A geometric proof of the Pythagorean theorem, visualized through a five-piece dissection, served as the primary calling card for Henry Perigal. This British mathematician and amateur astronomer, who lived from 1801 until 1898, gained attention both for his contributions to mechanical geometry and for his unconventional, persistent belief that the moon does not rotate in relation to the fixed stars.
Professional Life and Institutions
Born in Newington, Perigal was the eldest of six siblings from a Huguenot family. He spent his early career working as a clerk for the Privy Council Office before transitioning into roles as a business broker and bookkeeper in a London stockbrokerage during the 1840s. Beyond his professional duties, he maintained a deep involvement with scientific organizations. He was elected a fellow of the Royal Astronomical Society in 1850 and served as the treasurer for the Royal Meteorological Society for 45 years, holding the position from 1853 until he died in 1898. Additionally, he became a member of the London Mathematical Society in 1868 and joined the British Astronomical Association upon its formation in 1890.
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In his 1891 publication, Geometric Dissections and Transpositions, Perigal detailed a method for proving the Pythagorean theorem by dissecting two smaller squares and rearranging their parts into a single larger square. This specific five-piece dissection was printed on his business cards and remains engraved on his tombstone at St Mary and Peter’s Church in Wennington. In the same volume, he addressed the square trisection problem, proposing the first six-piece solution. Perigal also explored the complexities of circle-squaring, expressing an interest in using dissection-based methods to solve problems that were later formally addressed by mathematicians like Miklós Laczkovich.
Mechanical Interests and Beliefs
Perigal displayed significant skill as a lathe worker, constructing precise models of mathematical curves for the mathematician Augustus De Morgan. Despite his technical aptitude, he held a controversial stance regarding celestial mechanics. He argued that the moon did not rotate relative to fixed stars, an assertion he attempted to support using his understanding of curvilinear motion. He was a lifelong bachelor and a regular attendee of the Royal Institution, finally becoming a member in 1895 at the age of 94. His father, also long-lived, reached the age of 100.
Fast facts
- Born: 1801, Newington
- Died: 1898, St Giles
- Occupations: Mathematician, astronomer, business broker, bookseller
- Membership: Royal Astronomical Society, Royal Meteorological Society, London Mathematical Society
- Burial location: St Mary and St Peter's Church, Wennington
- Citizenship: United Kingdom of Great Britain and Ireland
- Employer: Privy Council Office
Questions readers ask
What is Henry Perigal best remembered for in mathematics?
He is primarily known for his dissection-based proof of the Pythagorean theorem, which he used on his business cards and memorialized on his gravestone.
Did Perigal hold any scientific society memberships?
Yes, he was a fellow of the Royal Astronomical Society, treasurer of the Royal Meteorological Society, and a member of the London Mathematical Society and the British Astronomical Association.
Achievements
- Held posts at Privy Council Office
- Fields: mathematics