Lot 544

Thomas Earnshaw, London, Movement No. 763, 58 mm, 150 g, circa 1805
A rare pocket chronometer with spring detent escapement and sugar-tongs temperature compensation
Case: outer case - 18k pink gold, smooth, à goutte, case maker punch mark "IM". Inner case - 18k pink gold, smooth, case maker punch mark "IM". Dial: enamel, radial Roman hours, auxiliary seconds, gold spade hands. Movm.: full plate movement, keywind, frosted, gilt, signed, chain/fusee, moulded movement pillars, spring detent escapement, three-arm steel balance, "sugar tongs"- temperature compensation for blued balance spring, florally engraved balance cock, engraved regulator scale, chatoned diamond endstone on balance, chatoned ruby endstone on escape wheel.
Thomas Earnshaw (born 1749 in Ashton under Lyne, Lancashire, died 1829 in London) worked from 1794 to 1795 at 119 High Holborn and then also at 87 Fenchurch Street. There can be no doubt that he is the inventor of a spring detent chronometer escapement that outperformed the competition and prevailed over the next one and a half centuries; he also formed the concept of a balance wheel made from brass and steel that was to become the foundation of the future compensation balance.
In his pamphlet "Longitude: An Appeal to the Public…" Earnshaw (apart from attacking his enemies) describes the development of his chronometer escapement in great detail. His competitor John Arnold had the support of prominent people such as Sir John Banks, President of the Royal Society and Alexander Dalrymple, Hydrographer of the Admiralty.
Many famous mariners used Earnshaw’s watches with great success though; for example, no. 520 was used by Matthew Flinders on his voyage around Australia and no. 465 was in the property of the astronomer Crosley, who travelled with Flinders.
When we look at the movement numbers listed by Tony Mercer in "Chronometer Makers of the World" on page 135, this pocket chronometer fits right into the series.

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