English large silver chronometer deck watch Circa 1875

Exceptional large chronometer deck watch by Dent
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An English exceptional large silver open faced chronometer deck watch, circa 1875. Gilt 3/4 plate movement, Earnshaw type duo-in-uno spring detent escapement, large free-sprung bimetallic compensation balance, blued steel duo-in-uno balance spring, diamond endstone. Plain polished silver cuvette with apertures for winding and hand-setting. White enamel dial with British Royal and Russian Imperial warrants, Roman numerals, outer minute track, subsidiary dials for up-and-down and seconds, blued steel hands. Plain polished case, leather-covered and glazed deck case, later short silver chain and key, with London hallmarks, movement signed Dent Watchmaker to the Queen, 33 Cockspur Street, Charing Cross, London, dial signed and numbered.
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Diameter: 67 mm
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Signed: Dent Watchmaker to the Queen 33 Cockspur Street Charing Cross London
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The movement incorporates Mercer’s auxiliary type ‘H’ as well as a rare duo-in-uno balance spring with a double terminal curve. The white enamel dial carries the medallions announcing appointments to the Queen and the Empress of Russia, the same warrants are also engraved on the movement.
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This watch is made by John Hammersley for Dent. Hammersley worked mainly for M.F. Dent and several others and was well known as a successful springer and adjuster. He also supplied a number of deck watches to the admiralty. He did make a small number of pocket watches signed with his name.
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Born in 1819, John Hammersley was a springer and adjuster of good reputation. Credited with the introduction of the duo-in-uno balance spring with A.P. Walsh, Hammersely frequently utilized this feature, though he is not acknowledged as its inventor. He was mostly employed by other makers and died in 1901.