Harrison , John

(1693–1776) English horologist

John Harrison was born at Foulby near Pontefract in Yorkshire, the son of a carpenter, a trade he originally took up himself.

In the early 18th century exploration and colonial expansion was an important concern of European governments. A number of naval disasters caused by navigation errors prompted the British Government to set up a Board of Longitude in 1714. The board offered a prize of £20,000 to anyone who discovered a practical method of measuring longitude accurately. The key to determining the position of a ship out of sight of land was accurate timekeeping. The board's conditions effectively meant the construction of a chronometer that kept time to an accuracy of 3 seconds per day.

Harrison became interested in the problem in 1728 and in 1735 completed his first instrument, H1. He improved his design over a period of many years and in 1762 his perfected chronometer, H4, was found to be in error by only 5 seconds (corresponding to 1.25' of longitude) after a voyage to Jamaica.

Harrison's chronometers all met the conditions set up by the Board of Longitude but he had problems obtaining the prize money. In 1763 he was given £5000 and it was not until 1773, after the intervention of King George III, that he received the full amount less expenses. His chronometer was used in 1776 by James Cook on his voyage to Australia and New Zealand.