John Harrison

John Harrison solved the longitude problem with a clock and spent forty years extracting the prize from a board that did not want to give it to him. He was a Lincolnshire carpenter, self-taught, who built his first pendulum clocks almost entirely out of wood, using lignum vitae for the bearings because it exudes its own oil and needs no lubrication. A ship's position east or west can be found by comparing local noon with the time at a known meridian, which requires a clock that keeps time at sea - through rolling, damp, and swings of temperature that alter the length of every metal component. The Longitude Act of 1714 offered £20,000, and the astronomical establishment expected the answer to come from the moon rather than from a machine. He produced five timekeepers over thirty years, the first three large braced constructions with balances linked so that motion affected both equally, and then abandoned the approach entirely: H4 is a watch five inches across, and on a voyage to Jamaica in 1761 it lost about five seconds in eighty-one days. The Board of Longitude demanded a second trial, then that he dismantle it and explain it, then that he build two more. He was finally paid in 1773 after George III intervened personally, at eighty, and never received the prize as such. Captain Cook carried a copy of H4 on his second voyage and called it his trusty friend the watch. The Board never awarded the prize to anyone, and its treatment of Harrison has been argued about ever since - partly a genuine scientific dispute about whether one working watch proved a method, partly the Astronomer Royal preferring his own solution. All five timekeepers survive at Greenwich, and the first three still run.

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