- Museum number
POCKET-CHRONOMETER MOVEMENT WITH ARNOLD'S SPRING DETENT ESCAPEMENT.
Pocket chronometer movement and dial.
Full-plate; separate barrel bridge; fusee; Harrison's maintaining power.
Arnold spring-detent escapement; Arnold Z balance; helical blued-steel balance spring. Under the balance cock a screwed-on semi-circular amplitude limiting device.
Later white enamel dial inscribed,'CHRONOMETER'.
Replacement hour and minute hands, seconds hand missing.
- Production date
Diameter: 40.30 millimetres (back-plate)
Diameter: 46.40 millimetres (dial)
Thickness: 17.70 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
John Roger Arnold, c. 1800
Signature: 'Jn° R Arnold London Invt. et Fecit No 1761'.
Dial and hands: The dial and dial plate are replacements. The continental-style dial inscribed CHRONOMETER and on the underside marked with the letter W. Secured by short feet and pins to the dial plate, the dial plate with four feet passing through holes in the front plate and secured by pins.
The hour and minute hands are replacements. The seconds hand missing.
For similar movements see registration nos 1958,1201.1948 and 1958,1201.1582, but again a new series.
Dial plate diam. 46.5 mm; front plate diam. 42.3 mm; back plate diam. 40.5 mm; frame h. 7.6 mm.
Frame: Similar to registration no. 1958,1201.1579, but with reduced thickness between the plates. Full plate construction with detachable barrel bridge. Four turned pillars the back plate retained by pins. The brass parts gilded. The case catch and spring fitted on the front plate under the dial, opposite the hinge on the dial plate at 12 o'clock. The balance cock engraved but not pierced.
Fusee: Keywind fusee fitted with the usual stop-work and maintaining power. The maintaining ratchet wheel of brass, the return spring for the maintaining detent a short piece of steel wire set in a screw in the back plate under the detent foot. Setting-up-work on the barrel bridge. The ratchet wheel partly cut away where it would overlap the edge of the bridge.
Going train: Similar train to that in 1958,1201.1579 except that the great wheel has only 58 teeth instead of 60. The brass train wheels gilded and the fourth pivot on the dial side extended to carry the seconds hands.
Jewelling: The pivots of the fourth and escapement arbors in pierced jewels, those of the escapement with endstones, a diamond on the balance cock. Impulse and discharge rollers and detent also jewelled.
Escapement: Arnold detent escapement with brass escape wheel, the acting surfaces of the teeth slightly out. Grey steel detent, the top of the foot polished, and with a steel passing spring held with two rivets. The detent banking against a small screw set in the back plate.
Balance: 'z' type, similar to 1958,1201.1579 except that the bimetallic rims do not each have an integral bracket to secure it to the crossbar. Instead, at each end of the crossbar a block is left standing above the plane of the bar, to which a bimetallic rim is secured by two radial screws. The timing screws at the ends of the crossbar pass through clearance holes in the rims and into a slotted hole in each block. Two timing screws at 90° to the bar probably not original. Diam. 18.9 mm, h. 2.55 mm.
Balance spring: Helical blued steel, 7 complete turns and terminal curves at each end. Square section pins used to secure the terminal curves to the collet, and the blued steel stud on the balance cock.
Under the balance cock is screwed a brass shield embracing the coils of the balance spring either as a protection or an amplitude limiting device although the spring cannot touch it now (see also 1958,1201.1579).
Balance cock: The decoration engraved on the upper surface only, no piercing.
Going-train counts: See entry under 'going train'.
Cannon pinion 12 leaves, minute pinion 14 leaves
Hour wheel 42 teeth, minute wheel 48 teeth
Provenance: Ilbert Collection; purchased by Ilbert from Arnold and Lewis of Manchester 1931.
- Not on display
Latest: 3 (2017)
3 (Sep 1995) Seconds hand missing.
- 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.1581 (Ilbert Collection)
Previous owner/ex-collection number: K71 (Ilbert Ledger)