- Museum number
POCKET-CHRONOMETER MOVEMENT WITH SPRING DETENT ESCAPEMENT.
Spring detent escapement.
- Production date
- 1850 (circa)
Diameter: 48.20 millimetres (back-plate)
Diameter: 52.20 millimetres (dial)
Thickness: 17.60 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Henry Golay, c. 1850
Signature: On the barrel bridge 'Hry Golay A Geneve No. 2766'.
Dial and hands: Unsigned flat enamel dial with subsidiary seconds secured directly to the front plate by two feet and pins; one pin broken. On the back of the dial in red 'Golay'. Blued steel spade hands.
Ebauche marks 381 H. GOLAY GENEVE.
Front plate diam. 52.4 mm; back plate diam. 48.5 mm; frame h. 9.9 mm.
Frame: Owing an obvious debt to English full plate construction. Full plate with four turned pillars, the back plate retained by pins. Detachable barrel bridge. The movement was held in its case by one heavy positioning peg and a blued steel dog screw. The balance potence with moulded edge to the foot. The escape wheel pivoted between the back plate and a potence passing into a clearance hole in the front plate. A separate bridge on the front plate for the lower third and fourth bearings. The fusee lower bearing also in a separate bridge. The brass parts apparently electro-gilded.
Fusee: Keywind fusee with English stop-work and Harrison's maintaining power following English general design and layout. The maintaining ratchet wheel steel with very fine teeth. The barrel without flange, relieved at the lower end to miss the great wheel. Polished setting-up-work on the barrel bridge, the barrel arbor squared at that end only.
Going train: Similar to English work, the pinions turned with deep undercuts. The centre pinion so much weakened by this that the centre wheel has turned.
Jewelling: The pivots of the centre, third, fourth and escapement arbors in finely-made pierced jewels. Only the pivots of the balance staff with endstones. The diamond endstone in the balance cock loose under a steel plate and not soldered as in English work. All the train jewels bombé (i.e. convex on the surfaces towards the pivot shoulders) except those for the escape pinion arbor. The top escape jewel in a screwed setting as is the balance jewellery.
Escapement: A derivative of the Earnshaw detent escapement. The steel escape wheel with tooth form similar to that used by Thomas Earnshaw, polished, and recessed to the rim. The impulse and discharge rollers mounted at the lower end of the balance staff. The impulse roller hollow with polished edge, and jewelled, the impulse pallet leaning towards a radial from the roller centre to its tip. The steel discharge roller also jewelled and with two grooves for adjusting. The detent secured by a screw in a groove in a block screwed to the underside of the back plate, and having another screw to move the detent towards or away from the balance. The detent itself now made up of three separate pieces riveted together, the foot, the central spring, and the end with the locking stone, having been repaired. The locking stone set in a groove, the steel passing spring held by a screw. Banking for the detent provided against a gold screw set in another separate block screwed to the underside of the back plate. The detent foot set well inside a tangent to the locked tooth of the escape wheel.
Balance: Bimetallic two-armed balance of Earnshaw type with gilded brass segment compensation weights held by screws from the inside. The balance itself held by two screws to a large integral flange on the balance staff. Platinum timing screws on the rim near the end of the arm. Diam. of the rim 19.0 mm, h. 1.63 mm.
Balance spring: Blued steel helical spring of small diameter having 6 complete turns. At the lower end a very short terminal curve to a poised brass collet, at the top no terminal curve, the spring pinned to a steel stud on the balance staff. An index is provided on the balance cock for mean time adjustment. The middle coils not reduced in thickness, so that the spring breathes badly.
Hand setting: From the back via an arbor with squared end, pivoted in the frame between the barrel and the fusee. An extended square under the dial carries a wheel engaging with the minute wheel.
Great wheel (fusee) 66 teeth
Centre pinion 12 leaves, wheel 80 teeth, 6 arms
Third pinion 10 leaves, wheel 75 teeth, 6 arms
Fourth pinion 10 leaves, wheel 80 teeth, 5 arms
Escape pinion 8 leaves, wheel 15 teeth, 5 arms
Beats per hour: 18,000
Cannon pinion 12 leaves, minute pinion 10 leaves
Hour wheel 40 teeth, minute wheel 36 teeth.
Provenance: Ilbert Collection, purchased by Ilbert from Wartski in 1932.
- Not on display
Latest: 3 (2017)
3 (Oct 1995) Top balance pivot broken.
- 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.1601 (Ilbert Collection)
Previous owner/ex-collection number: M73 (Ilbert Ledger)