- Museum number
- 1958,1201.3053
- Description
-
SUBSIDIARY SECONDS POCKET-CHRONOMETER BAR MOVEMENT WITH PIVOTED DETENT ESCAPEMENT AND UP-AND-DOWN INDICATION.
Chronometer watch.
Pivoted detent escapement; fusee keyless; large semi-circular up and down scale.
Enamel dial.
- Production date
- 1880-1900
- Dimensions
-
Diameter: 46.30 millimetres
-
Thickness: 14 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Maker Unknown, but Swiss, Late 19th century
Chronometer movement
Dials and hands: Flat enamel canister dial with sunk subsidiary seconds, with a single positioning peg. Up-and-down indicator concentric with the centre and registering over a graduated sector in the upper half of the dial, with thirty large divisions. The intermediate divisions, and the words 'Haut' and 'Bas' written in red enamel.
Only the up-and-down indicator hand of blued steel remaining.
Movement:
Ebauche marks 26096.
Front plate diam. 45.7 mm; frame h. 9.0 mm.
Frame: Built up on the front plate, and made of nickel silver. The movement was positioned by two pegs in the edge of the front plate, and two dog screws.
Fusee: Reversed fusee fitted with Harrison's maintaining power, the maintaining ratchet wheel of steel. Geneva stop-work fitted on the dial side of the front plate. Setting-up-work on the bridge over the barrel, the ratchet wheel with a spring ratchet, the barrel arbor with an extended square on that end only. The barrel with a flange on the opposite end to the cover.
Keyless work: The winding stem carries a crown and a castle wheel as in Swiss push-piece hand-set keyless work. The crown wheel is in permanent mesh with a steel wheel pivoted on a plate able to rock about a stout steel pillar in the front plate. On pressing a push-piece integral with the rocking plate, the latter turns and is then held by a spring operated catch, with the steel winding wheel in mesh with a larger steel wheel squared to the fusee arbor. Turning the winding button then winds the mainspring. A peg carried on the Maltese cross of the stop-work releases the catch holding the rocking plate when the mainspring is fully wound. Another push-piece would be provided in the band of the case to operate on the return spring of the castle wheel, causing this to slide and engage with the intermediate hand-set wheel for setting the hands.
Going train: Conventional train and layout, but with the addition of an extra pinion meshing with the third wheel, having an extended pivot carrying the seconds hand. A light friction spring bears on the arbor to take up the backlash in the gearing. The brass wheels gilded, the steel pinions and arbors well finished and polished.
Jewelling: The centre upper pivot and those of the rest of the going train and escapement in pierced jewels, those of the escapement with endstones. The maintaining detent pivots most unusually also in pierced jewels. All the visible jewels at the back of the movement in gold settings and fixed in recesses with polished steel screws.
Escapement: Pivoted detent escapement, the gilded brass escape wheel very lightly crossed out with the arms sunk below the level of the rim and teeth. The detent returned by a spiral spring and locking on the second tooth after the one which has just given impulse. Banking by the lower end of the locking stone against the edge of a hole in the escapement subplate. The locking stone missing. A gold passing spring held by a single screw to the detent near the arbor boss. The polished steel impulse roller with a jewel set with its impulse surface radial to the centre. The polished steel discharge roller jewelled with a flat slip of ruby, and having two notches for adjusting the escapement.
Balance: Two-armed double-sunk bimetallic balance (see Charles Nephew, registration no. 1958,1201.1610 for a similar one). Gold compensation screws. Diam. of rim 15.0 mm, h. 15.5 mm.
Balance spring: Blued steel helical spring of 9½ turns, with a terminal curve at the lower end only, pinned to a stud clamped under a polished steel plate on the balance cock and to a wedge-shaped nickel collet. An index is fitted to the balance cock.
Amplitude limiting device: A pin set vertically in one balance arm passes at each swing through the slot in a block pointing vertically downwards from the underside of the balance cock. A piece of shaped brass wire attached to a small block pinned to the uppermost coil of the balance spring moves to close the gap in the block when the balance arc reaches just less than a turn in either direction.
Going-train counts:
Great wheel (fusee) 76 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
There is an extra fourth pinion of 10 leaves carrying the seconds hand on its extended lower pivot.
Motion work:
Cannon pinion 12 leaves, minute pinion 10 leaves
Hour wheel missing but would have had 40 teeth, minute wheel 36 teeth
Keyless work:
Crown wheel 17 spur, 10 ratchet teeth
Castle wheel 14 contrate and 10 ratchet teeth
Intermediate winding wheel 36 teeth
Winding wheel on the fusee arbor 45 teeth
First intermediate hand-set wheel 35 teeth
Second intermediate hand-set wheel 16 teeth
Up-and-down work: Pinion on the fusee arbor 15 leaves, meshing with a wheel of 120 teeth turning free on the hour wheel pipe and carrying the indicating hand. A long semicircular cut out in the up-and-down wheel through which the pipe on the minute pinion extends serves no apparent purpose.
Note: This movement resembles that of registration no. 1958,1201.1138.
Provenance: Ilbert Collection; purchased by Ilbert from J. W. Benson in 1935.
- Location
- Not on display
- Condition
-
Latest: 3 (2017)
-
3 (Oct 1995) Hour, minute and seconds hands missing. Balance-pivot broken. Escape-wheel pivot broken.
- Acquisition date
- 1958
- 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.
- Department
- Britain, Europe and Prehistory
- Registration number
- 1958,1201.3053
- Additional IDs
-
Previous owner/ex-collection number: CAI.3053 (Ilbert Collection)
-
Previous owner/ex-collection number: N283 (Ilbert Ledger)
