English temperature compensation pocket chronometer Circa 1805

Gold pair-cased chronometer with spring detent escapement
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A rare English pocket chronometer by Thomas Earnshaw with spring detent escapement and sugar-tongs temperature compensation, circa 1805.
Two cases: outer case – 18 Carat pink gold, smooth, à goutte, with case maker punch mark IM; inner case – 18 Carat pink gold, smooth, with case maker punch mark IM. Enamel dial with radial Roman hours, auxiliary seconds, and gold spade hands. Full plate movement, keywind, frosted, gilt, and signed; with 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, and chatoned ruby endstone on the escape wheel.
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Diameter: 58 mm
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Weight: 150 g
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Signed: Thomas Earnshaw, London
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Thomas Earnshaw (born 1749 in Ashton under Lyne, Lancashire, died 1829 in London)
He worked from 1794 to 1795 at 119 High Holborn and then also at 87 FenchurchStreet.

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 the 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.