- Museum number
POCKET-CHRONOMETER MOVEMENT WITH PIVOTED DETENT ESCAPEMENT.
Pivoted detent escapement; full-plate, very large going-barrel; plain balance; regulator adjusted by star wheel.
Epicyclic gearing for minutes.
- Production date
Diameter: 51.20 millimetres (back plate)
Diameter: 55 millimetres (dial plate/ring)
Diameter: 51.20 millimetres (front plate)
Thickness: 6.20 millimetres (movement)
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Maker Unknown, possibly Swiss, Early 19th century
Dial and hands: None.
Dial ring diam. 55.0 mm; front plate diam. 51.2 mm; back plate diam. 51.2 mm; frame th. 6.2 mm.
Frame: Full plate construction with a dial ring held by four screws under the dial. Four turned pillars, the back plate held by pins. Engraved bridge cock and barrel bridge. The edge of the dial ring also engraved. All the brass parts gilded.
Going barrel: Of very large diameter extending beyond the centre of the frame. The ratchet and click on the barrel bridge. No stop-work. The mainspring hooked to the barrel wall by hook and eye, and with a brace. The barrel arbor with a steel centre and brass boss.
Going train: An early example of an offset train in which the centre wheel is displaced to leave room for a larger than normal barrel. No provision for a seconds hand.
Escapement: A crudely made pivoted detent without jewelling. The impulse plane leaning slightly towards a radial to the tip. Two steel discharge rollers, one above and one below the impulse roller, only the lower one now used to unlock the detent. The detent backed against a dog screw near the point of pivoting, and returned by a single leaf spring. Diam. 23.0 mm, h. 0.75 mm.
Balance: Plain three-armed brass balance, flat spiral spring of blued steel having 6¾ turns, without any thermal compensation. Rack and pinion gearing for mean time adjustment with triangular-shaped teeth. A and R marked on either side of the regulator.
Amplitude limiting device: The balance spring is below the balance. Above the balance a loose finger piece is adjusted on the balance staff and retained by a brass collar. Its movement is limited by a steel pin set in the balance boss. The loose piece is able to contact another pin set in the balance bridge and pointing down into its path. Such a device, although very ingenious and simple, introduces a variable friction during the motion of the balance.
Barrel 84 teeth.
Centre pinion 12 leaves, wheel 64 teeth, no crossings but 5 holes for lightening purposes
Third pinion 8 leaves, wheel 50 teeth, 4 arms
Fourth pinion 8 leaves, wheel 50 teeth, 4 arms
Escape pinion 8 leaves, wheel 15 teeth, 4 arms
Motion work: Mostly missing, a fixed wheel at the centre of 40 teeth remains. The offset centre arbor is hollow and carries the hand-setting arbor with a pinion of 8 leaves. This pinion must have driven some kind of epicyclic motion work now missing.
Provenance: Ilbert Collection; purchased by Ilbert from Lebrassier in 1938.
- Not on display
Latest: 3 (2017)
3 (Oct 1995) Dial and motion work 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.1827 (Ilbert Collection)
Previous owner/ex-collection number: Q4 (Ilbert Ledger)