Marine chronometer by Louis Berthoud

Description — British Museum

Marine chronometer; pivoted detent escapement; movement in brass drum gimballed in mahogany box; tipsy key; enamel regulator type dial; blued steel moon 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 Louis Berthoud, 1811 Marine Chronometer Signature: On the back plate 'Construite par Louis Berthoud No 127.' On the dial 'Louis Berthoud Horger de la Marine No 127 bis'(l) and DEPÔT DE LA MARINE written on top of the glaze.… Around the edge of the dial ring: 'No 127 Construite par Louis Berthoud'. Box: The movement contained in a brass drum in which it is held by a bayonet fastening and secret catch operated by pushing with a pin through a very small hole in the side. This arrangement also used by Motel. The threaded bezel, engraved DÉPÔT GAL DE LA MARINE, holds another similar unthreaded bezel with a raised glass, and similarly signed but without the GAL. The bottom is a push fit, secured by two screws in the edge and engraved 'No 127 Département de la Marine 9bre 1811'. In order to insert the key for winding, two overlapping escutcheon plates must be rotated until their holes coincide with a third in the bottom. The brass drum fits into a weighted brass cradle with a gimbal ring pivoted in a mahogany box similar to, but larger than, registration no. 1958,1201.1928. Inscribed on a diamond-shaped brass insert on the front of the top 'No 127 BIS'. There is a tipsy key in one corner of the box.(2) Dimensions: Brass drum, 82.9 mm diam, 43.5 mm h.; Mahogany box: base 140 mm square; sides 136 mm square; overall h. 114 mm. Dial and hands: Enamel regulator type of dial attached in a recess in the dial ring on the front plate by two feet passing through the front plate and pins. Blued steel moon hands. Movement: Dial ring diam. 80.1 mm; front plate diam. 75.1 mm; back plate diam. 74.6 mm; frame h. 17.0 mm. Frame: Similar to L. Berthoud, registration no. 1958,1201.1928, but larger. The brass parts smooth but not polished or gilded. The dial plate held by a small screw and four larger screws. If the small screw is removed and the others slackened, the dial ring can be rotated and removed. Fusee: Similar to L. Berthoud, registration no. 1958,1201.1928. The bride is still in place in the barrel. Going train: Similar to L. Berthoud, 1958,1201.1928. Jewelling: The pivots of the centre arbor and the third in the back plate, in detachable bushes held with screws. The third arbor in the front plate, both fourth arbor pivots and those of the escape pinion and balance staff in pierced jewels. Steel end-thrust plates, highly polished and held with a single screw, are fitted over all bearings except the centre and fourth at the front. Only the balance staff pivots run between endstones. Escapement: Similar to L. Berthoud, 1958,1201.1928. The brass escape wheel is sunk out on both sides and is exceptionally light. There is a brass stop-piece which can be swung into the path of the escape wheel teeth. The detent is banked by its tail resting against a brass peg set in the back plate, and there is a small hole in the locking surface at the height of locking. Balance: Bimetallic four-armed balance with brass seg¬ment weights, the free ends of the rim sections finely graduated to help in positioning the weights. Each weight is held by a small brass screw from the outside. There are two other screws in the outside of the weight, a fixed brass screw towards the fixed end of the rim section and a larger steel screw towards the free end. T here is a small brass clamping screw for each steel screw set in the end of the weight. The steel screws are for poising and bringing to time. The balance is held by two screws on a brass collet. Diam. of rim 27.0 mm; h. 2.1 mm. Balance spring: Blued steel helical spring of ¾ turns without terminal curves, clamped concentrically at full turns to both collet and stud. The stud has 3 levelling screws and a central fixing screw. Going-train counts: Great wheel (fusee) 108 teeth, 8 turns of groove Centre pinion 26 leaves, wheel 112 teeth, 4 arms 3rd pinion 14 leaves, wheel 105 teeth, 4 arms 4th pinion 14 leaves, wheel 120 teeth, 4 arms Escape pinion 10 leaves, wheel 15 teeth, 4 arms Beats per hour: 21,600 Motion work: Centre pinion 18 leaves, clamped to the arbor by a screw in a spring collar, minute pinion 16 leaves Hour wheel 64 teeth, minute wheel 54 teeth Provenance: Ilbert Collection; Ilbert in his inventory notebook records the acquisition of this chronometer from the Royal Observatory, Greenwich, on 22 November 1930. He also mentions that no. 108 is dated 1811. Presented by Mr Gilbert Edgar C.B.E. in 1958. Notes (1) The 'bis' on the dial and on the brass insert indicate that this was the second of two chronometers with the same number. (2) Inside the box lid there is a label: 'Les Huiles ont été mises en Janvier 1919 par E. Boudeaud 40, Rue Pergolèsi Paris Ancne Maison Winnerl and Callier. 127 bis'. Bibliography: Bertele 1981, p. 176.