Swiss silver marine chronometer pocket watch Circa 1792

Silver open faced watch with centre seconds
–
An extremely fine Swiss, unique and historically important high-precision pocket chronometer watch, circa 1792. With an innovative wheel train especially designed to produce decimal time, Berthoud’s spring detent chronometer escapement, anti-friction rollers, dead centre seconds and regulator dial. Accompanied by a mahogany deck box and specially bound booklet. The First Decimal Marine Watch – Made for the Chevalier de Borda by Louis Berthoud. Researched, planned and made between 27th January 1792 and 19th June 1793 for the Chevalier de Borda, famous mathematician, physicist, political scientist, navigator, and father of the standard Meter, the basis of the metric system. Considered by Berthoud to be his most important chronometer.
–
A polished case, the back engine-turned with engraved foliate monogram. Hinged silver cuvette. White enamel dial by Lucard (Place de Thionville), inner radial Roman numerals I-X, outer minutes and seconds track calibrated to 100 minutes/seconds, arrowhead five-second indexes. Blued steel spade hands. A frosted gilt full plate movement, cylindrical pillars, fusee with chain, Harrison’s maintaining power, five wheel train with specially cut numbers of teeth to produce decimal time, Berthoud’s pivoted detent escapement, ten toothed gold escape wheel, three-arm riveted bimetallic compensation balance with three wedge-shaped temperature adjustment weights, steel mean time screws, the balance staff fitted with a brass stud and adjustment screw, free-sprung blued steel helical balance spring with Berthoud’s stud with set screw, three anti-friction rollers on the upper balance pivot, each one with a steel endplate. Dial, dial-plate and movement signed. Property of an Italian Collector.

–
Diameter: 67 mm
–
Signed: Louis Berthoud (Horloger de la Marine) Swiss
–
We are indebted to Mr D. Reggiani of Savona, whose exhaustive technical and historical study in Italian (from which we have taken the draw­ings here published), done in 1982, will accompany this lot. This watch was considered by Louis Berthoud to be the most important of the chronometers he made.