thumb|200px|John Harrison(P.L. Tassaert's half-tone print of Thomas King's original 1767 portrait of John Harrison, located at the Science and Society Picture Library, London)'John Harrison (24 March 1693 – 24 March 1776) was an English clockmaker who revolutionised and extended the possibility of safe long distance sea travel in the Age of Sail by inventing a long-sought and critically-needed key piece in the problem of accurately establishing the East-West position, or longitude, of a ship at sea. The problem was so intractable that the British Parliament offered a huge fortune for the day (£20,000, roughly £6 million in 2007 terms),G. Allan: "Inflation: The value of the pound", House of commons library, November 2003, http://www.parliament.uk/commons/lib/research/rp2003/rp03-082.pdf for a solution. After steadfastly pursuing various methods during thirty years of experimentation, Harrison finally desi