John Joly
| John Joly | |
|---|---|
| Born |
1 November 1857 Bracknagh, County Offaly, Ireland |
| Died | 8 December 1933 (aged 76) Dublin, Ireland |
| Nationality | Irish |
| Fields | geology medicine |
| Known for |
radiotherapy cohesion-tension theory |
| Notable awards | Boyle Medal of the Royal Dublin Society (1911) Royal Medal of the Royal Society of London (1910) Murchison Medal of the Geological Society of London (1923) |
John Joly FRS (1 November 1857 – 8 December 1933) was an Irish physicist, 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.
Joly was born in Holywood House (the Church of Ireland Rectory), Bracknagh, County Offaly, Ireland. He was a second cousin of Charles Jasper Joly, the astronomer. He entered Trinity College, Dublin in 1876, graduating in Engineering in 1882 in first place with various special certificates in branches of engineering, at the same time obtaining a First Class Honours in modern literature. He worked as a demonstrator in Trinity's Engineering and Physics departments before succeeding William Johnson Sollas in the Chair of Geology and Mineralogy in 1897, a position which he held until his death in 1933 in Dublin.
Joly joined the Royal Dublin Society in 1881 while still a student, and was a frequent contributor of papers. His first scientific paper was published in 1883, on the use of meteorological instruments at a distance. During his career he wrote over 270 books and scientific papers.
On 17 May 1899 Joly read his paper, "An Estimate of the Geological Age of the Earth" to the Royal Dublin Society. In it, he proposed to calculate the age of the earth from the accumulation of sodium in the waters of the oceans. He calculated the rate at which the oceans should have accumulated sodium from erosion processes, and determined that the oceans were about 80 to 100 million years old. The paper was quickly published, appearing 4 months later in the Society's Scientific Transactions. Although this method was later considered inaccurate and was consequently superseded, it radically modified the results of other methods in use at the time.
In 1903 he published an article in Nature in which he discussed the possibility of using radium to date the Earth and went on to study the radioactive content of the Earth's crust to formulate a theory of thermal cycles, and examined the radioactive constituents of certain rocks as a means of calculating their age. Working in collaboration with Sir Ernest Rutherford, he used radioactive decay in minerals to estimate, in 1913, that the beginning of the Devonian period could not be less than 400 million years ago, an estimate which is in line with modern calculations.
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