</math> diagonal of a distinct great hexagon. The vertices of the invariant great hexagons of this rotation each make eleven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 120° <math>r_{11}</math> isocline chord makes eleven 12° turns. Four Clifford parallel {30/11} geodesic isoclines of circumference <math>22\pi</math> over <math>r_{11}</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_figure_2(15,4).svg|thumb|left|150px|{30/8}=2{15/4} <small><math>r_{13}=\sqrt{1}</math></small>]]
We can also rotate the 600-cell isoclinically in 12 Clifford parallel invariant decagon central planes containing its <math>r_{3}</math> edges, over <math>r_{13}=\sqrt{1}</math> isocline chords. This is the ''characteristic rotation of the 600-cell'' in its invariant edge planes. Its Clifford polygon is a skew {15/4} pentadecagram of <math>r_{13}</math> chords. The <math>r_{4}</math> chord is the 24-cell <math>r_2</math> chord. Successive <math>r_{13}</math> chords are edges of different 24-cells. The rotational curve over each <math>r_{13}</math> chord makes two 30° turns. Eight Clifford parallel {15/4} pentadecagon geodesic isoclines of circumference <math>5\pi</math> over <math>r_{13}</math> chords form a circular helix of eight twisted parallel strands 4{30/8}=8{15/4} that intersects each 600-cell vertex once.
In the 600-cell the characteristic isoclinic rotation by 36° in any invariant decagon central plane takes every great decagon to a Clifford parallel great decagon in a twisting displacement, as all the central planes tilt sideways 36° while rotating 36° internally. It also takes every great hexagon to a Clifford parallel great hexagon in another 24-cell, and every great square to a Clifford parallel great square in another 16-cell; it takes 24-cells to a non-disjoint 24-cell and 16-cells to a 16-cell in another 24-cell. The 24-cells revolve within the 600-cell, as the 16-cells revolve within the 24-cells. All 120 vertices move at once on eight Clifford parallel geodesic isoclines, displaced 60° in different directions.
The trajectory of each vertex over each 36° isoclinic rotational displacement is a one-fifteenth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>5\pi</math> over 15 <math>r_5</math> chords, and also traces an ordinary great circle in the plane 3 times, over the 5 edges of a great pentagon in a moving invariant rotation plane. In the course of a complete isoclinic revolution each vertex departs from 15 vertex positions just once and returns to its original position, and the 600-cell returns to its original orientation.
{{Clear}}
[[File:Regular_star_figure_6(5,2).svg|thumb|left|150px|{30/12}=6{5/2} <small><math>r_{12}=\sqrt{3.618\sim}</math></small>]]
In the 600-cell there is another distinct isoclinic rotation taking decagon planes to each other, over 144° <math>r_{12}</math> isocline chords. It also takes disjoint 24-cells to each other. This rotation has period 5 and visits every 12th vertex of a 600-cell Petrie polygon. Its Clifford polygon is a skew {5/2} pentagram of <math>r_{12}</math> chords. The invariant central planes of this rotation each intersect only one vertex of the 600-cell, which makes two orbits of a great pentagon within the moving invariant plane in the course of one complete isoclinic revolution of period 5. The rotational curve over each <math>r_{12}</math> chord makes twelve 12° turns. 24 Clifford parallel {5/2} pentagram geodesic isoclines of circumference <math>4\pi</math> over five <math>r_{12}</math> chords form a circular helix of 24 twisted parallel strands 4{30/12}=24{5/2} that intersects each 600-cell vertex once.
{{Clear}}
== Finally the 120-cell ==
The [[120-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{5,3,3\}</math></small>. It has 600 vertices, 1200 edges, 720 pentagon faces, and 120 dodecahedron cells. It is the four-dimensional analogue of the dodecahedron.
The 120-cell is the [[W:Dual polytope|dual polytope]] of the 600-cell. They have the same Petrie polygon, the regular skew triacontagon {30}, but the 120-cell is a construct of 40 Petrie {30}-gons of edge length <math>c_1</math>, two of which intersect in each tetrahedral vertex figure.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="9" |30 chords (15 180° pairs) make 15 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>c_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>c_{30}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>c_1</math>
|15.5~°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}
|164.5~°
| rowspan="3" |<math>c_{29}</math>
|- style="background: palegreen;" |
|{{radic|0.073~}}
|{{radic|3.927~}}
|- style="background: palegreen;" |
|0.270~
|1.982~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_2</math>
|25.2~°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|154.8~°
| rowspan="3" |<math>c_{28}</math>
|- style="background: gainsboro;" |
|{{radic|0.191~}}
|{{radic|3.809~}}
|- style="background: gainsboro;" |
|0.437~
|1.952~
|- style="background: yellow;" |
| rowspan="3" |<math>c_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>c_{27}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_4</math>
|41.4~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|138.6~°
| rowspan="3" |<math>c_{26}</math>
|- style="background: gainsboro;" |
|{{radic|0.5}}
|{{radic|3.5}}
|- style="background: gainsboro;" |
|0.707~
|1.871~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_5</math>
|44.5~°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|135.5~°
| rowspan="3" |<math>c_{25}</math>
|- style="background: palegreen;" |
|{{radic|0.573~}}
|{{radic|3.427~}}
|- style="background: palegreen;" |
|0.757~
|1.851~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_6</math>
|49.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|130.9~°
| rowspan="3" |<math>c_{24}</math>
|- style="background: gainsboro;" |
|{{radic|0.691~}}
|{{radic|3.309~}}
|- style="background: gainsboro;" |
|0.831~
|1.819~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_7</math>
|56°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|124°
| rowspan="3" |<math>c_{23}</math>
|- style="background: gainsboro;" |
|{{radic|0.882~}}
|{{radic|3.118~}}
|- style="background: gainsboro;" |
|0.939~
|1.766~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_8</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>c_{22}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_9</math>
|66.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|113.9~°
| rowspan="3" |<math>c_{21}</math>
|- style="background: gainsboro;" |
|{{radic|1.191~}}
|{{radic|2.809~}}
|- style="background: gainsboro;" |
|1.091~
|1.676~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{10}</math>
|69.8~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|110.2~°
| rowspan="3" |<math>c_{20}</math>
|- style="background: gainsboro;" |
|{{radic|1.309~}}
|{{radic|2.691~}}
|- style="background: gainsboro;" |
|1.144~
|1.640~
|- style="background: yellow;" |
| rowspan="3" |<math>c_{11}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>c_{19}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>c_{18}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{13}</math>
|81.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|98.9~°
| rowspan="3" |<math>c_{17}</math>
|- style="background: gainsboro;" |
|{{radic|1.691~}}
|{{radic|2.309~}}
|- style="background: gainsboro;" |
|1.300~
|1.520~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{14}</math>
|84.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|95.5~°
| rowspan="3" |<math>c_{16}</math>
|- style="background: gainsboro;" |
|{{radic|0.809~}}
|{{radic|2.191~}}
|- style="background: gainsboro;" |
|1.345~
|1.480~
|- style="background: seashell;" |
| rowspan="3" |<math>c_{15}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>c_{15}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The [[User:Dc.samizdat/Golden chords of the 120-cell#Thirty distinguished distances|table above]] of 30 chords <math>c_{t}</math> can be rearranged into a table of 16 rows and 2 columns with a pair of 180° complements in each row. This table first appears in [[w:Regular_Polytopes_(book)|''Regular Polytopes'']] (1947),{{Sfn|Coxeter|1973|loc=Table V(v): Simplified sections of {5,3,3} beginning with a vertex|pp=300-301}} where Coxeter identified each row with a distinct [[w:120-cell#Concentric_hulls|polyhedral section of the 120-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 29 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>c_1</math> is a tetrahedron vertex figure, and the largest section at radial distance <math>c_{15}</math> is a central section bisecting the 120-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>c_{15}</math> the successive complement-radius polyhedra decrease in size, to the antipodal tetrahedron vertex figure at distance <math>c_{29}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 29 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section). Each section also lies completely orthogonal to a congruent section.
Only 8 of the 30 chords in the table occur in the 600-cell and the planar {30)-gon. The 120-cell's additional chords arise originally from the regular 5-cell, in its interaction with the other regular 4-polytopes that compound to make the 120-cell. Since all those polytopes except the 5-cell occur in the 600-cell, and the 600-cell and the 120-cell have the same symmetry group, the 5-cell's symmetry group is what's new in the 120-cell.
...
{{Clear}}
== Conclusions ==
Fontaine and Hurley's discovery is more than a geometric formula for the reciprocal of a regular ''n''-polygon diagonal. It also yields the discrete sequence of isocline chords of the characteristic isoclinic rotation of a ''d''-dimensional polytope in its invariant edge planes. The characteristic rotational chord sequence of the ''d''-polytope can be represented geometrically in two dimensions on a distinct star polygon, but it lies on a geodesic circle through ''d''-dimensional space. Fontaine and Hurley discovered the geodesic topology of polytopes generally. Their procedure will reveal the geodesics of arbitrary non-uniform polytopes, since it can be applied to a polytope of any dimensionality and irregularity, by first fitting the polytope to the smallest regular polygon whose chords include its chords. [If what is meant by this is its Petrie polygon, it is not quite necessary or possible with respect to the planar polygon chords, e.g. the planar Petrie polygon of the 600-cell does not contain the <math>\sqrt{2}</math> chord. But perhaps it would work if the fit is to the smallest regular skew polygon in the ''d''-space.]
The discovery of a chordal construction for discrete isoclinic rotations generally closes the circuit on Kappraff and Adamson's discovery of a rotational connection between dynamical systems, Steinbach's golden fields, and Coxeter's Euclidean geometry of ''n'' dimensions. Application of the Fontaine and Hurley procedure in the 120-cell demonstrates why the connection exists: because polytope sequences generally, from Steinbach's golden chord sequences in polygons, to sequences of star polygons in isoclinic rotations, to subsumption relations in the sequence of regular 4-polytopes, arise as expressions of the reflections and rotations of distinct Coxeter symmetry groups, when those various groups interact.
== Appendix: Sequence of regular 4-polytopes ==
{{Regular convex 4-polytopes|wiki=W:|columns=7}}
== Notes ==
{{Notelist}}
== Citations ==
{{Reflist}}
== References ==
{{Refbegin}}
* {{Cite journal | last=Steinbach | first=Peter | year=1997 | title=Golden fields: A case for the Heptagon | journal=Mathematics Magazine | volume=70 | issue=Feb 1997 | pages=22–31 | doi=10.1080/0025570X.1997.11996494 | jstor=2691048 | ref={{SfnRef|Steinbach|1997}} }}
* {{Cite journal | last=Steinbach | first=Peter | year=2000 | title=Sections Beyond Golden| journal=Bridges: Mathematical Connections in Art, Music and Science | issue=2000 | pages=35-44 | url=https://archive.bridgesmathart.org/2000/bridges2000-35.pdf | ref={{SfnRef|Steinbach|2000}}}}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Jablan | first2=Slavik | last3=Adamson | first3=Gary | last4=Sazdanovich | first4=Radmila | year=2004 | title=Golden Fields, Generalized Fibonacci Sequences, and Chaotic Matrices | journal=Forma | volume=19 | pages=367-387 | url=https://archive.bridgesmathart.org/2005/bridges2005-369.pdf | ref={{SfnRef|Kappraff, Jablan, Adamson & Sazdanovich|2004}} }}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Adamson | first2=Gary | year=2004 | title=Polygons and Chaos | journal=Dynamical Systems and Geometric Theories | url=https://archive.bridgesmathart.org/2001/bridges2001-67.pdf | ref={{SfnRef|Kappraff & Adamson|2004}} }}
* {{Cite journal | last1=Fontaine | first1=Anne | last2=Hurley | first2=Susan | year=2006 | title=Proof by Picture: Products and Reciprocals of Diagonal Length Ratios in the Regular Polygon | journal=Forum Geometricorum | volume=6 | pages=97-101 | url=https://scispace.com/pdf/proof-by-picture-products-and-reciprocals-of-diagonal-length-1aian8mgp9.pdf }}
{{Refend}}
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/* The 600-cell */
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= Golden chords of the 120-cell =
{{align|center|David Brooks Christie}}
{{align|center|dc@samizdat.org}}
{{align|center|Draft in progress}}
{{align|center|January 2026 - June 2026}}
<blockquote>Steinbach discovered the formula for the ratios of diagonal to side in the regular polygons. Fontaine and Hurley extended this result, discovering a formula for the reciprocal of a regular polygon chord derived geometrically from the chord's star polygon. We observe that these findings in plane geometry apply more generally, to polytopes of any dimensionality. Fontaine and Hurley's geometric procedure for finding the reciprocals of the chords of a regular polygon from their star polygons also finds the rotational geodesics of any polytope of any dimensionality.</blockquote>
== Introduction ==
Steinbach discovered the Diagonal Product Formula and the Golden Fields family of ratios of diagonal to side in the regular polygons. He showed how this family extends beyond the pentagon {5} with its well-known golden bisection proportional to 𝜙, finding that the heptagon {7} has an analogous trisection, the nonagon {9} has an analogous quadrasection, and the hendecagon {11} has an analogous pentasection, an extended family of golden proportions with quasiperiodic properties.
Kappraff and Adamson extended these findings in plane geometry to a theory of Generalized Fibonacci Sequences, showing that the Golden Fields not only do not end with the hendecagon, they form an infinite number of periodic trajectories when operated on by the Mandelbrot operator. They found a relation between the edges of star polygons and dynamical systems in the state of chaos, revealing a connection between chaos theory, number, and rotations in Coxeter Euclidean geometry.
Fontaine and Hurley examined Steinbach's finding that the length of each chord of a regular polygon is both the product of two chords and the sum of a set of smaller chords, so that in rotations to add is to multiply. They illustrated Steinbach's sets of additive chords lying parallel to each other in the plane (pointing in the same direction), and by applying Steinbach's formula more generally they found another summation relation of signed parallel chords (pointing in opposite directions) which relates each chord length to its reciprocal, and relates the summation to a distinct star polygon rotation.
We examine these remarkable findings (which stem from study of the chords of humble regular polygons) in higher-dimensional spaces, specifically in the chords, polygons and rotations of the [[120-cell]], the largest four-dimensional regular convex polytope.
== Visualizing the 120-cell ==
{| class="wikitable floatright" width="400"
|style="vertical-align:top"|[[File:120-cell.gif|200px]]<br>Orthographic projection of the 600-point 120-cell <small><math>\{5,3,3\}</math></small> performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]].{{Sfn|Hise|2011|loc=File:120-cell.gif|ps=; "Created by Jason Hise with Maya and Macromedia Fireworks. A 3D projection of a 120-cell performing a [[W:SO(4)#Geometry of 4D rotations|simple rotation]]."}} In this simplified rendering only the 120-cell's own edges are shown; its 29 interior chords are not rendered. Therefore even though it is translucent, only its outer surface is visible. The complex interior parts of the 120-cell, all its inscribed 5-cells, 16-cells, 8-cells, 24-cells, 600-cells and its much larger inventory of polyhedra, are completely invisible in this view, as none of their edges are rendered at all.
|style="vertical-align:top"|[[File:Ortho solid 016-uniform polychoron p33-t0.png|200px]]<br>Orthographic projection of the 600-point [[W:Great grand stellated 120-cell|great grand stellated 120-cell]] <small><math>\{\tfrac{5}{2},3,3\}</math></small>.{{Sfn|Ruen: Great grand stellated 120-cell|2007}} The 120-cell is its convex hull. The projection to the left renders only the 120-cell's shortest chord, its 1200 edges. The projection above also renders only one of the 120-cell's 30 chords, the edges of its 120 inscribed regular 5-cells. The 120-cell itself (the convex hull) is invisible in this view, as its edges are not rendered.
|}
[[120-cell#Geometry|The 120-cell is the maximally complex regular 4-polytope]], containing inscribed instances of every regular 1-, 2-, 3-, and 4-polytope, except the regular polygons of more than {15} sides.
The 120-cell is the convex hull of a regular [[120-cell#Relationships among interior polytopes|compound of each of the 6 regular convex 4-polytopes]]. They are the [[5-cell|5-point (5-cell) 4-simplex]], the [[16-cell|8-point (16-cell) 4-orthoplex]], the [[W:Tesseract|16-point (8-cell) tesseract]], the [[24-cell|24-point (24-cell)]], the [[600-cell|120-point (600-cell)]], and the [[120-cell|600-point (120-cell)]]. The 120-cell is the convex hull of a compound of 120 disjoint regular 5-cells, of 75 disjoint 16-cells, of 25 disjoint 24-cells, and of 5 disjoint 600-cells.
The 120-cell contains an even larger inventory of irregular polytopes, created by the intersection of multiple instances of these component regular 4-polytopes. Many are quite unexpected, because they do not occur as components of any regular polytope smaller than the 120-cell. As just one example among the [[120-cell#Concentric hulls|sections of the 120-cell]], there is an irregular 24-point polyhedron with 16 triangle faces and 4 nonagon {9} faces.{{Sfn|Moxness|}}
Most renderings of the 120-cell, like the rotating projection here, only illustrate its outer surface, which is a honeycomb of face-bonded dodecahedral cells. Only the objects in its 3-dimensional surface are rendered, namely the 120 dodecahedra, their pentagon faces, and their edges. Although the 120-cell has chords of 30 distinct lengths, in this kind of simplified rendering only the 120-cell's own edges (its shortest chord) are shown. Its 29 interior chords, the edges of objects in the interior of the 120-cell, are not rendered, so interior objects are not visible at all.
Visualizing the complete interior of the 600-vertex 120-cell in a single image is impractical because of its complexity. Only four 120-cell edges are incident at each vertex, but [[120-cell#Chords|600 chords (of all 30 lengths)]] are incident at ''each'' vertex.
== Compounds in the 120-cell ==
The 8-point (16-cell), not the 5-point (5-cell), is the smallest building block; it compounds to every larger regular 4-polytope. The 5-point (5-cell) does compound to the 600-point (120-cell), but it does not fit into any smaller regular 4-polytope.
The 8-point (16-cell) compounds by 2 in the 16-point (8-cell), and by 3 in the 24-point (24-cell). The 16-point (8-cell) compounds in the 24-point (24-cell) by 3 non-disjoint instances of itself, with each of the 24 vertices shared by two 16-point (8-cells). The 24-point (24-cell) compounds by 5 disjoint instances of itself in the 120-point (600-cell), and the 120-point (600-cell) compounds by 5 disjoint instances of itself in the 600-point (120-cell).
The 24-point (24-cell) also compounds by 5<sup>2</sup> non-disjoint instances of itself in the 120-point (600-cell); it compounds in 5 disjoint instances of itself, 10 (not 5) different ways. Whichever set of 5 disjoint 24-point (24-cells) are assembled, the resulting 120-point (600-cell) contains 25 distinct 24-point (24-cells), not just 5 (or 10). This implies that 15 disjoint 8-point (16-cells) will construct a 120-point (600-cell), which will contain 75 distinct 8-point (16-cells).
The 600-point (120-cell) is 5 disjoint 120-point (600-cells), just 2 different ways (not 5 or 10 ways), so it is 10 distinct 120-point (600-cells). This implies that the 8-point (16-cell) compounds by 3 times 5<sup>2</sup> (75) disjoint instances of itself in the 600-point (120-cell), which contains 3<sup>2</sup> times 5<sup>2</sup> (225) distinct instances of the 24-point (24-cell), and 3<sup>3</sup> times 5<sup>2</sup> (675) distinct instances of the 8-point (16-cell).
These facts were discovered painstakingly by various researchers, and no one has found a general rule governing subsumption relations among regular polytopes. The reasons for some of their numeric incidence relations are far from obvious. [[W:Pieter Hendrik Schoute|Schoute]] was the first to see that the 120-point (600-cell) is a compound of 5 24-point (24-cells) ''10 different ways'', and after he saw it a hundred years lapsed until Denney, Hooker, Johnson, Robinson, Butler & Claiborne proved his result, and showed why.{{Sfn|Denney, Hooker, Johnson, Robinson, Butler & Claiborne|2020|loc=''The geometry of H4 polytopes''}}
So much for the compounds of 16-cells. The 120-cell is also the convex hull of the compound of 120 disjoint regular 5-cells. That stellated compound (without its convex hull of 120-cell edges) is the [[w:Great_grand_stellated_120-cell|great grand stellated 120-cell]] illustrated above, the final regular [[W:Stellation|stellation]] of the 120-cell, and the only [[W:Schläfli-Hess polychoron|regular star 4-polytope]] to have the 120-cell for its convex hull. The edges of the great grand stellated 120-cell are <math>\phi^6</math> as long as those of its 120-cell [[W:List of polyhedral stellations#Stellation process|stellation core]] deep inside.
The compound of 120 disjoint 5-point (5-cells) can be seen to be equivalent to the compound of 5 disjoint 120-point (600-cells), as follows. Beginning with a single 120-point (600-cell), expand each vertex into a regular 5-cell, by adding 4 new equidistant vertices, such that the 5 vertices form a regular 5-cell inscribed in the 3-sphere. The 120 5-cells are disjoint, and the 600 vertices form 5 disjoint 120-point (600-cells): a 120-cell.
== Thirty distinguished distances ==
The 30 numbers listed in the table are all-important in Euclidean geometry. A case can be made on symmetry grounds that their squares are the 30 most important numbers between 0 and 4. The 30 rows of the table are the 30 distinct [[120-cell#Geodesic rectangles|chord lengths of the unit-radius 120-cell]], the largest regular convex 4-polytope. Since the 120-cell subsumes all smaller regular polytopes, its 30 chords are the complete chord set of all the regular polytopes that can be constructed in the first four dimensions of Euclidean space, except for regular polygons of more than 15 sides.
{| class="wikitable" style="white-space:nowrap;text-align:center"
!rowspan=2|<math>c_t</math>
!rowspan=2|arc
!rowspan=2|<small><math>\left\{\frac{30}{n}\right\}</math></small>
!rowspan=2|<math>\left\{p\right\}</math>
!rowspan=2|<small><math>m\left\{\frac{k}{d}\right\}</math></small>
!rowspan=2|Steinbach roots
!colspan=7|Chord lengths of the unit 120-cell
|-
!colspan=5|unit-radius length <math>c_t</math>
!colspan=2|unit-edge length <math>c_t/c_1</math><br>in 120-cell of radius <math>c_8=\sqrt{2}\phi^2</math>
|-
|<small><math>c_{1,1}</math></small>
|<small><math>15.5{}^{\circ}</math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{30\right\}</math></small>
|<small><math>c_{4,1}-c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7-3 \sqrt{5}}</math></small>
|<small><math>0.270091</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi ^2}</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^4}}</math></small>
|<small><math>\sqrt{0.072949}</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|-
|<small><math>c_{2,1}</math></small>
|<small><math>25.2{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{2}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{15\right\}</math></small>
|<small><math>\frac{1}{2} \left(c_{18,1}-c_{4,1}\right)</math></small>
|<small><math>\frac{\sqrt{3-\sqrt{5}}}{2}</math></small>
|<small><math>0.437016</math></small>
|<small><math>\frac{1}{\sqrt{2} \phi }</math></small>
|<small><math>\sqrt{\frac{1}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.190983}</math></small>
|<small><math>\phi </math></small>
|<small><math>1.61803</math></small>
|-
|<small><math>c_{3,1}</math></small>
|<small><math>36{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{3}\right\}</math></small>
|<small><math>\left\{10\right\}</math></small>
|<small><math>3 \left\{\frac{10}{3}\right\}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right) c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(\sqrt{5}-1\right)</math></small>
|<small><math>0.618034</math></small>
|<small><math>\frac{1}{\phi }</math></small>
|<small><math>\sqrt{\frac{1}{\phi ^2}}</math></small>
|<small><math>\sqrt{0.381966}</math></small>
|<small><math>\sqrt{2} \phi </math></small>
|<small><math>2.28825</math></small>
|-
|<small><math>c_{4,1}</math></small>
|<small><math>41.4{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{7}\right\}</math></small>
|<small><math>\frac{c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>0.707107</math></small>
|<small><math>\frac{1}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{1}{2}}</math></small>
|<small><math>\sqrt{0.5}</math></small>
|<small><math>\phi ^2</math></small>
|<small><math>2.61803</math></small>
|-
|<small><math>c_{5,1}</math></small>
|<small><math>44.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{4}\right\}</math></small>
|<small><math></math></small>
|<small><math>2 \left\{\frac{15}{2}\right\}</math></small>
|<small><math>\sqrt{3} c_{2,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-3 \sqrt{5}}</math></small>
|<small><math>0.756934</math></small>
|<small><math>\frac{\sqrt{\frac{3}{2}}}{\phi }</math></small>
|<small><math>\sqrt{\frac{3}{2 \phi ^2}}</math></small>
|<small><math>\sqrt{0.572949}</math></small>
|<small><math>\sqrt{3} \phi </math></small>
|<small><math>2.80252</math></small>
|-
|<small><math>c_{6,1}</math></small>
|<small><math>49.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{17}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{5-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{5-\sqrt{5}}}{2}</math></small>
|<small><math>0.831254</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\frac{1}{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5}}{2 \phi }}</math></small>
|<small><math>\sqrt{0.690983}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^3}</math></small>
|<small><math>3.07768</math></small>
|-
|<small><math>c_{7,1}</math></small>
|<small><math>56.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{3}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>0.93913</math></small>
|<small><math>\frac{\sqrt{\frac{\psi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{0.881966}</math></small>
|<small><math>\sqrt{\psi \phi ^3}</math></small>
|<small><math>3.47709</math></small>
|-
|<small><math>c_{8,1}</math></small>
|<small><math>60{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{5}\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>\left\{6\right\}</math></small>
|<small><math>1</math></small>
|<small><math>1</math></small>
|<small><math>1.</math></small>
|<small><math>1</math></small>
|<small><math>\sqrt{1}</math></small>
|<small><math>\sqrt{1.}</math></small>
|<small><math>\sqrt{2} \phi ^2</math></small>
|<small><math>3.70246</math></small>
|-
|<small><math>c_{9,1}</math></small>
|<small><math>66.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{7}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{2 \phi }} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}-\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.09132</math></small>
|<small><math>\frac{\sqrt{\frac{\chi }{\phi }}}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\chi }{2 \phi }}</math></small>
|<small><math>\sqrt{1.19098}</math></small>
|<small><math>\sqrt{\chi \phi ^3}</math></small>
|<small><math>4.04057</math></small>
|-
|<small><math>c_{10,1}</math></small>
|<small><math>69.8{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{11}\right\}</math></small>
|<small><math>\phi c_{4,1}</math></small>
|<small><math>\frac{1+\sqrt{5}}{2 \sqrt{2}}</math></small>
|<small><math>1.14412</math></small>
|<small><math>\frac{\phi }{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^2}{2}}</math></small>
|<small><math>\sqrt{1.30902}</math></small>
|<small><math>\phi ^3</math></small>
|<small><math>4.23607</math></small>
|-
|<small><math>c_{11,1}</math></small>
|<small><math>72{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{6}\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\left\{5\right\}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{1}{\phi }} c_{8,1}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.17557</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{3-\phi }</math></small>
|<small><math>\sqrt{1.38197}</math></small>
|<small><math>\sqrt{2} \sqrt{3-\phi } \phi ^2</math></small>
|<small><math>4.3525</math></small>
|-
|<small><math>c_{12,1}</math></small>
|<small><math>75.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{24}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{3}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>1.22474</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{\frac{3}{2}}</math></small>
|<small><math>\sqrt{1.5}</math></small>
|<small><math>\sqrt{3} \phi ^2</math></small>
|<small><math>4.53457</math></small>
|-
|<small><math>c_{13,1}</math></small>
|<small><math>81.1{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{9-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>1.30038</math></small>
|<small><math>\frac{\sqrt{9-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(9-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{1.69098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(9-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>4.8146</math></small>
|-
|<small><math>c_{14,1}</math></small>
|<small><math>84.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{40}{9}\right\}</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi } c_{8,1}}{\sqrt{2}}</math></small>
|<small><math>\frac{1}{2} \sqrt[4]{5} \sqrt{1+\sqrt{5}}</math></small>
|<small><math>1.345</math></small>
|<small><math>\frac{\sqrt[4]{5} \sqrt{\phi }}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\sqrt{5} \phi }{2}}</math></small>
|<small><math>\sqrt{1.80902}</math></small>
|<small><math>\sqrt[4]{5} \sqrt{\phi ^5}</math></small>
|<small><math>4.9798</math></small>
|-
|<small><math>c_{15,1}</math></small>
|<small><math>90.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{7}\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>\left\{4\right\}</math></small>
|<small><math>2 c_{4,1}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>1.41421</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2}</math></small>
|<small><math>\sqrt{2.}</math></small>
|<small><math>2 \phi ^2</math></small>
|<small><math>5.23607</math></small>
|-
|<small><math>c_{16,1}</math></small>
|<small><math>95.5{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{29}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>1.4802</math></small>
|<small><math>\frac{\sqrt{11-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.19098}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(11-\sqrt{5}\right)} \phi ^2</math></small>
|<small><math>5.48037</math></small>
|-
|<small><math>c_{17,1}</math></small>
|<small><math>98.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{31}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>1.51954</math></small>
|<small><math>\frac{\sqrt{7+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(7+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.30902}</math></small>
|<small><math>\sqrt{\psi \phi ^5}</math></small>
|<small><math>5.62605</math></small>
|-
|<small><math>c_{18,1}</math></small>
|<small><math>104.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{8}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{4}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>1.58114</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{\frac{5}{2}}</math></small>
|<small><math>\sqrt{2.5}</math></small>
|<small><math>\sqrt{5} \sqrt{\phi ^4}</math></small>
|<small><math>5.8541</math></small>
|-
|<small><math>c_{19,1}</math></small>
|<small><math>108.0{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{9}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{10}{3}\right\}</math></small>
|<small><math>c_{3,1}+c_{8,1}</math></small>
|<small><math>\frac{1}{2} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.61803</math></small>
|<small><math>\phi </math></small>
|<small><math>\sqrt{1+\phi }</math></small>
|<small><math>\sqrt{2.61803}</math></small>
|<small><math>\sqrt{2} \phi ^3</math></small>
|<small><math>5.9907</math></small>
|-
|<small><math>c_{20,1}</math></small>
|<small><math>110.2{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13-\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>1.64042</math></small>
|<small><math>\frac{\sqrt{13-\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13-\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{2.69098}</math></small>
|<small><math>\phi ^2 \sqrt{8-\phi ^2}</math></small>
|<small><math>6.07359</math></small>
|-
|<small><math>c_{21,1}</math></small>
|<small><math>113.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{60}{19}\right\}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>1.67601</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{1}{1+\sqrt{5}}}</math></small>
|<small><math>\sqrt{2.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\chi }{\phi }}</math></small>
|<small><math>6.20537</math></small>
|-
|<small><math>c_{22,1}</math></small>
|<small><math>120{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{10}\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\left\{3\right\}</math></small>
|<small><math>\sqrt{3} c_{8,1}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>1.73205</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3}</math></small>
|<small><math>\sqrt{3.}</math></small>
|<small><math>\sqrt{6} \phi ^2</math></small>
|<small><math>6.41285</math></small>
|-
|<small><math>c_{23,1}</math></small>
|<small><math>124.0{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{120}{41}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{\phi }+\frac{5}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{5}{2}+\frac{2}{1+\sqrt{5}}}</math></small>
|<small><math>1.7658</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{4-\frac{\psi }{2 \phi }}</math></small>
|<small><math>\sqrt{3.11803}</math></small>
|<small><math>\sqrt{\chi \phi ^5}</math></small>
|<small><math>6.53779</math></small>
|-
|<small><math>c_{24,1}</math></small>
|<small><math>130.9{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{20}{7}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{11+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>1.81907</math></small>
|<small><math>\frac{\sqrt{11+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(11+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.30902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{\sqrt{5}}{\phi }}</math></small>
|<small><math>6.73503</math></small>
|-
|<small><math>c_{25,1}</math></small>
|<small><math>135.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{11}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{7+3 \sqrt{5}}</math></small>
|<small><math>1.85123</math></small>
|<small><math>\frac{\phi ^2}{\sqrt{2}}</math></small>
|<small><math>\sqrt{\frac{\phi ^4}{2}}</math></small>
|<small><math>\sqrt{3.42705}</math></small>
|<small><math>\phi ^4</math></small>
|<small><math>6.8541</math></small>
|-
|<small><math>c_{26,1}</math></small>
|<small><math>138.6{}^{\circ}</math></small>
|<small><math></math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{12}{5}\right\}</math></small>
|<small><math>\sqrt{\frac{7}{2}} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>1.87083</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{\frac{7}{2}}</math></small>
|<small><math>\sqrt{3.5}</math></small>
|<small><math>\sqrt{7} \phi ^2</math></small>
|<small><math>6.92667</math></small>
|-
|<small><math>c_{27,1}</math></small>
|<small><math>144{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{12}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{5}{2}\right\}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)} c_{8,1}</math></small>
|<small><math>\sqrt{\frac{1}{2} \left(5+\sqrt{5}\right)}</math></small>
|<small><math>1.90211</math></small>
|<small><math>\sqrt{\phi +2}</math></small>
|<small><math>\sqrt{2+\phi }</math></small>
|<small><math>\sqrt{3.61803}</math></small>
|<small><math>\phi ^2 \sqrt{2 \phi +4}</math></small>
|<small><math>7.0425</math></small>
|-
|<small><math>c_{28,1}</math></small>
|<small><math>154.8{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{30}{13}\right\}</math></small>
|<small><math>\frac{1}{2} \sqrt{13+\sqrt{5}} c_{8,1}</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>1.95167</math></small>
|<small><math>\frac{\sqrt{13+\sqrt{5}}}{2}</math></small>
|<small><math>\sqrt{\frac{1}{4} \left(13+\sqrt{5}\right)}</math></small>
|<small><math>\sqrt{3.80902}</math></small>
|<small><math>\phi ^2 \sqrt{8-\frac{1}{\phi ^2}}</math></small>
|<small><math>7.22598</math></small>
|-
|<small><math>c_{29,1}</math></small>
|<small><math>164.5{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{14}\right\}</math></small>
|<small><math></math></small>
|<small><math>\left\{\frac{15}{7}\right\}</math></small>
|<small><math>\phi c_{12,1}</math></small>
|<small><math>\frac{1}{2} \sqrt{\frac{3}{2}} \left(1+\sqrt{5}\right)</math></small>
|<small><math>1.98168</math></small>
|<small><math>\sqrt{\frac{3}{2}} \phi </math></small>
|<small><math>\sqrt{\frac{3 \phi ^2}{2}}</math></small>
|<small><math>\sqrt{3.92705}</math></small>
|<small><math>\sqrt{3} \phi ^3</math></small>
|<small><math>7.33708</math></small>
|-
|<small><math>c_{30,1}</math></small>
|<small><math>180{}^{\circ}</math></small>
|<small><math>\left\{\frac{30}{15}\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>\left\{2\right\}</math></small>
|<small><math>2 c_{8,1}</math></small>
|<small><math>2</math></small>
|<small><math>2.</math></small>
|<small><math>2</math></small>
|<small><math>\sqrt{4}</math></small>
|<small><math>\sqrt{4.}</math></small>
|<small><math>2 \sqrt{2} \phi ^2</math></small>
|<small><math>7.40492</math></small>
|-
|rowspan=4 colspan=6|
|rowspan=4 colspan=4|
<small><math>\phi</math></small> is the golden ratio:<br>
<small><math>\phi ^2-\phi -1=0</math></small><br>
<small><math>\frac{1}{\phi }+1=\phi</math></small>, and: <small><math>\phi+1=\phi^2</math></small><br>
<small><math>\frac{1}{\phi }::1::\phi ::\phi ^2</math></small><br>
<small><math>1/\phi</math></small> and <small><math>\phi</math></small> are the golden sections of <small><math>\sqrt{5}</math></small>:<br>
<small><math>\phi +\frac{1}{\phi }=\sqrt{5}</math></small>
|colspan=2|<small><math>\phi = (\sqrt{5} + 1)/2</math></small>
|<small><math>1.618034</math></small>
|-
|colspan=2|<small><math>\chi = (3\sqrt{5} + 1)/2</math></small>
|<small><math>3.854102</math></small>
|-
|colspan=2|<small><math>\psi = (3\sqrt{5} - 1)/2</math></small>
|<small><math>2.854102</math></small>
|-
|colspan=2|<small><math>\psi = 11/\chi = 22/(3\sqrt{5} + 1)</math></small>
|<small><math>2.854102</math></small>
|}
== The 5-cell 4-simplex ==
...
== The 16-cell 4-orthoplex ==
In 2-space we have the regular 8-point octagon, in 3-space the regular 8-point cube, and in 4-space the regular 8-point [[16-cell]].
A planar octagon with rigid edges of unit length has chords of length:
:<math>r_1=1,r_2=\sqrt{2+\sqrt{2}} \approx 1.848,r_3=\sqrt{2}+1 \approx 2.414,r_4=\sqrt{4 + \sqrt{8}} \approx 2.613</math>
The chord ratio <math>r_3=\sqrt{2}+1</math> is a geometrical proportion, the [[W:Silver ratio|silver ratio]]. Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_3-r_1-r_1=1/r_3 \approx 0.414</math>
Note that <math>r_3-2=1/r_3=\sqrt{2}-1</math>. The procedure rotates counterclockwise over three <math>r_3</math> chords of an {8/3} octagram. Over the first <math>r_3</math> chord the displacement is <math>\sqrt{2}+r_1</math>. Over the second <math>r_3</math> chord it moves in the opposite direction a distance of <math>-r_1</math> . Over the third <math>r_3</math> chord it moves a distance of <math>-r_1</math>.
If we embed the planar octagon in 3-space, we can make it skew, repositioning its vertices so that each is one unit-edge length distant from three others instead of two others, at the vertices of a unit-edge cube with chords of length:
:<math>r_1=1, r_2=\sqrt{2}, r_3=\sqrt{3}, r_4=\sqrt{2}</math>
If we embed this cube in 4-space, we can skew it some more, repositioning its vertices so that each is one unit-edge length distant from six others instead of three others, at the vertices of a unit-edge 4-polytope with chords of length:
:<math>r_1=1,r_2=1,r_3=1,r_4=\sqrt{2}</math>
All of its chords except its long diameters are the same unit length as its edge. In fact they are its 24 edges, and it is a 16-cell of radius <math>1/\sqrt{2}</math>.
[[File:octagon16cell.png|thumb|Orthogonal projection of a regular 16-cell to the [[16-cell#Projections|B<sub>4</sub> Coxeter plane]]. Only its edges are shown; its long diameter chords are not drawn. All 24 edges are the same length and none lie parallel to the projection plane. The octagon circumference is a Petrie polygon. The two disjoint squares lie in completely orthogonal central planes. The blue octagram is a Clifford polygon. ]]
The [[16-cell]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{3,3,4\}</math></small>. It has 8 vertices, 24 edges, 32 equilateral triangle faces, and 16 regular tetrahedron cells. It is the [[16-cell#Octahedral dipyramid|four-dimensional analogue of the octahedron]], and each of its four orthogonal central hyperplanes is an octahedron.
The only planar regular polygons found in the 16-cell are face triangles and central plane squares, but the 16-cell also contains a skew regular octagon, its [[W:Petrie polygon|Petrie polygon]].{{Efn|name=Petrie polygon of a honeycomb}} The chords of this regular octagon, which lies skew in 4-space, are those given above for the 16-cell, as opposed to those for the cube or the regular octagon in the plane. The 16-cell is a construct of 3 Petrie octagons which share the same 8 vertices but have disjoint sets of 8 edges each.
The regular octad has higher symmetry in 4-space than it does in 2-space. The 16-cell is the 4-[[w:Cross-polytope|orthoplex]], the simplest regular 4-polytope after the [[5-cell|4-simplex]]. All the larger regular convex 4-polytopes are compounds of the 16-cell. The regular octagon exhibits this high symmetry only when embedded in 4-space at the vertices of the 16-cell.
The 16-cell constitutes an [[W:Orthonormal basis|orthonormal basis]] for the choice of a 4-dimensional Cartesian reference frame, because its vertices define four orthogonal axes. The eight vertices of a unit-radius 16-cell are (±1, 0, 0, 0), (0, ±1, 0, 0), (0, 0, ±1, 0), (0, 0, 0, ±1). All vertices are connected by <math>\sqrt{2}</math> edges except opposite pairs.
The vertex coordinates of the 16-cell form 6 central squares lying in 6 pairwise [[W:Orthogonal|orthogonal]] coordinate planes. Great squares in opposite planes that do not share an axis (e.g. in the ''xy'' and ''wz'' planes) are completely disjoint (they do not intersect at any vertices). These planes are [[W:Completely orthogonal|completely orthogonal]].{{Efn|name=Six orthogonal planes of the Cartesian basis}}
Since the unit-radius coordinate system is convenient, let us derive the unit-radius 16-cell by skewing a unit-radius planar octagon, which has chords of length:
:<math>r_1=\sqrt{2-\sqrt{2}} \approx 0.765,r_2=\sqrt{2},r_3=\sqrt{2+\sqrt{2}} \approx 1.848,r_4=2</math>
We will need a planar octagon with rigid <math>r_2</math> chords, rather than one with rigid <math>r_1</math> edges. The octagon's <math>r_2</math> chords form two disjoint great squares, visible in the orthogonal projection, which we can reposition in 3-space to form a cube by making them parallel, and in 4-space to form a 16-cell by making them completely orthogonal.
Since the edges of the 16-cell are all the same length <math>r_1=\sqrt{2},r_2=\sqrt{2},r_3=\sqrt{2}</math>, those chords are distinct only in the context of a rotation. Each chord is a 4-vector with a length and a direction. The rotational curve over each <math>r_i</math> chord makes <math>i</math> 45° turns.
[[File:16-cell-orig.gif|thumb|Orthographic projection of the 8-point 16-cell <small><math>\{3,3,4\}</math></small> performing a double rotation.{{Sfn|Hise|2007}}]]
[[W:Rotations in 4-dimensional Euclidean space|Rotations in 4-dimensional Euclidean space]] can be seen as the composition of two 2-dimensional rotations in completely orthogonal planes. The general rotation in 4-space is a [[W:SO(4)#Double rotations|double rotation]] in pairs of completely orthogonal planes. Two completely orthogonal planes are called invariant planes of the rotation when all points in the plane rotate on circles that remain in the plane, even as the whole plane tilts sideways (like a coin flipping) into another plane. The two completely orthogonal rotations of each plane (like a wheel, and like a coin flipping) are simultaneous but independent, in that they are not geometrically constrained to turn at the same rate. However, the most circular kind of rotation (as opposed to an elliptical double rotation of a rigid spherical object) occurs when the completely orthogonal planes do rotate through the same angle in the same time interval. Such equi-angled double rotations are called [[w:SO(4)#Isoclinic_rotations|isoclinic]], also [[w:William_Kingdon_Clifford|Clifford]] displacements.
The <math>r_1</math> chords of the 16-cell form a Petrie polygon which zig-zags back and forth, in the left and right rotational directions, between two completely orthogonal great squares formed by <math>r_2</math> chords.
The <math>r_2</math> chords of two completely orthogonal great squares lie parallel and perpendicular to each other. A ''simple'' rotation of the 16-cell in ''one'' of those two square central planes rotates that square like a wheel, while the other square does not move.{{Efn|name=simple rotations}} The four vertices of the rotating square orbit on a great circle in the plane.
The <math>r_3</math> chords of the 16-cell form a circular helix, visible as a blue {8/3} octagram in the orthogonal projection. A ''double'' rotation of the 16-cell, in both of two completely orthogonal invariant <math>r_2</math> square planes at once by equal angles, moves the eight vertices along the circular helix over the <math>r_3</math> chords. The vertex motion is a [[w:Geodesic|geodesic]] circle orbit on the 3-sphere of a special kind: it does not lie in a central plane, its [[w:Winding_number|winding number]] is not 1 (it is 3 in this case), its circumference is not <math>2\pi</math>, and it moves in either a left or right handed circular spiral. We shall refer to such a chiral circle orbit as an ''isocline'', and to the skew polygram of its rotational chords as a ''Clifford polygon''.
The 16-cell is the simplest possible frame in which to [[16-cell#Rotations|observe 4-dimensional rotations]] because its characteristic rotations feature a single pair of invariant rotation planes. In the 16-cell an isoclinic rotation by 90° in any pair of invariant completely orthogonal square central planes takes every great square to its completely orthogonal great square in a twisting displacement, as the invariant planes tilt sideways 90° into each other's plane while rotating 90° internally. All the vertices move at once along the same circular helix geodesic isocline of <math>r_3</math> chords, displaced 90° in 8 orthogonal directions, and the rigid 16-cell assumes a new orientation in 4-space. When the 90° isoclinic rotation is continued in the same rotational direction through an additional 90°, each vertex is again displaced 90°, but from the new orientation in a direction orthogonal to its first 90° displacement. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. In 360° of isoclinic rotation over four <math>r_3</math> chords, each vertex makes six 90° turns and reaches its antipodal position.
The trajectory of each vertex over each 90° isoclinic rotational displacement is a one-eighth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>6\pi</math> over eight <math>r_3</math> chords, and also traces an ordinary great circle in the plane twice, over the four <math>r_2</math> edges of a great square in one of the two moving invariant rotation planes. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions just once and returns to its original position, and the 16-cell returns to its original orientation.
Because this is the isoclinic rotation of the 16-cell in its invariant edge planes we shall refer to it as the ''characteristic rotation of the 16-cell'', and note once again that it is Fontaine and Hurley's rotation over the <math>r_3</math> star polygon which constructs <math>1/r_3</math>.
== The 8-cell tesseract ==
The long diameter of the unit-edge [[W:Hypercube|hypercube]] of dimension <math>n</math> is <math>\sqrt{n}</math>, so the unit-edge [[w:Tesseract|4-hypercube, the 16-point (8-cell) tesseract,]] has chords:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
Uniquely in its 4-dimensional case, the hypercube's edge length equals its radius, like the hexagon. We call such polytopes ''radially equilateral'', because they can be constructed from equilateral triangles which meet at their center, each contributing two radii and an edge. The [[w:Cuboctahedron|cuboctahedron]] and the 24-cell are also radially equilateral.
[[File:8-cell.gif|thumb|Orthographic projection of the 16-point (8-cell) tesseract <small><math>\{4,3,3\}</math></small> performing a simple rotation about a plane in 4-space.{{Sfn|Hise|2007}} The stationary plane bisects the figure from front-left to back-right and top to bottom.]]
The [[W:Tesseract|tesseract]] is the [[W:Regular convex 4-polytope|regular convex 4-polytope]] with [[W:Schläfli symbol|Schläfli symbol]] <small><math>\{4,3,3\}</math></small>. It has 16 vertices, 32 edges, 24 square faces, and 8 cube cells. It is the four-dimensional analogue of the cube.
The 16-point tesseract is the convex hull of a compound of two 8-point 16-cells, in exact dimensional analogy to the way the 8-point cube is the convex hull of a [[W:Stellated octahedron|compound of two 4-point regular tetrahedra]]. The [[W:Demihypercube|demihypercubes]] occupy alternate vertices of the hypercubes. The diagonals of the square faces of the unit-edge, unit-radius tesseract are the <math>\sqrt{2}</math> edges of two unit-radius 16-cells, also the edges of the square central planes.
We can rotate the tesseract isoclinically the way we rotated the 16-cell, by 90° in completely orthogonal invariant square central planes, with the same effect on both alternate-position 16-cells. In the course of a 720° isoclinic rotation in invariant square central planes each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cell. The two skew {8/3} octagram Clifford polygons lie on two disjoint parallel isoclines of the same chirality, of circumference <math>6\pi</math> over <math>\sqrt{2}</math> chords. They form a circular double helix which intersects each vertex of the tesseract once.
The tesseract is the [[W:Dual polytope|dual polytope]] of the 16-cell. They have the same Petrie polygon, the regular skew octagon, but the tesseract is a construct of 4 Petrie octagons with disjoint sets of 8 tesseract edges each. We can construct the tesseract by skewing two planar octagons. Because the tesseract is radially equilateral (unlike the 16-cell), we use two octagons of unit-edge length to build the unit-radius tesseract. To start we embed the planar octagons in 4-space at the same point and make them completely orthogonal. Then we skew each planar octagon into a cube, so we have a compound of two completely orthogonal cubes, provided we skewed them both in the same direction. The 16 vertices will be the vertices of a tesseract with half its 32 edges missing.
Because the tesseract contains two 16-cells in alternate positions it has two sets of 6 orthogonal square central planes. Two angles are required to specify the relationship between two planes in 4-space. Pairs of square central planes within each 16-cell are 90° apart in one angle, and either 0° or 90° apart in the other angle. They are 90° apart in both angles if and only if they are completely orthogonal planes, 90° apart by isoclinic rotation, with no vertices in common. Otherwise they are 0° apart in one of the angles, 90° apart by simple rotation, and they intersect in one axis and lie in a common 3-dimensional hyperplane.{{Efn|A double rotation in which one of the two angles of rotation is 0°, so that one of the completely orthogonal invariant planes does not rotate, is called a simple rotation. Ordinary rotations observed in a 3-dimensional space are simple rotations.|name=simple rotations}}
A pair of square central planes from alternate-position 16-cells are 60° apart by isoclinic rotation, with their corresponding vertices 120° apart. The planes are not orthogonal or parallel, so they intersect in a line somewhere, but they have no vertices in common, they have no 3-dimensional hyperplane in common, and they cannot reach each other by simple rotation. Such pairs of objects are called [[W:Clifford parallel|Clifford parallel]] because all their corresponding pairs of vertices are the same distance apart, although they are not parallel in the usual sense, because they have a common center. Not only the alternate-position 16-cells' corresponding square central planes, but also the 16-cells themselves, are Clifford parallel objects. More generally, multiple disjoint instances of a 4-polytope which compound to make a larger 4-polytope are Clifford parallel objects.
== The 24-cell ==
[[File:24-cell vertex geometry.png|thumb|Planar geometry of the radially equilateral 24-cell, showing its 3 great circle polygons and its 4 chord lengths.]]
In 2-space we have the radially equilateral 6-point hexagon. In 3-space we have the radially equilateral 12-point cuboctahedron, with 4 hexagonal central planes. In 4-space we have the radially equilateral 24-point 24-cell, with 12 cuboctahedron central hyperplanes and 16 hexagonal central planes.
The [[24-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,4,3\}</math></small>. It has 24 vertices, 96 edges, 96 equilateral triangle faces, and 24 octahedron cells. It is the four-dimensional analogue of the cuboctahedron.
The 24-cell has the same chord set as the 4-hypercube tesseract:
:<math>r_1=\sqrt{1},r_2=\sqrt{2},r_3=\sqrt{3},r_4=\sqrt{4}</math>
[[Image:24-cell.gif|thumb|Orthographic projection of the 24-point 24-cell <small><math>\{3,4,3\}</math></small> performing a simple rotation.{{Sfn|Hise|2007}} The 3-dimensional surface made of 24 octahedra is visible.]]
The 24-cell is [[W:Dual polytope|self-dual]], like the regular polygons and regular simplexes. It is the maximal regular construct of triangles and squares (with no pentagons). It is the convex hull of a compound of three disjoint 8-point 16-cells, rotated 60° isoclinically with respect to each other. Each of the three pairs of 16-cells is a tesseract. Each 24-cell edge is also a tesseract edge. The corresponding vertices of two 16-cells or two tesseracts are 120° apart by a <math>\sqrt{3}</math> chord. Each tesseract has 8 cube cells, and each cube has four <math>\sqrt{3}</math> long diameters. The <math>\sqrt{3}</math> chords joining the corresponding vertices of two tesseracts belong to the third tesseract as cell long diameters.
The 24-cell's Petrie polygon is the regular dodecagon {12}, which has chords:
:<math>r_1=\tfrac{\sqrt{3}-1}{\sqrt{2}} \approx 0.518,r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\tfrac{\sqrt{3}+1}{\sqrt{2}} \approx 1.932,r_6=\sqrt{4}</math>
Fontaine and Hurley's procedure for obtaining the reciprocal of a chord tells us that:
:<math>r_5-r_3+r_1+r_1-r_3=1/r_5</math>
when <math>r_1=1</math>. The procedure rotates counterclockwise over five <math>r_5</math> chords of a {12/5} dodecagram. In the system of unit-radius coordinates <math>r_1=1/r_5</math>.
The <math>r_1</math> and <math>r_5</math> chords of the planar dodecagon do not occur in the 24-cell, which is a construct of eight skew dodecagons with disjoint sets of twelve <math>\sqrt{1}</math> edges each. In the skew dodecagons the chord lengths are:
:<math>r_1=\sqrt{1},r_2=\sqrt{1},r_3=\sqrt{2},r_4=\sqrt{3},r_5=\sqrt{3},r_6=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
[[File:dodecagon24cell.png|thumb|Orthogonal projection of half a 24-cell to the [[24-cell#Geodesics|F<sub>4</sub> Coxeter plane]]. Only one Petrie dodecagon {12} of the 24-cell is shown. In a unit-radius 24-cell, all black lines are 24-cell edges of unit length, also tesseract edges. The two disjoint hexagons lie in Clifford parallel central planes. Blue chords are <math>\sqrt{2}</math> 16-cell edges, also isocline chords in square rotations. Green chords are <math>\sqrt{3}</math> distances between corresponding vertices of two 16-cells, also isocline chords in hexagonal rotations. Note the {12/5} dodecagram.]]
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_3=\sqrt{2}</math></small>]]
We can rotate the 24-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in completely orthogonal invariant great square planes, with the same effect on all three 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, but it does not visit the vertex positions of the other 16-cells. The <math>r_3=\sqrt{2}</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Three Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_3</math> chords form a circular triple helix {24/9}=3{8/3} that intersects each 24-cell vertex once.
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_5=\sqrt{3}</math></small> ]]
We can also rotate the 24-cell isoclinically in 4 Clifford parallel invariant great hexagon planes containing its vertices, over <math>r_{5}=\sqrt{3}</math> isocline chords. This is the ''characteristic rotation of the 24-cell'' in its invariant edge planes, also Fontaine and Hurley's rotation over the <math>r_5</math> star polygon which constructs <math>1/r_5</math>. A complete hexagonal isoclinic revolution requires 720° like a complete square isoclinic revolution, but it is completed in 12 isoclinic displacements of 60° each rather than 8 isoclinic displacements of 90° each. The rotational curve over each 120° <math>r_5</math> chord makes five 30° turns. Two Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_5</math> chords form a circular double helix {24/10}=2{12/5} that intersects each 24-cell vertex once.
In the 24-cell the characteristic isoclinic rotation by 60° in any invariant hexagon central plane takes every great hexagon to a Clifford parallel great hexagon in a twisting displacement, as all the central planes tilt sideways 60° while rotating 60° internally. It also takes every great square to a Clifford parallel great square in another 16-cell; it takes every 16-cell to another 16-cell. The 16-cells revolve within the 24-cell as well as rotating within it. All 24 vertices move at once on two Clifford parallel geodesic isoclines, displaced 120° in different directions.
The trajectory of each vertex over each 60° isoclinic rotational displacement is a one-twelfth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>10\pi</math> over twelve <math>\sqrt{3}</math> chords, and also traces an ordinary great circle in the plane twice, over the six <math>\sqrt{1}</math> edges of a great hexagon in a moving invariant rotation plane. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions just once and returns to its original position, and the 24-cell returns to its original orientation.
== The 600-cell ==
[[Image:600-cell.gif|thumb|Orthographic projection of the 120-point 600-cell <small><math>\{3,3,5\}</math></small> performing a simple rotation.{{Sfn|Hise|2011}} The 3-dimensional surface made of 600 tetrahedra is visible. Invisible in this rendering are 25 inscribed instances of the 24-cell (above), which occur in the 600-cell as interior boundary envelopes.]]
The [[600-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{3,3,5\}</math></small>. It has 120 vertices, 720 edges, 1200 equilateral triangle faces, and 600 tetrahedron cells. It is the four-dimensional analogue of the icosahedron.
The 600-cell rounds out the 24-cell by adding 96 more vertices (four more disjoint 24-cells) between the 24-cell's existing 24 vertices, in effect adding twenty-four more distinct 24-cells inscribed in the 600-cell. The new surface thus formed is a honeycomb of smaller, more numerous cells: tetrahedra of edge length <math>\phi^{-1} \approx 0.618</math> instead of octahedra of edge length <math>\sqrt{1}</math>. It encloses the <math>\sqrt{1}</math> edges of the 24-cells, which become invisible interior chords in the 600-cell, like the <math>\sqrt{2}</math> and <math>\sqrt{3}</math> chords.
Since the tetrahedra are made of shorter triangle edges than the octahedra (by a factor of <math>\phi^{-1}</math>, the inverse golden ratio), the 600-cell is not radially equilateral like the 24-cell and the tesseract. Like them it is radially triangular in a special way, but one in which [[w:Golden_triangle_(mathematics)|golden triangles]] rather than equilateral triangles meet at the center.
In 2-space we have the ''radially golden'' [[W:Decagon#The golden ratio in decagon|regular decagon]]. In 3-space we have the radially golden 30-point [[W:icosidodecahedron|icosidodecahedron]], with 6 decagon central planes. In 4-space we have the radially golden 120-point 600-cell, with 60 icosidodecahedron central hyperplanes and 72 decagon central planes.
The 600-cell's Petrie polygon is the regular [[w:Triacontagon|triacontagon {30}]]. The unit-radius planar {30}-gon has these distinct chords:
:<math>r_1=2 \sin (\tfrac{\pi}{15}/2) \approx 0.209</math>
:<math>r_2=2 \sin (\tfrac{2\pi}{15}/2) \approx 0.416</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{4\pi}{15}/2) \approx 0.813</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{7\pi}{15}/2) \approx 1.338</math>
:<math>r_8=2 \cos (\tfrac{7\pi}{15}/2) \approx 1.486</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{11}=2 \cos (\tfrac{4\pi}{15}/2) \approx 1.827</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \cos (\tfrac{2\pi}{15}/2) \approx 1.956</math>
:<math>r_{14}=2 \cos (\tfrac{\pi}{15}/2) \approx 1.989</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Only the chord lengths <math>r_3</math>, <math>r_5</math>, <math>r_6</math>, <math>\sqrt{2}</math>, <math>r_9</math>, <math>r_{10}</math>, <math>r_{12}</math>, <math>r_{15}</math> occur in the 600-cell, which is a construct of 24 Petrie {30}-gons of edge length <math>r_3</math>, six of which intersect in each icosahedral vertex figure. In the skew {30}-gons the chord lengths are:
[[File:600-cell vertex geometry.png|thumb|Planar geometry of the 600-cell, showing its 5 regular great circle polygons and its 8 chord lengths with angles of arc. The golden ratio governs the fractional roots of every other chord, and the radial golden triangles which meet at the center.|400x400px]]
:<math>r_1=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_2=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_3=2 \sin (\tfrac{\pi}{5}/2)=\phi^{-1} \approx 0.618</math>
:<math>r_4=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}</math>
:<math>r_5=2 \sin (\tfrac{\pi}{3}/2)=\sqrt{1}=\text{24-cell-}r_2</math>
:<math>r_6=2 \sin (\tfrac{2\pi}{5}/2)=\sqrt{3-\phi} \approx 1.176</math>
:<math>r_7=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}</math>
:<math>r_8=2 \sin (\tfrac{\pi}{2}/2)=\sqrt{2}=\text{16-cell-}r_3</math>
:<math>r_9=2 \sin (\tfrac{3\pi}{5}/2)=\phi \approx 1.618</math>
:<math>r_{10}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}=\text{24-cell-}r_5</math>
:<math>r_{11}=2 \sin (\tfrac{2\pi}{3}/2)=\sqrt{3}</math>
:<math>r_{12}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{13}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{14}=2 \sin (\tfrac{4\pi}{5}/2)=\sqrt{2+\phi} \approx 1.902</math>
:<math>r_{15}=2 \sin (\pi/2)=\sqrt{4}</math>
Where chords are the same length, they are distinct only in the context of a rotation.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="7" |15 chords (4 distinct 180° pairs) make 4 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>r_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>r_{15}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>r_1</math>
|36°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}=2{15/7}
|144°
| rowspan="3" |<math>r_{14}</math>
|- style="background: palegreen;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: palegreen;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>r_2</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|144°
| rowspan="3" |<math>r_{13}</math>
|- style="background: gainsboro;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: gainsboro;" |
|0.618~
|1.902~
|- style="background: yellow;" |
| rowspan="3" |<math>r_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |[[File:V1 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>r_{12}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_4</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|120°
| rowspan="3" |<math>r_{11}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: palegreen;" |
| rowspan="3" |<math>r_5</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |[[File:V2 dodecahedron.png|100px]]<br>Dodecahedron
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>r_{10}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: yellow;" |
| rowspan="3" |<math>r_{6}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |[[File:V3 icosahedron.png|100px]]<br>Icosahedron
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>r_{9}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: seashell;" |
| rowspan="3" |<math>r_{7}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |[[File:V4 icosidodecahedron.png|100px]]<br>Icosidodecahedron
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>r_{8}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The list of 600-cell chords <math>r_{i}</math> can be rearranged into a table of 8 rows and 2 columns with a pair of 180° complements in each row. The short chord and long chord each have their characteristic {30}-gon. Each row identifies a discrete isoclinic rotation of the 600-cell in invariant central planes containing the edges of the short chord {30}-gon, over the isocline chords of the long chord {30}-gon, the rotation's Clifford polygon.
Each distinct pair of complementary chord lengths is identified with a distinct [[w:600-cell#Polyhedral sections|polyhedral section of the 600-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 7 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>\phi^{-1}</math> is a icosahedron vertex figure, and the largest section at radial distance <math>\sqrt{2}</math> is an [[W:Icosidodecahedron|icosidodecahedron]] central section bisecting the 600-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>\sqrt{2}</math> the successive complement-radius polyhedra decrease in size, to the antipodal icosahedron vertex figure at distance <math>\sqrt{2+\phi}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 7 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section).
[[File:Regular_star_figure_3(8,3).svg|thumb|left|150px|{24/9}=3{8/3} <small><math>r_8=\sqrt{2}</math></small>]]
We can rotate the 600-cell isoclinically in the characteristic rotation of the 16-cell, by 90° in two completely orthogonal invariant great square planes over <math>r_8=\sqrt{2}</math> isocline chords, with the same effect on 15 disjoint 16-cells. In the course of a 720° isoclinic rotation each vertex departs from all 8 vertex positions of its 16-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_8</math> chord is the 16-cell <math>r_3</math> chord. The rotational curve over each 90° <math>r_3</math> chord makes three 45° turns. Fifteen Clifford parallel {8/3} octagram geodesic isoclines of circumference <math>6\pi</math> over <math>r_8</math> chords form a circular helix of 15 twisted parallel strands 5{24/9}=15{8/3} that intersects each 600-cell vertex once.
In the 600-cell this 90° isoclinic rotation in completely orthogonal great square planes takes place over <math>r_7</math> edge chords and <math>r_8</math> isocline chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/7} polygon is a skew helix with each edge belonging to a distinct great square. The vertices of the invariant great squares of this rotation each make seven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 90° {30/7} isocline chord makes seven 12° turns. Four Clifford parallel {30/7} geodesic isoclines of circumference <math>14\pi</math> form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular star figure 2(12,5).svg|thumb|left|150px|{24/10}=2{12/5} <small><math>r_{11}=\sqrt{3}</math></small> ]]
We can also rotate the 600-cell isoclinically in the characteristic rotation of the 24-cell, by 60° in great hexagon planes, with the same effect on 5 disjoint 24-cells. In the course of a 720° isoclinic rotation each vertex departs from 12 vertex positions of its 24-cell just once and returns to its original position, without visiting other vertex positions. The <math>r_{5}</math> chord is the 24-cell <math>r_2</math> chord, and the <math>r_{10}</math> chord is the 24-cell <math>r_5</math> chord. The rotational curve over each <math>r_{10}</math> chord makes five 30° turns. Ten Clifford parallel {12/5} dodecagram geodesic isoclines of circumference <math>10\pi</math> over <math>r_{10}</math> chords form a circular helix of 10 twisted parallel strands 5{24/10}=10{12/5} that intersects each 600-cell vertex once.
In the 600-cell this 60° isoclinic rotation in great hexagon planes takes place over <math>r_{4}=\sqrt{1}</math> edge chords and <math>r_{11}=\sqrt{3}</math> isocline chords, where it has period 30 and visits every vertex of a 600-cell Petrie polygon. The {30/11} polygon is a skew helix with each <math>r_{11}</math> chord the <math>\sqrt{3}</math> diagonal of a distinct great hexagon. The vertices of the invariant great hexagons of this rotation each make eleven orbits on a great circle within the moving invariant plane in the course of one complete isoclinic revolution. The rotational curve over each 120° <math>r_{11}</math> isocline chord makes eleven 12° turns. Four Clifford parallel {30/11} geodesic isoclines of circumference <math>22\pi</math> over <math>r_{11}</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
{{Clear}}
[[File:Regular_star_figure_2(15,4).svg|thumb|left|150px|{30/8}=2{15/4} <small><math>r_{13}=\sqrt{1}</math></small>]]
We can also rotate the 600-cell isoclinically in 12 Clifford parallel invariant decagon central planes containing its 36° <math>r_{3}</math> edges, over 144° <math>r_{13}</math> isocline chords. This is the ''characteristic rotation of the 600-cell'' in its invariant edge planes. Its Clifford polygon is a skew {30/13} polygram of <math>r_{13}</math> chords. The rotational curve over each <math>r_{13}</math> chord makes thirteen 12° turns. Four Clifford parallel {30/13} geodesic isoclines of circumference <math>26\pi</math> over <math>r_{13}</math> chords form a circular quadruple helix that intersects each 600-cell vertex once.
In the 600-cell this characteristic isoclinic rotation by 36° in any invariant decagon central plane takes every great decagon to a Clifford parallel great decagon in a twisting displacement, as all the central planes tilt sideways 36° while rotating 36° internally. It also takes every great hexagon to a Clifford parallel great hexagon in another 24-cell, and every great square to a Clifford parallel great square in another 16-cell; it takes 24-cells to a non-disjoint 24-cell and 16-cells to a 16-cell in another 24-cell. The 24-cells revolve within the 600-cell, as the 16-cells revolve within the 24-cells. All 120 vertices move at once on four Clifford parallel geodesic isoclines, displaced 144° in different directions.
The trajectory of each vertex over each 36° isoclinic rotational displacement is a one-fifteenth segment of its geodesic orbit. Its entire orbit traces an isocline circle in 4-space of circumference <math>5\pi</math> over 15 <math>r_5</math> chords, and also traces an ordinary great circle in the plane 3 times, over the 5 edges of a great pentagon in a moving invariant rotation plane. In the course of a complete isoclinic revolution each vertex departs from 15 vertex positions just once and returns to its original position, and the 600-cell returns to its original orientation.
{{Clear}}
[[File:Regular_star_figure_6(5,2).svg|thumb|left|150px|{30/12}=6{5/2} <small><math>r_{12}=\sqrt{3.618\sim}</math></small>]]
In the 600-cell there is another distinct isoclinic rotation taking decagon planes to each other, over 144° <math>r_{12}</math> isocline chords. It also takes disjoint 24-cells to each other. This rotation has period 5 and visits every 12th vertex of a 600-cell Petrie polygon. Its Clifford polygon is a skew {5/2} pentagram of <math>r_{12}</math> chords. The invariant central planes of this rotation each intersect only one vertex of the 600-cell, which makes two orbits of a great pentagon within the moving invariant plane in the course of one complete isoclinic revolution of period 5. The rotational curve over each <math>r_{12}</math> chord makes twelve 12° turns. 24 Clifford parallel {5/2} pentagram geodesic isoclines of circumference <math>4\pi</math> over five <math>r_{12}</math> chords form a circular helix of 24 twisted parallel strands 4{30/12}=24{5/2} that intersects each 600-cell vertex once.
{{Clear}}
== Finally the 120-cell ==
The [[120-cell]] is the regular convex 4-polytope with Schläfli symbol <small><math>\{5,3,3\}</math></small>. It has 600 vertices, 1200 edges, 720 pentagon faces, and 120 dodecahedron cells. It is the four-dimensional analogue of the dodecahedron.
The 120-cell is the [[W:Dual polytope|dual polytope]] of the 600-cell. They have the same Petrie polygon, the regular skew triacontagon {30}, but the 120-cell is a construct of 40 Petrie {30}-gons of edge length <math>c_1</math>, two of which intersect in each tetrahedral vertex figure.
{| class="wikitable floatright" style="white-space:nowrap;text-align:center"
! colspan="9" |30 chords (15 180° pairs) make 15 distinct section polyhedra
|-
! colspan="3" |Short chord
! Section
! colspan="3" |Long chord
|- style="background: palegreen;" |
| rowspan="3" |<math>c_0</math>
|0°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_15(2,1).svg|100px]]<br>{30/15}=15{2}
|180°
| rowspan="3" |<math>c_{30}</math>
|- style="background: palegreen;" |
|{{radic|0}}
|{{radic|4}}
|- style="background: palegreen;" |
|0
|2
|- style="background: palegreen;" |
| rowspan="3" |<math>c_1</math>
|15.5~°
| rowspan="3" |[[File:Regular_polygon_30.svg|100px]]<br>{30/1}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,7).svg|100px]]<br>{30/14}
|164.5~°
| rowspan="3" |<math>c_{29}</math>
|- style="background: palegreen;" |
|{{radic|0.073~}}
|{{radic|3.927~}}
|- style="background: palegreen;" |
|0.270~
|1.982~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_2</math>
|25.2~°
| rowspan="3" |[[File:Regular_star_figure_2(15,1).svg|100px]]<br>{30/2}=2{15}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-13.svg|100px]]<br>{30/13}
|154.8~°
| rowspan="3" |<math>c_{28}</math>
|- style="background: gainsboro;" |
|{{radic|0.191~}}
|{{radic|3.809~}}
|- style="background: gainsboro;" |
|0.437~
|1.952~
|- style="background: yellow;" |
| rowspan="3" |<math>c_3</math>
|36°
| rowspan="3" |[[File:Regular_star_figure_3(10,1).svg|100px]]<br>{30/3}=3{10}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_6(5,2).svg|100px]]<br>{30/12}=6{5/2}
|144°
| rowspan="3" |<math>c_{27}</math>
|- style="background: yellow;" |
|{{radic|0.382~}}
|{{radic|3.618~}}
|- style="background: yellow;" |
|0.618~
|1.902~
|- style="background: gainsboro;" |
| rowspan="3" |<math>c_4</math>
|41.4~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|138.6~°
| rowspan="3" |<math>c_{26}</math>
|- style="background: gainsboro;" |
|{{radic|0.5}}
|{{radic|3.5}}
|- style="background: gainsboro;" |
|0.707~
|1.871~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_5</math>
|44.5~°
| rowspan="3" |[[File:Regular_star_figure_2(15,2).svg|100px]]<br>{30/4}=2{15/2}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-11.svg|100px]]<br>{30/11}
|135.5~°
| rowspan="3" |<math>c_{25}</math>
|- style="background: palegreen;" |
|{{radic|0.573~}}
|{{radic|3.427~}}
|- style="background: palegreen;" |
|0.757~
|1.851~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_6</math>
|49.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|130.9~°
| rowspan="3" |<math>c_{24}</math>
|- style="background: gainsboro;" |
|{{radic|0.691~}}
|{{radic|3.309~}}
|- style="background: gainsboro;" |
|0.831~
|1.819~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_7</math>
|56°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|124°
| rowspan="3" |<math>c_{23}</math>
|- style="background: gainsboro;" |
|{{radic|0.882~}}
|{{radic|3.118~}}
|- style="background: gainsboro;" |
|0.939~
|1.766~
|- style="background: palegreen;" |
| rowspan="3" |<math>c_8</math>
|60°
| rowspan="3" |[[File:Regular_star_figure_5(6,1).svg|100px]]<br>{30/5}=5{6}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_10(3,1).svg|100px]]<br>{30/10}=10{3}
|120°
| rowspan="3" |<math>c_{22}</math>
|- style="background: palegreen;" |
|{{radic|1}}
|{{radic|3}}
|- style="background: palegreen;" |
|1
|1.732~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_9</math>
|66.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|113.9~°
| rowspan="3" |<math>c_{21}</math>
|- style="background: gainsboro;" |
|{{radic|1.191~}}
|{{radic|2.809~}}
|- style="background: gainsboro;" |
|1.091~
|1.676~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{10}</math>
|69.8~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|110.2~°
| rowspan="3" |<math>c_{20}</math>
|- style="background: gainsboro;" |
|{{radic|1.309~}}
|{{radic|2.691~}}
|- style="background: gainsboro;" |
|1.144~
|1.640~
|- style="background: yellow;" |
| rowspan="3" |<math>c_{11}</math>
|72°
| rowspan="3" |[[File:Regular_star_figure_6(5,1).svg|100px]]<br>{30/6}=6{5}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_3(10,3).svg|100px]]<br>{30/9}=3{10/3}
|108°
| rowspan="3" |<math>c_{19}</math>
|- style="background: yellow;" |
|{{radic|1.382~}}
|{{radic|2.618~}}
|- style="background: yellow;" |
|1.176~
|1.618~
|- style="background: palegreen; height:50px" |
| rowspan="3" |<math>c_{12}</math>
|75.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_figure_2(15,4).svg|100px]]<br>{30/8}=2{15/4}
|104.5~°
| rowspan="3" |<math>c_{18}</math>
|- style="background: palegreen;" |
|{{radic|1.5}}
|{{radic|2.5}}
|- style="background: palegreen;" |
|1.224~
|1.581~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{13}</math>
|81.1~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|98.9~°
| rowspan="3" |<math>c_{17}</math>
|- style="background: gainsboro;" |
|{{radic|1.691~}}
|{{radic|2.309~}}
|- style="background: gainsboro;" |
|1.300~
|1.520~
|- style="background: gainsboro; height:50px" |
| rowspan="3" |<math>c_{14}</math>
|84.5~°
| rowspan="3" |
| rowspan="3" |
| rowspan="3" |
|95.5~°
| rowspan="3" |<math>c_{16}</math>
|- style="background: gainsboro;" |
|{{radic|0.809~}}
|{{radic|2.191~}}
|- style="background: gainsboro;" |
|1.345~
|1.480~
|- style="background: seashell;" |
| rowspan="3" |<math>c_{15}</math>
|90°
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
| rowspan="3" |
| rowspan="3" |[[File:Regular_star_polygon_30-7.svg|100px]]<br>{30/7}
|90°
| rowspan="3" |<math>c_{15}</math>
|- style="background: seashell;" |
|{{radic|2}}
|{{radic|2}}
|- style="background: seashell;" |
|1.414~
|1.414~
|}
The [[User:Dc.samizdat/Golden chords of the 120-cell#Thirty distinguished distances|table above]] of 30 chords <math>c_{t}</math> can be rearranged into a table of 16 rows and 2 columns with a pair of 180° complements in each row. This table first appears in [[w:Regular_Polytopes_(book)|''Regular Polytopes'']] (1947),{{Sfn|Coxeter|1973|loc=Table V(v): Simplified sections of {5,3,3} beginning with a vertex|pp=300-301}} where Coxeter identified each row with a distinct [[w:120-cell#Concentric_hulls|polyhedral section of the 120-cell]] beginning with a vertex. In spherical [[w:3-sphere|3-dimensional space <math>\mathbb{S}^3</math>]], every vertex is the center of a set of 29 concentric polyhedra of increasing radii that nest like [[w:Matryoshka_doll|Russian dolls.]] The smallest polyhedral section at radial distance <math>c_1</math> is a tetrahedron vertex figure, and the largest section at radial distance <math>c_{15}</math> is a central section bisecting the 120-cell. Because [[w:3-sphere|<math>\mathbb{S}^3</math>]] is spherical, at radial distances greater than <math>c_{15}</math> the successive complement-radius polyhedra decrease in size, to the antipodal tetrahedron vertex figure at distance <math>c_{29}</math>. In Euclidean 4-dimensional space <math>\mathbb{R}^4</math>, every vertex is the apex of 29 [[w:Hyperpyramid|polyhedral pyramids]], where the pyramid's lateral edge length is the radial distance and its base polyhedron is the section. Each section lies parallel to a congruent complement-radius section (or coincident with it, in the case of the central section). Each section also lies completely orthogonal to a congruent section.
Only 8 of the 30 chords in the table occur in the 600-cell and the planar {30)-gon. The 120-cell's additional chords arise originally from the regular 5-cell, in its interaction with the other regular 4-polytopes that compound to make the 120-cell. Since all those polytopes except the 5-cell occur in the 600-cell, and the 600-cell and the 120-cell have the same symmetry group, the 5-cell's symmetry group is what's new in the 120-cell.
...
{{Clear}}
== Conclusions ==
Fontaine and Hurley's discovery is more than a geometric formula for the reciprocal of a regular ''n''-polygon diagonal. It also yields the discrete sequence of isocline chords of the characteristic isoclinic rotation of a ''d''-dimensional polytope in its invariant edge planes. The characteristic rotational chord sequence of the ''d''-polytope can be represented geometrically in two dimensions on a distinct star polygon, but it lies on a geodesic circle through ''d''-dimensional space. Fontaine and Hurley discovered the geodesic topology of polytopes generally. Their procedure will reveal the geodesics of arbitrary non-uniform polytopes, since it can be applied to a polytope of any dimensionality and irregularity, by first fitting the polytope to the smallest regular polygon whose chords include its chords. [If what is meant by this is its Petrie polygon, it is not quite necessary or possible with respect to the planar polygon chords, e.g. the planar Petrie polygon of the 600-cell does not contain the <math>\sqrt{2}</math> chord. But perhaps it would work if the fit is to the smallest regular skew polygon in the ''d''-space.]
The discovery of a chordal construction for discrete isoclinic rotations generally closes the circuit on Kappraff and Adamson's discovery of a rotational connection between dynamical systems, Steinbach's golden fields, and Coxeter's Euclidean geometry of ''n'' dimensions. Application of the Fontaine and Hurley procedure in the 120-cell demonstrates why the connection exists: because polytope sequences generally, from Steinbach's golden chord sequences in polygons, to sequences of star polygons in isoclinic rotations, to subsumption relations in the sequence of regular 4-polytopes, arise as expressions of the reflections and rotations of distinct Coxeter symmetry groups, when those various groups interact.
== Appendix: Sequence of regular 4-polytopes ==
{{Regular convex 4-polytopes|wiki=W:|columns=7}}
== Notes ==
{{Notelist}}
== Citations ==
{{Reflist}}
== References ==
{{Refbegin}}
* {{Cite journal | last=Steinbach | first=Peter | year=1997 | title=Golden fields: A case for the Heptagon | journal=Mathematics Magazine | volume=70 | issue=Feb 1997 | pages=22–31 | doi=10.1080/0025570X.1997.11996494 | jstor=2691048 | ref={{SfnRef|Steinbach|1997}} }}
* {{Cite journal | last=Steinbach | first=Peter | year=2000 | title=Sections Beyond Golden| journal=Bridges: Mathematical Connections in Art, Music and Science | issue=2000 | pages=35-44 | url=https://archive.bridgesmathart.org/2000/bridges2000-35.pdf | ref={{SfnRef|Steinbach|2000}}}}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Jablan | first2=Slavik | last3=Adamson | first3=Gary | last4=Sazdanovich | first4=Radmila | year=2004 | title=Golden Fields, Generalized Fibonacci Sequences, and Chaotic Matrices | journal=Forma | volume=19 | pages=367-387 | url=https://archive.bridgesmathart.org/2005/bridges2005-369.pdf | ref={{SfnRef|Kappraff, Jablan, Adamson & Sazdanovich|2004}} }}
* {{Cite journal | last1=Kappraff | first1=Jay | last2=Adamson | first2=Gary | year=2004 | title=Polygons and Chaos | journal=Dynamical Systems and Geometric Theories | url=https://archive.bridgesmathart.org/2001/bridges2001-67.pdf | ref={{SfnRef|Kappraff & Adamson|2004}} }}
* {{Cite journal | last1=Fontaine | first1=Anne | last2=Hurley | first2=Susan | year=2006 | title=Proof by Picture: Products and Reciprocals of Diagonal Length Ratios in the Regular Polygon | journal=Forum Geometricorum | volume=6 | pages=97-101 | url=https://scispace.com/pdf/proof-by-picture-products-and-reciprocals-of-diagonal-length-1aian8mgp9.pdf }}
{{Refend}}
5a8h86auj1pey3086eog64ssdhrq5er
Social Victorians/Irish Aristocracy
0
329829
2816310
2816250
2026-06-19T18:54:56Z
Scogdill
1331941
/* Irish Aristocrats at the Duchess of Devonshire's 1897 Fancy-dress Ball */
2816310
wikitext
text/x-wiki
= The Irish Aristocracy at the End of the 19th Century =
== The Irish Peerage ==
Minus the people who attended the ball, which are in [[Social Victorians/Irish Aristocracy#Irish Aristocrats at the Duchess of Devonshire's 1897 Fancy-dress Ball|this section, below]].
=== Dukes and Duchesses ===
==== Duke of Leinster ====
Irish peerage
* Gerald FitzGerald, 5th Duke of Leinster (16 August 1851 – 1 December 1893)<ref>{{Cite web|url=https://www.thepeerage.com/p1207.htm#i12063|title=Gerald FitzGerald, 5th Duke of Leinster|website=www.thepeerage.com|access-date=2026-05-24}}</ref>
* Maurice FitzGerald, 6th Duke of Leinster, 6 years old when he succeeded to the dukedom<ref>{{Cite web|url=https://www.thepeerage.com/p2767.htm#i27667|title=Maurice FitzGerald, 6th Duke of Leinster|website=www.thepeerage.com|access-date=2026-05-24}}</ref>
* Subsidiary Titles
# Marquess of Kildare (Irish peerage), did not attend the ball.
# Earl of Kildare (Irish peerage), did not attend the ball.
# Earl of Offaly (Irish peerage)
# Viscount Leinster of Taplow (GB peerage)
# Baron Offaly (Irish peerage)
# Baron Kildare of Kildare (UK peerage)
=== Marquesses and Marchionesses ===
==== Marquess Conyngham<ref>{{Cite journal|date=2026-01-13|title=Marquess Conyngham|url=https://en.wikipedia.org/w/index.php?title=Marquess_Conyngham&oldid=1332742873|journal=Wikipedia|language=en}}</ref> ====
* Did not attend the ball but did attend a number of social events about this time.
* Pronounced "''Cunn''ingum."<ref>{{Cite journal|date=2026-01-13|title=Marquess Conyngham|url=https://en.wikipedia.org/w/index.php?title=Marquess_Conyngham&oldid=1332742873|journal=Wikipedia|language=en}}</ref>
* Henry Francis Conyngham, 4th Marquess Conyngham (1857–1897)<ref>"Henry Francis Conyngham, 4th Marquess Conyngham." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 7198
https://www.thepeerage.com/p7199.htm#i71982.</ref>
* Victor George Henry Francis Conyngham, 5th Marquess Conyngham (1883–1918)<ref>"Victor George Henry Francis Conyngham, 5th Marquess Conyngham." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 7198 https://www.thepeerage.com/p7199.htm#i71983.</ref>
* Subsidiary Titles
** Earl of Conyngham
** Viscount Conyngham
** Viscount Mount Charles
==== Marquess of Donegall ====
* Did not attend the ball.
* Subsidiary Titles
** Earl of Donegall, did not attend the ball.
** Viscount Chichester — did not attend the ball; some Chichesters attended social events at about this time.
==== Marquess and Marchioness of Downshire ====
* Arthur Wills John Wellington Trumbull Blundell Hill, 6th Marquess of Downshire (2 July 1871 – 29 May 1918) in 1893 married Katherine Mary ("Kitty") Hare (1872–1959)<ref>{{Cite journal|date=2025-02-10|title=Arthur Hill, 6th Marquess of Downshire|url=https://en.wikipedia.org/w/index.php?title=Arthur_Hill,_6th_Marquess_of_Downshire&oldid=1274976272|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball.
* Subsidiary Titles
** Earl of Hillsborough, did not attend the ball, also not at any social events described so far.
** Viscount Kilwarlin — 6th, Arthur Wills John Wellington Trumbull Hill (31 March 1874 – 29 May 1918)<ref>"Arthur Wills John Wellington Trumbull '''Hill''', 6th Marquess of Downshire." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page #3810
https://www.thepeerage.com/p3811.htm#i38104.</ref>
==== Marquess of Ely ====
* Did not attend the ball, but members of the Loftus family attended a number of social events at about this time.
* 4th Marquess: John Henry Wellington Graham Loftus (15 July 1857 – 3 April 1889)<ref>"John Henry Wellington Graham Loftus, 4th Marquess of Ely." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 8545 https://www.thepeerage.com/p8545.htm#i85450.</ref>
* 5th Marquess: John Henry Loftus (3 April 1889 – 18 December 1925)<ref>"John Henry Loftus, 5th Marquess of Ely." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 8546 https://www.thepeerage.com/p8546.htm#i85459.</ref>
* Subsidiary Titles
** Earl of Ely — did not attend the ball.
** Viscount Loftus
==== [[Social Victorians/People/Bective|Marquess and Marchioness of Headfort]] ====
* Did not attend the ball, but a number of people in this family attended many social events at about this time.
* Subsidiary Titles
** [[Social Victorians/People/Bective|Earl of Bective]]
** Viscount Headfort<ref name=":1" />
*** 4th: Thomas Taylour (6 December 1870 – 22 July 1894)
*** 5th: Geoffrey Thomas Taylour (22 July 1894 – 29 January 1943)
*Papers
==== Marquess of Sligo ====
* Did not attend the ball, but many people with the surname Browne attended a number of social events at about this time.
* Subsidiary Titles
** Earl of Altamont. Did not attend the ball; did not attend any social events analyzed so far.
** Earl of Clanricarde — Did not attend the ball but did attend a few social events about this time.
** Viscount of Westport<ref name=":1">"Index to Viscounts and Viscountesses." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''.
https://www.thepeerage.com/index_viscount.htm.</ref>
*** 5th: George John Browne (26 January 1845 – 30 December 1896), 5th Marquess
*** 6th: John Thomas Browne (30 December 1896 – 30 December 1903), 6th Marquess
==== Marquess of Waterford ====
* John Henry de La Poer Beresford, 5th Marquess of Waterford (1844–1895)
* Henry de La Poer Beresford, 6th Marquess of Waterford (1875–1911)<ref>{{Cite journal|date=2026-02-10|title=Henry Beresford, 6th Marquess of Waterford|url=https://en.wikipedia.org/w/index.php?title=Henry_Beresford,_6th_Marquess_of_Waterford&oldid=1337565707|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but members of the Beresford family were prominent socially at about this time.
* Subsidiary Titles
** Viscount Tyrone
=== Earls and Countesses ===
==== Earl of Annesley ====
* Did not attend the ball but did attend a number of social events in the 1890s.
* Subsidiary Title
** Viscount Glerawly<ref name=":1" />: 6th: Hugh Annesley (10 August 1874 – 15 December 1908), 6th Earl of Annesley
==== Earl of Bessborough ====
* Frederick George Brabazon Ponsonby, 6th Earl of Bessborough (1815–1895)
* Walter William Brabazon Ponsonby, 7th Earl of Bessborough (1821–1906), would have been Viscount Duncannon 1880–1895
* Edward Ponsonby, 8th Earl of Bessborough (1851–1920), would have been Viscount Duncannon 1895–1906
* Did not attend the ball, but the [[Social Victorians/People/Ponsonby|Ponsonby]] family attended many social events at about this time, including mention of Lady Duncannon's school that taught fabric arts.
* Subsidiary Titles
** Viscount Duncannon
==== Earl of Caledon ====
* Did not attend the ball but did attend a number of social events about this time.
* James Alexander, 4th Earl of Caledon (1846–1898)<ref>{{Cite journal|date=2025-11-21|title=James Alexander, 4th Earl of Caledon|url=https://en.wikipedia.org/w/index.php?title=James_Alexander,_4th_Earl_of_Caledon&oldid=1323312651|journal=Wikipedia|language=en}}</ref>
* Eric James Desmond Alexander, 5th Earl of Caledon (1885–1968), succeeded as earl in 1898.<ref>{{Cite journal|date=2025-11-21|title=Eric Alexander, 5th Earl of Caledon|url=https://en.wikipedia.org/w/index.php?title=Eric_Alexander,_5th_Earl_of_Caledon&oldid=1323313583|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Caledon
==== Earl of Carrick ====
* Did not attend the ball.
==== Earl Castle Stewart ====
* Did not attend the ball.
* 5th Earl: Henry James Stuart-Richardson (12 September 1874 – 5 June 1914)<ref>"Henry James Stuart-Richardson, 5th Earl Castle Stewart." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 2412 https://www.thepeerage.com/p12413.htm#i124125.</ref>
* Subsidiary Title
** Viscount Castle Stewart
==== Earl of Cavan ====
* Did not attend the ball.
==== Earl of Clancarty ====
* Did not attend the ball and attended few social events researched so far.
* Richard Somerset Le Poer Trench, 4th Earl of Clancarty (1834–1891)<ref>{{Cite journal|date=2026-01-10|title=Richard Trench, 4th Earl of Clancarty|url=https://en.wikipedia.org/w/index.php?title=Richard_Trench,_4th_Earl_of_Clancarty&oldid=1332219771|journal=Wikipedia|language=en}}</ref>
* William Frederick Le Poer Trench, 5th Earl of Clancarty (1868–1929)<ref>{{Cite journal|date=2025-11-05|title=William Trench, 5th Earl of Clancarty|url=https://en.wikipedia.org/w/index.php?title=William_Trench,_5th_Earl_of_Clancarty&oldid=1320532351|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Dunlo
==== [[Social Victorians/People/Clanwilliam|Earl and Countess of Clanwilliam]] ====
* Did not attend the ball.
* Subsidiary Title
** Viscount Clanwilliam<ref name=":1" />: 4th: Richard James Meade (7 October 1879 – 4 August 1907), 4th Earl
==== Earl of Cork, Earl of Orrery ====
* Cork and Orrery, did attend the ball.
==== Earl of Courtown ====
* Did not attend the ball.
==== Earl of Darnley ====
* John Bligh, 6th Earl of Darnley (1827–1896), British<ref>{{Cite journal|date=2026-02-07|title=John Bligh, 6th Earl of Darnley|url=https://en.wikipedia.org/w/index.php?title=John_Bligh,_6th_Earl_of_Darnley&oldid=1337113925|journal=Wikipedia|language=en}}</ref>
* Edward Bligh, 7th Earl of Darnley (1851–1900), Lord Clifton much of his adult life, "English"<ref>{{Cite journal|date=2026-05-05|title=Edward Bligh, 7th Earl of Darnley|url=https://en.wikipedia.org/w/index.php?title=Edward_Bligh,_7th_Earl_of_Darnley&oldid=1352607379|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but the Bligh family attended some social events from about this time.
* Subsidiary Titles:
** Viscount Darnley
==== Earl of Desmond ====
* Did not attend the ball.
==== [[Social Victorians/People/Donoughmore|Earl of Donoughmore]] ====
* Did not attend the ball but did attend a number of social events about this time.
* John Luke George Hely-Hutchinson, 5th Earl of Donoughmore (1848–1900)<ref>{{Cite journal|date=2025-05-01|title=John Hely-Hutchinson, 5th Earl of Donoughmore|url=https://en.wikipedia.org/w/index.php?title=John_Hely-Hutchinson,_5th_Earl_of_Donoughmore&oldid=1288332715|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Donoughmore
==== Earl of Drogheda ====
* Did not attend the ball.
* Subsidiary Titles
** Viscount Moore — no evidence of the Viscount or Viscountess Moore at social events at about this time.
==== Earl of Granard ====
* Did not attend the ball.
* Bernard Arthur William Patrick Hastings Forbes, 8th Earl of Granard (17 September 1874 – 10 September 1948)[https://en.wikipedia.org/wiki/Bernard_Forbes,_8th_Earl_of_Granard]
* Anglo-Irish
* Subsidiary Titles
** Bernard Arthur William Patrick Hastings Forbes, styled Viscount Forbes from 1874 to 1889
==== Earl of Kingston ====
* Did not attend the ball.
* Subsidiary Title
** Viscount Kingsborough (of Viscount Kingston of Kingborough, co. Sligo)<ref name=":1" />
*** 8th: Henry Newcomen King-Tenison (21 June 1871 – 13 January 1896)
*** 9th: Henry Edwyn King-Tenison (13 January 1896 – 11 January 1946)
**Viscount Lorton
==== Earl of Lisburne ====
* Did not attend the ball.
* Ernest Augustus Malet Vaughan, 5th Earl of Lisburne (1836–1888)<ref>{{Cite journal|date=2025-12-03|title=Ernest Augustus Malet Vaughan, 5th Earl of Lisburne|url=https://en.wikipedia.org/w/index.php?title=Ernest_Augustus_Malet_Vaughan,_5th_Earl_of_Lisburne&oldid=1325511612|journal=Wikipedia|language=en}}</ref>
** Owned a lot of land in Cardiganshire, Wales
** Conservative, but withdrew from politics
* George Henry Arthur Vaughan, 6th Earl of Lisburne (1862–1899)
* Ernest Edmund Henry Malet Vaughan, 7th Earl of Lisburne (1892–1965)
** Welsh nobleman, of Trawsgoed, Cardiganshire. 7 years old when he succeeded to the earldom
==== Earl of Longford ====
* Did not attend the ball.
==== Earl and Countess of Meath ====
* Did not attend the ball.
==== Earl of Mexborough ====
* Did not attend the ball
==== Earl of Mornington ====
* Subsidiary title of the Duke of Wellington (in the peerage of the UK).
==== Earl of Normanton ====
* Did not attend the ball, but did attend some social events in the 1880s and 1890s.
* James Charles Herbert Welbore Ellis Agar, 3rd Earl of Normanton (1818–1896)<ref>{{Cite journal|date=2025-10-06|title=James Agar, 3rd Earl of Normanton|url=https://en.wikipedia.org/w/index.php?title=James_Agar,_3rd_Earl_of_Normanton&oldid=1315461436|journal=Wikipedia|language=en}}</ref>
* Sidney James Agar, 4th Earl of Normanton (1865–1933)<ref>{{Cite journal|date=2026-05-19|title=Sidney James Agar, 4th Earl of Normanton|url=https://en.wikipedia.org/w/index.php?title=Sidney_James_Agar,_4th_Earl_of_Normanton&oldid=1355064165|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Somerton
==== Earl of Portarlington ====
* Did not attend the ball. Members of this family attended a few social events at about this time.
* Subsidiary Title
** Viscount Carlow<ref name=":1" />
*** 5th: Lionel Seymour William Dawson-Damer (1 March 1889 – 17 December 1892), Earl of Portarlington
*** 6th: Lionel George Henry Seymour Dawson-Damer (17 December 1892 – 31 August 1900)
==== Earl of Roden ====
* Did not attend the ball.
* Subsidiary Title
** Viscount Jocelyn<ref name=":1" />
*** 6th: John Strange Jocelyn (9 January 1880 – 3 July 1897)
*** 7th: William Henry Jocelyn (3 July 1897 – 23 January 1910)
==== Earl of Shannon ====
* Did not attend the ball.
==== Earl of Shelburne ====
* Subsidiary title of the Marquess of Lansdowne (in the peerage of Great Britain).
* Did not attend the ball, and did not attend any social events analyzed so far.
==== Earl of Tyrone ====
* Did not attend
==== Earl of Waterford ====
* Not a subsidiary title of the Marquess of Waterford but of the Earl of Shrewsbury in the peerage of England.
==== Earl of Westmeath ====
* Did not attend the ball.
==== Earl of Winterton ====
* Did not attend the ball.
=== Viscounts and Viscountesses ===
==== Viscount Ashbrook ====
* William Spencer Flower, 7th Viscount Ashbrook (1830–1906)<ref>{{Cite journal|date=2025-12-01|title=Viscount Ashbrook|url=https://en.wikipedia.org/w/index.php?title=Viscount_Ashbrook&oldid=1325071512|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, has no social presence at about this time.
==== Viscount Banger ====
* Did not attend the ball but attended a few social events at about this time.
* Edward Ward, 4th Viscount Bangor (1827–1881)<ref>{{Cite journal|date=2026-03-16|title=Edward Ward, 4th Viscount Bangor|url=https://en.wikipedia.org/w/index.php?title=Edward_Ward,_4th_Viscount_Bangor&oldid=1343882576|journal=Wikipedia|language=en}}</ref>
* Henry William Crosbie Ward, 5th Viscount Bangor (1828–1911)<ref>{{Cite journal|date=2026-03-02|title=Henry Ward, 5th Viscount Bangor|url=https://en.wikipedia.org/w/index.php?title=Henry_Ward,_5th_Viscount_Bangor&oldid=1341354058|journal=Wikipedia|language=en}}</ref>
==== Viscount Boyne ====
* Did not attend the ball, but did attend a number of events at about this time.
==== Viscount Callan ====
* Did not attend the ball, and does not have much if any social presence at about this time.
* The Viscount Callan is a subsidiary title of the Earl of Denbigh in the Peerage of England.
==== Viscount Charlemont ====
* Did not attend the ball.
* Colonel James Alfred Caulfeild, 7th Viscount Charlemont (20 March 1830 – 4 July 1913), Irish<ref>{{Cite journal|date=2026-05-02|title=James Caulfeild, 7th Viscount Charlemont|url=https://en.wikipedia.org/w/index.php?title=James_Caulfeild,_7th_Viscount_Charlemont&oldid=1352129469|journal=Wikipedia|language=en}}</ref>
* Unionist
==== Viscount Chetwynd ====
* Does not seem to have attended the ball, but Chetwynds were socially very active at about this time.
* Godfrey John Boyle Chetwynd, 8th Viscount Chetwynd (1863–1936), British<ref>{{Cite journal|date=2026-05-24|title=Godfrey Chetwynd, 8th Viscount Chetwynd|url=https://en.wikipedia.org/w/index.php?title=Godfrey_Chetwynd,_8th_Viscount_Chetwynd&oldid=1355878192|journal=Wikipedia|language=en}}</ref>
==== Viscount de Vesci ====
* Did not attend the ball but attended several social events at about this time.
* 4th Viscount de Vesci: John Robert William Vesey (23 December 1875 – 6 July 1903)<ref name=":1" />
* "The family seat was Abbeyleix House, near Abbeyleix, County Laois."<ref>{{Cite journal|date=2026-02-09|title=Viscount de Vesci|url=https://en.wikipedia.org/w/index.php?title=Viscount_de_Vesci&oldid=1337491855|journal=Wikipedia|language=en}}</ref>
==== Viscount Dillon ====
* Did not attend the ball, but several Dillons attended other social events at about this time.
==== Viscount Doneraile<ref>{{Cite journal|date=2026-01-16|title=Viscount Doneraile|url=https://en.wikipedia.org/w/index.php?title=Viscount_Doneraile&oldid=1333262628|journal=Wikipedia|language=en}}</ref> ====
* Did not attend the ball, but did attend the Warwick Bal Poudré and few other social events at about this time.
* Hayes St Leger, 4th Viscount Doneraile (1818–1887)
* Richard Arthur St Leger, 5th Viscount Doneraile (1825–1891)
* Edward St Leger, 6th Viscount Doneraile (1866–1941)
==== [[Social Victorians/People/Downe|Viscount Downe]] ====
* Did not attend the ball but attended many social events at about this time.
* Major-General Hugh Richard Dawnay, 8th Viscount Downe (20 July 1844 – 21 January 1924)<ref>{{Cite journal|date=2026-03-24|title=Hugh Dawnay, 8th Viscount Downe|url=https://en.wikipedia.org/w/index.php?title=Hugh_Dawnay,_8th_Viscount_Downe&oldid=1345146095|journal=Wikipedia|language=en}}</ref>
* British Army general
==== Viscount Ferrard ====
* See Viscount Massereene, below. By the end of the century, it was the Viscount and Viscountess of Massereene and Ferrard.
==== Viscount Fitzmaurice ====
* A subsidiary title of the Marquess of Lansdowne (in the Peerage of Great Britain).
* 6th Viscount Fitzmaurice, Henry Charles Keith Petty-FitzMaurice (5 July 1866 – 3 June 1927)<ref>"Henry Charles Keith Petty-FitzMaurice, 5th Marquess of Lansdowne." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 958
https://www.thepeerage.com/p959.htm#i9586.</ref>
==== Viscount Gage ====
* Henry Charles Gage, 5th Viscount Gage (1854–1912)<ref>{{Cite journal|date=2025-06-21|title=Viscount Gage|url=https://en.wikipedia.org/w/index.php?title=Viscount_Gage&oldid=1296646030|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but members of this family attended a number of social events at about this time.
==== Viscount Galway ====
* George Edmund Milnes Monckton-Arundell, 7th Viscount Galway (1844–1931), British conservative<ref>{{Cite journal|date=2025-08-08|title=George Monckton-Arundell, 7th Viscount Galway|url=https://en.wikipedia.org/w/index.php?title=George_Monckton-Arundell,_7th_Viscount_Galway&oldid=1304770631|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but Viscount and Viscountess Galway attended many social events at about this time.
* Subsidiary Title
** Baron Monckton (in the Peerage of the United Kingdom)
==== Viscount Gormanston ====
* Did not attend the ball, has no social presence in the late 19th-century newspapers at this time.
==== [[Social Victorians/People/Gort|Viscount Gort]] ====
* Did not attend the ball, but attended some social events at about this time.
* Standish Prendergast Vereker, 4th Viscount Gort (1819–1900)<ref>"Standish Prendergast Vereker, 4th Viscount Gort." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 4626 https://www.thepeerage.com/p4627.htm#i46261.</ref>
* John Gage Prendergast Vereker, 5th Viscount Gort (1849–1902)<ref>{{Cite journal|date=2025-05-28|title=John Vereker, 5th Viscount Gort|url=https://en.wikipedia.org/w/index.php?title=John_Vereker,_5th_Viscount_Gort&oldid=1292670203|journal=Wikipedia|language=en}}</ref>
==== Viscount Grandison ====
* Did not attend the ball, has no social presence in the late 19th-century newspapers at this time.
* The Viscount Grandison is a subsidiary title of the Earl of Jersey in the Peerage of England.
==== Viscount Grimston ====
* Subsidiary title of the Earl of Verulam (in the Peerage of the United Kingdom)
* Did not attend the ball, but a number of members of this family attended social events at about this time.
==== Viscount Harberton ====
* Did not attend the ball; Viscountess Harberton is mentioned once in social events at about this time so far.
* James Spencer Pomeroy, 6th Viscount Harberton (1836–1912)<ref>"James Spencer Pomeroy, 6th Viscount Harberton." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person Page 4315 https://www.thepeerage.com/p43151.htm#i431502.</ref>
* Florence Wallace Pomeroy, Viscountess Harberton (1843–1911), suffragette, cyclist, President of the Rational Dress Society<ref>{{Cite journal|date=2026-03-12|title=Florence Wallace Pomeroy, Viscountess Harberton|url=https://en.wikipedia.org/w/index.php?title=Florence_Wallace_Pomeroy,_Viscountess_Harberton&oldid=1343082631|journal=Wikipedia|language=en}}</ref>
==== Viscount Lifford ====
* Did not attend the ball; the only social event at about this time so far is the Queen's Diamond Jubilee garden party.
* James Hewitt, 4th Viscount Lifford (1811–1887)<ref>{{Cite journal|date=2025-09-11|title=James Hewitt, 4th Viscount Lifford|url=https://en.wikipedia.org/w/index.php?title=James_Hewitt,_4th_Viscount_Lifford&oldid=1310741456|journal=Wikipedia|language=en}}</ref>
* James Wilfrid Hewitt, 5th Viscount Lifford (12 October 1837 – 20 March 1913)<ref>"James Wilfrid Hewitt, 5th Viscount Lifford." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person Page 2227 https://www.thepeerage.com/p22271.htm#i222701.</ref>
==== Earl of Listowel ====
* Pronounced "Lish-''toe''-ell."<ref>{{Cite journal|date=2024-10-15|title=Earl of Listowel|url=https://en.wikipedia.org/w/index.php?title=Earl_of_Listowel&oldid=1251322273|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but hosted and attended social events at about this time.
* William Hare, 3rd Earl of Listowel (1833–1924)<ref>{{Cite journal|date=2026-04-17|title=William Hare, 3rd Earl of Listowel|url=https://en.wikipedia.org/w/index.php?title=William_Hare,_3rd_Earl_of_Listowel&oldid=1349570352|journal=Wikipedia|language=en}}</ref>, Irish peer
* Subsidiary Title
** Viscount Ennismore and Listowel
** Baron Ennismore
==== Viscount Massereene ====
* Did not attend the ball but did attend a few events at about this time. See Viscount Ferrard, above. By the end of the century, it was the Viscount and Viscountess of Massereene and Ferrard.
* Anglo-Irish
* Clotworthy John Eyre Skeffington, 11th Viscount Massereene (9 October 1842 – 26 June 1905)<ref>{{Cite journal|date=2024-11-23|title=Clotworthy Skeffington, 11th Viscount Massereene|url=https://en.wikipedia.org/w/index.php?title=Clotworthy_Skeffington,_11th_Viscount_Massereene&oldid=1259199982|journal=Wikipedia|language=en}}</ref> and 4th Viscount Ferrard (28 April 1863 – 26 June 1905)
==== Viscount Molesworth ====
* Did not attend the ball, but attended the Warwick Bal Poudré and a number of other social events at about this time.
* Samuel Molesworth, 8th Viscount Molesworth (1829–1906), may have been a Quaker
==== Viscount Monck ====
* Did not attend the ball, but attended a number of social events at about this time.
* Charles Stanley Monck, 4th Viscount Monck (1819–1894)<ref>{{Cite journal|date=2026-04-05|title=Charles Monck, 4th Viscount Monck|url=https://en.wikipedia.org/w/index.php?title=Charles_Monck,_4th_Viscount_Monck&oldid=1347311992|journal=Wikipedia|language=en}}</ref>, British
* Henry Power Charles Stanley Monck, 5th Viscount Monck (1849–1927)<ref>"Henry Power Charles Stanley Monck, 5th Viscount Monck of Ballytrammon." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 3880 https://www.thepeerage.com/p3881.htm#i38802.</ref>
==== Viscount Mountgarret ====
* Did not attend the ball, has no social presence in the late 19th-century newspapers at this time.
==== [[Social Victorians/People/Powerscourt|Viscount Powerscourt]] ====
* Mervyn Wingfield, 7th Viscount Powerscourt (1836–1904)<ref name=":0">{{Cite journal|date=2026-02-18|title=Mervyn Wingfield, 7th Viscount Powerscourt|url=https://en.wikipedia.org/w/index.php?title=Mervyn_Wingfield,_7th_Viscount_Powerscourt&oldid=1339057453|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but members of this family attended a number of social events at about this time.
* Subsidiary Title
** Baron Powerscourt (in the Peerage of the United Kingdom), 1885<ref name=":0" />
==== Viscount Southwell ====
* Did not attend the ball, though the Viscount and Viscountess attended a few social events at about this time.
* 5th<ref name=":1" />: Arthur Robert Pyers Southwell (26 April 1878 – 5 October 1944)<ref>"Arthur Robert Pyers Southwell, 5th Viscount Southwell of Castle Mattress." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page
https://www.thepeerage.com/p7550.htm#i75497.</ref>
==== Viscount Valentia ====
* Did not attend the ball, attended some social events at about this time. Was on the Welcome Council for the 1887 American Exhibition.
=== Barons and Baronesses ===
Not all the barons extant at the end of the 19th century and listed on the Wikipedia [[wikipedia:Peerage_of_Ireland|Peerage of Ireland]] page are here — only the ones who were active socially.
==== Baron Conway and Killultagh ====
* Did not attend the ball, but people from the Conway and Seymour families attended a number of social events at about this time.
* Subsidiary title of the Marquess of Hertford (in the Peerage of England and Great Britain).
* Francis Hugh George Seymour, 5th Marquess of Hertford (1812–1884)<ref>{{Cite journal|date=2026-04-05|title=Francis Seymour, 5th Marquess of Hertford|url=https://en.wikipedia.org/w/index.php?title=Francis_Seymour,_5th_Marquess_of_Hertford&oldid=1347294689|journal=Wikipedia|language=en}}</ref>
* Hugh de Grey Seymour, 6th Marquess of Hertford (1843–1912)<ref>{{Cite journal|date=2026-04-05|title=Hugh Seymour, 6th Marquess of Hertford|url=https://en.wikipedia.org/w/index.php?title=Hugh_Seymour,_6th_Marquess_of_Hertford&oldid=1347303090|journal=Wikipedia|language=en}}</ref>
==== Baron Digby ====
* Did not attend the ball, but people from this family attended a number of social events at about this time.
* Edward St Vincent Digby, 9th and 3rd Baron Digby (1809–1889)<ref>{{Cite journal|date=2025-12-15|title=Edward Digby, 9th Baron Digby|url=https://en.wikipedia.org/w/index.php?title=Edward_Digby,_9th_Baron_Digby&oldid=1327712265|journal=Wikipedia|language=en}}</ref>
* Edward Henry Trafalgar Digby, 10th and 4th Baron Digby (1846–1920)<ref>{{Cite journal|date=2026-01-26|title=Edward Digby, 10th Baron Digby|url=https://en.wikipedia.org/w/index.php?title=Edward_Digby,_10th_Baron_Digby&oldid=1334892957|journal=Wikipedia|language=en}}</ref>
==== Baron Inchiquin ====
* Did not attend the ball, but people from this family attended a number of social events at about this time.
* Edward Donough O'Brien, 14th Baron Inchiquin (1839–1900)<ref>{{Cite journal|date=2026-04-28|title=Edward O'Brien, 14th Baron Inchiquin|url=https://en.wikipedia.org/w/index.php?title=Edward_O%27Brien,_14th_Baron_Inchiquin&oldid=1351543832|journal=Wikipedia|language=en}}</ref>
== Peerage of the United Kingdom of Great Britain and Ireland ==
After the forced 1801 Act of Union.
=== Earls and Countesses ===
==== Earl of Limerick ====
* Did not attend the ball, but did attend a number of events at about this time.
==== Earl of Norbury ====
* Did not attend the ball, but attended some social events at about this time.
* Subsidiary Title
** Baron Norbury
==== Earl of Ranfurly ====
* Did not attend the ball, and they have a small social presence in the newspapers in the 1880s and 1890s.
==== Earl of Rosse ====
* Did not attend the ball, but did attend a few events at about this time.
== Peerage of the United Kingdom ==
* Lurgan
== Irish Nationalists ==
== Irish Unionists ==
== Irish Aristocrats at the Duchess of Devonshire's 1897 Fancy-dress Ball ==
==== [[Social Victorians/People/Abercorn|Duke and Duchess of Abercorn]] ====
* This dukedom is in the peerage of the United Kingdom of Great Britain and Ireland
* James Hamilton, 1st Duke of Abercorn (1811–1885), elder son of Lord Hamilton, "styled Viscount Hamilton from 1814 to 1818 and The Marquess of Abercorn from 1818 to 1868, was a Conservative statesman who twice served as Lord Lieutenant of Ireland."<ref>{{Cite journal|date=2026-04-05|title=James Hamilton, 1st Duke of Abercorn|url=https://en.wikipedia.org/w/index.php?title=James_Hamilton,_1st_Duke_of_Abercorn&oldid=1347253763|journal=Wikipedia|language=en}}</ref>
* James Hamilton, 2nd Duke of Abercorn (1838–1913), eldest son of the 1st Duke, "styled Viscount Hamilton until 1868 and Marquess of Hamilton from 1868 to 1885, was a British nobleman, courtier, and diplomat."<ref>{{Cite journal|date=2026-01-25|title=James Hamilton, 2nd Duke of Abercorn|url=https://en.wikipedia.org/w/index.php?title=James_Hamilton,_2nd_Duke_of_Abercorn&oldid=1334676058|journal=Wikipedia|language=en}}</ref>
* The Hamilton who became the 3rd duke attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, as did a few other members of this family.
* Subsidiary Titles
** Marquess of Abercorn
** Viscount Hamilton
** Viscount Strabane, county Tyrone
*Papers
**PRONI for the Abercorn papers [GB 0255 PRONI/D623]
**Some individuals' papers (the Tighe Hamilton Howard papers, https://iar.ie/archive/tighe-hamilton-howard-papers) from the Hamilton family are in the National Library of Ireland. "An item level catalogue is available online. These papers form part of the Wicklow Papers (Collection List 69) that are held in the Department of Manuscripts at the National Library of Ireland."
***VII. Sarah Howard Papers, 1830-1887.
****[***] VII.ii. Letters from Sarah Howard to her husband the Hon. Rev. Francis Howard, [n.d.] Call number: '''MS 38,639/2/2'''
****[***] VII.iii. Correspondence between Sarah Howard and her daughter Lady Caroline Howard, ca. 1851 - ca. 1891. Call number: '''MS 38,639/2/3'''
****VII.iv. Correspondence between Sarah Howard and her son Charles Howard, 5th Earl of Wicklow, 1853-ca.1870. Call number: '''MS 38,639/2/4'''
****VII.v. Correpondence between Sarah Howard and her son Cecil Howard, 6th Earl of Wicklow, ca. 1855-1876. Call number: '''MS 38,639/2/5'''
****[***] VII.vi. Correspondence between Sarah Howard and her daughters Lady Louisa and Lady Alice Howard, 1855-ca. 1877. Call number: '''MS 38,639/2/6'''
****[***] VII.vix. Additional correspondence of Sarah Howard of Wingfield, Bray Co. Wicklow, 1865-1887. Call number: '''MS 38,639/2/9'''
***VIII. Lady Caroline Howard Papers, 1852-1919.
****VIII.i. Correspondence between Lady Caroline Howard and her brother Charles, Earl of Wicklow, 1852-1880. Call number: '''MS 38,639/2/11'''
****VIII.iv. Additional correspondence of Lady Caroline Howard, 1868-1919. Call number: '''MS 38,639/2/14'''
****VIII.v. Additional papers of Lady Caroline Howard, 1900. Call number: '''MS 38,639/2/15'''
***IX. Additional Howard family correspondence, 1773-1900.
****[**] IX.vii. Correspondence and papers of Lady Louisa Howard, 1856-1907. Call number: '''MS 38,639/2/22'''
****[***] IX.viii. Correspondence and papers of Lady Alice Howard, [n.d.] Call number: '''MS 38,639/2/23'''
***XI. Other papers, 1737-1913.
****XI.i. Miscellaneous correspondence, 1753-1891. Call number: '''MS 38,639/2/27'''
***Wicklow Papers
****[**] Journals of Lady Caroline Howard including some accounts of her tours abroad, 1873 Jan. - March, 1875 Aug. - Sept., & 1882 Jan. - April. Call number: '''MS 3586-3588'''
****[**] Diaries of Lady Louisa Howard including accounts of her travels on the Continent, 1862 Oct. - 1869 June, 1871 April - 1873 April and 1877 Oct. - 1883 July. Call number: '''MS 3589-3593'''
****Diaries of Lady Caroline Howard, 1862 Oct. - 1870 May. Call number: '''MS 3594-3599'''
****[***] Diaries of Lady Alice Howard, Shelton Abbey and Bray, Co. Wicklow, 1874-1922. Call number: '''MS 3600-3625'''
***[**] Journals of Lady Alice Howard, including account of tours on the Continent, 1860 June - Oct, 1865 Aug. - 1866 Feb., 1869 Nov. - 1870 Nov. Call number: '''MS 4793-4795'''
==== [[Social Victorians/People/Londonderry|Marquess and Marchioness of Londonderry]] ====
* The Marquess and Marchioness attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, she led one of the courts as Maria Thérèse, plus two of their children attended, one of whom is Viscount Castlereagh.
* Charles Stewart Vane-Tempest-Stewart, 6th Marquess of Londonderry<ref>"Charles Stewart Vane-Tempest-Stewart, 6th Marquess of Londonderry." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 1277 https://www.thepeerage.com/p1278.htm#i12772.</ref>
* Lady Theresa Susey Helen Chetwynd-Talbot, Marchioness of Londonderry<ref>"Lady Theresa Susey Helen Chetwynd-Talbot." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 1277 https://www.thepeerage.com/p1278.htm#i12771.</ref>
* Subsidiary Titles
** [[Social Victorians/People/Londonderry|Earl of Londonderry]]
** Viscount Castlereagh — Charles Stewart Henry Vane-Tempest-Stewart (6 November 1884 – 8 February 1915)
*Papers
**In PRONI [GB 0255 PRONI/D2846]: "The Theresa, Lady Londonderry Papers comprise c.4,600 papers and 15 volumes of diaries, scrapbooks, etc, 1858-1919, mainly of Theresa, Marchioness of Londonderry (1856-1919), wife/widow of the 6th Marquess, but including some papers of the 6th Marquess himself, of and about his mother, Mary Cornelia, widow of the 5th Marquess, and of his brothers Lords Henry and Herbert Vane-Tempest."<ref>{{Cite web|url=https://iar.ie/archive/theresa-lady-londonderry-papers/|title=Theresa, Lady Londonderry Papers|website=Irish Archives Resource|language=en-US|access-date=2026-06-06}}</ref>
**In PRONI [GB 0255 PRONI/D3099]: the "Papers of the 7th Marquess of Londonderry and his wife Edith" collection also hold the papers of Edith's father, [[Social Victorians/People/Henry Chaplin|Henry, 1st Viscount Chaplin]], who attended the ball, as did she and a brother. [D3099/1 Henry, 1st Viscount Chaplin, father-in-law of 7th Marquess of Londonderry. Political and personal papers; D3099/3 Edith Helen Chaplin, wife of 7th Marquess of Londonderry. Personal letters and papers]<ref>{{Cite web|url=https://iar.ie/archive/papers-7th-marquess-londonderry-wife-edith/|title=Papers of the 7th Marquess of Londonderry and his wife Edith|website=Irish Archives Resource|language=en-US|access-date=2026-06-06}}</ref>
==== [[Social Victorians/People/Lucan|Earl of Lucan]] ====
* Some members of the family attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, and the family attended a number of social events at this time.
* Papers: Irish Archives Resource has one listing for Lucan, but it doesn't seem to be relevant: too late and not about the family.
==== [[Social Victorians/People/Ormonde|Marquess and Marchioness of Ormonde]] ====
* The marchioness and her daughters attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, though nobody mentions the Marquess.
* James Edward Butler, 3rd Marquess of Ormonde and 21st Earl of Ormonde (1844–1919)<ref>{{Cite journal|date=2026-05-03|title=Earl of Ormond (Ireland)|url=https://en.wikipedia.org/w/index.php?title=Earl_of_Ormond_(Ireland)&oldid=1352334266|journal=Wikipedia|language=en}}</ref> Now extinct; earldom dormant. Castle Kilkenny was their manor, but they don't appear to have any papers.
* Subsidiary Titles
* Papers: Irish Archives Resource has one listing, but it's not about the family, the name of a road uses the word ''Ormonde''.
==== [[Social Victorians/People/Antrim|Earl of Antrim]] ====
* The earl and countess did not attend the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, but two of his brothers did.
* Papers
** [https://iar.ie/archive/earl-antrim-estate-papers/ Estate papers of the Earls of Antrim] [GB 0255 PRONI/D2977] are in PRONI. I don't see personal papers listed, but the collection has 50,000 documents 1603–1967.
** Also "D4091 Papers of Sir Schomberg MacDonnell, Louisa Countess of Antrim and the Stuart family of Dalness. MIC615 The diaries of Louisa, Countess of Antrim."<ref>{{Cite web|url=https://iar.ie/archive/earl-antrim-estate-papers/|title=Earl of Antrim Estate Papers|website=Irish Archives Resource|language=en-US|access-date=2026-06-06}}</ref>
==== [[Social Victorians/People/Arran|Earl of Arran]] ====
* Attended the ball.
* Subsidiary Titles
** Viscount Sudley: 5th: Arthur Saunders William Charles Fox Gore (25 Jun 1884-14 Mar 1901), 5th Earl of Arran<ref name=":1" />
*Papers
==== [[Social Victorians/People/Belmore|Earl Belmore]] ====
* Did not attend the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, although [[Social Victorians/People/Rowton|Montagu Lowry-Corry, 1st Baron Rowton]] did, but did attend a number of social events about this time.
* 4th Earl: Somerset Richard Lowry-Corry (17 Dec 1845-6 Apr 1913)<ref>{{Cite journal|date=2026-04-17|title=Somerset Lowry-Corry, 4th Earl Belmore|url=https://en.wikipedia.org/w/index.php?title=Somerset_Lowry-Corry,_4th_Earl_Belmore&oldid=1349375684|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Belmore (though the subsidiary title for the heir apparent is Viscount Corry?)
*Papers: Belmore Papers [GB 0255 PRONI/D3007]<ref>{{Cite web|url=https://iar.ie/archive/belmore-papers/|title=Belmore Papers|website=Irish Archives Resource|language=en-US|access-date=2026-06-07}}</ref>
**D3007/B Rentals and account books (estate, household and personal papers)
**D3007/F Curiosa and personal ephemera
**D3007/I Private and family letters to Honoria Gladstone, Countess Belmore
**D3007/Y Letters and papers of Viscount Corry and the Hon. Cecil Corry, later 5th and 6th Earls Belmore respectively
**D3007/Z Family and other photographs
==== [[Social Victorians/People/Dunraven|Earl of Dunraven and Mount-Earl]] ====
* The [[Social Victorians/People/Dunraven|Earl of Dunraven and Mount-Earl]] and Countess of Dunraven, and their daughter Lady Aileen May Wyndham-Quin attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Windham Wyndham-Quin, 4th Earl of Dunraven and Mount-Earl (1841–1926)<ref>{{Cite journal|date=2026-05-22|title=Windham Wyndham-Quin, 4th Earl of Dunraven and Mount-Earl|url=https://en.wikipedia.org/w/index.php?title=Windham_Wyndham-Quin,_4th_Earl_of_Dunraven_and_Mount-Earl&oldid=1355461019|journal=Wikipedia|language=en}}</ref>, Anglo-Irish
* Papers
==== [[Social Victorians/People/Cole|Earl and Countess of Enniskillen]] ====
* The Earl and Countess and a daughter attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House. Papers in PRONI.
* Subsidiary Title
** 4th Viscount Enniskillen: Lowry Egerton Cole (12 November 1886 – 28 April 1924)<ref name=":1" />
*Papers
==== [[Social Victorians/People/Crichton|Earl of Erne]] ====
* Some members of the family attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* The newspapers were very inconsistent in the spelling of the family name Crichton.
* Subsidiary Title
** Viscount Erne<ref name=":1" />
*** 3rd Earl of Erne: John Crichton (10 June 1842 – 3 October 1885)
*** 4th Earl of Erne: John Henry Crichton (3 October 1885 – 2 December 1914)
*Papers: in PRONI.
==== [[Social Victorians/People/Gosford|Earl of Gosford]] ====
* The Earl and Countess of Gosford attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, as did a son and a daughter. They attended many social events at about this time.
* Subsidiary Title
** Viscount Gosford of Market Hill, co. Armagh<ref name=":1" />
*** 5th Earl of Gosford: Archibald Brabazon Sparrow Acheson (15 June 1864 – 11 April 1922)
*Papers
==== Earl of Kerry ====
* Subsidiary title of the [[Social Victorians/People/Lansdowne|Marquess of Lansdowne]] (in the peerage of Great Britain). Attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Subsidiary Titles
** Viscount Clanmaurice
*Papers
==== [[Social Victorians/People/Kilmorey|Earl of Kilmorey]] ====
* Anglo-Irish
* Nellie Countess of Kilmorey attended the ball; Francis, 3rd Earl was alive at the time, did he attend? Both he and she attended a number of social events from about this time.
* Papers
==== [[Social Victorians/People/Mayo|Earl of Mayo]] ====
* Some members of the family attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Viscount Mayo of Monycrower, co. Mayo<ref name=":1" />
** 7th Earl of Mayo: Dermot Robert Wyndham Bourke (8 February 1872 – 31 December 1927)
*Papers
==== [[Social Victorians/People/Midleton|Viscount Midleton]] ====
* Some people from this family seem to have attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House as well as many other social events at about this time.
* William Brodrick, 8th Viscount Midleton (6 January 1830 – 18 April 1907), "Irish peer, landowner and Conservative politician in both Houses of Parliament"<ref>{{Cite journal|date=2025-01-05|title=William Brodrick, 8th Viscount Midleton|url=https://en.wikipedia.org/w/index.php?title=William_Brodrick,_8th_Viscount_Midleton&oldid=1267418489|journal=Wikipedia|language=en}}</ref>
* Sight and hearing disabilities caused by intermarriage. A daughter became a Republican.
* Papers
==== [[Social Victorians/People/Lurgan|Baron Lurgan]] ====
* The Baron, his wife and probably his uncle attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
** Emily Lady Lurgan
** William Brownlow, Baron Lurgan
** Hon. Cecil Brownlow
* Papers, PRONI<ref>{{Cite web|url=https://iar.ie/archive/brownlow-papers/|title=Brownlow Papers|website=Irish Archives Resource|language=en-US|access-date=2026-06-07}}</ref>
==== Baron Carrington ====
* [[Social Victorians/People/Carrington|Charles Robert Wynn-Carington, 1st Marquess of Lincolnshire]] (1843–1928) attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Baron Carrington is a subsidiary title of the Marquess of Lincolnshire (created in 1912; Earl Carrington created in 1895).<ref>{{Cite journal|date=2026-05-20|title=Baron Carrington|url=https://en.wikipedia.org/w/index.php?title=Baron_Carrington&oldid=1355207880|journal=Wikipedia|language=en}}</ref>
* Papers
==== Baron Dufferin and Claneboye<ref>{{Cite journal|date=2026-02-07|title=Baron Dufferin and Claneboye|url=https://en.wikipedia.org/w/index.php?title=Baron_Dufferin_and_Claneboye&oldid=1337113957|journal=Wikipedia|language=en}}</ref> ====
* Members of this family did attend the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House as well as many social events at about this time.
* [[Social Victorians/People/Hamilton Temple Blackwood|Frederick Temple Hamilton-Temple-Blackwood]], 1st Marquess of Dufferin and Ava (1826–1902)<ref>{{Cite journal|date=2026-05-27|title=Frederick Hamilton-Temple-Blackwood, 1st Marquess of Dufferin and Ava|url=https://en.wikipedia.org/w/index.php?title=Frederick_Hamilton-Temple-Blackwood,_1st_Marquess_of_Dufferin_and_Ava&oldid=1356387854|journal=Wikipedia|language=en}}</ref>
* Papers
==== Baron Garvagh ====
* [[Social Victorians/People/Garvagh|Florence Canning, Lady Garvagh]] attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Charles John Spencer George Canning, 3rd Baron Garvagh (1852–1915)<ref>{{Cite journal|date=2026-02-06|title=Baron Garvagh|url=https://en.wikipedia.org/w/index.php?title=Baron_Garvagh&oldid=1336941309|journal=Wikipedia|language=en}}</ref>
* Papers
==== Baron Rossmore of Monaghan ====
* A [[Social Victorians/People/Naylor|Miss Naylor]] (Lady Rossmore's sister) of this family attended the ball.
* Derrick Warner William Westenra, 5th Baron Rossmore (1853–1921)<ref>{{Cite journal|date=2024-08-27|title=Derrick Westenra, 5th Baron Rossmore|url=https://en.wikipedia.org/w/index.php?title=Derrick_Westenra,_5th_Baron_Rossmore&oldid=1242602083|journal=Wikipedia|language=en}}</ref>
* Papers
== References ==
{{reflist}}
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= The Irish Aristocracy at the End of the 19th Century =
== The Irish Peerage ==
Minus the people who attended the ball, which are in [[Social Victorians/Irish Aristocracy#Irish Aristocrats at the Duchess of Devonshire's 1897 Fancy-dress Ball|this section, below]].
=== Dukes and Duchesses ===
==== Duke of Leinster ====
Irish peerage
* Gerald FitzGerald, 5th Duke of Leinster (16 August 1851 – 1 December 1893)<ref>{{Cite web|url=https://www.thepeerage.com/p1207.htm#i12063|title=Gerald FitzGerald, 5th Duke of Leinster|website=www.thepeerage.com|access-date=2026-05-24}}</ref>
* Maurice FitzGerald, 6th Duke of Leinster, 6 years old when he succeeded to the dukedom<ref>{{Cite web|url=https://www.thepeerage.com/p2767.htm#i27667|title=Maurice FitzGerald, 6th Duke of Leinster|website=www.thepeerage.com|access-date=2026-05-24}}</ref>
* Subsidiary Titles
# Marquess of Kildare (Irish peerage), did not attend the ball.
# Earl of Kildare (Irish peerage), did not attend the ball.
# Earl of Offaly (Irish peerage)
# Viscount Leinster of Taplow (GB peerage)
# Baron Offaly (Irish peerage)
# Baron Kildare of Kildare (UK peerage)
=== Marquesses and Marchionesses ===
==== Marquess Conyngham<ref>{{Cite journal|date=2026-01-13|title=Marquess Conyngham|url=https://en.wikipedia.org/w/index.php?title=Marquess_Conyngham&oldid=1332742873|journal=Wikipedia|language=en}}</ref> ====
* Did not attend the ball but did attend a number of social events about this time.
* Pronounced "''Cunn''ingum."<ref>{{Cite journal|date=2026-01-13|title=Marquess Conyngham|url=https://en.wikipedia.org/w/index.php?title=Marquess_Conyngham&oldid=1332742873|journal=Wikipedia|language=en}}</ref>
* Henry Francis Conyngham, 4th Marquess Conyngham (1857–1897)<ref>"Henry Francis Conyngham, 4th Marquess Conyngham." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 7198
https://www.thepeerage.com/p7199.htm#i71982.</ref>
* Victor George Henry Francis Conyngham, 5th Marquess Conyngham (1883–1918)<ref>"Victor George Henry Francis Conyngham, 5th Marquess Conyngham." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 7198 https://www.thepeerage.com/p7199.htm#i71983.</ref>
* Subsidiary Titles
** Earl of Conyngham
** Viscount Conyngham
** Viscount Mount Charles
==== Marquess of Donegall ====
* Did not attend the ball.
* Subsidiary Titles
** Earl of Donegall, did not attend the ball.
** Viscount Chichester — did not attend the ball; some Chichesters attended social events at about this time.
==== Marquess and Marchioness of Downshire ====
* Arthur Wills John Wellington Trumbull Blundell Hill, 6th Marquess of Downshire (2 July 1871 – 29 May 1918) in 1893 married Katherine Mary ("Kitty") Hare (1872–1959)<ref>{{Cite journal|date=2025-02-10|title=Arthur Hill, 6th Marquess of Downshire|url=https://en.wikipedia.org/w/index.php?title=Arthur_Hill,_6th_Marquess_of_Downshire&oldid=1274976272|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball.
* Subsidiary Titles
** Earl of Hillsborough, did not attend the ball, also not at any social events described so far.
** Viscount Kilwarlin — 6th, Arthur Wills John Wellington Trumbull Hill (31 March 1874 – 29 May 1918)<ref>"Arthur Wills John Wellington Trumbull '''Hill''', 6th Marquess of Downshire." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page #3810
https://www.thepeerage.com/p3811.htm#i38104.</ref>
==== Marquess of Ely ====
* Did not attend the ball, but members of the Loftus family attended a number of social events at about this time.
* 4th Marquess: John Henry Wellington Graham Loftus (15 July 1857 – 3 April 1889)<ref>"John Henry Wellington Graham Loftus, 4th Marquess of Ely." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 8545 https://www.thepeerage.com/p8545.htm#i85450.</ref>
* 5th Marquess: John Henry Loftus (3 April 1889 – 18 December 1925)<ref>"John Henry Loftus, 5th Marquess of Ely." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 8546 https://www.thepeerage.com/p8546.htm#i85459.</ref>
* Subsidiary Titles
** Earl of Ely — did not attend the ball.
** Viscount Loftus
==== [[Social Victorians/People/Bective|Marquess and Marchioness of Headfort]] ====
* Did not attend the ball, but a number of people in this family attended many social events at about this time.
* Subsidiary Titles
** [[Social Victorians/People/Bective|Earl of Bective]]
** Viscount Headfort<ref name=":1" />
*** 4th: Thomas Taylour (6 December 1870 – 22 July 1894)
*** 5th: Geoffrey Thomas Taylour (22 July 1894 – 29 January 1943)
*Papers
==== Marquess of Sligo ====
* Did not attend the ball, but many people with the surname Browne attended a number of social events at about this time.
* Subsidiary Titles
** Earl of Altamont. Did not attend the ball; did not attend any social events analyzed so far.
** Earl of Clanricarde — Did not attend the ball but did attend a few social events about this time.
** Viscount of Westport<ref name=":1">"Index to Viscounts and Viscountesses." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''.
https://www.thepeerage.com/index_viscount.htm.</ref>
*** 5th: George John Browne (26 January 1845 – 30 December 1896), 5th Marquess
*** 6th: John Thomas Browne (30 December 1896 – 30 December 1903), 6th Marquess
==== Marquess of Waterford ====
* John Henry de La Poer Beresford, 5th Marquess of Waterford (1844–1895)
* Henry de La Poer Beresford, 6th Marquess of Waterford (1875–1911)<ref>{{Cite journal|date=2026-02-10|title=Henry Beresford, 6th Marquess of Waterford|url=https://en.wikipedia.org/w/index.php?title=Henry_Beresford,_6th_Marquess_of_Waterford&oldid=1337565707|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but members of the Beresford family were prominent socially at about this time.
* Subsidiary Titles
** Viscount Tyrone
=== Earls and Countesses ===
==== Earl of Annesley ====
* Did not attend the ball but did attend a number of social events in the 1890s.
* Subsidiary Title
** Viscount Glerawly<ref name=":1" />: 6th: Hugh Annesley (10 August 1874 – 15 December 1908), 6th Earl of Annesley
==== Earl of Bessborough ====
* Frederick George Brabazon Ponsonby, 6th Earl of Bessborough (1815–1895)
* Walter William Brabazon Ponsonby, 7th Earl of Bessborough (1821–1906), would have been Viscount Duncannon 1880–1895
* Edward Ponsonby, 8th Earl of Bessborough (1851–1920), would have been Viscount Duncannon 1895–1906
* Did not attend the ball, but the [[Social Victorians/People/Ponsonby|Ponsonby]] family attended many social events at about this time, including mention of Lady Duncannon's school that taught fabric arts.
* Subsidiary Titles
** Viscount Duncannon
==== Earl of Caledon ====
* Did not attend the ball but did attend a number of social events about this time.
* James Alexander, 4th Earl of Caledon (1846–1898)<ref>{{Cite journal|date=2025-11-21|title=James Alexander, 4th Earl of Caledon|url=https://en.wikipedia.org/w/index.php?title=James_Alexander,_4th_Earl_of_Caledon&oldid=1323312651|journal=Wikipedia|language=en}}</ref>
* Eric James Desmond Alexander, 5th Earl of Caledon (1885–1968), succeeded as earl in 1898.<ref>{{Cite journal|date=2025-11-21|title=Eric Alexander, 5th Earl of Caledon|url=https://en.wikipedia.org/w/index.php?title=Eric_Alexander,_5th_Earl_of_Caledon&oldid=1323313583|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Caledon
==== Earl of Carrick ====
* Did not attend the ball.
==== Earl Castle Stewart ====
* Did not attend the ball.
* 5th Earl: Henry James Stuart-Richardson (12 September 1874 – 5 June 1914)<ref>"Henry James Stuart-Richardson, 5th Earl Castle Stewart." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 2412 https://www.thepeerage.com/p12413.htm#i124125.</ref>
* Subsidiary Title
** Viscount Castle Stewart
==== Earl of Cavan ====
* Did not attend the ball.
==== Earl of Clancarty ====
* Did not attend the ball and attended few social events researched so far.
* Richard Somerset Le Poer Trench, 4th Earl of Clancarty (1834–1891)<ref>{{Cite journal|date=2026-01-10|title=Richard Trench, 4th Earl of Clancarty|url=https://en.wikipedia.org/w/index.php?title=Richard_Trench,_4th_Earl_of_Clancarty&oldid=1332219771|journal=Wikipedia|language=en}}</ref>
* William Frederick Le Poer Trench, 5th Earl of Clancarty (1868–1929)<ref>{{Cite journal|date=2025-11-05|title=William Trench, 5th Earl of Clancarty|url=https://en.wikipedia.org/w/index.php?title=William_Trench,_5th_Earl_of_Clancarty&oldid=1320532351|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Dunlo
==== [[Social Victorians/People/Clanwilliam|Earl and Countess of Clanwilliam]] ====
* Did not attend the ball.
* Subsidiary Title
** Viscount Clanwilliam<ref name=":1" />: 4th: Richard James Meade (7 October 1879 – 4 August 1907), 4th Earl
==== Earl of Cork, Earl of Orrery ====
* Cork and Orrery, did attend the ball.
==== Earl of Courtown ====
* Did not attend the ball.
==== Earl of Darnley ====
* John Bligh, 6th Earl of Darnley (1827–1896), British<ref>{{Cite journal|date=2026-02-07|title=John Bligh, 6th Earl of Darnley|url=https://en.wikipedia.org/w/index.php?title=John_Bligh,_6th_Earl_of_Darnley&oldid=1337113925|journal=Wikipedia|language=en}}</ref>
* Edward Bligh, 7th Earl of Darnley (1851–1900), Lord Clifton much of his adult life, "English"<ref>{{Cite journal|date=2026-05-05|title=Edward Bligh, 7th Earl of Darnley|url=https://en.wikipedia.org/w/index.php?title=Edward_Bligh,_7th_Earl_of_Darnley&oldid=1352607379|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but the Bligh family attended some social events from about this time.
* Subsidiary Titles:
** Viscount Darnley
==== Earl of Desmond ====
* Did not attend the ball.
==== [[Social Victorians/People/Donoughmore|Earl of Donoughmore]] ====
* Did not attend the ball but did attend a number of social events about this time.
* John Luke George Hely-Hutchinson, 5th Earl of Donoughmore (1848–1900)<ref>{{Cite journal|date=2025-05-01|title=John Hely-Hutchinson, 5th Earl of Donoughmore|url=https://en.wikipedia.org/w/index.php?title=John_Hely-Hutchinson,_5th_Earl_of_Donoughmore&oldid=1288332715|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Donoughmore
==== Earl of Drogheda ====
* Did not attend the ball.
* Subsidiary Titles
** Viscount Moore — no evidence of the Viscount or Viscountess Moore at social events at about this time.
==== Earl of Granard ====
* Did not attend the ball.
* Bernard Arthur William Patrick Hastings Forbes, 8th Earl of Granard (17 September 1874 – 10 September 1948)[https://en.wikipedia.org/wiki/Bernard_Forbes,_8th_Earl_of_Granard]
* Anglo-Irish
* Subsidiary Titles
** Bernard Arthur William Patrick Hastings Forbes, styled Viscount Forbes from 1874 to 1889
==== Earl of Kingston ====
* Did not attend the ball.
* Subsidiary Title
** Viscount Kingsborough (of Viscount Kingston of Kingborough, co. Sligo)<ref name=":1" />
*** 8th: Henry Newcomen King-Tenison (21 June 1871 – 13 January 1896)
*** 9th: Henry Edwyn King-Tenison (13 January 1896 – 11 January 1946)
**Viscount Lorton
==== Earl of Lisburne ====
* Did not attend the ball.
* Ernest Augustus Malet Vaughan, 5th Earl of Lisburne (1836–1888)<ref>{{Cite journal|date=2025-12-03|title=Ernest Augustus Malet Vaughan, 5th Earl of Lisburne|url=https://en.wikipedia.org/w/index.php?title=Ernest_Augustus_Malet_Vaughan,_5th_Earl_of_Lisburne&oldid=1325511612|journal=Wikipedia|language=en}}</ref>
** Owned a lot of land in Cardiganshire, Wales
** Conservative, but withdrew from politics
* George Henry Arthur Vaughan, 6th Earl of Lisburne (1862–1899)
* Ernest Edmund Henry Malet Vaughan, 7th Earl of Lisburne (1892–1965)
** Welsh nobleman, of Trawsgoed, Cardiganshire. 7 years old when he succeeded to the earldom
==== Earl of Longford ====
* Did not attend the ball.
==== Earl and Countess of Meath ====
* Did not attend the ball.
==== Earl of Mexborough ====
* Did not attend the ball
==== Earl of Mornington ====
* Subsidiary title of the Duke of Wellington (in the peerage of the UK).
==== Earl of Normanton ====
* Did not attend the ball, but did attend some social events in the 1880s and 1890s.
* James Charles Herbert Welbore Ellis Agar, 3rd Earl of Normanton (1818–1896)<ref>{{Cite journal|date=2025-10-06|title=James Agar, 3rd Earl of Normanton|url=https://en.wikipedia.org/w/index.php?title=James_Agar,_3rd_Earl_of_Normanton&oldid=1315461436|journal=Wikipedia|language=en}}</ref>
* Sidney James Agar, 4th Earl of Normanton (1865–1933)<ref>{{Cite journal|date=2026-05-19|title=Sidney James Agar, 4th Earl of Normanton|url=https://en.wikipedia.org/w/index.php?title=Sidney_James_Agar,_4th_Earl_of_Normanton&oldid=1355064165|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Somerton
==== Earl of Portarlington ====
* Did not attend the ball. Members of this family attended a few social events at about this time.
* Subsidiary Title
** Viscount Carlow<ref name=":1" />
*** 5th: Lionel Seymour William Dawson-Damer (1 March 1889 – 17 December 1892), Earl of Portarlington
*** 6th: Lionel George Henry Seymour Dawson-Damer (17 December 1892 – 31 August 1900)
==== Earl of Roden ====
* Did not attend the ball.
* Subsidiary Title
** Viscount Jocelyn<ref name=":1" />
*** 6th: John Strange Jocelyn (9 January 1880 – 3 July 1897)
*** 7th: William Henry Jocelyn (3 July 1897 – 23 January 1910)
==== Earl of Shannon ====
* Did not attend the ball.
==== Earl of Shelburne ====
* Subsidiary title of the Marquess of Lansdowne (in the peerage of Great Britain).
* Did not attend the ball, and did not attend any social events analyzed so far.
==== Earl of Tyrone ====
* Did not attend
==== Earl of Waterford ====
* Not a subsidiary title of the Marquess of Waterford but of the Earl of Shrewsbury in the peerage of England.
==== Earl of Westmeath ====
* Did not attend the ball.
==== Earl of Winterton ====
* Did not attend the ball.
=== Viscounts and Viscountesses ===
==== Viscount Ashbrook ====
* William Spencer Flower, 7th Viscount Ashbrook (1830–1906)<ref>{{Cite journal|date=2025-12-01|title=Viscount Ashbrook|url=https://en.wikipedia.org/w/index.php?title=Viscount_Ashbrook&oldid=1325071512|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, has no social presence at about this time.
==== Viscount Banger ====
* Did not attend the ball but attended a few social events at about this time.
* Edward Ward, 4th Viscount Bangor (1827–1881)<ref>{{Cite journal|date=2026-03-16|title=Edward Ward, 4th Viscount Bangor|url=https://en.wikipedia.org/w/index.php?title=Edward_Ward,_4th_Viscount_Bangor&oldid=1343882576|journal=Wikipedia|language=en}}</ref>
* Henry William Crosbie Ward, 5th Viscount Bangor (1828–1911)<ref>{{Cite journal|date=2026-03-02|title=Henry Ward, 5th Viscount Bangor|url=https://en.wikipedia.org/w/index.php?title=Henry_Ward,_5th_Viscount_Bangor&oldid=1341354058|journal=Wikipedia|language=en}}</ref>
==== Viscount Boyne ====
* Did not attend the ball, but did attend a number of events at about this time.
==== Viscount Callan ====
* Did not attend the ball, and does not have much if any social presence at about this time.
* The Viscount Callan is a subsidiary title of the Earl of Denbigh in the Peerage of England.
==== Viscount Charlemont ====
* Did not attend the ball.
* Colonel James Alfred Caulfeild, 7th Viscount Charlemont (20 March 1830 – 4 July 1913), Irish<ref>{{Cite journal|date=2026-05-02|title=James Caulfeild, 7th Viscount Charlemont|url=https://en.wikipedia.org/w/index.php?title=James_Caulfeild,_7th_Viscount_Charlemont&oldid=1352129469|journal=Wikipedia|language=en}}</ref>
* Unionist
==== Viscount Chetwynd ====
* Does not seem to have attended the ball, but Chetwynds were socially very active at about this time.
* Godfrey John Boyle Chetwynd, 8th Viscount Chetwynd (1863–1936), British<ref>{{Cite journal|date=2026-05-24|title=Godfrey Chetwynd, 8th Viscount Chetwynd|url=https://en.wikipedia.org/w/index.php?title=Godfrey_Chetwynd,_8th_Viscount_Chetwynd&oldid=1355878192|journal=Wikipedia|language=en}}</ref>
==== Viscount de Vesci ====
* Did not attend the ball but attended several social events at about this time.
* 4th Viscount de Vesci: John Robert William Vesey (23 December 1875 – 6 July 1903)<ref name=":1" />
* "The family seat was Abbeyleix House, near Abbeyleix, County Laois."<ref>{{Cite journal|date=2026-02-09|title=Viscount de Vesci|url=https://en.wikipedia.org/w/index.php?title=Viscount_de_Vesci&oldid=1337491855|journal=Wikipedia|language=en}}</ref>
==== Viscount Dillon ====
* Did not attend the ball, but several Dillons attended other social events at about this time.
==== Viscount Doneraile<ref>{{Cite journal|date=2026-01-16|title=Viscount Doneraile|url=https://en.wikipedia.org/w/index.php?title=Viscount_Doneraile&oldid=1333262628|journal=Wikipedia|language=en}}</ref> ====
* Did not attend the ball, but did attend the Warwick Bal Poudré and few other social events at about this time.
* Hayes St Leger, 4th Viscount Doneraile (1818–1887)
* Richard Arthur St Leger, 5th Viscount Doneraile (1825–1891)
* Edward St Leger, 6th Viscount Doneraile (1866–1941)
==== [[Social Victorians/People/Downe|Viscount Downe]] ====
* Did not attend the ball but attended many social events at about this time.
* Major-General Hugh Richard Dawnay, 8th Viscount Downe (20 July 1844 – 21 January 1924)<ref>{{Cite journal|date=2026-03-24|title=Hugh Dawnay, 8th Viscount Downe|url=https://en.wikipedia.org/w/index.php?title=Hugh_Dawnay,_8th_Viscount_Downe&oldid=1345146095|journal=Wikipedia|language=en}}</ref>
* British Army general
==== Viscount Ferrard ====
* See Viscount Massereene, below. By the end of the century, it was the Viscount and Viscountess of Massereene and Ferrard.
==== Viscount Fitzmaurice ====
* A subsidiary title of the Marquess of Lansdowne (in the Peerage of Great Britain).
* 6th Viscount Fitzmaurice, Henry Charles Keith Petty-FitzMaurice (5 July 1866 – 3 June 1927)<ref>"Henry Charles Keith Petty-FitzMaurice, 5th Marquess of Lansdowne." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 958
https://www.thepeerage.com/p959.htm#i9586.</ref>
==== Viscount Gage ====
* Henry Charles Gage, 5th Viscount Gage (1854–1912)<ref>{{Cite journal|date=2025-06-21|title=Viscount Gage|url=https://en.wikipedia.org/w/index.php?title=Viscount_Gage&oldid=1296646030|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but members of this family attended a number of social events at about this time.
==== Viscount Galway ====
* George Edmund Milnes Monckton-Arundell, 7th Viscount Galway (1844–1931), British conservative<ref>{{Cite journal|date=2025-08-08|title=George Monckton-Arundell, 7th Viscount Galway|url=https://en.wikipedia.org/w/index.php?title=George_Monckton-Arundell,_7th_Viscount_Galway&oldid=1304770631|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but Viscount and Viscountess Galway attended many social events at about this time.
* Subsidiary Title
** Baron Monckton (in the Peerage of the United Kingdom)
==== Viscount Gormanston ====
* Did not attend the ball, has no social presence in the late 19th-century newspapers at this time.
==== [[Social Victorians/People/Gort|Viscount Gort]] ====
* Did not attend the ball, but attended some social events at about this time.
* Standish Prendergast Vereker, 4th Viscount Gort (1819–1900)<ref>"Standish Prendergast Vereker, 4th Viscount Gort." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 4626 https://www.thepeerage.com/p4627.htm#i46261.</ref>
* John Gage Prendergast Vereker, 5th Viscount Gort (1849–1902)<ref>{{Cite journal|date=2025-05-28|title=John Vereker, 5th Viscount Gort|url=https://en.wikipedia.org/w/index.php?title=John_Vereker,_5th_Viscount_Gort&oldid=1292670203|journal=Wikipedia|language=en}}</ref>
==== Viscount Grandison ====
* Did not attend the ball, has no social presence in the late 19th-century newspapers at this time.
* The Viscount Grandison is a subsidiary title of the Earl of Jersey in the Peerage of England.
==== Viscount Grimston ====
* Subsidiary title of the Earl of Verulam (in the Peerage of the United Kingdom)
* Did not attend the ball, but a number of members of this family attended social events at about this time.
==== Viscount Harberton ====
* Did not attend the ball; Viscountess Harberton is mentioned once in social events at about this time so far.
* James Spencer Pomeroy, 6th Viscount Harberton (1836–1912)<ref>"James Spencer Pomeroy, 6th Viscount Harberton." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person Page 4315 https://www.thepeerage.com/p43151.htm#i431502.</ref>
* Florence Wallace Pomeroy, Viscountess Harberton (1843–1911), suffragette, cyclist, President of the Rational Dress Society<ref>{{Cite journal|date=2026-03-12|title=Florence Wallace Pomeroy, Viscountess Harberton|url=https://en.wikipedia.org/w/index.php?title=Florence_Wallace_Pomeroy,_Viscountess_Harberton&oldid=1343082631|journal=Wikipedia|language=en}}</ref>
==== Viscount Lifford ====
* Did not attend the ball; the only social event at about this time so far is the Queen's Diamond Jubilee garden party.
* James Hewitt, 4th Viscount Lifford (1811–1887)<ref>{{Cite journal|date=2025-09-11|title=James Hewitt, 4th Viscount Lifford|url=https://en.wikipedia.org/w/index.php?title=James_Hewitt,_4th_Viscount_Lifford&oldid=1310741456|journal=Wikipedia|language=en}}</ref>
* James Wilfrid Hewitt, 5th Viscount Lifford (12 October 1837 – 20 March 1913)<ref>"James Wilfrid Hewitt, 5th Viscount Lifford." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person Page 2227 https://www.thepeerage.com/p22271.htm#i222701.</ref>
==== Earl of Listowel ====
* Pronounced "Lish-''toe''-ell."<ref>{{Cite journal|date=2024-10-15|title=Earl of Listowel|url=https://en.wikipedia.org/w/index.php?title=Earl_of_Listowel&oldid=1251322273|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but hosted and attended social events at about this time.
* William Hare, 3rd Earl of Listowel (1833–1924)<ref>{{Cite journal|date=2026-04-17|title=William Hare, 3rd Earl of Listowel|url=https://en.wikipedia.org/w/index.php?title=William_Hare,_3rd_Earl_of_Listowel&oldid=1349570352|journal=Wikipedia|language=en}}</ref>, Irish peer
* Subsidiary Title
** Viscount Ennismore and Listowel
** Baron Ennismore
==== Viscount Massereene ====
* Did not attend the ball but did attend a few events at about this time. See Viscount Ferrard, above. By the end of the century, it was the Viscount and Viscountess of Massereene and Ferrard.
* Anglo-Irish
* Clotworthy John Eyre Skeffington, 11th Viscount Massereene (9 October 1842 – 26 June 1905)<ref>{{Cite journal|date=2024-11-23|title=Clotworthy Skeffington, 11th Viscount Massereene|url=https://en.wikipedia.org/w/index.php?title=Clotworthy_Skeffington,_11th_Viscount_Massereene&oldid=1259199982|journal=Wikipedia|language=en}}</ref> and 4th Viscount Ferrard (28 April 1863 – 26 June 1905)
==== Viscount Molesworth ====
* Did not attend the ball, but attended the Warwick Bal Poudré and a number of other social events at about this time.
* Samuel Molesworth, 8th Viscount Molesworth (1829–1906), may have been a Quaker
==== Viscount Monck ====
* Did not attend the ball, but attended a number of social events at about this time.
* Charles Stanley Monck, 4th Viscount Monck (1819–1894)<ref>{{Cite journal|date=2026-04-05|title=Charles Monck, 4th Viscount Monck|url=https://en.wikipedia.org/w/index.php?title=Charles_Monck,_4th_Viscount_Monck&oldid=1347311992|journal=Wikipedia|language=en}}</ref>, British
* Henry Power Charles Stanley Monck, 5th Viscount Monck (1849–1927)<ref>"Henry Power Charles Stanley Monck, 5th Viscount Monck of Ballytrammon." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 3880 https://www.thepeerage.com/p3881.htm#i38802.</ref>
==== Viscount Mountgarret ====
* Did not attend the ball, has no social presence in the late 19th-century newspapers at this time.
==== [[Social Victorians/People/Powerscourt|Viscount Powerscourt]] ====
* Mervyn Wingfield, 7th Viscount Powerscourt (1836–1904)<ref name=":0">{{Cite journal|date=2026-02-18|title=Mervyn Wingfield, 7th Viscount Powerscourt|url=https://en.wikipedia.org/w/index.php?title=Mervyn_Wingfield,_7th_Viscount_Powerscourt&oldid=1339057453|journal=Wikipedia|language=en}}</ref>
* Did not attend the ball, but members of this family attended a number of social events at about this time.
* Subsidiary Title
** Baron Powerscourt (in the Peerage of the United Kingdom), 1885<ref name=":0" />
==== Viscount Southwell ====
* Did not attend the ball, though the Viscount and Viscountess attended a few social events at about this time.
* 5th<ref name=":1" />: Arthur Robert Pyers Southwell (26 April 1878 – 5 October 1944)<ref>"Arthur Robert Pyers Southwell, 5th Viscount Southwell of Castle Mattress." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page
https://www.thepeerage.com/p7550.htm#i75497.</ref>
==== Viscount Valentia ====
* Did not attend the ball, attended some social events at about this time. Was on the Welcome Council for the 1887 American Exhibition.
=== Barons and Baronesses ===
Not all the barons extant at the end of the 19th century and listed on the Wikipedia [[wikipedia:Peerage_of_Ireland|Peerage of Ireland]] page are here — only the ones who were active socially.
==== Baron Conway and Killultagh ====
* Did not attend the ball, but people from the Conway and Seymour families attended a number of social events at about this time.
* Subsidiary title of the Marquess of Hertford (in the Peerage of England and Great Britain).
* Francis Hugh George Seymour, 5th Marquess of Hertford (1812–1884)<ref>{{Cite journal|date=2026-04-05|title=Francis Seymour, 5th Marquess of Hertford|url=https://en.wikipedia.org/w/index.php?title=Francis_Seymour,_5th_Marquess_of_Hertford&oldid=1347294689|journal=Wikipedia|language=en}}</ref>
* Hugh de Grey Seymour, 6th Marquess of Hertford (1843–1912)<ref>{{Cite journal|date=2026-04-05|title=Hugh Seymour, 6th Marquess of Hertford|url=https://en.wikipedia.org/w/index.php?title=Hugh_Seymour,_6th_Marquess_of_Hertford&oldid=1347303090|journal=Wikipedia|language=en}}</ref>
==== Baron Digby ====
* Did not attend the ball, but people from this family attended a number of social events at about this time.
* Edward St Vincent Digby, 9th and 3rd Baron Digby (1809–1889)<ref>{{Cite journal|date=2025-12-15|title=Edward Digby, 9th Baron Digby|url=https://en.wikipedia.org/w/index.php?title=Edward_Digby,_9th_Baron_Digby&oldid=1327712265|journal=Wikipedia|language=en}}</ref>
* Edward Henry Trafalgar Digby, 10th and 4th Baron Digby (1846–1920)<ref>{{Cite journal|date=2026-01-26|title=Edward Digby, 10th Baron Digby|url=https://en.wikipedia.org/w/index.php?title=Edward_Digby,_10th_Baron_Digby&oldid=1334892957|journal=Wikipedia|language=en}}</ref>
==== Baron Inchiquin ====
* Did not attend the ball, but people from this family attended a number of social events at about this time.
* Edward Donough O'Brien, 14th Baron Inchiquin (1839–1900)<ref>{{Cite journal|date=2026-04-28|title=Edward O'Brien, 14th Baron Inchiquin|url=https://en.wikipedia.org/w/index.php?title=Edward_O%27Brien,_14th_Baron_Inchiquin&oldid=1351543832|journal=Wikipedia|language=en}}</ref>
== Peerage of the United Kingdom of Great Britain and Ireland ==
After the forced 1801 Act of Union.
=== Earls and Countesses ===
==== Earl of Limerick ====
* Did not attend the ball, but did attend a number of events at about this time.
==== Earl of Norbury ====
* Did not attend the ball, but attended some social events at about this time.
* Subsidiary Title
** Baron Norbury
==== Earl of Ranfurly ====
* Did not attend the ball, and they have a small social presence in the newspapers in the 1880s and 1890s.
==== Earl of Rosse ====
* Did not attend the ball, but did attend a few events at about this time.
== Peerage of the United Kingdom ==
* Lurgan
== Irish Nationalists ==
== Irish Unionists ==
== Irish Aristocrats at the Duchess of Devonshire's 1897 Fancy-dress Ball ==
==== [[Social Victorians/People/Abercorn|Duke and Duchess of Abercorn]] ====
* This dukedom is in the peerage of the United Kingdom of Great Britain and Ireland
* James Hamilton, 1st Duke of Abercorn (1811–1885), elder son of Lord Hamilton, "styled Viscount Hamilton from 1814 to 1818 and The Marquess of Abercorn from 1818 to 1868, was a Conservative statesman who twice served as Lord Lieutenant of Ireland."<ref>{{Cite journal|date=2026-04-05|title=James Hamilton, 1st Duke of Abercorn|url=https://en.wikipedia.org/w/index.php?title=James_Hamilton,_1st_Duke_of_Abercorn&oldid=1347253763|journal=Wikipedia|language=en}}</ref>
* James Hamilton, 2nd Duke of Abercorn (1838–1913), eldest son of the 1st Duke, "styled Viscount Hamilton until 1868 and Marquess of Hamilton from 1868 to 1885, was a British nobleman, courtier, and diplomat."<ref>{{Cite journal|date=2026-01-25|title=James Hamilton, 2nd Duke of Abercorn|url=https://en.wikipedia.org/w/index.php?title=James_Hamilton,_2nd_Duke_of_Abercorn&oldid=1334676058|journal=Wikipedia|language=en}}</ref>
* The Hamilton who became the 3rd duke attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, as did a few other members of this family.
* Subsidiary Titles
** Marquess of Abercorn
** Viscount Hamilton
** Viscount Strabane, county Tyrone
*Papers
**PRONI for the Abercorn papers [GB 0255 PRONI/D623]
**Some individuals' papers (the Tighe Hamilton Howard papers, https://iar.ie/archive/tighe-hamilton-howard-papers) from the Hamilton family are in the National Library of Ireland. "An item level catalogue is available online. These papers form part of the Wicklow Papers (Collection List 69) that are held in the Department of Manuscripts at the National Library of Ireland."
***VII. Sarah Howard Papers, 1830-1887.
****[***] VII.ii. Letters from Sarah Howard to her husband the Hon. Rev. Francis Howard, [n.d.] Call number: '''MS 38,639/2/2'''
****[***] VII.iii. Correspondence between Sarah Howard and her daughter Lady Caroline Howard, ca. 1851 - ca. 1891. Call number: '''MS 38,639/2/3'''
****VII.iv. Correspondence between Sarah Howard and her son Charles Howard, 5th Earl of Wicklow, 1853-ca.1870. Call number: '''MS 38,639/2/4'''
****VII.v. Correpondence between Sarah Howard and her son Cecil Howard, 6th Earl of Wicklow, ca. 1855-1876. Call number: '''MS 38,639/2/5'''
****[***] VII.vi. Correspondence between Sarah Howard and her daughters Lady Louisa and Lady Alice Howard, 1855-ca. 1877. Call number: '''MS 38,639/2/6'''
****[***] VII.vix. Additional correspondence of Sarah Howard of Wingfield, Bray Co. Wicklow, 1865-1887. Call number: '''MS 38,639/2/9'''
***VIII. Lady Caroline Howard Papers, 1852-1919.
****[**] VIII.i. Correspondence between Lady Caroline Howard and her brother Charles, Earl of Wicklow, 1852-1880. Call number: '''MS 38,639/2/11'''
****[**] VIII.iv. Additional correspondence of Lady Caroline Howard, 1868-1919. Call number: '''MS 38,639/2/14'''
****[**] VIII.v. Additional papers of Lady Caroline Howard, 1900. Call number: '''MS 38,639/2/15'''
***IX. Additional Howard family correspondence, 1773-1900.
****[**] IX.vii. Correspondence and papers of Lady Louisa Howard, 1856-1907. Call number: '''MS 38,639/2/22'''
****[***] IX.viii. Correspondence and papers of Lady Alice Howard, [n.d.] Call number: '''MS 38,639/2/23'''
***XI. Other papers, 1737-1913.
****XI.i. Miscellaneous correspondence, 1753-1891. Call number: '''MS 38,639/2/27'''
***Wicklow Papers
****[**] Journals of Lady Caroline Howard including some accounts of her tours abroad, 1873 Jan. - March, 1875 Aug. - Sept., & 1882 Jan. - April. Call number: '''MS 3586-3588'''
****[**] Diaries of Lady Louisa Howard including accounts of her travels on the Continent, 1862 Oct. - 1869 June, 1871 April - 1873 April and 1877 Oct. - 1883 July. Call number: '''MS 3589-3593'''
****Diaries of Lady Caroline Howard, 1862 Oct. - 1870 May. Call number: '''MS 3594-3599'''
****[***] Diaries of Lady Alice Howard, Shelton Abbey and Bray, Co. Wicklow, 1874-1922. Call number: '''MS 3600-3625'''
***[**] Journals of Lady Alice Howard, including account of tours on the Continent, 1860 June - Oct, 1865 Aug. - 1866 Feb., 1869 Nov. - 1870 Nov. Call number: '''MS 4793-4795'''
==== [[Social Victorians/People/Londonderry|Marquess and Marchioness of Londonderry]] ====
* The Marquess and Marchioness attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, she led one of the courts as Maria Thérèse, plus two of their children attended, one of whom is Viscount Castlereagh.
* Charles Stewart Vane-Tempest-Stewart, 6th Marquess of Londonderry<ref>"Charles Stewart Vane-Tempest-Stewart, 6th Marquess of Londonderry." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 1277 https://www.thepeerage.com/p1278.htm#i12772.</ref>
* Lady Theresa Susey Helen Chetwynd-Talbot, Marchioness of Londonderry<ref>"Lady Theresa Susey Helen Chetwynd-Talbot." ''The Peerage: A Genealogical Survey of the Peerage of Britain as Well as the Royal Families of Europe''. Person page 1277 https://www.thepeerage.com/p1278.htm#i12771.</ref>
* Subsidiary Titles
** [[Social Victorians/People/Londonderry|Earl of Londonderry]]
** Viscount Castlereagh — Charles Stewart Henry Vane-Tempest-Stewart (6 November 1884 – 8 February 1915)
*Papers
**In PRONI [GB 0255 PRONI/D2846]: "The Theresa, Lady Londonderry Papers comprise c.4,600 papers and 15 volumes of diaries, scrapbooks, etc, 1858-1919, mainly of Theresa, Marchioness of Londonderry (1856-1919), wife/widow of the 6th Marquess, but including some papers of the 6th Marquess himself, of and about his mother, Mary Cornelia, widow of the 5th Marquess, and of his brothers Lords Henry and Herbert Vane-Tempest."<ref>{{Cite web|url=https://iar.ie/archive/theresa-lady-londonderry-papers/|title=Theresa, Lady Londonderry Papers|website=Irish Archives Resource|language=en-US|access-date=2026-06-06}}</ref>
**In PRONI [GB 0255 PRONI/D3099]: the "Papers of the 7th Marquess of Londonderry and his wife Edith" collection also hold the papers of Edith's father, [[Social Victorians/People/Henry Chaplin|Henry, 1st Viscount Chaplin]], who attended the ball, as did she and a brother. [D3099/1 Henry, 1st Viscount Chaplin, father-in-law of 7th Marquess of Londonderry. Political and personal papers; D3099/3 Edith Helen Chaplin, wife of 7th Marquess of Londonderry. Personal letters and papers]<ref>{{Cite web|url=https://iar.ie/archive/papers-7th-marquess-londonderry-wife-edith/|title=Papers of the 7th Marquess of Londonderry and his wife Edith|website=Irish Archives Resource|language=en-US|access-date=2026-06-06}}</ref>
==== [[Social Victorians/People/Lucan|Earl of Lucan]] ====
* Some members of the family attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, and the family attended a number of social events at this time.
* Papers: Irish Archives Resource has one listing for Lucan, but it doesn't seem to be relevant: too late and not about the family.
==== [[Social Victorians/People/Ormonde|Marquess and Marchioness of Ormonde]] ====
* The marchioness and her daughters attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, though nobody mentions the Marquess.
* James Edward Butler, 3rd Marquess of Ormonde and 21st Earl of Ormonde (1844–1919)<ref>{{Cite journal|date=2026-05-03|title=Earl of Ormond (Ireland)|url=https://en.wikipedia.org/w/index.php?title=Earl_of_Ormond_(Ireland)&oldid=1352334266|journal=Wikipedia|language=en}}</ref> Now extinct; earldom dormant. Castle Kilkenny was their manor, but they don't appear to have any papers.
* Subsidiary Titles
* Papers: Irish Archives Resource has one listing, but it's not about the family, the name of a road uses the word ''Ormonde''.
==== [[Social Victorians/People/Antrim|Earl of Antrim]] ====
* The earl and countess did not attend the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, but two of his brothers did.
* Papers
** [https://iar.ie/archive/earl-antrim-estate-papers/ Estate papers of the Earls of Antrim] [GB 0255 PRONI/D2977] are in PRONI. I don't see personal papers listed, but the collection has 50,000 documents 1603–1967.
** Also "D4091 Papers of Sir Schomberg MacDonnell, Louisa Countess of Antrim and the Stuart family of Dalness. MIC615 The diaries of Louisa, Countess of Antrim."<ref>{{Cite web|url=https://iar.ie/archive/earl-antrim-estate-papers/|title=Earl of Antrim Estate Papers|website=Irish Archives Resource|language=en-US|access-date=2026-06-06}}</ref>
==== [[Social Victorians/People/Arran|Earl of Arran]] ====
* Attended the ball.
* Subsidiary Titles
** Viscount Sudley: 5th: Arthur Saunders William Charles Fox Gore (25 Jun 1884-14 Mar 1901), 5th Earl of Arran<ref name=":1" />
*Papers
==== [[Social Victorians/People/Belmore|Earl Belmore]] ====
* Did not attend the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, although [[Social Victorians/People/Rowton|Montagu Lowry-Corry, 1st Baron Rowton]] did, but did attend a number of social events about this time.
* 4th Earl: Somerset Richard Lowry-Corry (17 Dec 1845-6 Apr 1913)<ref>{{Cite journal|date=2026-04-17|title=Somerset Lowry-Corry, 4th Earl Belmore|url=https://en.wikipedia.org/w/index.php?title=Somerset_Lowry-Corry,_4th_Earl_Belmore&oldid=1349375684|journal=Wikipedia|language=en}}</ref>
* Subsidiary Title
** Viscount Belmore (though the subsidiary title for the heir apparent is Viscount Corry?)
*Papers: Belmore Papers [GB 0255 PRONI/D3007]<ref>{{Cite web|url=https://iar.ie/archive/belmore-papers/|title=Belmore Papers|website=Irish Archives Resource|language=en-US|access-date=2026-06-07}}</ref>
**D3007/B Rentals and account books (estate, household and personal papers)
**D3007/F Curiosa and personal ephemera
**D3007/I Private and family letters to Honoria Gladstone, Countess Belmore
**D3007/Y Letters and papers of Viscount Corry and the Hon. Cecil Corry, later 5th and 6th Earls Belmore respectively
**D3007/Z Family and other photographs
==== [[Social Victorians/People/Dunraven|Earl of Dunraven and Mount-Earl]] ====
* The [[Social Victorians/People/Dunraven|Earl of Dunraven and Mount-Earl]] and Countess of Dunraven, and their daughter Lady Aileen May Wyndham-Quin attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Windham Wyndham-Quin, 4th Earl of Dunraven and Mount-Earl (1841–1926)<ref>{{Cite journal|date=2026-05-22|title=Windham Wyndham-Quin, 4th Earl of Dunraven and Mount-Earl|url=https://en.wikipedia.org/w/index.php?title=Windham_Wyndham-Quin,_4th_Earl_of_Dunraven_and_Mount-Earl&oldid=1355461019|journal=Wikipedia|language=en}}</ref>, Anglo-Irish
* Papers
==== [[Social Victorians/People/Cole|Earl and Countess of Enniskillen]] ====
* The Earl and Countess and a daughter attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House. Papers in PRONI.
* Subsidiary Title
** 4th Viscount Enniskillen: Lowry Egerton Cole (12 November 1886 – 28 April 1924)<ref name=":1" />
*Papers
==== [[Social Victorians/People/Crichton|Earl of Erne]] ====
* Some members of the family attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* The newspapers were very inconsistent in the spelling of the family name Crichton.
* Subsidiary Title
** Viscount Erne<ref name=":1" />
*** 3rd Earl of Erne: John Crichton (10 June 1842 – 3 October 1885)
*** 4th Earl of Erne: John Henry Crichton (3 October 1885 – 2 December 1914)
*Papers: in PRONI.
==== [[Social Victorians/People/Gosford|Earl of Gosford]] ====
* The Earl and Countess of Gosford attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House, as did a son and a daughter. They attended many social events at about this time.
* Subsidiary Title
** Viscount Gosford of Market Hill, co. Armagh<ref name=":1" />
*** 5th Earl of Gosford: Archibald Brabazon Sparrow Acheson (15 June 1864 – 11 April 1922)
*Papers
==== Earl of Kerry ====
* Subsidiary title of the [[Social Victorians/People/Lansdowne|Marquess of Lansdowne]] (in the peerage of Great Britain). Attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Subsidiary Titles
** Viscount Clanmaurice
*Papers
==== [[Social Victorians/People/Kilmorey|Earl of Kilmorey]] ====
* Anglo-Irish
* Nellie Countess of Kilmorey attended the ball; Francis, 3rd Earl was alive at the time, did he attend? Both he and she attended a number of social events from about this time.
* Papers
==== [[Social Victorians/People/Mayo|Earl of Mayo]] ====
* Some members of the family attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Viscount Mayo of Monycrower, co. Mayo<ref name=":1" />
** 7th Earl of Mayo: Dermot Robert Wyndham Bourke (8 February 1872 – 31 December 1927)
*Papers
==== [[Social Victorians/People/Midleton|Viscount Midleton]] ====
* Some people from this family seem to have attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House as well as many other social events at about this time.
* William Brodrick, 8th Viscount Midleton (6 January 1830 – 18 April 1907), "Irish peer, landowner and Conservative politician in both Houses of Parliament"<ref>{{Cite journal|date=2025-01-05|title=William Brodrick, 8th Viscount Midleton|url=https://en.wikipedia.org/w/index.php?title=William_Brodrick,_8th_Viscount_Midleton&oldid=1267418489|journal=Wikipedia|language=en}}</ref>
* Sight and hearing disabilities caused by intermarriage. A daughter became a Republican.
* Papers
==== [[Social Victorians/People/Lurgan|Baron Lurgan]] ====
* The Baron, his wife and probably his uncle attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
** Emily Lady Lurgan
** William Brownlow, Baron Lurgan
** Hon. Cecil Brownlow
* Papers, PRONI<ref>{{Cite web|url=https://iar.ie/archive/brownlow-papers/|title=Brownlow Papers|website=Irish Archives Resource|language=en-US|access-date=2026-06-07}}</ref>
==== Baron Carrington ====
* [[Social Victorians/People/Carrington|Charles Robert Wynn-Carington, 1st Marquess of Lincolnshire]] (1843–1928) attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Baron Carrington is a subsidiary title of the Marquess of Lincolnshire (created in 1912; Earl Carrington created in 1895).<ref>{{Cite journal|date=2026-05-20|title=Baron Carrington|url=https://en.wikipedia.org/w/index.php?title=Baron_Carrington&oldid=1355207880|journal=Wikipedia|language=en}}</ref>
* Papers
==== Baron Dufferin and Claneboye<ref>{{Cite journal|date=2026-02-07|title=Baron Dufferin and Claneboye|url=https://en.wikipedia.org/w/index.php?title=Baron_Dufferin_and_Claneboye&oldid=1337113957|journal=Wikipedia|language=en}}</ref> ====
* Members of this family did attend the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House as well as many social events at about this time.
* [[Social Victorians/People/Hamilton Temple Blackwood|Frederick Temple Hamilton-Temple-Blackwood]], 1st Marquess of Dufferin and Ava (1826–1902)<ref>{{Cite journal|date=2026-05-27|title=Frederick Hamilton-Temple-Blackwood, 1st Marquess of Dufferin and Ava|url=https://en.wikipedia.org/w/index.php?title=Frederick_Hamilton-Temple-Blackwood,_1st_Marquess_of_Dufferin_and_Ava&oldid=1356387854|journal=Wikipedia|language=en}}</ref>
* Papers
==== Baron Garvagh ====
* [[Social Victorians/People/Garvagh|Florence Canning, Lady Garvagh]] attended the [[Social Victorians/1897 Fancy Dress Ball|Duchess of Devonshire's fancy-dress ball]] at Devonshire House.
* Charles John Spencer George Canning, 3rd Baron Garvagh (1852–1915)<ref>{{Cite journal|date=2026-02-06|title=Baron Garvagh|url=https://en.wikipedia.org/w/index.php?title=Baron_Garvagh&oldid=1336941309|journal=Wikipedia|language=en}}</ref>
* Papers
==== Baron Rossmore of Monaghan ====
* A [[Social Victorians/People/Naylor|Miss Naylor]] (Lady Rossmore's sister) of this family attended the ball.
* Derrick Warner William Westenra, 5th Baron Rossmore (1853–1921)<ref>{{Cite journal|date=2024-08-27|title=Derrick Westenra, 5th Baron Rossmore|url=https://en.wikipedia.org/w/index.php?title=Derrick_Westenra,_5th_Baron_Rossmore&oldid=1242602083|journal=Wikipedia|language=en}}</ref>
* Papers
== References ==
{{reflist}}
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<div class="mw-content-ltr" dir="ltr" style="text-align: left" lang="en">[[File:Information.svg|25px|alt=Information icon]] Hello. Apologies for writing this in English, but I wanted to let you know that one or more of [[Special:Contributions/Abidkhanyusafzai|your recent contributions]] have been undone because they appeared to be promotional. [[:m:en:WP:SOAPBOX|Advertising or using <span style="white-space:nowrap">Wikiversity</span> as a "soapbox"]] are not permitted. Take a look at the welcome pages to learn more about <span style="white-space:nowrap">Wikiversity</span>. Thanks. </div><!-- Glow-advert1 @ 1781874827017.6s --><nowiki></nowiki> [[User:MathXplore|MathXplore]] ([[User talk:MathXplore|discuss]] • [[Special:Contributions/MathXplore|contribs]]) 13:13, 19 June 2026 (UTC)
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hello! i'm kit!
you need to know little about me, but i'll give a few tidbits!
- i've done several wiki projects on other wikis, not wikimedia foundation ones, but i wrote the journal page on the tally hall wiki, took me a week of wayback machine shenanigans, and i also did the news corner on there.
- my dad did a ton of wiki projects for kingdom of loathing way before i was born, so i think the desire to do so is genetic (joke!).
- i was born in 2008. yes, i'm gen z.
- i am diagnosed with undifferentiated schizophrenia, mostly because the way i think/speak is too confusing for psychiatrists to understand. other reasons may include: constant, non-stop hallucinations, lucid dreams, disorganized speech, and mild catatonia. i was previously on large amounts of antidepressants and antipsychotics, but i quit them for unrelated reasons, and felt a lot better afterwards, so i just stayed off them. i recently read up, and realized serotonin and dopamine aren't likely the causes of negative mood and schizophrenia respectively, so i don't plan to take any of those ever again!
- i have a lot of very strange theories, which i plan to publish once i can complete papers on them. if you're here because you read one of those theories and you think it's worth experimenting on, and you want to run an experiment to try to prove or disprove it, please let me know in the talk page, i'd love to help.
- i've recently hit a blockade in my self-understanding during routine daily introspection. i believe this blockade comes from my newfound understanding that i lack a "self" at all. once i figure out how to explain all of this in a way that makes sense, i'll write about it, but until then i have not much to say.
i hope you enjoy my presence on this website. i will certainly enjoy helping out!
kit :)
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hello! i'm kit!
you need to know little about me, but i'll give a few tidbits!
- i've done several wiki projects on other wikis, not wikimedia foundation ones, but i wrote the journal page on the tally hall wiki, took me a week of wayback machine shenanigans, and i also did the news corner on there.
- my dad did a ton of wiki projects for kingdom of loathing way before i was born, so i think the desire to do so is genetic (joke!).
- i was born in 2008. yes, i'm gen z.
- i am diagnosed with undifferentiated schizophrenia, mostly because the way i think/speak is too confusing for psychiatrists to understand. other reasons may include: constant, non-stop hallucinations, lucid dreams, disorganized speech, and mild catatonia. i was previously on large amounts of antidepressants and antipsychotics, but i quit them for unrelated reasons, and felt a lot better afterwards, so i just stayed off them. i recently read up, and realized serotonin and dopamine aren't likely the causes of negative mood and schizophrenia respectively, so i don't plan to take any of those ever again!
- i have a lot of very strange theories, which i plan to publish once i can complete papers on them. if you're here because you read one of those theories and you think it's worth experimenting on, and you want to run an experiment to try to prove or disprove it, please let me know in the talk page, i'd love to help.
- i've recently hit a blockade in my self-understanding during routine daily introspection. i believe this blockade comes from my newfound understanding that i lack a "self" at all. once i figure out how to explain all of this in a way that makes sense, i'll write about it, but until then i have not much to say.
i hope you enjoy my presence on this website. i will certainly enjoy helping out!
kit :)
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File:VLSI.Arith.2A.CLA.20260619.pdf
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User talk:Kitseigler
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/* Welcome */ new section
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==Welcome==
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