English watch with spring detent escapement Circa 1820/1871

Heavy gold pocket chronometer by Robert Molyneux
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A heavy English pocket chronometer with spring detent escapement according to Thomas Earnshaw, circa 1820/1871. Accompanied with the original mahogany box with a numbered ivory shield.
18 Carat gold, tiered, polished case with a gold dome and case maker’s punch mark JM (John Martin, London). Signed, off-white, enamel dial with radial Roman hours, auxiliary seconds, and gold spade hands. Signed, keywind, frosted gilt full plate movement with chain/fusee, bimetallic Z-chronometer balance with four screws and two movable trapezoid weights according to Thomas Earnshaw, free-sprung blued helical balance spring, and chatoned diamond endstone on balance.
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Diameter: 59 mm
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Weight: 185 g
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Signed: Robert Molyneux, London
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Robert Molyneux
Robert Molyneux was a pupil of Thomas Earnshaw and adopted his master’s methods; when this watch was produced, he had his workshop at 44 Devonshire Square near today’s Liverpool Street Station. Molyneux was initially in a working partnership with his fellow apprentice Charles John Cope at Earnshaw’s workshop; when Parry and Lyon went on an expedition in 1821, they took amongst other things the chronometer no. 405 by Molyneux & Cope with them on their ships Hecla and Fury. Molyneux later moved to 30 Southampton Row and took his sons Henry and Robert into his business. He developed a chronometer with a thermometer and useful temperature compensation for chronometer balances at the same time as Eiffe. In England, the name Molyneux appears around 1572, which was the time of the emigration of the Huguenots from France.