Clockmaker highly regarded at the European courts of his day. His contributions to the development of his craft were guided by the principle of "art for art's sake." Apprenticed to George Graham (1673-1751), he became his partner and is regarded as his successor. In 1754, devised the free anchor escapement, an invention of incalculable consequences. But he did not build the first watch with free anchor escapement until 1769. In 1755, formed a partnership with William Dutton. In 1771, retired to Plymouth, devoting himself entirely to research on marine chronometers, but his firm remained in business until c. 1790.