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John Harrison

John Harrison in 1766John Harrison in 1766 John Harrison (1693–1776) was an English clockmaker. He had decided to enter a competition for the Longitude Prize, announced by the British Government in 1714. The prize would be given to whoever found a method of accurately plotting the East-West position, or longitude, of a ship at sea. Born in Foulby, Yorkshire, Harrison's family moved to Lincolnshire while he was still a boy. He became a clockmaker, designing and building precision clocks with a high degree of accuracy. He planned to win the prize by inventing a clock that kept time at sea to the same accuracy as those he had already designed.


A painting of a ship running aground, 1690s.A painting of a ship running aground, 1690s.

Measuring longitude

As long-distance sea travel became increasingly common in the late 17th and early 18th century, it became more and more important for sailors to be able to accurately determine their position at sea, in order to pinpoint their exact position on a map and avoid hazards, such as reefs and shallow water. Finding latitude—how far north or south they were—was no problem, as that could be easily established by measuring the height of the Sun in the sky. But longitude was much more difficult to work out.

The £20,000 Longitude Prize offered in 1714 would be worth £2.5 million in today's money.

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