- Museum number
POCKET-CHRONOMETER MOVEMENT WITH SPRING DETENT ESCAPEMENT.
Spring detent escapement.
- Production date
- 1806 - 1807
Diameter: 42 millimetres (back-plate)
Diameter: 50 millimetres (dial)
Thickness: 18.20 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Thomas Earnshaw, 1807.(1)
Signature: On the back plate 'Thos Earnshaw Invt et Fecit 866' the 8 an upside down ampersand sign, the 6 partly obscured by a screw. On the barrel bridge 'London'. On the dial centrally below the XII 'THOS EARNSHAW INVT ET FECIT NO. 866.
Dials and hands: Enamel dial with slightly curved edge, similar to registration nos 1958,1201.1732; 1958,1201.1733 and 1958,1201.1592, chipped and cracked near XII. There is a faint circle on the dial passing through the minute dots, visible only with a strong lens.
Gold minute and hour hands, blued steel seconds hand with a long tail, riveted to its pipe.
Dial plate diam. 49.7 mm; front plate diam. 43.0 mm; back plate diam. 42.0 mm; frame h. 7.63 mm.
Frame: Similar to 1958,1201.1592, but the dial plate much wider than the front plate to accommodate the overlapping barrel. The hinge has been torn from the dial plate. Both frame and dial plate gilded but not much on the front plate under the dial. The steel parts hardened and tempered, and finished to the usual English standard. The balance potence with a moulding at the outer edge of the foot.
Fusee: Similar to 1958,1201.1592, the steel parts prepared and finished as for those of the frame.
Going train: The third and fourth wheels gilded, the arbors and pinion ends finished and polished.
Jewelling: Similar to 1958,1201.1592, but the endstone in the balance cock a piece of clear sapphire set in a blued steel ring.
Escapement: The brass escape wheel may well be a replacement as the teeth are not of the usual form. Instead they are narrow and stand almost radially off the rim of the wheel. The impulse and discharge rollers are similar to 1958,1201.1592. The original detent and brass arm removed and replaced by a detent with gold passing spring, jewelled and with solid foot, the retaining screw for this covering part of the last 6 of the engraved number on the back plate. The original holes for the two steady pins and screw for the brass arm are visible by the end of a pillar at the end of the signature.
Balance: Inverted bimetallic balance with two steel timing screws and brass segment weights, the steel part of the rims blued. The free movement of the rims limited by brass pegs in the segment weights going into holes in rings at the end of a thin steel cross arm on the balance. Diam. of rim 18.6 mm, h. 1.65 mm.
Balance spring: Flat blued steel spiral spring under the balance, free sprung without overcoil to a stud in the back plate by the third arbor pivot hole. The collet of brass.
Great wheel (fusee) 60 teeth
Centre pinion 12 leaves, wheel 64 teeth, no crossings
Third pinion 8 leaves, wheel 60 teeth, 4 arms
Fourth pinion 8 leaves, wheel 70 teeth, 4 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 from Benson in 1935.
(1) No. 867, which is similar, is in a silver pair case dated 1807 by the Chester hallmark on the inner case.
- Not on display
Latest: 3 (2017)
3 (Oct 1995) Dial chipped at 12.
- 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.1593 (Ilbert Collection)
Previous owner/ex-collection number: N284 (Ilbert Ledger)