Born at Brecon, 15 June 1851, son of Henry Griffiths. He was educated at Owens College, Manchester, and Sidney Sussex College, Cambridge (Sc.D., 1902), of which he was elected a Fellow and later an Honorary Fellow. In 1890 he carried out heat measurements of fundamental importance, culminating in 1893 in the determination of the mechanical equivalent of heat by the electrical method. He was elected F.R.S. in 1895. In 1902 he was appointed to the principalship of the University College of South Wales and Monmouthshire, Cardiff, in succession to J. Viriamu Jones, the first principal of the college. Active experimental work ceased pending the erection and equipment of a research laboratory, and administrative and educational duties absorbed his time for a number of years. He devoted much energy to the furthering of the scheme for the building of new college buildings in Cathays Park, and was particularly interested in one of the buildings, the Viriamu Jones Memorial Research Laboratory, to the equipment of which he devoted a great deal of his leisure time. The only scientific work in which he participated at Cardiff was an investigation of the thermal capacities of metals from liquid air temperatures up to 100 degrees centigrade. In 1918 he retired to Cambridge, and for some years threw himself wholeheartedly into the work of the British Association for the Advancement of Science, of which he became treasurer. He continued this work until incapacitated by a long and painful illness. He died 3 March 1932.