Rare Swiss 18 carat gold pocket chronometer with tourbillon Circa 1865

Gold tourbillon watch 
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An extremely rare Swiss 18 carat gold hunting cased pocket chronometer with tourbillon made by DuBois & Le Roy in Le Locle, circa 1865. Retailed by Ducommun in Marseille, France. A numbered polished case with maker’s mark LBF, the cuvette engraved with technical details and signed Ducommun à Marseille. White enamel dial with Roman hours, an outer minute track, outermost Arabic five minute numerals, subsidiary seconds at 6 o’clock and blued steel spade hands. A signed tourbillon movement of very high quality with wolf teeth and screwed gold chatons.
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Diameter: 52 mm
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Weight: 145 g
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Signed: DuBois & LeRoy Le Locle
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The signature on this timepiece is interesting because the first two places in the 1866 chronometer competition of the Neuchâtel Observatory went to DuBois & Le Roy from Le Locle and Ducommun from La Chaux-de-Fonds!
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At that time, some of the finest tourbillons were made in Le Locle, especially specimens by Ernest Guinand.
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Tourbillon
A system devised, and in 1801 patented by Abraham-Louis Breguet, to compensate for errors of rate caused by the earth’s gravitational force in upright positions. The escapement is mounted in a revolving cage with the balance in the center. The escape wheel pinion turns about the fixed fourth wheel. The cage generally revolves once a minute, and in doing so, compensates for errors of rate caused by the vertical position in which pocket watches spend most of their time. This delicate and complex structure is one of watchmaking’s most ingenious mechanisms. A simplified and more robust alternative is the carrousel, where the cage is driven not by the fourth wheel but by the third wheel. A tourbillon can contain a lever or a detent escapement.