Joly ' s work on radioactivity and geology

John Joly (Figure 1) was born on 1 November 1857 in County Offaly, Ireland (Nudds, 1996). After the sudden death of his father when he was still an infant, Joly, his mother and two elder brothers moved to Dublin, where he received his education at the celebrated Rathmines School, and later at Trinity College, Dublin, where he remained for the rest of his life. He followed courses in classics and modern literature but later concentrated on engineering. In 1882 he sat for the degree of Bachelor of Engineering and gained first place in the class. Soon afterwards he took up a position as assistant to the Professor of Engineering, and began his own researches on the density of gases, and the measurement of small pressures. At this time he invented the steam calorimeter for measuring the specific heat of minerals, which later played an important role in the kinetic theory of gases. In 1891 Joly was appointed Assistant to the Professor of Natural and Experimental Philosophy (now known as Physics), and was in 1892 elected a Fellow of the Royal Society of London for his work on the specific heat of gases. Two years later he and his life-long friend Henry Dixon (later Professor of Botany at Trinity College, Dublin) published their seminal paper on the mechanism of the ascent of sap in plants. In 1895 a further product of his inventive mind and capabilities was his development of the first successful method of producing colour photographic images from a single plate; this was achieved by combining the three primary colours on to a single glass plate. The 'Joly Process' is still the basis of the method used in colour photography today. In 1897 Joly succeeded William Sollas in the Chair of Geology and Mineralogy, a position he retained until his death in 1933. During his period of tenure he carried out valuable geological research in three areas. He made determinations of the age of the Earth using various methods (Wyse Jackson, 2001); he pioneered research on radioactivity and geology, which is the subject of this communication; and finally he introduced theories of global tectonics which he felt explained the nature of the Earth's surface features. Joly was by all accounts a very popular man, and loved and respected by many. He was tall, with hair swept off his forehead, a bushy moustache, and spectacles perched on his nose. He spoke with what was considered to be a foreign accent. In reality his rolled r's were used to conceal a slight lisp (Dixon, 1941). For recreation he was a keen traveller and yachtsman — he owned several craft and learned to drive an automobile at an advanced age. He died on 8 December 1933 and was buried close to his beloved university at Mount Jerome Cemetery in Dublin. John Joly was probably the finest scientist working in Ireland in the latter half of the nineteenth and first third of the twentieth centuries. He published nearly 270 papers and several books. He received medals from the Royal Dublin Society and the Geological Society of London, and received several honorary degrees from universities on both sides of the Atlantic. He was commemorated after his death by having a crater on Mars named in his honour.