- Museum number
SUBSIDIARY SECONDS POCKET-CHRONOMETER MOVEMENT WITH TOURBILLON AND SPRING DETENT ESCAPEMENT.
Spring detent escapement, gold escape wheel.
Diameter: 46.80 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
Dial and hands: Flat enamel dial with sunk subsidiary seconds. The space between the hour markings decorated with a very faint pattern in the enamel based on a fleur de lis motif. The centre of the subsidiary seconds dial similarly decorated but with a geometrical design and bolder. The canister-type dial snapped into a nickel ring itself snapping onto the edge of the front plate, and with a single positioning peg.
Blued steel hands, the seconds hand purple.
Ebauche marks 20419
Front plate diam. 45.6 mm; back plate diam. 44.0 mm; frame h. 9.0 mm.
Frame: Three-quarter plate construction with three turned pillars, the back plate secured with recessed polished steel screws. A bridge on the recessed front plate under the dial carries the lower third and tourbillon arbor bearings. Top bearing in a cock, the jewel in a screwed gold setting. The tourbillon is protected by a chain guard between itself and the barrel. The movement was secured in its case by a peg in the edge of the front plate, and two dog screws accessible from under the dial. All the brass parts appear to have been electro-gilded a whitish colour.
Fusee: Keywind fusee fitted with Geneva stop-work on the dial side of the front plate and Harrison's maintaining power. The maintaining ratchet wheel steel. The fusee arbor upper pivot is run in a large bush protruding below the back plate and with a dust tube on the other end secured in a recess by three screws. Setting-up-work on the front plate under the dial, the barrel arbor with an extended square on that end only. A flange on the cover end of the barrel.
Going train: Laid out as for a one-minute tourbillon, but with the third arbor upper bearing in the back plate instead of a separate cock under the carriage. The centre pinion hollow for the squared hand-set arbor carrying the cannon pinion. The fourth pinion mounted on a boss screwed to the bottom of the carriage, and with an extended fourth pivot for the seconds hand. The steel pinions and arbors finished and polished to a fair standard, the brass wheels electro-gilded over a granular finish. The fixed fourth wheel secured by two screws and with two steady pins.
Jewelling: The upper pivot of the centre arbor and those of the third and carriage in pierced jewels in gold screwed settings. The escape arbor and balance staff pivots in pierced jewels with endstones.
Carriage: The lower frame member made of nickel and its cock made of nickel brass. The three pillars and the upper frame member made of polished steel. Each pillar having two screws at each end securing the frame members. The lower balance bearings fitted into the boss carrying the fourth pinion and secured to the lower frame member by three screws and two steady pins. The upper balance pierced jewel set in a brass ring held by two screws from the underside of the upper frame member. The endstone set in a steel boss secured by three screws and three steady pins. The finish on the steel parts is good but marred by many fine scratches, suggesting that these parts were not sufficiently hardened. Several of the screws are stripped, particularly where threaded into nickel brass. The carriage poised by virtue of the asymmetrical design of the lower frame member.
Escapement: A development of Earnshaw's spring detent escapement. The gold escape wheel very lightly made and with the arms and rim sunk below the level of the teeth. Locking occurs on the second tooth after the one which has just given impulse, an unusual feature of this type of escapement. The detent is planted with its foot at right angles to the spring so as to give the maximum effective length to the detent. The detent angle outside a tangent to the locked tooth, and there is only a small amount of draw. The ruby locking stone is of D-shaped section. The passing spring of gold is held with a screw, banking the detent with its head against a foot screwed to the lower carriage frame. The polished steel impulse roller has a jewel with its impulse face radial to the roller centre. The discharge roller is made from a solid piece of ruby.
Balance: Bimetallic two-armed balance, the arms of sage-leaf pattern, positioned midway in the rim. Gold screws and quarter nuts. Diam. of rim 14.2 mm, h. 14.0 mm.
Balance spring: Blued steel spiral spring of approximately 15 turns, with an overcoil and terminal curve having a reversed bend, free sprung to a self-aligning stud clamped under a polished steel plate with two screws, and a round brass collet.
Great wheel (fusee) 76 teeth
Centre pinion 12 leaves, wheel 80 teeth, 5 arms
Third pinion 10 leaves, wheel 90 teeth, 5 arms
Fourth pinion 12 leaves, wheel 70 teeth, no crossings
Escape pinion 7 leaves, wheel 15 teeth, 4 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 Bevan in 1937.
- Not on display
Latest: 3 (2017) minute hand loose
4 (Oct 1995)
- 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.3135 (Ilbert Collection)
Previous owner/ex-collection number: P203 (Ilbert Ledger)