Harrison

On the eighteenth of November 1761, in the cabin of HMS Deptford lying at anchor at Spithead, John Harrison's son William, thirty-three years old, climbed aboard with the silver pocket-watch H4, the fourth and final marine chronometer designed by John Harrison (1693–1776), the Yorkshire carpenter who had spent the previous forty-eight years on the problem of finding longitude at sea. The Board of Longitude, by the Longitude Act of 1714, had offered a reward of £20,000 to anyone who could devise a method for determining a ship's longitude to within half a degree (about thirty miles at the equator) on a voyage from Britain to the West Indies. H4 was, by the test of the Deptford's eighty-one-day voyage to Port Royal in Jamaica, accurate to within five seconds over the voyage (the equivalent of about one and a half miles of longitude). The Board took thirteen further years and three more trials to formally award the prize; Harrison received £8,750 in 1773 and the remainder by direct Parliamentary grant of 1773 after the personal intervention of George III, on the principle that the Board had withheld the prize unjustly. Harrison was eighty by the time he received the payment. The marine chronometer is the foundational navigational instrument of the modern age.

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