English gold open faced split seconds chronograph Circa 1873

Single button split seconds chronograph lever watch by Nicole Nielsen
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An unusual English 18 carat gold open faced single button split seconds chronograph keyless lever watch with box, circa 1873-1874. 3/4 plate gilt finished jewelled movement, spring detent type escapement, Nicole Nielsen’s patented winding system, chronograph mechanism on the top plate. White enamel dial with Roman numerals, blued steel spade hands and outer red Arabic five minute divisions. Plain case, snap on back engraved George Brown from John I. Thornycroft and John Donaldson – Chiswick 1883, split seconds chronograph mechanism operated through the crown. Case numbered and stamped with casemaker’s mark ‘AN’ for Adolphe Nicole, dial signed.
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Diameter: 50 mm
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Weight: 117 g
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Signed: Nicole Nielsen & Co London