- Museum number
ALUMINIUM GLAZED-BACK CASED SUBSIDIARY SECONDS POCKET-CHRONOMETER WITH SPRING DETENT ESCAPEMENT AND UP-AND-DOWN INDICATION.
Spring detent escapement; duo-in-uno balance spring.
Later aluminium case with glazed back, commissioned by Ilbert.
- Production date
Diameter: 43.40 millimetres (case)
Diameter: 39.20 millimetres (dial)
Thickness: 12.20 millimetres
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Charles Frodsham, c. 1880
Signature: On the back plate 'Chas Frodsham 84 Strand London 8645'. On the dial 'CHARLES FRODSHAM AD. F.m.s.z. 8645'.
Case: Later open face aluminium case, glazed on both sides. Originally cased as a half hunter.
Dial and hands: Enamel dial with sunk subsidiary seconds and up-and-down indicator secured directly to the front plate by three feet and pins.
Blued steel spade hands, the hour a double spade.
Ebauche marks R.D. (possibly Richard Doke) C.F., 12, 2°.
Front plate diam. 37.75 mm; back plate diam. 34.6 mm; frame h. 5.9 mm; front plate thickness 2.2 mm (reduced to 125 mm).
Frame: Unusually small half plate chronometer, with three turned pillars, the back plate retained by blued steel screws. The movement hinge and case catch mounted on the dial side of the front plate. A separate bridge on the front plate for the third, fourth and escapement bearings.
Fusee: Reversed fusee with integral stop-piece and return spring, and maintaining power, the maintaining ratchet wheel steel. The setting-up-work under the dial on the front plate, the barrel arbor squared on that end only. A pinion mounted on the reduced end of the fusee arbor pivot in the front plate drives the up-and-down work.
Going train: Similar to registration no. 1958,1201.1600, the centre pinion hollow for the hand-set arbor.
Jewelling: The lower centre arbor pivot, and those of the third, fourth and escapement arbors in pierced clear jewels. The upper fourth pivot and escapement with endstones, a diamond endstone in the balance cock.
Escapement: A development of the Earnshaw detent escapement. The brass escape wheel with arms and rim sunk below the level of the teeth in the upper side. The detent banked by a screw set in a short arm integral with a polished steel split ring set in a turned recess concentric with the balance jewel, and retained by a polished steel screw. The diminutive detent, just over 8 mm long, with polished foot, gold passing spring held by a screw, and round locking stone is planted with the foot well inside a tangent from the locked tooth. Polished steel impulse roller with radial impulse face not jewelled. Polished steel discharge roller without a flat for adjusting, jewelled in the usual way. Note that the axis of the detent is almost parallel with a vertical plane when the watch is pendant up. This refinement, also used by Victor Kullberg, reduces the effect of gravity on the escapement which produces positional errors.
Balance: Bimetallic two-armed balance with gold compensation screws, and quarter nuts on screws set in the rim. Diam. 15.5 mm, h. 1.58 mm.
Balance spring: Blued steel duo-in-uno with terminal curve to a polished steel stud, the spiral part of the spring pinned to a polished steel collet.
Great wheel (fusee) 72 teeth
Centre pinion 12 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, 3 arms
Beats per hour: 18,000
Cannon pinion 10 leaves, minute pinion 12 leaves
Hour wheel 36 teeth, minute wheel 40 teeth
Up-and-down work: The large wheel carrying the hand has 60 teeth, driven by a wheel of 30 teeth, driven by a pinion of 10 leaves.
Provenance: Ilbert Collection; purchased by Ilbert from Malcolm Gardner in 1932.
Note: It would be difficult to imagine any significant improvement to the proportions or finish of this movement which is still in mint condition. The escapement, balance and balance spring in particular can only be admired for their perfection.
- Not on display
Latest: 3 (2017)
2 (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.1833 (Ilbert Collection)
Previous owner/ex-collection number: M17 (Ilbert Ledger)