English pair-cased watch with jumping centre seconds Circa 1790

Heavy large silver pocket watch by Josiah Jessop
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A heavy, large English pair-cased pocket watch with jumping centre seconds and special form pivoted, detent, chronometer escapement, circa 1790.
Two cases: outer case – silver, tiered, polished, à goutte, with a large lateral hinge; and inner case – silver, polished, with a signed and numbered movement protection cap and slide to stop the centre seconds. Signed enamel dial with radial Roman numerals on an eccentric hour chapter ring, centre seconds, and blued Breguet hands. Fine full plate movement, keywind, frosted, gilt, lavishly hand-engraved with foliate scrolls, signed, chain/fusee, three-arm steel balance, fine florally engraved, pierced balance cock with mascaron, and large chatoned diamond endstone on balance.
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Diameter: 60 mm
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Weight: 184 g
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Signed: Josiah Jessop, London
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Josiah Jessop worked in London around 1780-1794, as the records show; his workshop was at 38 Southampton Street, Covent Garden. Some of his pieces are now kept by museums: there is a centre second watch in the British Museum that was formerly part of the Ilbert collection, a gold enamel watch that was part of the Sternberger collection and a third watch held by the Metropolitan Museum of Art.