John Harrison was an English horologist who invented the first practical marine chronometer, which enabled navigators to compute accurately their longitude at sea.
Background
John Harrison was born in Foulby, near Wakefield in the West Riding of Yorkshire, the first of five children in his family. His father worked as a carpenter at the nearby Nostell Priory estate. A house on the site of what may have been the family home bears a blue plaque. In around 1700, the Harrison family moved to the Lincolnshire village of Barrow upon Humber. Following his father's trade as a carpenter, Harrison built and repaired clocks in his spare time. Legend has it that at the age of six, while in bed with smallpox, he was given a watch to amuse himself and he spent hours listening to it and studying its moving parts. He also had a fascination for music, eventually becoming choirmaster for Barrow parish church.
Career
Harrison first constructed surveyors instruments. In 1715 he is said to have made an eight-day clock with wooden wheels. He devised a gridiron pendulum in 1726 in which the bob was suspended by a series of parallel rods of brass and steel to offset the change in length caused by variations in temperature.
Harrison also is credited with the invention of the maintaining-power spring arrangement which kept a clock going during the period of winding.
His first chronometer, completed in 1735, was checked on a ship that went to Lisbon in 1736.
In 1737 the device was tested on a voyage to Lisbon.
Unsatisfactory, it was not tried at sea.
James returned home and John began a third machine, not ready for test until 1757.
Next Harrison conceived of a radically different timekeeper in the form of a large watch—although, of course, with an entirely different escapement.
As accurate as the third machine and far more convenient in size, it alone was tested on a voyage to Jamaica in 1761.
On arrival, more than nine weeks later, it was only five seconds slow, about 1. 25 minutes of arc, well within the 30 minutes of arc or longitude required.
A second trial, to rule out a possibly fortuitous combination of circumstances, was held in 1764, and the results were also well within the limits. Half the prize was now paid, but many previously unstipulated obstacles were raised.
Accusations that the Board of Longitude was unfair and in some degree favored a system of lunar distances for finding longitude reached George III, who took Harrison’s side.
Harrison’s last instrument was tested at the king’s private observatory at Kew, and on the basis of its performance there, Harrison petitioned the House of Commons in 1772.
The Board of Longitude, now on the defensive, dropped its opposition, and the award was made in 1773.
He had much difficulty in getting his claim accepted and then received only small payments until June 14, 1773, when, by the personal intervention of King George III, he finally received the remainder of the £20, 000.
Although soon supplanted by simpler mechanisms, the use of timekeepers to find longitude stemmed directly from Harrison’s persistence and ability.