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| John Joly |
John Joly (1857-1933) 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.
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.
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.
More information: Trinity College
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.
In 1914 he developed a method of extracting radium and applied it in the treatment of cancer. As a Governor of Dr Steevens' Hospital in Dublin, in collaboration with Walter Stevenson he devised radiotherapy methods and promoted the establishment by the Royal Dublin Society of the Irish Radium Institute where they pioneered the Dublin method of using a hollow needle for deep radiotherapy, a technique that later entered worldwide use. The Radium Institute also supplied capillary tubes containing radon to hospitals for some years for use in the treatment of tumours.
Joly also invented a photometer for measuring light intensity, a meldometer for measuring the melting points of minerals, a differential steam calorimeter for measuring specific heats and a constant-volume gas thermometer, all of which bear his name, together with one of the first color photographic processes, the Joly Colour process. It was the first successful process for producing color images from a single photographic plate.
More information: Engineers Journal
Geological age plays the same part in our views of the duration
of the universe as the Earth's orbital radius does in our views
of the immensity of space.
John Joly
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