- Museum number
GOLD PAIR-CASED SUBSIDIARY SECONDS POCKET-CHRONOMETER WITH PETO CROSS DETENT ESCAPEMENT.
Peto cross detent escapement.
Gold pair cases, 18-carat.
- Production date
Diameter: 48.20 millimetres (dial)
Diameter: 56.80 millimetres (outer case)
Thickness: 19.80 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Brockbank, 1800
Signature: On the barrel bridge in characteristic script 'Brockbanks' and 'LONDON' and 'No. 4302'. On the dial 'BROCKBANKS LONDON'.
Case: 18-carat gold pair cases with the London hallmark for 1800 and maker's mark T.C. surmounted by an axe (see registration no. 1958,1201.1733).
Dial and hands: Engine divided. Enamel dial (see registration no. 1958,1201.1589) slightly curved at the edge and fixed to the dial plate by short feet and pins. Roman hour, Arabic minute numerals, signed in the upper half 'BROCKBANKS LONDON' in small capitals, subsidiary seconds to 6 o'clock.
Flat red gold hand, the minute tapered, the hour with shaped and polished heart end, the seconds missing.
Dial plate diam. 46.9 mm; front plate diam. 43.5 mm; back plate diam. 40.9 mm; frame h. 6.2 mm.
Frame: Full plate with four turned pillars, the back plate secured by pins. Detachable barrel bridge. The movement hinge screwed to the dial plate, the case catch and spring on the front plate under the dial. No dust cover.
Fusee: Keywind fusee, with stop-work, and maintaining power with a steel ratchet wheel. The setting-up-work under the dial on the front plate. The maintaining detent and its return spring of polished steel screwed to the inside of the front plate. Barrel arbor with an extended square at both ends.
Going train: The fourth wheel has 68 teeth and drives an escape pinion of 7 leaves, giving the unusual number of 17,485 5/7 beats per hour.
Jewelling: Only the escapement pivots running in pierced jewels with endstones. A diamond endstone set in a blued steel ring on the balance cock.
Escapement: Peto cross detent escapement, the gilded brass escape wheel teeth have their leading edges almost on a radial from the wheel centre. Polished steel impulse roller, not jewelled, with the impulse surface leaning towards a radial from the centre. The usual jewelled discharge roller. Steel detent, the top of its foot polished, the rest left grey. Steel passing spring pinned in a square hole in a polished steel arm screwed to the underside of the top plate. A steel block, with an adjusting screw to move the passing spring towards or away from the balance staff by bending the steel arm, fixed to the balance potence foot (see registration no. 1958,1201.1723). The leading edges of the escape wheel teeth are marked, and the detent is worn where the passing spring has rubbed.
Balance: Plain gilded brass with four arms, and four steel screws set in the rim near the end of each arm. Diam. 20.5 mm, h. 1.25 mm.
Balance spring: Blued steel spiral spring of 7 turns and without any form of thermal compensation, pinned to an oval brass collet on the balance staff and a polished steel stud on the back plate. Polished steel index on the balance cock, its tail over a graduated scale.
Balance cock: with an engraved decoration.
Great wheel (fusee) 65 teeth
Centre pinion 10 leaves, wheel 64 teeth, no crossings
Third pinion 8 leaves, wheel 60 teeth, 4 arms
Fourth pinion 8 leaves, wheel 68 teeth, 4 arms
Escape pinion 7 leaves, wheel 15 teeth, 3 arms
Beats per hour: 17,485 5/7
Cannon pinion 12 leaves, minute pinion 14 leaves
Hour wheel 42 teeth, minute wheel 48 teeth
The polished steel minute pinion adjusted on to a brass tube on the minute wheel.
Provenance: Ilbert Collection; purchased by Ilbert from Malcolm Gardner in 1936.
- Not on display
Latest: 3 (2017) verdigris (green deposits) on outer case
2 (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.1722 (Ilbert Collection)
Previous owner/ex-collection number: P106 (Ilbert Ledger)