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Thomas Earnshaw (4 February 1749 in Ashton-under-Lynemarker1 March 1829 in Londonmarker) was an Englishmarker watchmaker who first simplified the process of marine chronometer production, making them available to the general public. He's also known for his improvements to the transit clock at the Royal Greenwich Observatorymarker in London and his invention of the chronometer escapement and the bimetallic compensation balance.

In 1783 he invented and patented the spring detent escapement which became standard in marine chronometers (John Arnold invented a similar escapement in 1779). In 1805, Earnshaw and Arnold were granted awards by the Board of Longitude for their improvements to chronometers; Earnshaw received £2500 and John Arnold's son John Roger Arnold received £1672. The bimetallic compensation balance and the spring detent escapement in the forms designed by Earnshaw have been used essentially universally in marine chronometers since then, and for this reason Earnshaw is generally regarded as the "father of the chronometer".

Although, he was principly a watchmaker, he didn't shy away from building clocks. When asked by Nevil Maskelyne, he produced a clock for the Armagh Observatorymarker, which is recognised by horologists today as one of the world's most important clocks.

This clock incorporated Earnshaw's new design of escapement and had a number of novel features including an air-tight case (designed to reduce dust and draughts). It was highly praised by John Thomas Romney Robinson in the 19th century who at that time believed it to be the most accurate clock in the world. In 1794, its purchase price was £100 and Earnshaw charged £100 to travel with it to Armagh and set it up in the new Observatory.

The Observatory also purchased Earnshaw's second clock which was operated at sidereal rate with Edward Troughton's Equatorial Telescope.

In June 1801, Matthew Flinders' ship, HMS Investigator, carried two boxed Timekeepers by Earnshaw E520 and E543, at a cost of 100 Guiness each. Investigator also carried two of Arnled's timekeepers on the first circumnavigation and mapping of the coastline of Australia. The chronometer, E520, is mounted in a wooden box with gimbals to compensate for the motion of the ship. Flinders went to shore regularly to check the settings of the chronometers against the stars. The Earnshaw chronometer was the only one working at the end of the journey, causing Flinders to refer to it in his book A Voyage to Terra Australis as "this excellent timekeeper". Flinders was taken prisoner-of-war by the French in Mauritiusmarker. In 1805 Captain Aken, a fellow prisoner, was released and returned to England. Flinders gave him the chronometers to return to the Greenwich Observatorymarker. By some unknown sequence of events Earnshaw 520 was sold to an Australian collector and in 1937 became the property of the Museum of Applied Arts and Sciences (Powerhouse Museummarker) in Sydneymarker. It was not until 1976 that it was identified as the chronometer of Flinders' historic journey.


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