John Harrison's third marine timekeeper, H3.

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