born March 1693, Foulby, Yorkshire, Eng.
died March 24, 1776, London
British horologist.
The son of a carpenter, in 1735 he invented the first practical marine chronometer . He followed it with three later instruments, each smaller and more accurate than its predecessor, and in 1762 his No. 4 chronometer was found to be in error by only five seconds (1 1/4′ longitude) after a voyage from England to Jamaica. Chronometers gave mariners their first practical method of fixing position at sea from celestial observations. See also Ferdinand Berthoud .