Harrison's First Sea Clock, H1
John Harrison (1693 to 1776) · 1730 to 1735
The gleaming brass machine in this case is the first serious attempt in history to build a clock that could keep accurate time at sea. In seventeen fourteen Parliament offered a prize of twenty thousand pounds, a fortune, to anyone who could find a practical way of measuring longitude on a ship. A clock set to the time at a home port, compared with local noon measured from the sun, would give the answer, but no pendulum clock could survive the roll of a ship. John Harrison, a self-taught carpenter and clockmaker from Lincolnshire, set out to build one that could.
Look at the two pairs of dumbbell-shaped balances at the top. They swing towards and away from each other, linked by springs, so that the motion of the ship affects them equally and cancels out. That was Harrison's great idea. The movement uses almost no oil, because the bearings and some of the wheels are made of lignum vitae, a wood so dense and oily that it lubricates itself. The four dials show hours, minutes, seconds and the day of the month. The whole machine is still capable of running, and the museum keeps it going so that you can watch the balances rock.
Harrison took H1 on a trial voyage to Lisbon in seventeen thirty six and it performed well enough to earn him money to continue. It was followed by H2 and H3, which stand beside it, and by the watch H4 that finally won the prize. All were locked away at the Admiralty for over a century until a naval officer, Rupert Gould, restored them in the nineteen twenties. The story of Harrison's long struggle with the Board of Longitude was retold in Dava Sobel's book Longitude, which brought crowds to this room.
Did You Know? H1 weighs about thirty four kilograms, yet its designer went on to shrink the same idea into a watch that fitted in a coat pocket.
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