- Museum number
POCKET-CHRONOMETER MOVEMENT WITH SPRING DETENT ESCAPEMENT AND DUST-CAP.
Spring detent escapement.
- Production date
Diameter: 46.60 millimetres (dial)
Diameter: 43.70 millimetres (dust-cap)
Thickness: 17.40 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by James McCabe, c. 1850
Signature: On the back plate 'Jas. Mc.Cabe Royal Exchange No 10254 LONDON'. On the enamel dial, in the upper half 'JAs. Mc.CABE Royal Exchange LONDON, 10254'. On the dust cover 'Jas. Mc.Cabe Royal Exchange LONDON 10254'.
Dial and hands: Flat enamel dial with subsidiary seconds attached to the dial plate by three short feet and pins. The hands missing.
Ebauche marks punched under the dial on the front plate, on the inside of the back plate and on the underside of the barrel bridge I.M.C. 10254. Also on the back plate under the setting-up ratchet 0 1.61.
Dial plate diam. 47.0mm; front plate diam. 44.1 mm; back plate diam. 41.9 mm; frame h. 8.0 mm.
Frame: Full plate construction with detachable barrel bridge, four turned pillars, the back plate retained by pins. The dial plate secured to the front plate by three pillars and pins, and carrying the movement hinge. The case catch and spring mounted on the front plate under the dial. A well-fitting dust cover, cut away from the table of the balance cock, secured by a clip to two pillars on the back plate, marker's mark R.E. All brass parts gilded. On the balance cock four arrows and a cross superimposed.
Fusee: Keywind fusee fitted with continental stop-work, and the usual Harrison's maintaining power. The maintaining ratchet wheel brass. The setting-up-work fitted on the front plate under the dial, the barrel arbor with an extended square on that end only.
Going train: Well made and finished, the brass wheels gilded. The centre arbor and fourth lower pivot broken.
Jewelling: The fourth arbor lower pivot in a pierced jewel, the pivots of the escapement arbors in pierced jewels with endstones, a diamond endstone in a wide blued steel ring in the balance cock. All the jewelling in screwed settings.
Escapement: A development of Earnshaw's spring detent escapement. The brass escape wheel with rim and arms below the level of the teeth. The impulse roller not jewelled but with a radial impulse face formed in a similar way to that of Earnshaw's (cf. cat. no. 63). All the surfaces polished except the top. The usual polished steel jewelled discharge roller without an adjusting flat. The detent screwed to the side of a gilded brass block with integral banking, dovetailed into the back plate and secured by a single screw. The detent planted well inside a tangent to the locked tooth so that both detent and passing spring are straight. The locking stone of half-round section, the spring part of the detent about 0015 mm thick, and showing no sign of buckling, twisting or other strain. The gold passing spring secured by a screw.
Balance: Bimetallic two-armed balance, the rims cut through unusually far from the arms. Brass compensation and quarter screws. The balance riveted on a brass collet on the balance staff. Diam. 23.5 mm, h. 2.07 mm.
Balance spring: Blued steel spiral spring of 8 open coils, free sprung to a brass stud held in a slot under a polished steel plate on the balance cock. The brass stud with two pin holes. A round brass collet on the balance cock. Steel regulator.
Centre pinion 12 leaves, wheel 64 teeth, no crossings
Third pinion 8 leaves, wheel 60 teeth, 6 arms
Fourth pinion 8 leaves, wheel 70 teeth, 6 arms
Escape pinion 7 leaves, wheel 15 teeth, 3 arms
Beats per hour: 18,000
Cannon pinion 12 leaves, brass minute pinion 14 leaves
Hour wheel 42 teeth, minute wheel 48 teeth.
Provenance: Ilbert Collection, purchased by Ilbert in 1946.
- Not on display
Latest: 3 (2017)
3 (Oct 1995) Hands and second hand arbour 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.1607 (Ilbert Collection)
Previous owner/ex-collection number: Q120 (Ilbert Ledger)