John Harrison's first marine timekeeper, H1.

John Harrison's first marine timekeeper, H1. © National Maritime Museum, London

Repro ID: D6783_1

Description: John Harrison (1693-1776) made his first prototype marine timekeeper in Barrow-on-Humber between 1730 and 1735 as a first step towards solving the longitude problem and winning the £20,000 prize offered by the British government. Now known as H1, the timekeeper is unaffected by the motion of a ship owing to its two interconnected swinging balances. It compensates for changes in temperature and, thanks to extensive anti-friction devices, runs without any lubrication. It is one of the great milestones in clockmaking history.

Creator: John Harrison

Date: 1730-35