- Museum number
POCKET-CHRONOMETER MOVEMENT WITH ARNOLD'S SPRING DETENT ESCAPEMENT.
Spring detent escapement; Arnold-type wheel.
Enamel dial; large subsidiary seconds intersecting eccentric time dial.
- Production date
Diameter: 41.50 millimetres (back-plate)
Diameter: 48.80 millimetres (dial)
Thickness: 19.60 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by J. Grant, c. l800
Signature: On the back plate 'GRANT Fleet Street London 2444'. On the enamel dial 'GRANT Fleet Street LONDON No 2444'.
Dial and hands: Flat enamel dial with intersecting offset minute and hour, and seconds circles, secured by four short feet and pins to the dial plate. Signed in red on the reverse W and W or, more probably, M and M.
Gold hands of the solid moon type.
Dial plate diameter 48.1 mm; front plate diam. 44.6 mm; back plate diam. 41.6 mm; frame h. 7.5 mm.
Frame: Full plate with four turned pillars, the back plate retained by pins, detachable barrel bridge engraved with scrolling foliage. The dial plate carrying the hinge and fixed to the front plate by four short feet and pins, GRANT scratched on this plate. The case catch and spring mounted on the front plate under the dial. The balance cock engraved with scrolling foliage and a mask.
Fusee: Keywind fusee with normal stop-work and maintaining power, the maintaining ratchet wheel brass. Setting-up-work under the dial on the front plate, the barrel arbor squared at that end only. The barrel with a flange at the cover end.
Going train: The brass wheels gilded, the steel pinions and arbors well finished and polished. The train count chosen to give the unusual number of 16,875 beats per hour.
Jewelling: The pivots of the fourth and escapement arbors in pierced jewels, those of the escapement with endstones, a diamond on the balance cock, set in a blued steel ring.
Escapement: An Arnold type of detent escapement, with brass escape wheel, the impulse faces of the teeth marked. The steel impulse roller set with a jewel leaning towards a radial to its slightly rounded acting tip as for an Earnshaw type of escapement. The discharge roller jewelled, and with two flats for adjusting. The detent of very similar design to that used by the Arnolds, the steel passing spring held by a single rivet. The detent banking provided by a steel strip and single screw, lodged in a slot in the top of the back plate.
Balance: Bimetallic two-armed balance with cylindrical brass compensation weights held by polished steel screws. Steel timing screws set in the rim near the ends of the arms. Diam. of rim 20.0 mm, h. 1.47 mm.
Balance spring: Blued steel helical spring, 4½ turns and with terminal curves, free sprung to a blued steel stud on the balance cock. The steel collet having a short thick piece of gold wire set in a hole opposite the pinning point of the spring, to act as a counterpoise.
Great wheel (fusee) 60 teeth
Centre pinion 12 leaves, wheel 75 teeth, no crossings
Third pinion 10 leaves, wheel 64 teeth, 6 arms
Fourth pinion 8 leaves, wheel 75 teeth, 6 arms
Escape pinion 8 leaves, wheel 15 teeth, 3 arms
Beats per hour: 16,875
Cannon pinion 14 leaves, minute pinion 18 leaves
Hour wheel 54 teeth, minute wheel 56 teeth
Provenance: Ilbert Collection, purchased by Ilbert from Biggs of Maidenhead.
- Not on display
Latest: 2 (2017)
2 (Oct 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.1602 (Ilbert Collection)
Previous owner/ex-collection number: M200 (Ilbert Ledger)