John Joly

Geologist and physicist, born in Holywood, Co Down, SE Northern Ireland, UK. He studied at Trinity College, Dublin, where he became professor of geology and mineralogy in 1897. He invented a photometer in 1888, calculated the age of the Earth (as 100 million years) by measuring the sodium content of the sea, and pointed out that radioactivity provides a source of terrestrial heating. With Walter Stevenson he evolved the ‘Dublin method’ in radiotherapy, and pioneered colour photography and the radium treatment of cancer. He became a fellow of the Royal Society in 1892.

John Joly (November 1, 1857 – December 8, 1933) was an Irish scientist, possibly most famous for his development of radiotherapy in the treatment of cancer.

Joly was born in Hollywood House, Bracknagh, County Offaly, Ireland. He entered Trinity College, Dublin, to become a graduate in engineering in 1882 and later become Professor of Geology there.

Joly's paper "Uranium and Geology" was given as an address to the British Association for the Advancement of Science which met in Dublin in 1908.

Joly, along with Henry Horatio Dixon, put forward the cohesion-tension method.

He died in Dublin, Ireland.

His second cousin Charles Jasper Joly became Astronomer Royal for Ireland in 1897.

A crater on Mars was named in his honor.