- Museum number
POCKET-CHRONOMETER MOVEMENT WITH ARNOLD'S SPRING DETENT ESCAPEMENT.
Pocket-chronometer watch, movement.
Full-plate; fusee; Harrison's maintaining power now missing.
Arnold spring-detent escapement. Arnold 'OZ" Balance, helical balance spring.
Dial and motion-work missing
- Production date
Diameter: 39.70 millimetres (back-plate)
Diameter: 42.80 millimetres (front-plate)
Thickness: 17.30 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by John Arnold and Son, 1787-1799
Signature: Engraved on the back plate 'John Arnold and Son London Inv.' et Fecit No 186/487.
Dial and hands: Missing, but see registration no. 1958,1201.1578.
No dial plate (the dial was fixed directly to the front plate). Front plate diam. 42.8 mm; back plate diam. 40.0 mm; frame h. 9.7 mm.
Frame: Full plate with four turned pillars, the back plate retained by pins, gilded brass. The case push-piece and spring once fitted between the plates on the front plate are both missing. The hinge to attach the movement to its case on the dial side of the front plate also removed. There is evidence that the watch was once fitted into a replacement case, in the form of case screws which have been fitted to the front plate.
Fusee: Keywind fusee with the usual stop-work and maintaining power, the maintaining ratchet wheel brass. The return spring for the maintaining detent a fine wire set in a screw in the back plate, the wire now broken.
Barrel: With flange at the top and relieved at the bottom to clear the great wheel, the arbor squared at both ends. Setting-up-work on the front plate under the dial, the ratchet with an integral spring now broken.
Going train: Wheels of gilded brass, the pinions of polished steel nicely finished. The teeth of the third and fourth wheels particularly thin. Rather low numbers of teeth in the wheels and pinions.
Jewelling: Only the escapement pivots in jewelled holes with endstone jewels. In the balance cock a diamond endstone set in a blued steel plate, not original, the other endstone ruby. The impulse and discharge rollers and the detent jewelled.
Escapement: Arnold spring detent escapement with brass escape wheel, the curved impulse faces of the teeth slightly marked. The detent with polished top to the foot, and with a steel passing spring riveted on, banking against a screw set in the back plate.
Balance: Made up of a polished steel wheel with three arms and two bimetallic rims screwed on with brackets diametrically opposite each other. The bimetallic rims blued steel on the inside, brass on the outside. A gold pin in the steel rim possibly for poising. This type of balance is known as 'oz'. The amount of compensation can be adjusted by turning the brass weights on the threaded portions at the free ends of the rims thus moving them towards the ends to increase, or away from the ends to decrease, the amount of compensation. Two steel timing screws set radially, one in each bimetallic rim above the fixing bracket. Diam. 19.8 mm, h. 2.0 mm.
Balance spring: Blued steel helical spring of 7 turns with terminal curves at each end. The upper one pinned to a blued steel stud screwed to the balance cock, the stud brass with round hole and D-shaped pin.
Balance cock: Finely pierced and engraved.
Great wheel (fusee) 60
Centre pinion 12 leaves, wheel 64 teeth, no crossings
Third pinion 8 leaves, wheel 60 teeth, 4 arms
Fourth pinion 8 leaves, wheel 60 teeth, 4 arms
Escape pinion 6 leaves, wheel 15 teeth, 4 arms
Beats per hour: 18,000
Motion work: Missing.
Provenance: Ilbert Collection; purchased by Ilbert from Jauncey in 1936.
- Not on display
- Exhibition history
1998-1999 04 Dec-18 Apr, London, National Maritime Museum, Arnold & Earnshaw, Pioneers of the Chronometer
Latest: 3 (2017)
3 (Sep 1995)
- Acquisition date
- Acquisition notes
- Following the successful acquisition of the celebrated Ilbert collection of clocks (1958,1006 collection), prints and other related materials made possible by the generous donation of funds by Gilbert Edgar CBE Ilbert's watches were then acquired using funds provided by Gilbert Edgar, public donations and government funds.
- Britain, Europe and Prehistory
- Registration number
- Additional IDs
Previous owner/ex-collection number: CAI.1576 (Ilbert Collection)
Previous owner/ex-collection number: P57 (Ilbert Ledger)