Marine chronometer by Breguet & Fils

Description — British Museum

Marine chronometer; Earnshaw spring detent escapement; movement in brass bowl gimballed in mahogany box; flat engraved and silvered brass dial; blued steel hands.

Curator's comments — British Museum

Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990) Made by Breguet et Fils, 1829 Marine Chronometer Signature: On the dial 'Breguet et fils No 4324'. Box: The movement contained in a brass bowl directly pivoted in the gimbal ring, and secured by two screws in the edge of the bowl. There is a bezel fitting friction tight on the dial plate and also secured by two screws in the side, glazed with a flat bevel-edged glass drilled for winding through the dial. The gimbal ring is pivoted in a mahogany box, and fitted with a locking device in the bottom of the box operated by a lever at the side of the gimbal ring. Turning the lever clockwise causes a brass frame pivoted in the sides of the box to rise against a spring and press against the bottom of the drum. The box is fitted with handles, a lock, and a glazed aperture in the top covered by a hinged lid. There are also spring-loaded wood screws in the sides of the box, to secure this to a wooden surface (c.f. Breguet et Fils No. 2741, registration no. 1958,1201.2066). Base 250 mm square, h. 228 mm. Dial and hands: Flat engraved and silvered brass dial held by a single screw near the centre in a shallow recess in the dial plate so that the dial stands proud. A large bush is fitted in the hole for winding, to protect the dial from damage when the key is inserted. Blued steel hands for the small time of day and seconds dials and for the up-and-down sector. Movement: Punched on the inside of the front plate 4524. Dial plate diameter 139 mm; dial plate overall th. 22.2 mm; front plate diam. 126.5 mm; back plate diam. 122.3 mm; frame h. 53.6 mm. Frame: Remarkably similar in construction and layout to the English eight-day chronometer calibre with cut-away back plate and a platform for the escapement mounted on the front plate (cf. Barrauds No. 982, registration no. 1958,1201.1939). A type of half plate construction with three straight cylindrical pillars, held by recessed steel screws in the front plate, steel screws and polished washers on the back plate. The platform on which the escapement is mounted is secured by steel screws to three short brass pillars held by screws recessed in the front plate. The cast dial ring has a knurled flange on the outer edge, the front plate fits into it from the front and is secured by three screws passing through the plate into cast lugs on the dial ring. The brass parts are finished with radiating patterns applied with Water-of-Ayr or similar stone. There are various holes to view the gearing. Fusee: Reversed fusee with Continental stop-work and Harrison's maintaining power, the ratchet wheel steel, the detent returned by a tapered wire fitted in a screw in the back plate. The setting-up-work mounted on the back plate. The well-made tapered unblued mainspring signed 'Vincent Avril 1826 76° 4325 ', scratched in the surface of the outside of the spring. It is hooked by hook and eye to the barrel and to the unsnailed brass boss on the arbor. There is a bride for the outer coil of the spring near the hooking. Going train: The offset centre and third arbors carried between the plates, the fourth arbor between the front plate and a cock under the escapement platform with a large steel endplate. The wheels are held each with three screws on a brass collet on the arbor. The steel pinions and arbors are well finished and polished. The tooth form is remarkable in that the bottom of both wheel teeth and pinion leaves are rounded, from the great wheel to the fourth pinion inclusive. The centre and third wheels, and the third and fourth pinions appear to be the same pitch. The great wheel and centre pinion teeth have a finer pitch. Jewelling: Only the balance staff pivot in the balance cock and the escape wheel pivot in its cock run in pierced jewels, both with diamond endstones. The other escapement pivots run in detachable brass bushes with steel endstone plates. Escapement: Mounted on a separate detachable platform of lenticular shape with a fourth wheel lock operated by removing one of the fixing screws. There is not the usual separate number on the platform. The escapement of Earnshaw type has a brass escape wheel sunk out leaving the rim and teeth the full height, and is held with two screws on a brass collet on its arbor. The steel impulse roller is jewelled, the jewel leaning towards a radial to the tip. There are large passing and counterpoising holes. The escape wheel teeth show no signs of cutting or wear. The discharge roller, with two adjusting notches, is fitted above the impulse roller, towards the balance. It is jewelled and polished, the jewel being rounded on the passing side. The detent is attached by the spring portion under a piece of brass strip on a detachable bracket. Banking is by an eccentric brass plate held under a screw on an overhanging part of the detent fixing bracket. The locking stone is made from a cylindrical piece of pink ruby with two flats ground on the acting part. The passing spring appears to be brass, and is held under a screw on an integral bracket standing up from the detent. The end of the detent horn has an upstanding piece for the free end of the passing spring to rest against. Balance: Bimetallic two-armed balance, the steel parts blued, the non-ferrous part a whitish metal tarnished yellow grey. Large brass quarter nuts are fitted on studs screwed into the rim, each against a flange. The free ends of the rim drilled with a series of tapped holes very close together, each rim section has a small gold screw to go in any one of these holes to alter the amount of compensation. The balance is held by two screws on a brass collet on the staff. Diam. of rim 34.8 mm, h. 3.30 mm. Balance spring: Grey steel helical spring of 8⅝ turns, without terminal curves, clamped concentrically at the full diameter of the spring to both collet and stud. The stud is clamped under a steel strip on a brass stand with three levelling screws. The.