French gold watch with detent chronometer escapement Circa 1844

Gold watch with chain and Breguet ratchet key 
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A very fine and extremely rare French, 18K gold garde temps pocket watch with detent chronometer escapement, circa 1844. With a heavy 18K gold chain and gold double-ended Breguet ratchet key. Accompanied by a Breguet fitted box and certificate. Sold to a member of an important banking family for 1,500 Francs. A solid case with master mark JP, engine-turned bezel and band, the back engine-turned. Gold cuvette with an aperture for winding and secured by a screw. White enamel dial by Droz, with radial Roman numerals, outer minute track, subsidiary seconds at 12, secret signature above 6, secured by a single steel screw. Yellow gold Breguet hands.
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A frosted gilt movement, half-plate, cylindrical steel pillars with blued steel screws, fusee and chain, Harrison’s maintaining power, Earnshaw-type fully jewelled escapement, 16-tooth escape wheel, pivoted spring detent with secondary parallel mounted detent to keep the detent in tension, steel roller and pallet, free-sprung bimetallic Z balance with temperature and meantime adjustment screws, blued steel helical balance spring with terminal curves, mobile stud bearer. Dial, cuvette and movement signed. Case with Paris gold marks for post-1838.
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Diameter: 53 mm
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Signed: Breguet  Paris
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This watch was made as a high-precision timepiece, the balance with blued steel arm and inner laminae and adjustment screws only is the type used in Breguet marine chronometers dating from the second quarter of the nineteenth century. Louis Clement Francois Breguet was responsible for the development of these on his return from Switzerland. The detent of the present watch is interesting and unusual in that a second separate detent spring is mounted above and parallel to the detent and acts to keep tension on the detent. This has a similar operational effect to the detent arrangement in the Peto cross detent escapement.