George Sinclair died in Glasgow. Nothing is known of him until 1654, when he is recorded as having been a teacher in St Andrews. On 18 October 1654 he was appointed a regent at the University of Glasgow, and his interest in applied mathematics soon manifested itself. He constructed a sundial at the College, and in 1655 helped to design a diving bell which was used to explore the wreck of a ship from the Spanish armada which lay off the Isle of Mull. Sinclair also published a student textbook, the Tyrocinia mathematica (1661), which covers arithmetic, spherical geometry and geography, and illustrates the largely elementary and practical character of his teaching. But despite his contributions to the University, he was forced to resign his post in March 1666 because he refused to conform to the new Episcopalian regime in Scotland.
From The Continuum Encyclopedia of British Philosophy in Oxford Reference.