John Casey (mathematician)

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John Casey
John Casey photo.
Born(1820-05-12)12 May 1820
Died3 January 1891(1891-01-03) (aged 70)
EducationTrinity College Dublin
Occupation(s)geometer, teacher
Employer(s)University College, Stephen's Green
Known forCasey's theorem
  • William Casey (father)

John Casey (12 May 1820, Kilbehenny, County Limerick, Ireland – 3 January 1891, Dublin) was a respected Irish geometer. He is most famous for Casey's theorem on a circle that is tangent to four other circles, an extension of Ptolemy's theorem. However, he contributed several novel proofs and perspectives on Euclidean geometry. He and Émile Lemoine are considered to be the co-founders of the modern geometry of the circle and the triangle.[1]


He was born at Kilbehenny in Limerick, Ireland and educated locally at Mitchelstown, before becoming a teacher under the Board of National Education. He later became headmaster of the Central Model Schools in Kilkenny City. He subsequently entered Trinity College Dublin in 1858, where he was elected a Scholar in 1861 and was awarded the degree of BA in 1862. He was then Mathematics Master at Kingston School (1862–1873), Professor of Higher Mathematics and Mathematical Physics at the newly founded Catholic University of Ireland (1873–1881) and Lecturer in Mathematics at its successor, the University College Dublin (1881–1891).[2] 

Honours and awards[edit]

In 1869, the University of Dublin awarded Casey the Honorary Degree of Doctor of Laws. He was elected a Fellow of the Royal Society in June 1875.[3] He was elected to the Royal Irish Academy and in 1880 became a member of its council. In 1878 the Academy conferred upon him the much coveted Cunningham Gold Medal.[4] His work was also acknowledged by the Norwegian Government, among others. He was elected a member of the Societe Mathematique de France in 1884 and received the honorary degree of Doctor of Laws from the Royal University of Ireland in 1885.

Major works[edit]


  1. ^ In tribute to John Casey, founder of modern geometry The Irish Times, May 12, 2020
  2. ^ John Casey: a Founder of Modern Geometry ThatsMaths, May 7, 2020 Irish Times
  3. ^ O'Connor, John J.; Robertson, Edmund F., "John Casey", MacTutor History of Mathematics Archive, University of St Andrews
  4. ^ "Proceedings of the Royal Irish Academy, 1878". Retrieved 10 December 2014.


  • Irish Monthly (1891), XIX, 106, 152
  • Proc. Royal Society (1891), XLIX, 30, p. xxiv.

Further reading[edit]

External links[edit]