The Sandberg Watch Collection

Hotel Richemond, Geneva, Mar 31, 2001

LOT 142

Ferdinand Berthoud, Montre Astronomique No. 3, Invenit 1775, Reduite et Executee par Jean Martin An 1806, casemaker's mark PBT, No. 2591, for P.B. Tavernier.Extremely fine and unique silver astronomical pocket chronometer with centre seconds and balance amplitude indication, made for Jean Chaptal, Comte de Chanteloup, celebrated physician and politician.

CHF 70,000 - 90,000

USD 42,000 - 54,000

Sold: CHF 163,000

C. Four-body, 'Empire', reeded band, the polished back engraved with the crest of Jean Antoine Claude Chaptal, Comte de Chanteloup, silver hinged cuvette. D. Small eccentric silver chapter ring with Roman chapters and outer Arabic minute ring, silver Arabic seconds numerals ring on the border of the bezel. Frosted and gilt dial plate with glazed aperture for the balance amplitude indication at 4 o'clock. Blued-steel Breguet hands with skeletonised tips. M. 51 mm o, gilt brass bridge calibre, fuse and chain, fully jewelled including the fusee, Harrison's maintaining power, early form of pivoted detent with jewelled pallets and impulse pin, four-arm compensation balance with gold nut poising weights and gold timing screws, and around its edge, four bimetallic strips with gold poising nuts on their free ends, free-sprung blued-steel balance spring mounted in a stud between two blocks with a slot in the middle for a screw, this arrangement allowing the balance spring to be set concentricaly with the balance staff.Signed on the dial plate. Signed on the dial, case stamped with casemaker's markDiam. 59 mm. Published in the Sandberg book, page 184-185.


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Grading System
Grade:
Case: 3

Good
Movement: 3 - 6*
Dial: 3 - 01

Notes

This watch was described by Ferdinand Berthoud himself, in his Supplément au Traîté des Montres à Longitudes, 1807, pp. 29-31.It was also described in 'Ferdinand Berthoud- 1727 - 1807, Horloger Mécanicien du Roi et de la Marine', published by the Musée International d'Horlogerie de la Chaux-de-Fonds, in the catalogue of the Exhibition, pp. 224-225.The watch was made by Jean Martin in 1806 following the model of No. 73, but on a reduced scale. Berthoud had originally intended to use watch No.72 as his model but eventually settled on No.73 which has centre-seconds with eccentric hours and minutes. In No. 3, the wheels have the same tooth count and even the same diameter, but the watch was made smaller by removing the rollers, the compensation mechanism and the stop pallets of the balance. Thus the dial plate became smaller than in watch No.73.The balance beats four to the second with arcs of 260°, and the pivot holes are ruby. It has temperature compensation by four bimetallic weights for which the strips are formed in arcs of a circle, and carries four small weights for adjustment in the different positions. The whole train is jewelled. The balance spring is mounted in a stud between two blocks without the slightest distortion to the shape, it has a slot in the middle for a screw, which arrangement allows the spring to be set concenrically with the balance staff.Berthoud used this watch as a reason to offer a 'New explanation of the principles and methods on which the exactness of astronomical watches is based, with some conclusions concerning their use'. He notes that it is very well made and fulfills all the conditions necessary to satisfy connoisseurs. He specifies however that when used to determine longitude, it is preferable to use the watch always in its horizontal position, like the watch No. 73.For this reason, instead of the ruby end-stone of No. 73, he used a diamond one, and made the suspension so that it would always be horizontal. He notes that these changes worked perfectly, since in the horizontal position the watch had a constant rate. With this arrangement, watch No. 3 could be worn vertically as a pocket watch, or placed horizontally to become a small longitude time-keeper.