By Martin Gleeson
Born in Hollywood House, Bracknagh, Co. Offaly (then called the King’s County) in November 1857, John Joly got his secondary education in Rathmines School, Dublin. He entered Trinity College in 1876 and graduated in Engineering in 1882. He remained in Trinity and his first position was as a demonstrator in both Trinity’s Engineering and Physics departments, acting as assistant to the professors.
While doing this work he used his engineering mind to invent various scientific instruments. These were so successful that he was able to sell some of them commercially to scientific instrument companies in both Ireland and Britain. In 1897 Joly was appointed Chair of Geology and Mineralogy in Trinity College and he held this position for 36 years. He joined the Royal Dublin Society in 1881 and during his lifetime wrote over 270 books and scientific papers in the fields of geology and medicine.
Joly was the first to discover that when an object like your shoe touches the surface of a sheet of ice, local contact pressure forces the ice into a liquid form. This thin film of water lubricates the ice, and this explains why you skid.
Botanists had been puzzled for years by the fact that water in plants and trees rises from the soil and goes to the top of the flowers and leaves against the force of gravity. Joly and a botanist friend solved the mystery by publishing the ‘cohesion tension theory’. It explained that evaporation from leaves brought about pressure difference, which caused the sap to rise in flora.
Joly measured the accumulation of sodium by erosion in the waters of the oceans. He used this to calculate the age of the seas. He published a paper that the earth was about 80 to 100 million years old. Although this figure was later proved to be shorter than what we know now (4.54 billion years), it was an improvement on other guesses that were available at the time.
In 1914 Joly developed a way of extracting radium and applied it in the treatment of cancer. His idea was to not use the extremely expensive radium itself but the radioactive radon gas that it gave off. This was called the ‘Dublin Method’. As Governor of Dr Steevens’ Hospital, he devised radiotherapy methods for the treatment of tumours. Anyone who had received radiotherapy for the curing of cancer owes a debt of gratitude to the pioneering scientist John Joly.
Joly invented a device for measuring light intensity called the photometer. He also developed a meldometer for measuring the melting points of minerals and the steam colorimeter for measuring heat. Many other scientific inventions bear his name.
To take colour pictures, Joly used a glass photographic plate with fine vertical red, green and blue lines printed on it. His method of enabling colour photographs to be taken was launched in 1895 and remained on the market for a few years. This was the world’s introduction to colour photographs. It was later adopted by Kodak. However, Joly’s colour pictures were expensive, and the colour paints available at the time were not very sensitive to light so that the pictures did not achieve a natural look. Joly took many colour pictures of botanical subjects and these colour slides are today in the National Library of Ireland.
Even though Trinity College had been open to Catholics since 1793, they were prohibited from gaining positions of prestige for another 80 years. Joly campaigned to make the college more welcoming Catholics. He also campaigned for better facilities for students especially those studying science. He wanted better education not just for the elite but also for the working classes and he often gave lectures at the YMCA in Dublin. In those days, Trinity College students were mainly male, and Joly was very much in favour of ladies’ involvement in college education. He became Warden of the Alexandra College for Higher Education of Women.
John Joly, probably Ireland’s most eminent man of science, died in December 1933. His many inventions are still used today and in 1973 a crater on the planet Mars was named in his honour. In September 2015, a commemorative plaque to John Joly was unveiled on the front of the house (Hollywood House, Bracknagh, Co. Offaly), in which he had been born.
