John Harrison, English inventor and horologist, 1767.
© Science Museum / Science & Society Picture Library
Engraving by William Holl of the mezzotint by P L Tasaert, 1768, after an original oil painting by Thomas King of 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 next to the H4 marine chronometer which was to make him world-famous.