Josiah Latimer Clark was born in Great Marlow, Buckinghamshire, and was younger brother to Edwin Clark. Latimer Clark studied chemistry at school. His first job was a large Dublin chemical manufacturing establishment. In 1848 he started to work in his brother Edwin's civil engineering practice and became assistant engineer at the Menai Strait bridge. Two years later, when his brother was appointed Engineer to the Electric Telegraph Company, he again acted as his assistant, and subsequently succeeded him as Chief Engineer. In 1854, he took out a patent "for conveying letters or parcels between places by the pressure of air and vacuum," and later, in 1863, was concerned in the construction, by the London Pneumatic Despatch Company, of a tube between the London North-West Districtpost office and Euston station, London. About the same period he was engaged in experimental researches on the propagation of the electric current in submarine cables, on which he published a pamphlet in 1855, and in 1859 he was a member of the committee that was appointed by the government to consider the numerous failures of submarine cable enterprises. He later realised that Francis Ronalds had described the risk and cause of signal retardation in telegraph lines as early as 1816 and he thereafter devoted significant effort to bringing Ronalds’ telegraphic achievements to public attention. He was President of the Society of Telegraph Engineers in 1875 when Ronalds’ renowned electrical library was gifted to the new Society. Clark paid much attention to the subject of electrical measurement, and besides designing various improvements in method and apparatus and inventing the Clark standard cell, he took a leading part in the movement for the systematization of electrical standards, which was inaugurated by the paper which he and Sir CT Bright read on the question before the British Association in 1861. With Bright also he devised improvements in the insulation of submarine cables. In the later part of his life he was a member of several firms engaged in laying submarine cables, in manufacturing electrical appliances, and in hydraulic engineering. Clark was one of the first authors to attach the metric prefixesmega- and micro- to units other than the metre. Clark died in London on 30 October 1898.
Family
In 1854 Clark married Margaret Helen Preece, sister of Sir William Preece. They had two children. They divorced in 1861.
Publications
Besides professional papers, Clark published an Elementary Treatise on Electrical Measurement, together with a memoir of Sir W. F. Cooke. 'A Treatise on the Transit Instrument' 1882. 'The Star Guide' 1886.
