- Museum number
SILVER-CASED SUBSIDIARY SECONDS POCKET-CHRONOMETER WITH PETO CROSS DETENT ESCAPEMENT.
Peto cross detent escapement; overbanking device.
Minute hand not original.
- Production date
Diameter: 69 millimetres (case)
Diameter: 60.40 millimetres (dial)
Thickness: 30.20 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, c. 1785
Signature: On the barrel bridge in characteristic script 'Brockbanks', and 'LONDON' and 'No 3834'
Case: Silver consular case with the London hallmark for 1781 and maker's mark J.D. The case appears to have been made before the movement, the latter with its cross detent escapement could not have been made before 1785. Diam. 68.8 mm, overall h. 29.0 mm.
Dial and hands: Flat enamel dial attached to the dial plate by short feet and pins. The rings and markings for minutes and seconds appear to have been marked directly on the dial with a diamond point without any prior marking. Steel hands, the minute hand a replacement.
Dial plate diam. 60.9 mm; front plate diam. 57.3 mm; back plate diam. 55.9 mm; frame h. 10.5 mm.
Frame: Similar to registration no. 1958,1201.1589.
Fusee: Keywind fusee with stop-work and maintaining power with a brass ratchet wheel. The setting-up-work of blued steel under the dial on the front plate. The maintaining detent and its return spring screwed to the inside of the front plate of blued steel. The barrel arbor with an extended square at both ends. Scratched on the dial plate 'Leah 1836-2'.
Jewelling: The pivots of the third, fourth and escapement arbors run in pierced jewels, the escapement with endstones. The third and fourth jewels on the back plate made of very large clear white sapphires and very well polished.
Escapement: Similar to registration nos 1958,1201.1722 and 1958,1201.1589. Peto cross detent escapement with very highly polished steel escape wheel, the leading edges of the teeth only slightly raked forward. Steel passing spring. The detent has been repaired by the substitution of a new foot and spring blade, crudely made and soldered to the original detent. The gilding on both sides of the back plate, particularly on the inside, has been damaged. The locking stone is a replacement made of steel. Usual jewelled and polished discharge roller. The steel impulse roller with only the edge polished and with a jewelled pallet leaning towards a radial to the tip, which has resulted in slight damage to the leading edges of the escape wheel teeth.
Balance: Similar to registration no. 1958,1201.1589 except that the brass segment weights are secured by steel screws only and that the pieces limiting the travel of the free ends (in both directions) of the bimetallic rims are integral with the arms. The steel stud on one of the arms that once acted with the amplitude limiting device still present. Diam. of rim 25.2 mm, h. 1.7 mm.
Balance spring: Blued-steel helical spring of 3½ turns with terminal curves, the upper one rather short and attached to a screwed block on the overhanging adjustable stud. The lower terminal curve pinned with a half-round pin to a poised steel collet. There was once an amplitude limiting device similar to that fitted to registration no. 1958,1201.1589 mounted on the barrel bridge, the holes for which are still visible, one filled with a small screw.
Balance cock: All the upper surfaces heavily engraved.
Great wheel (fusee) 80 teeth, badly worn
Centre pinion 16 leaves, wheel 90 teeth, no crossings
Third pinion 12 leaves, wheel 80 teeth, 6 arms
Fourth pinion 10 leaves, wheel 80 teeth, 6 arms
Escape pinion 8 leaves, wheel 15 teeth, 6 arms
Cannon pinion (snap on) 14 leaves, minute pinion 18 leaves
Hour wheel 54 teeth, minute wheel 56 teeth
The polished steel minute pinion on a tube on the minute wheel.
Provenance: Ilbert Collection, purchased by Ilbert from Malcolm Gardner in 1952.
Note: For another example of a marine chronometer by Brockbanks with a Peto cross detent see cat. no. 601 in the Collection of the Worshipful Company of Clockmakers. It is dated about 1785.
Bibliography: 'Catalogue of the Collection of the Worshipful Company of Clockmakers', London, 1975, p. 99.
- Not on display
Latest: 2 (2017)
2 (Oct 1995)
- 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.1723 (Ilbert Collection)
Previous owner/ex-collection number: Q206 (Ilbert Ledger)