- 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.
White enamel dial, badly damaged. hours I-XII, subsidiary seconds.
- Production date
Diameter: 41.50 millimetres (back-plate)
Diameter: 45.10 millimetres (dial)
Thickness: 19 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 Roger Arnold, c. 1805 (No. 1922 has the hallmark for 1805 and No. 1984 for 1806)
Signature: 'Jo° R. Arnold London Invt. et Fecit No 1975.'
Dial and hands: Badly damaged enamel dial, remains of the signature in capitals only (see registration no. 1958,1201.1580). Hands missing.
For similar movements see registration nos 1958,1201.1580-1
Dial plate diam. 45.1 mm; front plate diam. 42.1 mm; back plate diam. 41.6 mm; frame h. 8.1 mm.
Frame: Similar to 1958,1201.1581, but the dial plate foot near the case catch retained by a blued steel screw. The case hinge torn out.
Fusee: Similar to 1958,1201.1581. The setting-up ratchet wheel on the barrel bridge is not original, the foot of the return spring for the click has been shortened.
The maintaining detent spring instead of being part of a screw pointing down from the back plate is a normal blued steel spring screwed to the front plate on the movement side.
Going train: Similar to 1958,1201.1581.
Jewelling: Similar to 1958,1201.1581 except for a ruby endstone on the balance cock instead of a diamond, and the impulse roller not jewelled.
Escapement: Similar to 1958,1201.1581. The impulse roller is unusual in that it is not jewelled and has a small hole drilled opposite the impulse face for poising. The impulse corner is rounded. The escape wheel teeth practically unmarked on the impulse faces.
Balance: Similar to 1958,1201.1581 but the blocks on the ends of the crossbar finished differently. Diam. 18.3 mm, h. 2.6 mm.
Balance spring: Possibly a later blued steel helical spring because the securing pins to collet and stud are round instead of square in section, and a new round hole has been drilled in the stud above the original square hole. The spring has 7 complete turns, with terminal curves.
Balance cock: Engraved decoration similar to registration nos 1958,1201.1580-1 and 1958,1201.1583.
Great wheel (fusee) 60 teeth
Centre pinion 12 leaves, wheel 64 teeth, no crossings
Third pinion 8 leaves, wheel 60 teeth, 4 arms
Fourth pinion 8 leaves, wheel 80 teeth, 4 arms
Escape pinion 8 leaves, wheel 15 teeth, 4 arms
Beats per hour: 18,000
Cannon pinion 12 leaves, hour wheel 42 teeth
Minute wheel and pinion missing but no doubt 48 teeth and 14 leaves respectively.
Provenance: Ilbert Collection; purchased by Ilbert from Malcolm Gardner in 1934.
- Not on display
Latest: 3 (2017)
3 (Sep 1995) Hands missing. Dial severely damaged.
- 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.1582 (Ilbert Collection)
Previous owner/ex-collection number: N317 (Ilbert Ledger)