- Museum number
CENTRE-SECONDS POCKET-CHRONOMETER MOVEMENT WITH ROBIN TYPE LEVER ESCAPEMENT.
Pocket chronometer movement and dial.
3/4 plate; fusee; Harrison's maintaining power.
Robin-type chronometer escapement; compensation balance.
White enamel dial, hours I-XII, sunk centre, signed.
Gold hour and minute hands, steel centre seconds hand.
- Production date
Diameter: 42 millimetres (back-plate)
Diameter: 45.80 millimetres (dial)
Thickness: 10.60 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Arnold and Lewis, c. 1865
Movement with Robin Type Escapement
Signature: On the back plate 'Arnold and Lewis late Simmons 7 St. Anns Square Manchester. Patent Union Chronometer 3001'.
Dial and hands: Flat enamel dial pinned directly to the front plate, the centre recessed. Roman hour numerals and an inscription in the upper half Chronometer 3001 Arnold and Lewis Late Simmons Manchester. On the reverse the marks 01 and B (see registration nos 1958,1201.1828, 1958,1201.1832 and1958,1201.1829).
Gold minute and hour hands, steel sweep centre seconds hand.
Ebauche marks 16 2 H.F. and 3001 on the front plate under the dial, c embracing an o, 01 under the balance cock and c embracing an o under the cock on the plate (see registration nos 1958,1201.1829 and 1958,1201.1828). Front plate diam. 44.8mm; back plate diam. 42.1 mm; frame h. 8.2 mm.
Frame: Three-quarter plate with three turned pillars, the back plate secured by blued steel screws. No dial plate but a thick front plate recessed on the dial side, and with sinks turned on the other side to accommodate the going train wheels. The movement was secured in its case by a brass peg and a dog screw on the back plate.
Fusee: Keywind reversed fusee fitted with stop-work and maintaining power, the setting-up-work under the dial on the front plate. The maintaining ratchet wheel steel.
Going train: The brass wheels not gilded but finished by polishing or burnishing flat. The centre wheel offset, and hollow for the hand-set arbor carrying the steel wheel connecting with the motion work at the centre. The fourth wheel planted at the centre.
Jewelling: All the bearings of the going train jewelled as far as the centre wheel: escapement bearings with endstones, a ruby in the balance cock. A slotted ruby passing roller fitted on the balance staff. The pallets jewelled.
Escapement: Patent Union Chronometer. The escape wheel, with teeth in two planes like a duplex escape wheel, is mounted on its pinion so that the short resting teeth standing radially from the rim are in the same plane as a pair of pallets. These pallets are pivoted between the front plate and an adjustable cock to rock them towards or away from the escape wheel as in registration nos 1958,1201.1829; 1958,1201.1742 and 1958,1201.1828). Below the pallet frame and fixed to it is a pointed steel arm working between banking pins and intersecting the slotted ruby roller on the balance staff.
When trying to turn, the escape wheel is held by one of the pallets, whose faces are inclined to have negative draw so that the pallet frame in turn tries to rotate. It is prevented from doing so, and hence the escape wheel from turning, by the arm touching the ruby roller on the balance staff. When the balance returns clockwise, seen from the back, the passing roller allows the steel arm to pass from one side to the other. A resting escape tooth leaves one pallet and at once falls onto the other, the wheel hardly advancing. The steel arm at once returns against the balance staff where it is held while the balance continues clockwise and starts to return anti-clockwise. At an appropriate moment near the rest position of the balance and spring, the steel arm is again allowed to pass. As soon as the escape wheel is released one of the short teeth standing vertically on its rim contacts the jewelled pallet on the impulse roller and impulse is given. The escape wheel is then locked again on the first pallet.
Impulse is given at each anticlockwise swing of the balance. With a 14,400 train the sweep centre seconds hand advances by a half second jump.
This escapement is something of a composite of the duplex, the lever and the chronometer. Although it is not a detached escapement, since the steel arm is in rubbing contact with the passing roller, the pressure with which the arm rubs is less than in the duplex owing to the mechanical démultiplication.(1)
Balance: Bimetallic, gold quarter and compensation screws. Diam. 18.0 mm, h. 1.7 mm.
Balance spring: Blued steel helical spring, 7 complete turns with terminal curves at each end. The upper terminal curve pinned directly to a stud on the balance cock.
Great wheel (fusee) 70 teeth
Centre pinion 10 leaves, wheel 64 teeth, 5 arms
Third pinion 8 leaves, wheel 60 teeth, 5 arms
Fourth pinion 8 leaves, wheel 56 teeth, 5 arms
Escape pinion 7 leaves, wheel 15 teeth, 3 arms
Beats per hour: 14,400
Cannon pinion 36 teeth free on a hollow steel centre post, minute wheel 36 teeth
Driving wheel 36 teeth, friction tight on the end of the hand-set arbor running through the hollow offset centre pinion arbor
Hour wheel 72 teeth, minute pinion 6 leaves
Provenance: Ilbert Collection; purchased from Messrs Arnold and Lewis in 1931.
(1) The first patent, No. 2432, with dealing with an early form of this escapement was taken out by G. Morton in 1856. An improvement, Patent No. 233, was patented in 1859 by C. G. Kelvey and W. Holland. The patent for the final form of the Patent Union Chronometer escapement, No. 2184, was taken out in 1863, also by Kelvey and Holland.
- Not on display
Latest: 4 (2017)
4 (Oct 1995) Fusee chain broken.
- 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.1830 (Ilbert Collection)
Previous owner/ex-collection number: H72 (Ilbert Ledger)