- Museum number
MINUTE-REPEATING POCKET-CHRONOMETER MOVEMENT WITH SPRING DETENT ESCAPEMENT AND UP-AND-DOWN INDICATION.
Minute-repeating chronometer watch.
Spring detent escapement; fusee-keyless; micrometer regulator; up and down indication; stop-start device acting on a pin on underside of a balance arm.
- Production date
Diameter: 49.90 millimetres
Thickness: 12.70 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. 1875
Signature: On the back plate 'Chas Frodsham 84 Strand London 02418'.
Case: No case, but was open face. The winding button and stem, winding pinion, the case springs and the two slides survive.
Dial and hands: The dial missing.
Dummy hour and minute hands. The up and down hand blued steel, the seconds hand missing.
Scratched on the front plate, under dial side 93079.
Front plate diam. 50.0 mm; back plate diam. 43.8 mm; frame h. 9.1 mm.
Frame: Three-quarter plate with five turned pillars, the back plate retained by blued steel screws whose threads do not correspond with those of registration no. 1958,1201.1599, otherwise a similar movement. The dial was retained by screws in the edge of the front plate and positioned by pegs pointing inwards from the edge into the recess in the front plate. The movement was retained in its case by two dog screws and a positioning peg. All the brass parts gilded. The escape cock has no less than four steady pins.
Fusee: Keyless fusee with normal stop-work and maintaining power, the maintaining ratchet wheel steel. The polished setting-up-work on the back plate with click spring, the barrel arbor squared at both ends.
Keyless work: Presumably a later addition after the back plate had been engraved as so much of the engraving is covered up by this complicated system. On turning the winding button in the direction of wind, the various steel wheels transmit the force to the largest steel wheel with a second set of upstanding triangular-shaped teeth. This particular wheel has a large central hole, and turns on an upstanding collar on the steel plate beneath it which is pivoted on a shoulder screw. It is held in place by the steel ratchet wheel mounted on the squared fusee arbor. These two wheels turn together and winding occurs. On reversing the direction of rotation of the winding button, the triangular-shaped teeth click over those of the ratchet wheel, the pivoted plate moving against a return spring to permit this.
To set the hands, two levers swing the pivoted plate with the largest wheel mounted on it against its return spring towards the centre of the movement. The triangular-shaped teeth are then completely disengaged from the ratchet wheel and those on the edge mesh with those of the central steel wheel. This wheel is on the end of an arbor passing through the hollow centre wheel and carrying the cannon pinion on the other end.
Up-and-down indicator: Also apparently an afterthought as it was added after gilding. A pinion on the end of the fusee arbor meshes with a six-armed wheel carrying the hand and pivoted on a stud, via two more pinions and another wheel. The surprise piece first has had to be modified to miss the arbor on which the two pinions are mounted, this has been quite crudely done by filing a piece out of it.
Jewelling: The pivots of the centre, third, fourth and escapement arbors in jewel holes with screwed settings, the escapement with endstones. The repeating runner pivots, without exception, in plain holes in the frame.
Escapement: Earnshaw detent escapement, with polished steel sunk escape wheel, the detent mounted on a lyre-shaped gilded brass frame carrying the banking screw and thus inaccessible without partially dismantling the movement. The polished steel impulse roller not jewelled, receiving impulse on a radial impulse face. The discharge roller jewelled, without a flat for adjusting. The detent foot is planted well inside a tangent to the locked tooth of the escape wheel. The detent with D-section locking stone and gold passing spring.
Balance: Bimetallic two-armed balance with gold compensation and quarter screws, except the last screw nearest the free end of each rim which is of platinum. One arm carries a pin pointing downwards and working with a balance stop device once operated by a slide in the band of the case. Diam. 17.5 mm, h. 1.54 mm.
Balance spring: A palladium spiral spring with overcoil and terminal curve to a steel stud on the balance cock. The collet of brass resembling a modern Swiss collet.
Index: With micrometer regulator and return spring, all of steel and finished to a very high degree. A pointed tool is used to turn the faceted head of the fine adjustment screw. A steel nut on the thread moves the index tail which moves over an index to make the watch go faster or slower as indicated on either side of the faceted nut.
Minute repeating work: Of Swiss design if not manufacture and of a type used by the firm of Le Coultre at Le Sentier and others. It is operated by a slide in the band of the case and the hammers strike on wire gongs. The repeating train wheels are gilded to a different colour to that of the other brass parts. The surprise piece acts on the minute flirt on the cannon pinion during the normal running of the watch and not only when the repeating work is operated as in later repeating work. This introduced a considerable and varying drag on the going train. In later repeating work the surprise piece only contacts the minute flirt when the repeating work is operated.
Going train counts:
Great wheel (fusee) 72 teeth
Centre pinion 12 leaves, wheel 80 teeth, 6 arms
Third pinion 10 leaves, wheel 75 teeth, 6 arms
Fourth pinion 10 leaves, wheel 80 teeth, 6 arms
Escape pinion 8 leaves, wheel 15 teeth, 3 arms
Beats per hour: 18,000
Cannon pinion 12 leaves, minute pinion 10 leaves
Hour wheel 40 teeth, minute wheel 36 teeth
The three pinions, 12 leaves each
The two wheels 30 and 72 teeth respectively, not gilded
First wheel 64 teeth, first pinion 8 leaves, the other 4 of 6 leaves each
Second wheel 40 teeth each, the last pinion carrying a small steel fly of diamond section
Third wheel 34 teeth
Fourth wheel 30 teeth
Fifth wheel 30 teeth
Provenance: Ilbert Collection; purchased by Ilbert from Malcolm Gardner in 1936.
Note: A keyless work similar to the one fitted to this movement is described in the 'Revue Chronometrique' 1876-7. It was manufactured by the Société Genevoise some time after 1868 following a competition for the design of a good medium quality watch 'of simple construction and mechanically sound, to be made available to a large number of purchasers and lending itself to bulk production'. Obviously simplicity is in the eye of the beholder!
- Not on display
Latest: 2 (2017)
3 (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.1598 (Ilbert Collection)
Previous owner/ex-collection number: P92 (Ilbert Ledger)