D6785-2

Marine timekeeper H3, back and side Long Caption: Marine timekeeper, H3. Started in 1740, this third timekeeper took Harrison nearly 19 years to build and adjust, although it was not to win him the great 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 nearly all modern mechanical engineering. Credit line: © National Maritime Museum, Greenwich, London, Ministry of Defence Art Collection Object: ZAA0036 Artist: John Harrison Date: 1757 Medium: brass; bronze; steel; glass Size: overall display height: 622 mm Click here to buy a bespoke print of this image.