English rare gold chronometer “of the second kind” Circa 1783

Gold open faced pocket watch by John Arnold, Invt. et Fecit
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An extremely rare English chronometer “of the second kind” with early and large “OZ” balance of John Arnold, circa 1783.
18 carat pink gold consular à goutte case with case maker’s punch mark “WW” (William West) and large lateral hinge. Enamel dial with radial Roman numerals, auxiliary seconds and gold Poker & Beetle hands. Full plate movement, firegilt, signed, numbered, chain/fusee, round pillars, Arnold’s spring detent escapement, OZ balance, blued freesprung helical balance spring, very finely engraved pierced balance cock, chatoned diamond endstone on balance.
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Diameter: 52 mm
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Weight: 129 g
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Signed: John Arnold, London
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John Arnold (1736-1799) After his apprenticeship with his father in Cornwall, John Arnold settled in London in 1760. In 1764 he presented King George III with a half quarter repeating cylinder watch mounted in a ring. By the time he was 28, Arnold’s watches, be they verge or cylinder, displayed interesting original components such as straight-line compensation curbs and minute repeating by increments of 10 minutes (instead of the more common 15 minutes). Around 1768 Arnold began his research into marine chronometers. He established himself at 2 Adam Street, Adelphi Buildings, Strand, in 1771 and carried out most of his research into marine chronometers here over the next eleven years. By 1774 Arnold had constructed a marine chronometer with pivoted detents; he invented terminal curves for the cylindrical balance spring in 1776 and included this construction in the patent for a bimetallic compensated balance he took out in 1782. He subsequently devised numerous different balances such as the Double T, Double S, Z, O-Z and U. Arnold, who was admitted to the Clockmakers’ Company in 1783, was the first to employ the term chronometer in the modern sense and to successfully find a way to simplify Harrison’s timekeeper design. In 1787 he took his son, John Roger Arnold, into partnership and changed the business name to “Arnold & Son”, which it retained until his death.
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Lit.: Described and illustrated in Hans Staeger “100 Jahre Praezisionsuhren von John Arnold bis Arnold & Frodsham 1763-1862” Filderstadt 1997, pages 69f and 161f.