- Museum number
SUBSIDIARY SECONDS POCKET-CHRONOMETER MOVEMENT WITH SPRING DETENT ESCAPEMENT AND DUST-CAP.
Arnold spring detent escapement.
- Production date
Diameter: 47.50 millimetres (dial)
Diameter: 45.60 millimetres (dust-cap)
Thickness: 19.90 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Thomas Percival, 1802-8
Signature: On the back plate 'Thos. Percival London No 815'; repeated on the dial.
Dial and hands: Flat enamel dial signed THOS PERCIVAL LONDON 815, probably later, attached to the dial plate by three feet and pins.
Brass minute and hour hands, not original. Blued steel seconds hand.
Dial plate diameter 47.5 mm; front plate diam. 45.2 mm; back plate diam. 42.8 mm; frame h. 8.7 mm.
Frame: Full plate construction with four turned pillars, the back plate retained by pins. The escape wheel arbor lower bearing carried in a cock on the dial side of the front plate. A small plate screwed to the front plate on the inside under the barrel, to act as a chain guard. The dial plate with the movement hinge attached by screws, fixed to the front plate by four feet and pins. Repair marks on the dial plate: 'W. Hislop 1880 Ea Matthews 1918 Collin 1811' or possibly 1818. The case catch and spring on the front plate under the dial. The dust cover pierced for the balance cock table and overhanging part of the stud, held by a polished steel clip to two studs on the back plate. All the brass parts gilded.
Fusee: Keywind fusee with the usual stop-work and maintaining power, the maintaining ratchet wheel brass. The setting-up-work on the front plate under the dial, the barrel arbor with an extended square on that end only.
Going train: Well made and finished but unusual in the train count and the third and fourth wheels having six arms for what is apparently so early a watch.
Jewelling: The pivots of the fusee, the lower centre, third, fourth and escapement arbors in jewelled holes, those of the escapement with endstones. The pierced jewels have adequate oil sinks, the endstone jewels are flat, except the diamond set in a polished steel ring on the balance cock.
Escapement: Arnold spring detent escapement with solid, blue-white, sapphire impulse roller. The steel discharge roller integral with the steel boss for the balance has the unlocking jewel crossing the centre and dovetailed in place. The detent jewelled with a piece of jewel having the locking side straight, the back sloping and the slot dovetailed to take the jewel. A steel passing spring held by two rivets. The escape wheel of steel with all surfaces polished except the sunk portions of the rim and arms. Some marking has occurred on the impulse surfaces of the teeth where they contact the corner of the impulse face of the roller. The escapement as set has only a moderate amount of drop-on.
Balance: Similar to John Arnold's 'oz' balance, built up on a three-armed gilded brass wheel with attached bimetallic rims. The compensation nuts brass, the quarter screws steel. The wheel itself held with two screws on a steel boss on the balance staff. Diam. 22.0 mm, h. 2.0 mm.
Balance spring: Blued steel helical spring of 4½ turns, with terminal curves, free sprung to an adjustable stud overhanging the balance and screwed to the back plate. The brass collet drilled with a poising hole on the same side as the pinning and with an extended boss at the balance staff.
Great wheel (fusee) 54 teeth
Centre pinion 12 leaves, wheel 75 teeth, no crossings
Third pinion 10 leaves, wheel 64 teeth, 6 arms
Fourth pinion 8 leaves, wheel 65 teeth, 6 arms
Escape pinion 7 leaves, wheel 16 teeth, 4 arms
Beats per hour: 17,828 4/7
Cannon pinion 16 leaves, minute pinion 20 leaves
Hour wheel 60 teeth, minute wheel 64 teeth.
Provenance: Ilbert Collection, purchased by Ilbert from Benson in 1935.
Note: The layout and construction show a strong resemblance to the series of small chronometers made by the Arnolds, father and son.
- Not on display
Latest: 3 (2017)
4 (Oct 1995) Seconds hand 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.1744 (Ilbert Collection)
Previous owner/ex-collection number: N281 (Ilbert Ledger)