- Museum number
Full-plate; fusee; Harrison's maintaining power;
Arnold pivoted detent escapement; Arnold Z balance.
White enamel dial, hours I-XII, minutes 5-60, subsidiary seconds.
Blued steel hands.
Silver-gilt case, hallmark and maker's mark.
- Production date
- 1776 (case)
- Curator's comments
- Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by John Arnold, 1776
Signature: On the back plate 'John Arnold Invt et Fecit No 29'
Case: Silver-gilt consular case with fixed back, no dome and a swivelling pendant. London hallmark for 1776, maker's mark MR. The winding hole in the case back covered by a disc which can be moved aside for winding. Diam. 63.7 mm, h. 30.3 mm.
Dial and hands: Enamel dial, with hairline crack, inscribed JOHN ARNOLD LONDON.
Flat blued steel hands, minute hand boss squared and hand retained by screw.
Dial plate diam. 52.5 mm; front plate diam. 48.3 mm; back plate diam. 56.7 mm; frame h. 10.1 mm.
Frame: Separate dial plate with four short turned pillars pinned to front plate. Hinge attached to dial plate at 12 o'clock. Case catch opposite and mounted with its return spring on the inside of the front plate.
Various unused holes in the movement are either empty or plugged, the reasons for this now only a matter for conjecture. A square hole is cut in the front plate to clear the escape wheel potence table.
Scratched in fine cursive script on the front plate beneath the dial under the minute wheel: 'Repaired and improved by Haley, Wigmore St., Cavendish Square, London'.(1)
Fusee: Fitted with Harrison's maintaining power and fixed on its arbor by a steel plate which is friction tight on the arbor and not by the more usual transverse pin. Maintaining ratchet wheel steel. Maintaining ratchet spring a piece of wire friction tight in the top plate.
Jewelling: Third, fourth and detent arbor pivots in flat pierced jewels. Very small oil sinks. Balance and escape wheel pivots in domed jewels, with endstones set blind into brass end pieces. Locking pallet and discharged roller also jewelled.
Escapement: Pivoted detent escapement which appears to be original,(2) described and illustrated in the Introduction. Very light ungilded escape wheel. Detent and escape wheel planted between the back plate and separate potences. Balance not original - this was probably a plain balance without compensation with flat spiral steel spring. The compensation probably provided by a bimetallic curb fitted to the balance cock foot, as the two unfilled holes in the cock would seem to indicate.
Balance: The present balance was quite possibly put in by Arnold himself as he frequently updated his work. It is an early 'z' type with brass crossbar with a short integral T-piece at each end screwed to a bimetallic rim (perhaps silver and platinum) with a screw at the free end of each rim for adjusting the compensation.
Gold regulating screws with threaded holes pass through clearance holes in the rims and engage with threaded rods that are integral with brass pieces that in turn are screwed to the crossbar. Diam. of rim 21.0 mm, h. 0.85 mm.
Balance spring: Steel helical spring with 7 complete turns and terminal curve at each end. The upper end attached to an overhanging glided brass stud with round hole screwed to the back plate, this stud obscuring part of the engraving. Collet also brass, with a round hole for the pin.
Balance cock: Has a symmetrical foot. The screws for the jewelling now pass through the table of the cock and into tapped holes in a blued steel plate fitted to the underside of the table.
Train: Appears to be original. The third and fourth wheel teeth show signs of having been 'topped' to a more pointed tooth form.
Fusee great wheel 48 teeth
Centre pinion 12 leaves, wheel 75 teeth, no crossings
Third pinion 10 leaves, wheel 64 teeth, 4 arms
Fourth pinion 8 leaves, wheel 70 teeth, 4 arms
Escape pinion 7 leaves, wheel 15 teeth, 4 arms
Beats per hour: 18,000
Cannon pinion 16 leaves, minute pinion 20 leaves
Hour wheel 60 teeth, minute wheel 64 teeth
Provenance: Ilbert Collection; Ilbert purchased this chronometer from Christie's in 1933.
(1) Charles Haley is recorded in Baillie 1951 as working in Wigmore Street from 1781 to 1825 and Free of the Clockmakers' Company in 1781, whilst John Arnold was negotiating to be made Free. He was one of those called upon by the Commissioners of the Board of Longitude to examine John Arnold's description of his timekeepers and their mode of construction prior to publication.
(2) This watch was made at a time when John Arnold was constantly trying new ideas to improve his timekeepers and so could have been altered in the course of manufacture.
- Not on display
Latest: 5 (Jan 2019) glass dirty, clean and monitor for weeping. otherwise a 3
- 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.1838 (Ilbert Collection)
Previous owner/ex-collection number: N75 (Ilbert Ledger)