John Harrison
John Harrison (3 April  [O.S. 24 March] 1693– 24 March 1776) was a self-educated English carpenter and clockmaker. He invented the marine chronometer, a long-sought after device for solving the problem of establishing the East-West position or longitude of a ship at sea, thus revolutionising and extending the possibility of safe long-distance sea travel in the Age of Sail. The problem was considered so intractable, and following the Scilly naval disaster of 1707 so important, that the British Parliament offered the Longitude prize of £20,000 (£2.75 million). Harrison came 39th in the BBC's 2002 public poll of the 100 Greatest Britons.