John Joly (November 1 1857 – December 8 1933) was a scientist, possibly most famous for his development of radiotherapy in the treatment of cancer. He is also known for developing techniques to accurately estimate the age of a geological period, based on radioactive elements present in minerals.

He entered Trinity College, Dublin, to become a graduate in engineering in 1882 and later become Professor of Geology there. In his career he wrote over 270 books and scientific papers. In 1884 he patented a method of colour photography.

John Joly's paper "Uranium and Geology", given as an address to the British Association for the Advancement of Science which met in Dublin in 1908. This work described radioactive materials in rocks and their part in the generation of the Earth's internal heat.

His younger brother Charles Jasper Joly became Astronomer Royal for Ireland in 1897. Their father was Rev. John Swilt Joly, rector of Tullamore from 1861 to 1869.

A crater on Mars was named in his honor.

External links

• http://www.europhysicsnews.com/full/08/article2/article2.html
• http://www.irishmidlandsancestry.com/content/offaly/people/literature_irish.htm