- Museum number
SUBSIDIARY SECONDS POCKET-CHRONOMETER MOVEMENT WITH PIVOTED DETENT ESCAPEMENT.
- Production date
- 1856 (c.)
Diameter: 41.40 millimetres (back-plate)
Diameter: 45.70 millimetres (dial)
Thickness: 10.90 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 Pritchard, c. 1856
Signature: On back plate 'Thos Pritchard Liverpool N° 1859'. On the dial 'PRITCHARD'S PATENT CHRONOMETER LIVERPOOL' in the upper half.
Dials and hands: Flat enamel dial with subsidiary seconds having the centre sunk, secured to the front plate of the movement by three feet and pins.
White gold fleur-de-lis minute and hour hands, hour hand has a piece broken off, blued steel seconds hand.
Ebauche marks 18, 0.
Front plate diam. 458 mm; back plate diam. 41.8 mm; frame h. 7.0 mm.
Frame: Three-quarter plate construction with three turned pillars, the back plate retained by recessed blued steel screws. There was once a movement hinge attached to the dial side of the front plate, now missing, but no provision for a case catch. The movement retained in its case by two dog screws and two pegs set in the edge of the front plate.
Fusee: Keywind fusee with the usual stop-work and maintaining power, the maintaining ratchet wheel steel. The setting-up-work in a shallow recess on the front plate under the dial, the barrel arbor with an extended square on that end only.
Going train: The centre arbor drilled for the hand-set arbor which is integral with the cannon pinion and pinned to the hand-set square. The escape wheel is placed below its pinion instead of above and the fourth wheel higher than usual. The brass wheels burnished and not gilded, the steel pinions and arbors well finished and polished. The central bosses of the centre and third wheels and the underside of the great wheel with a frosted finish.
Jewelling: The pivots of the fourth arbor and those of the escapement in pierced jewels, only those of the balance with endstones. A diamond endstone set in a blued steel ring in the balance cock. The escape and pallet arbor jewels with curved faces against the pivot shoulders.
Escapement: A form of pivoted detent escapement, patented on 8 January 1856, No. 62, by H. Stuart and T. Pritchard. The brass escape wheel resembles that for an English ratchet-tooth lever escapement. On the arbor of the pivoted detent is a jewelled steel locking pallet, and above this a polished steel detent carrying the steel passing spring. The free end of the passing spring is banked against a pin at the balance end of the detent. There is no return spring for the detent but its tail is banked against a pin when the escape wheel is locked.
Immediately below the collet supporting the balance on its staff is a steel roller carrying a triangular-shaped ruby pin pointing downwards. The passing spring is in the path of this pin and is contacted by it for unlocking and passing action. Another pin stands upwards from a short continuation of the detent at the side of the balance staff. This provides safety action against the polished edge of the roller. A crescent-shaped notch in the roller allows the pin to move towards the detent during unlocking, and then returns the detent by the end of the notch striking the pin. A triangular-shaped steel pallet on the balance staff below the jewelled roller receives impulse from the escape wheel teeth. There is apparently either no draw at all, or else only a very slight amount between the escape wheel teeth and the detent locking pallet.(1)
Balance: Bimetallic two-armed balance with gold screws, unusually small in proportion to the rest of the movement. Diam. 17.5 mm, h. 1.1 mm.
Balance spring: Blued steel flat spiral spring of 8½ turns. A polished steel stud on the back plate, and index on the balance cock. The brass collet is round and split.
Great wheel (fusee) 74 teeth
Centre pinion 10 leaves, wheel 64 teeth, 5 arms
Third pinion 8 leaves, wheel 60 teeth, 5 arms
Fourth pinion 8 leaves, wheel 70 teeth, 5 arms
Escape pinion 7 leaves, wheel 15 teeth, 5 arms
Beats per hour: 18,000
Cannon pinion 12 leaves, minute pinion 10 leaves
Hour wheel 40 teeth, minute wheel 36 teeth
Provenance: Ilbert Collection; purchased by Ilbert from Malcolm Gardner in 1939.
(1) The small size of the balance and the strength of the mainspring suggest that the escapement has a low mechanical efficiency.
- Not on display
Latest: 3 (2017)
3 (Oct 1995) Hour hand 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.1746 (Ilbert Collection)
Previous owner/ex-collection number: Q14 (Ilbert Ledger)