- Museum number
POCKET-CHRONOMETER MOVEMENT WITH PIVOTED DETENT ESCAPEMENT.
Pivoted detent escapement, no passing spring.
- Production date
Diameter: 43.50 millimetres
Thickness: 10.50 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by C. Hanson, English c. 1860
Signature: On the back plate 'C.Hanson's No. 28 Patent Chronometer'.
Dial and hands: None.
Ebauche marks J.W. 16, 2, 28.
Front plate diam. 43.9 mm; back plate diam. 40.0 mm; frame h. 6.3 mm
Frame: Full plate construction, the back plate retained by screws, turned pillars, detachable barrel bridge. The movement hinge and case catch lodged on the recessed front plate under the dial. No dial plate, the dial feet passing through holes in the front plate and retained by pins. The back plate recessed for the balance, fitting flush with the plate, and having an engraved shaped balance cock. A separate bridge for the upper escapement bearings screwed to the under side of the back plate. All the brass parts gilded.
Fusee: Keywind fusee of the usual construction, with maintaining power having a steel ratchet wheel.
Going train: Usual construction and layout.
Jewelling: The balance staff and lower escape arbor pivots in pierced jewels with endstones. The upper escape arbor pivot in a pierced jewel. No other jewelling.
Escapement: A type of pivoted detent without the usual passing spring. The escape wheel teeth are locked on a hollow crescent resembling the cylinder of a cylinder escapement. On the impulse swing of the balance, a steel pin below the impulse roller contacts the nose of the detent. This turns the crescent, releasing a tooth of the escape wheel to give impulse. A light spring acting on a flat on the detent arbor returns the detent ready to lock the escape wheel. On the return of the balance the detent is moved so that the escape tooth is locked deeper on the edge of the crescent.(1)
Balance: Plain steel three-armed balance, flat spiral balance spring of 10 full turns, with an index on the balance cock. No compensation. Diam. 16.0 mm, h. 0.76 mm.
Great wheel (fusee) 75 teeth
Centre pinion 10 leaves, wheel 64 teeth, 5 arms
Third pinion 8 leaves, wheel 60 teeth, 5 arms
Fourth pinion 8 leaves, wheel 70 teeth, 5 arms
Escape pinion 7 leaves, wheel 15 teeth, 3 arms
Beats per hour: 18,000
Canon pinion 12 leaves remainder missing.
Provenance: Ilbert Collection; purchased by Ilbert in the Caledonian Market in 1932.
(1) The patent, No. 1950, was granted on 27 August, 1859. Although this watch cannot have been intended for precision work, the variant of the pivoted detent escapement is ingenious and easier to make than a normal pivoted detent. It is also lighter and more robust.
- Not on display
Latest: 3 (2017)
3 (Oct 1995) Original jewel-hole and endstone for bottom escape wheel pivot, minute-wheel, hour-wheel 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.1604 (Ilbert Collection)
Previous owner/ex-collection number: M305 (Ilbert Ledger)