Thomas Earnshaw

Thomas Earnshaw was born in Ashton-under-Lyne, Lancashire (now Greater Manchester) and apprenticed to a watchmaker at the age of fourteen. He established his own business in London, where he would remain for most of his life.  

Although he was principally a watchmaker, Thomas Earnshaw did not shy away from building clocks. He improved and simplified a transit clock at Greenwich Observatory made by clockmaker George Graham. It is not too surprising, then, that the Astronomer Royal Nevil Maskelyne asked him to produce a regulator for the newly-founded Armagh Observatory when his aid was requested from Armagh. The clock he produced incorporated Earnshaw’s new design of escapement and had a number of novel features, including an airtight case (designed to reduce dust and draughts). It was highly praised by Director Thomas Romney Robinson, 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. Another Earnshaw regulator was purchased by the Observatory thereafter. 

Like a number of his contemporary watch- and clockmaking peers, Earnshaw vied for the Board of Longitude Prize, for which he had some support by Maskelyne. He is best known for his invention of a simple and accurate marine chronometer design. Though the main awardee of the Longitude Prize is John Harrison, Earnshaw eventually won £3000 of the Prize for his design and improvements to the chronometers. Earnshaw’s design, simpler than Harrison’s, is in fact the one that became essentially universally used in marine chronometers until the electronic era. When vying for part of the Longitude Prize, he wrote ‘An Appeal to the Public’ in 1808, which contains four testimonials from Rev. Dr Hamilton, first Director of Armagh Observatory, as to the excellence of the Armagh clock.