Thomas Earnshaw

From Wikipedia, the free encyclopedia

Thomas Earnshaw
Born	February 4, 1749(1749-02-04) Ashton-under-Lyne
Died	March 1, 1829 (aged 80) London
Occupation	Watchmaker

Thomas Earnshaw (born February 4, 1749 in Ashton-under-Lyne - died March 1, 1829 in London) was an English 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 Observatory in London and his invention of the chronometer escapement and the bimetallic compensation balance. ^[1]

In 1783 he invented and patented the spring detent escapement which became standard in marine chronometers^[2] (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". ^[3]

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.^{[citation needed]}

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. ^[4]

The Observatory also purchased Earnshaw's second clock ^[5] which was operated at sidereal rate with Edward Troughton's Equatorial Telescope.

[edit] References

1. ^ Thomas Earnshaw at Encyclopaedia Britannica Online.
2. ^ Details on Earnshaw's spring indent escapement
3. ^ Gould, Rupert T. (1923). The Marine Chronometer. Its History and Development. London: J. D. Potter, 116-128. ISBN 0-907462-05-7. 
4. ^ Information on Earnshaw's first clock at the Armagh Observatory website.
5. ^ Information on Earnshaw's second clock at the Armagh Observatory website.