John Casey

author

John Casey

1820–1891

An Irish geometer remembered for sharp, elegant thinking, he is best known for Casey’s theorem, a result in circle geometry that extends the classical problem of Apollonius. His work helped keep synthetic geometry lively in the late 19th century.

1 Audiobook

The First Six Books of the Elements of Euclid

The First Six Books of the Elements of Euclid

by John Casey, Euclid

About the author

Born in County Limerick, Ireland, in 1820, John Casey became a respected mathematician and teacher with a lasting reputation in geometry. He is most closely associated with Casey’s theorem, a result about circles tangent to four other circles, and he died in Dublin in 1891.

Casey wrote mathematical works that were valued for their clarity and helped spread interest in Euclidean and synthetic geometry. His name remains familiar to students of classical geometry because his theorem connects beautifully with older traditions while pushing them a step further.

Though not a household name today, he holds an honored place in the history of Irish mathematics. Readers interested in elegant proofs and the enduring charm of geometric ideas will find him an appealing figure.