Josiah Latimer Clark was born in
Great Marlow, Buckinghamshire, and was the younger brother to
Edwin Clark (1814–1894). 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 District post 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 prefixes
mega- and
micro- to units other than the metre. Clark died in London on 30 October 1898. ==Family==