- Museum number
Detent escapement; regulator over dust-cap.
Enamel dial with subsidiary seconds.
Gold consular case.
The movement is retained in the case by two screws in the inner case rim. Removing these allows the movement to be lifted out. The dust cap is the retained by a further two screws in the dial plate edge. The cap cannot be removed when the movement is in the case.
- Production date
- 1778 (case)
Diameter: 37.40 millimetres (back plate)
Diameter: 50.20 millimetres (case (over glass))
Diameter: 41 millimetres (dial plate)
Diameter: 38.50 millimetres (front plate)
Height: 24 millimetres (case)
Thickness: 10 millimetres (movement)
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Josiah Emery, 1778
Signature: On the back plate 'Josiah Emery Charing Cross London 781'. On the dust cover 'Josh Emery Charing Cross, London, 781'. On the dial 'Josiah Emery London'.
Case: Gold consular case with the London hallmark for 1778 and an indistinct maker's mark possibly 'IM'. The case catch in the band of the case operates catches for both bezel and back. The book hinge has seven knuckles. Diam. 50.2 mm, h. over glass 24.0 mm.
The following inscription has been engraved on the inside of the back :
This CHRONOMETER, worn by the 2D & 3D DUKES-of -NORTHUMBERLAND was presented by ALGERNON the 4th DUKE to WILLIAM LAWS of PRUDHOE CASTLE, as a Mark of Respect and in remembrance of nearly 40 Years Service as BAILIFF & COMMISSIONER to three successive DUKES. April 1847.
Dial and hands: Enamel dial with curved edge, fixed to the dial plate by two short feet and pins.
Gold minute and hour hands, blued steel seconds hand.
Dial plate diam. 41.0 mm; front plate diam. 38.5 mm; back plate diam. 37.4 mm; frame h. 10.0 mm.
Frame: Similar to registration no. 1958,1201.806; note the shape of the bridge on the front plate carrying the fourth and escape bearings with a piece to protect the fourth wheel. The front plate has been recessed to allow room for the dial feet and pins in the thin dial plate. There is no provision for a movement hinge on the dial plate, the movement is retained in its case by two polished screws in the band of the case going into the edge of the dial plate. There is no evidence of any provision for a case catch and spring, but a balance stop mechanism (now missing), was operated by a push between 4 o'clock and 5 o'clock. The middle of the case has been prepared for a movement hinge, a piece of tube having been soldered in place but never used. The dial plate fixed to the front plate by three feet and pins.
Fusee: Keywind fusee with normal stop-work and maintaining power. The maintaining power ratchet wheel of brass. The shape of the foot of the maintaining detent return spring similar to that of registration no. 1958,1201.806. The setting-up-work on the inside of the front plate, the click and spring made from the solid, the spring tail now broken off. Compare with John Arnold registration no. 1958,1201.1838 and Emery registration no. 1958,1201.1645. The top of the barrel flanged and the lower end of the barrel reduced to clear the centre pinion. The great wheel most unusually the same size as the brass maintaining wheel.
Going train: Similar to registration no. 1958,1201.806, the great wheel with the unusual number of 51 teeth. The number of beats per hour is also remarkable: 18,102 and six sevenths.
Jewelling: All the pivots of the going train run in pierced jewels made from clear sapphire. Only the fourth upper has an obvious oil reservoir, the remainder are without. The pivots of the escape pinion arbor, the detent arbor and the balance staff run in pierced jewels with endstones. The endstones in the plates are set blind in brass plates, retained by screws. Those in the balance and detent potences are set in wedge-shaped pieces of brass. There is the correct gap in each case between the curved top of the pierced jewel and the bottom of the corresponding endstone.
Escapement: Pivoted detent escapement with polished steel escape wheel, the detent made in two parts, one a jewelled arm for locking the escape wheel and the other a triangular-shaped piece carrying the passing spring, made of blued steel. The lower pivot of the detent supported by a curious potence with a broad and engraved edge. The grained steel impulse roller with inset impulse jewel, the impulse face leaning slightly towards a radial from the roller centre to the tip. Three holes drilled in the impulse roller opposite the impulse jewel for poising. The discharge roller jewelled in the usual way. The return spring for the detent a leaf spring set in a separate block and with a screw to adjust the tension. The tail of the jewelled arm of the detent banking against another adjustable screw set in the detent potence.
Balance: Gilded brass three-armed balance with various notches filed in the underside of the rim for poising, no screws or weights. Diameter of rim 19.9 mm, h. 0.94 mm.
Balance spring: Blued steel helical balance spring of 6 turns without terminal curves. The lower end clamped to an elaborate poised brass collet on the balance staff, the upper end clamped to a stud overhanging the balance and screwed in a slot in the compensation framework. The stud consists of two pieces, one of gilded brass fixed to the top plate and the other a wedge-shaped steel piece running in a matching slot in the first piece.
Thermal compensation: One end of a steel index on the balance bridge is acted on by a coiled bimetallic strip.
At the other end of the index, brass pins embrace the upper coil of the balance spring. The index is retained by a blued steel plate and two screws. The coiled bimetallic strip is screwed inside a bridge, itself screwed to a framework mounted on the back plate, with a toothed sector engaged by a steel pinion with squared arbor. This arbor receives the regulation index whose boss passes through the dust cover on which is marked the scale against which the tail of the index registers for mean time regulation. This whole assembly with its engraved retaining bridge held by four screws on the back plate. It appears to have undergone a certain amount of modification as certain holes are now unfilled.
Great wheel (fusee) 51 teeth
Centre pinion 12 leaves, wheel 64 teeth, no crossings
Third pinion 8 leaves, wheel 60 teeth, 4 arms
Fourth pinion 8 leaves, wheel 66 teeth, 4 arms
Escape pinion 7 leaves, wheel 16 teeth, 4 arms
Beats per hour: 18,102 6/7
Cannon pinion 14 leaves, minute pinion 18 leaves
Hour wheel 54 teeth, minute wheel 56 teeth
The cannon pinion was retained by a pin through the end of the centre arbor which is now broken back to the hole.
Provenance: as the inscription in the case. Subsequently part of the collection of S.E. Prestige; purchased from the executors of the will of S.E. Prestige's widow.
- Not on display
- Latest: 2 (2017)
- Acquisition date
- Britain, Europe and Prehistory
- Registration number