- Museum number
SUBSIDIARY SECONDS POCKET-CHRONOMETER MOVEMENT WITH PIVOTED DETENT ESCAPEMENT, UP-AND-DOWN INDICATION AND KEYLESS WINDING.
Pivoted chronometer detent escapement; up and down indicating mechanism unusual.
White enamel dial.
- Production date
Diameter: 12.20 millimetres
Diameter: 45.30 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Maker Unknown, probably Maisonette and therefore Swiss, c. 1905
Dial and hands: Flat enamel dial with the central portion and the subsidiary seconds sunk, attached by two feet passing into holes in the front plate, with screws accessible from the edge of the plate. A reserve of going indication in the upper part of the sunk central part of the dial. Blued steel hands.
Ebauche marks in a lozenge-shaped cartouche, FJ and G and elsewhere on the dial side of the front plate 5224 and 18.
Front plate diam. 45.3 mm; back plate diam. 43.0 mm; frame h. 8.7 mm.
Frame: A type of three-quarter plate construction, the back plate made from the solid and relieved on the underside to accommodate the mobiles, and secured by three screws and three steady pins. The movement was secured in its case by a single dog screw and a positioning peg in the edge of the front plate. All the brass parts electro-gilded a whitish colour. Marked on the top plate 'Chronometer No 48486'.
Going barrel and keyless work: A normal going barrel fitted with four-turn Geneva stop-work on the cover end. Typical Swiss sliding-pinion keyless work with hand-set operated by a touch-piece projecting from the edge of the front plate under the dial near the pendant.
Going train: Typical layout and construction, the brass wheels gilded like the frame, the steel pinions and arbors polished.
Jewelling: The rear centre pivot and those of the third, fourth and escapement arbors in pierced jewels, those of the balance staff with endstones. The train jewels on the back plate appear to be garnet. They are in base metal settings secured by screws.
Escapement: Pivoted detent escapement, the gilded brass escape wheel left the full thickness and locked by the second tooth after the one which has just given impulse. The detent set with a half-round locking jewel extending into a banking hole in the front plate. The gold passing spring held with a screw to the arbor boss and extending into a slot in the front plate behind the detent to act as the return spring. The detent horn formed at right angles to the detent itself, and holding the passing spring clear except of the locking stone boss (see registration no. 1958,1201.1750 for a similar arrangement). The impulse roller of polished steel, and set with an impulse pallet with its impulse face on a radial. The discharge roller a later replacement crudely made of steel. The detent planted with its pivoting axis well outside a tangent to the locked tooth, and lying on a centre line from the balance centre to the locked tooth.
Balance: Bimetallic two-armed balance with brass screws. Diam. of rim 15.5 mm, h. 1.38 mm.
Balance spring: Blued steel helical spring of 7½ turns, with terminal curves, pinned to a brass stud clamped under a steel plate on the balance cock and to a round brass collet. The index on the balance cock fitted with a fine adjustment for regulation, operated by a screw.
Up-and-down indicator: A planar differential is fitted between the barrel ratchet wheel A and a brass wheel fitted on the barrel cover B. A meshes with a steel wheel C pivoted on a shoulder screw, and itself meshing with a smaller steel wheel D on a main arbor passing through the frame. The front plate has a turned sink on the dial side to accommodate a brass wheel E in mesh with B. E pivots freely on the main arbor coming through from the back and is held, with a little shake, by a steel wheel F pushed tight on the main arbor. F meshes with another, G, mounted on a pinion H, turning on a shoulder screw, on the loose brass wheel E.
On turning the winding button to wind the watch, A turns to wind the spring, and turns with it C and D, and F on the other end of the main arbor, F then drives G carrying H which in turn drives J. J is a brass wheel mounted on a pinion K fitting freely on a cannon integral with F. K is in mesh with the large crossed out wheel L carrying the indicator hand and having a pivot passing into the front plate.
During the running of the watch B turns driving E. This results in G and H being carried round F and J with which they are in mesh. This differential motion causes J to turn the opposite way to winding so that K and L turn backwards also. The numbers of teeth are chosen so that one turn of A causes J to advance by one turn, which it will return on one turn of B.
The counts of the wheels are:
A is a steel wheel of 44 teeth
B is a brass wheel of 80 teeth
C is a steel wheel of 20 teeth
D is a steel wheel of 11 teeth
E is a brass wheel of 60 teeth
F is a steel wheel of 18 teeth
G is a steel wheel of 18 teeth
H is a steel pinion of 10 leaves
J is a brass wheel of 40 teeth
K is a steel pinion of 12 leaves
L is a brass wheel of 96 teeth
Great wheel (going barrel) 80 teeth
Centre pinion 10 leaves, wheel 80 teeth, 5 arms
Third pinion 10 leaves, wheel 75 teeth, 5 arms
Fourth pinion 10 leaves, wheel 70 teeth, 5 arms
Escape pinion 7 leaves, wheel 15 teeth, 4 arms
Beats per hour: 18,000
Cannon pinion 10 leaves, minute pinion 10 leaves
Hour wheel 40 teeth, minute wheel 30 teeth
Crown wheel 11 ratchet 20 spur teeth Castle wheel 11 ratchet 22 contrate teeth Intermediate winding wheel 41 spur teeth Intermediate hand set wheel 41 spur teeth
Provenance: Purchased 1972.
- Not on display
Latest: 3 (Nov 2018) intermediate wheel and screw from up and down work missing (cock is present).
5 (2017) active rust Intermediate wheel, screw and cock to up-and-down work missing.
5 (Oct 1995)
- Acquisition date
- Britain, Europe and Prehistory
- Registration number