John Harrison, English inventor and horologist, 1767.
© Science Museum / Science & Society Picture Library
Mezzotint of 1768 by P L Tasaert after an oil painting by Thomas King, 1767. Harrison (1693-1776), became famous for resolving one of the most problematic isues of his day - how to determine longitude while at sea. This was to take him over forty years, during which time he devised many other ways to improve the accuracy of time-keeping. The celebrated horologist is shown seated in front of two of his inventions, the gridiron pendulum invented in 1726 (behind him) and the H3 version of his marine chronometer (on the wall to his right).