John Joly

John Joly FRS (1 November 1857 – 8 December 1933) was an Irish physicist and geology professor at the University of Dublin, best known for developing radiation for cancer treatment. He is also notable for establishing uranium-thorium dating techniques, which use radioactive elements found in minerals to more reliably estimate the age of a geological epoch.

This Irish scientist made contributions to geology, physics, and medicine. John Joly created possibly the most significant aspect of his legacy when he discovered a novel technique to use radium to cure cancer. The element had already been recognized for its ability to combat the disease, but Joly's technology made radiotherapy less expensive and more precise. Radiation therapy is still used today. Among his other endeavors, he sought to estimate the age of the Earth by measuring the radioactive decay of elements in rock and shown that the decay rate is constant. Although we now know Earth is far older, he established an age of 100 million years, which was remarkable at the time.

Joly was elected a Fellow of the Royal Society of London in 1892, received the Royal Dublin Society's Boyle Medal in 1911, the Royal Society of London's Royal Medal in 1910, and the Geological Society of London's Murchison Medal in 1923. Honorary degrees were also bestowed to him by the National University of Ireland, the University of Cambridge, and the University of Michigan. Following his death, his friends contributed £1,700 to establish a memorial fund, which is now used to support the annual Joly Memorial Lectures at the University of Dublin, which were established in 1935 by Sir Ernest Rutherford. The Joly Geological Society, a student geological association founded in 1960, also remembers him. In 1930, Trinity College Dublin and the Royal Dublin Society commissioned Oliver Sheppard to create reproductions of a bust of Joly. In 1973, a crater on Mars was named after him.