- Museum number
MOVEMENT, DIAL AND DUST-CAP OF A LEVER WATCH.
Full-plate; fusee; Harrison's maintaining power.
Ratchet-tooth lever escapement; Earnshaw chronometer balance.
White enamel dial with subsidiary seconds.
Gold spade hour and minute hands; blued steel seconds hand, the tail missing.
Gilt brass dust cap.
- Production date
- 1827 (case)
Diameter: 44.40 millimetres (dial)
Diameter: 42 millimetres (dust-cap)
Thickness: 15.30 millimetres
- Curator's comments
Case missing; mentioned by Ilbert but not possessed by him; hallmark on case was understood to be London 1827.
Comment from Richard Good, Catalogue of Watches in the British Museum. Vol. V (Unpublished manuscript)
Made by Thomas Earnshaw Junior
Movement of a ratchet tooth lever watch.
Signature: On the dial 'THOs. EARNSHAW LONDON No.4615' and on the back plate 'Thos. Earnshaw, No 4615.' and '119 High Holborn, LONDON.' on the barrel bridge.
Dial & hands: A flat dial with a subsidiary seconds dial. Gold spade pattern hour and minute hands, blued steel seconds hand, the tail broken off.
Dial-plate: Scratched 'Thos Earnshaw London No 4615 Ehaw'.
Dust-cap: Stamped 'L x R' on the inside. There is an extra cut-out for the high balance spring stud.
Ebauche Marks: None.
Frame: A full plate layout, the back plate supported by four turned pillars. The balance potence has a straight moulded foot, a deep semi-circular recess for the balance staff and an extra deep recess for the roller. The balance cock is engraved with a foliate design on the foot and a radial pattern around the endstone setting. Both the balance cock foot and the barrel bridge have engraved decoration around the chamfered edge. The balance cock foot is scratch-numbered '4615' on the underside.
Fusee Barrel and Mainspring:
Fusee: six-turn fusee with Harrison's maintaining power with a steel maintaining ratchet wheel.
Barrel: internal diameter 16.7 mm, height 3.1 mm.
Mainspring: height 2.8 mm, thickness 0.21 mm.
Barrel Arbor: diameter 5.6 mm, not snailed.
Train: Wheels gilded, the centre wheel solid, the third and fourth wheels with five crossings.
Jewelling: Jewelled bearings for the escape wheel and balance only, with ruby endstones in screwed settings except for that in the potence which is in a wedge. A diamond endstone in a screwed setting in the balance cock.
Escapement: An obtuse-angle layout ratchet tooth lever escapement with short lever, single roller and D-shaped impulse pin (but the impulse pin not original). A gold lever with a steel pallet frame. The enclosed pallet stones are convex on both impulse faces and on the entrance locking face, the exit locking face is flat. There an extra hole in the back plate between the two banking pins which appears to be a later modification and to have no purpose. The polished brass escape wheel has three crossings.
An equal impulse escapement.
No. of teeth embraced 32.
Balance & Spring: An Earnshaw bimetallic balance with two segmental brass weights and two brass timing screws. Balance diameter 18.0 mm over the rim and 20.7 mm over the weights, thickness 1.8 mm. A blued-steel flat spiral spring with 7 3 turns pinned to a gilded stud screwed to the back plate.
Means of Regulation: An index on the balance cock registers against a divided scale with 'SLOW' and 'FAST', with a fleur-de-lys between, engraved on the balance cock table.
Train Counts and Beat Rate:
Great wheel 60 (fusee)
Centre wheel 64 pinion 12
Third wheel 60 pinion 8
Fourth wheel 60 pinion 8
Escape wheel 15 pinion 7
Beat rate: 15,428.571
Motion work: cannon pinion 12
minute wheel 48, minute pinion 14
hour wheel 42
Winding System: Key wound.
Movement: diameter 44.2 mm, height 15.2 mm, pillar height 4.3 mm.
Provenance: Formerly in the Ilbert Collection. Ilbert purchased this from Malcolm Gardner in July 1954.
(1) Ilbert states, in his ledger, that this movement was originally housed in a gold case hallmarked London 1827.
Anthony Randall in 'Thomas Earnshaw's Numbering Sequence', AH Vol XVII (Summer 1988) p. 371 gives watch No.4607 with a case hallmarked 1826, no. 4620 hallmarked 1821 and no. 4770 hallmarked 1829.
- Not on display
Latest: 3 (2017)
- 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.0987 (Ilbert Collection)
Previous owner/ex-collection number: Q263 (Ilbert Ledger)