Thomas Earnshaw (born on February 4, 1749 in in Ashton-under-Lyne - died March 1, 1829 in London) was an English watchmaker who first simplified the process of chronometer production, making them available to the general public. He's also known for his improvements to the transit clock at the Royal Greenwich Observatory in London and his invention of the cylindrical balance spring and the bimetallic compensation balance. Thomas Earnshaw at Encyclopaedia Britannica Online.

In the 1780s he also invented the spring detent escapement which became standard in marine chronometers (John Arnold invented his own version of the escapement) Details on Earnshaw's spring indent escapement. Both Earnshaw and Arnold were awarded a bounty of £3000 by the Board of Longitude for their improvements to chronometers and are nowadays referred to as the joint parents of the standard 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 Observatory, 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. Information on Earnshaw's first clock at the Armagh Observatory website.

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

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