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John Harrison's third marine timekeeper, H3.

John Harrison's third marine timekeeper, H3.
John Harrison's third marine timekeeper, H3.
© National Maritime Museum, London
Repro ID: D6785_1
Description: Started in 1740, H3 took Harrison nearly 19 years to build and adjust, although it was not to win him the longitude prize: he found that he just could not persuade the two large, heavy, circular balances to keep time well enough. Nevertheless, H3 incorporates two extremely important inventions both relevant today: the bimetallic strip (still in use worldwide in thermostats of all kinds) and the caged roller bearing, a device found in almost every modern machine.
Creator: John Harrison.
Date: 1740-59
Credit line: Hydrographer of the Navy
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National Maritime Museum/Royal Observatory GreenwichNew Opportunities Fund 
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