- Museum number
MOVEMENT, DIAL AND DUST-CAP OF A LEVER WATCH.
Full-plate; fusee; Harrison's maintaining power; ratchet-tooth lever escapement; split bi-metallic balance.
White enamel dial with sunk subsidiary seconds.
Hands not original.
- Production date
Diameter: 46.60 millimetres (dial)
Diameter: 42.80 millimetres (dust-cap)
Thickness: 12.70 millimetres
- Curator's comments
- Comment from Richard Good, Catalogue of Watches in the British Museum. Vol. V (Unpublished manuscript)
Made by John Forrest.(1)
London c. 1860
Movement of a ratchet tooth lever watch.
Signature: On the dust-cap 'John Forrest 17434 LONDON E.C.', on the dial 'John Forrest London 17434', on the back plate 'Chronometer MAKER TO the ADMIRALTY' and on the barrel bridge 'LONDON. E.C. 17434'.
Dial & Hands: A flat dial, the subsidiary seconds dial with a sunk centre. On the back of the dial in the counter-enamel, the number 34. The brass spade hour hand and the red gold minute hand are both replacements. The steel seconds hand now lacks its counterpoised end.
Dial-plate: None intended, the dial is pinned directly to the front plate but the edge of the front plate is shaped to resemble a dial plate.
Dust-cap: Punched I.B on the inside. Inscribed inside the barrel bulge '434' and 'X' which aligns with the X position on the dial.
Ebauche Marks: W & JC 18 0 17434.(2)
Frame: A full plate layout, the back plate supported by four turned pillars and secured by screws. Stamped '17434' on the inside of the back plate. The balance cock is engraved with foliate scrolls on both the table and foot. An escapement protection post fitted into the back plate.
Fusee, Barrel and Mainspring:
Fusee: A four-turn fusee with Harrison's maintaining power with a steel maintaining ratchet wheel.
Barrel: internal diameter 17.2 mm, height 2.9 mm.
Mainspring: height 2.65 mm, thickness 0.25 mm.
Barrel Arbor: diameter 5.65 mm, not snailed.
Train: Wheels gilded, the centre wheel solid, the third and fourth wheels with five crossings.
Jewelling: Jewelled bearings for the third wheel onwards. The third and fourth wheel jewels in the front plate rubbed in, the rest in screwed settings. The pallet holes are not jewelled. Ruby endstones for the escape wheel; a ruby endstone in a wedge in the potence and a diamond in the balance cock.
Escapement: A right-angle layout ratchet tooth lever escapement with short lever, single roller and round impulse pin. The enclosed pallet stones have convex impulse and locking faces. Brass escape wheel with three crossings.
An equal impulse escapement.
No. of teeth embraced 32.
Balance & Spring: A split bimetallic balance with gold compensation and quarter screws. Balance diameter 20.25 mm, thickness 1.3 mm. Blued-steel flat spiral spring with eleven turns pinned to a polished steel stud screwed on the back plate.
Means of Regulation: An index on the balance cock registers against a silver scale screwed to the back plate, the latter engraved 'Slow' and 'Fast'.
Train Counts and Beat Rate:
Great wheel 76 (fusee)
Centre wheel 64 pinion 10
Third wheel 60 pinion 8
Fourth wheel 63 pinion 8
Escape wheel 15 pinion 7
Beat Rate: 16,200
Motion work: cannon pinion 12, minute wheel 48,
minute pinion 14, hour wheel 42.
Winding System: Key wound.
Movement: diameter 46.5 mm, height 13.0 mm, pillar height 2.9 mm.
Provenance: Formerly in the Ilbert Collection. Ilbert purchased this from Cockburn in Edinburgh in 1930.
(1) For a discussion of John Forrest and his work see David J. Boullin, 'John Forrest, Chronometer Maker to the Admiralty', H J, Vol 133 No. 2. August 1990, pp. 52-56.
(2) William and John Copple, ebauche makers of Prescot.
- Not on display
Latest: 4 (2017) rust on seconds hand and slide
4 (1994) Centre arbor and hands very dirty.
- 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.0991 (Ilbert Collection)
Previous owner/ex-collection number: D28 (Ilbert Ledger)