John Joly 1857-1933

Some scientists gain fame for one major discovery, and never reach the same heights of achievement again. There are others who keep on making important and useful discoveries. One of the most fertile of Irish scientific minds was surely that of John Joly. He was born in 1857 in Hollywood House - the Church of Ireland Rectory - at Bracknagh in Co. Offaly. He entered Trinity College in 1876 and graduated in Engineering in 1882. He worked in the Engineering and Physics Departments before becoming Professor of Geology and Mineralogy, a post he held for 36 years, from 1897-1933. He spent all his working life in Trinity.

John had a wide range of interests and made many contributions to science, writing about 270 scientific papers and several books. He invented quite a few scientific instruments, the best known being a meldometer for measuring the melting points of minerals, his steam calorimeter for measuring specific heats, and his photometer for measuring light intensity.

One of his claims to fame was the making of an accurate estimate of the age of a geological period - an essential step in estimating the age of the Earth. Working in collaboration with Sir Ernest Rutherford in Cambridge, and using the decay in radioactivity in minerals, he estimated, in 1913, that the beginning of the Devonian period - the geological period between the Silurian and Carboniferous - was not less than 400 million years ago, an age which is in line with that accepted to-day. This makes the Earth about 4,500 million years old. A previous Trinity academic - Archbishop James Ussher - using chronological information in the Bible, had estimated the date of creation as 4004 BC!

Another practical achievement was John's successful collaboration with Dr Walter Stevenson of Dr Steeven s Hospital in Dublin - of which Joly was a Governor - in the use of radiation for the treatment of cancer. He had used radium bromide sealed in glass tubes to treat successfully an otherwise intractable "facial rodent ulcer", brought to his attention by Dr Stevenson, at that time a junior surgeon in the hospital. In 1914, he persuaded the Royal Dublin Society to set up the Radium Institute, and this provided capillary tubes containing radium emanation - the gas now known as radon - to hospitals for many years for the treatment of tumours.

In 1894, John patented his method for colour photography, the first successful method of producing colour photographs from a single plate. What he did was effectively to place three filters on the one glass screen by ruling fine lines - about 200 per inch - successively in red/orange, yellow/green, and blue/violet. The resulting transparency, when viewed through a similar screen, "appears in vivid colour and with all the realism and relief conferred by colour and colour perspective".

He collaborated with his close friend Henry Horatio Dixon in explaining how sap rises in plants, the first time this had been done. They found that the motive force was largely due to evaporation from leaves. Nobody believed them at first, but they had the satisfaction of proving their point and demonstrating that they were right and their critics wrong.

John Joly, one of Ireland's great achievers, died in Dublin on December 8th, 1933.

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