Josiah Latimer Clark FRS[1] FRAS[2] (10 March 1822 – 30 October 1898), was an English electrical engineer, born in Great Marlow, Buckinghamshire.

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.

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.

[9] Clark was one of the first authors to attach the metric prefixes mega- and micro- to units other than the metre.

[2] Elementary Treatise on Electrical Measurement, for the use of Telegraph Inspectors and Operators (1868), Electrical Tables and Formulæ, for the use of Telegraph Inspectors and Operators (1871), A Treatise on the Transit Instrument as Applied to the Determination of Time, for the use of Country Gentlemen (1882), A Manual of the Transit Instrument (1882), The Star Guide (with Herbert Sadler, 1886), Transit Tables (annually 1884-1888), A Dictionary of Metric and other useful Measures (1891), A Memoir of Sir W. F. Cooke (1895).