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John Harrison's fourth marine timekeeper, H4.

John Harrison's fourth marine timekeeper, H4.
John Harrison's fourth marine timekeeper, H4.
© National Maritime Museum, London
Repro ID: D0789_1
Description: Harrison had been working on improving watches as a sideline to his development of the much larger H3. In 1753 a pocket watch was made for Harrison, to his design, by watchmaker John Jefferys. This went so well that Harrison began to realise it pointed to a longitude solution that lay not in H3 but in smaller watches. Work began on H4 in 1755, and, with its very stable, high-frequency balance, it proved the successful design. It is probably the most important timekeeper ever made.
Creator: John Harrison.
Date: 1755-1759
Credit line: Hydrographer of the Navy
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National Maritime Museum/Royal Observatory GreenwichNew Opportunities Fund 
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