Who invented the chronometer?

John Harrison (1693-1776), an English clockmaker and carpenter, is credited with the invention of the chronometer in 1761, although his first (of five) prototype chronometers was actually completed in 1735 (H.1 1735, H.2 1739, H.3 1741, H.4 1761, H.5 1772). The result of years of experimentation and a government sponsored competition aiming to improve the accuracy of their ships' navigation, he persevered with entirely new designs, each time attempting to minimise size and weight while increasing accuracy, until the fourth version (in 1761) finally was up to the required standards for the British navy.

The necessity for an accurate portable timepiece to determine GMT vs local time and thereby the ship's longitude had long been known to be necessary, but what Harrison did was perfect other technologies along with a few breakthrough ideas of his own to present an accurate balance-spring based portable chronometer. He picked up today's equivalent of two million dollars for his efforts – though this was not presented to him until another ten years had passed and King George III intervened on his behalf after seeing for himself how successful Harrison’s fifth and final longitude time-keeper (which had been completed in 1772 and was mechanically very similar to the fourth) actually was.

In 1712 the British government announced a reward for anyone who could make a device to determine a ship’s longitude within 30 nautical miles at the end of a six-week-long voyage. In 1735 English carpenter John Harrison met the British government’s challenge, submitting a marine chronometer that he designed and constructed. In the next three decades, Harrison built three more chronometers, each smaller and more accurate than the previous one. His fourth marine chronometer, completed in 1762, was accurate to five seconds even after an 81-day voyage aboard ship.

In 1763 French clockmaker Pierre Le Roy created a chronometer resistant to errors caused by changes in temperature. Continued improvements in chronometers and the establishment of the prime meridian in 1884, from which all measurements of longitude are made, made determining longitude more accurate. In the 1920s governments began to use radio to broadcast accurate time throughout the world, so shipboard chronometers became less important.

john harrison invented it in 1720