- Museum number
Spring detent escapement; sugar-tong compensation curb.
Gold winding key attached to large diameter gold split-ring.
White watch-paper with printed coat of arms.
- Production date
- 1800 (case)
Diameter: 59.16 millimetres (watch-paper)
- Curator's comments
Text from 'Watches', by David Thompson, London, 2008, p. 104-105.
GOLD PAIR-CASED POCKET CHRONOMETER
SIGNED: 'Thos. Earnshaw, Invt et Fecit No. 506, London 2849'
"The Doctor [Nevil Maskeleyne] likewise told me, that Mr. Brookbank [John Brockbank] said the reason of my watches going better than his and Arnold's was that I had the advantage of them in being so nice a workman. Well then, as the Doctor knew that the plan they made their watches on, was mine; and as Brookbank acknowledged that I knew better how to execute them, surely then, this was a full acknowledgement from them of my superiority which Mr. Dalrymple so jeers and doubts. The Doctor was inclined to believe Brookbank's assertion, and questioned me much upon it, saying, that if my plan depended so much on very extraordinary workmanship, it would militate much against it, as it could not become generally useful. These observations of the Doctor's do not savour much of the early partiality, which Mr. Dalrymple says the Doctor had for me.
From the impression which Brookbank's observations had made on the Doctor, that "I had the advantage over him and Arnold, being myself so excellent a workman;" an observation which no watch-maker ever favoured them with, I resolved to take the most certain way possible of convincing the Doctor and the world, that my plans did not depend on the excellency and nicety of workmanship. Immediately I left out of my timekeepers every sort of fine workmanship; and when any one bespoke a timekeeper, I asked them what they wanted it for, well going or fine workmanship"
Thomas Earnshaw, 'Longitude. An Appeal to the Public . . .', 1808
Thomas Earnshaw made this pocket chronometer in 1800 as one of his 'well going' watches to prove that fine gilding and decoration were unnecessary for precision timekeeping and that fine finish was only necessary on the acting surfaces of the components.
The movement, signed 'Thos Earnshaw Inv et Fecit N°506, London 2849', has a spring detent escapement of Earnshaw's design, with a plain steel balance and the 'sugar tongs' form of temperature compensation. Here the action of the two bimetallic arms changes the position of the curb pins in relation to the balance spring to compensate for changes in the size of the balance and, more importantly, for changes in the elasticity of the balance spring caused by variations in temperature. The gold pair-cases were made by Thomas Carpenter of Islington Road, Clerkenwell, whose mark, 'TC' surmounted by an axe, is punched inside the case along with the London hallmarks for 1800-1.
This pocket chronometer was very likely the property of Charles George Perceval, 2nd Baron Arden (1756-1840).The outer case contains a printed paper bearing the shield of arms of the Barony of Arden in
Warwickshire and Lohort Castle in County Cork, Ireland: 'Argent on a Chief indented gules three crosses patte of the field', with the motto 'sub cruce Candida' beneath the white cross. Charles George Perceval was the son of John Perceval, 2nd Earl of Egmont, and Catherine Compton, created Baroness Arden of Lohort in 1770. In addition to being a Member of Parliament for Launceston, Charles George Perceval was a Lord of the
Admiralty, Commissioner for India Affairs and in 1804 was appointed Lord of the Bedchamber during King George III's illness. He also held office as Registrar of Court of Admiralty. In these offices he would have been well acquainted with Earnshaw's marine chronometers. As well as Lohort Castle in County Cork, Lord Arden also lived at Nork-House near Ewell in Surrey and in St James's Place in London. The watch passed by descent to the Right Honourable Frederick Joseph Trevelyan Perceval, 10th Earl of Egmont, and, following his death, was sold at Christie's on 12 July 1933, lot 40, where Courtenay Ilbert purchased it at a hammer price of 14 guineas.
Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Thomas Earnshaw, 1800
Signature: On the back plate 'Thos Earnshaw Inv' et Fecit No 506'. On the barrel bridge 'LONDON 2849'. On the dial 'THOMAS EARNSHAW INVT ET FECIT N° 506'.
Case: Gold pair cases both with the London hallmark for 1800 and the maker's mark T.C. with an axe above (cf. registration no. 1958,1201.1733). Outer case diam. 58.0 mm, h. 16.7 mm, inner case diam. 51.4 mm, h. 20.6 mm. In the case a watch paper bearing the arms of Charles George Perceval, Baron Arden (1756-1840).
Dial and hands: Enamel dial with slightly curved edge faintly signed on the back, in red in the enamel 'Earn 5'. Gold hands.
Dial plate diameter 47.7 mm; front plate diam. 42.9 mm; back plate diam. 41.5 mm; frame h. 7.5 mm.
Frame: Similar construction to 1958,1201.1733 but finished as 1958,1201.1592. The movement held in its case by one positioning pin and two screws through the side of the case into the gilded dial plate. The back plate retained by pins except the pillar near the regulator sector which has been shortened so as to be flush with the top of the plate and fitted with a screw. All the screws left grey and apparently not hardened and tempered. The dust-excluding tube missing, the retaining hole visible near the winding square.
Fusee: Similar to 1958,1201.1592, the barrel arbor with an extended square only on the end under the dial carrying the setting-up ratchet wheel.
Jewelling: Only the pivots of the escape pinion arbor and balance staff running in pierced jewels with endstones. The endstone in the balance cock a piece of ruby set in a steel ring. The endstone jewels curved on their outer surfaces.
Escapement: Original Earnshaw detent escapement similar to registration no. 1958,1201.1593. The detent locking stone is also of polished steel and is of small diameter and looks fragile. The brass escape wheel teeth show signs of wear.
Balance: Steel three-armed balance, polished on both sides, mounted on a brass collet on the balance staff. Diam. 25.5 mm, h. 0.57 mm.
Balance spring: Blued steel flat spiral spring of 7 open turns without overcoil or terminal curve fitted under the balance and pinned to a brass stud screwed to the back plate.
Compensation: Sugar tongs (see 1958,1201.1733).
Great wheel (fusee) 60 teeth, worn
Centre pinion 12 leaves, wheel 64 teeth, no crossings
Third pinion 8 leaves, wheel 60 teeth, 4 arms
Fourth pinion 8 leaves, wheel 70 teeth, 4 arms
Escape pinion 7 leaves, wheel 15 teeth, 3 arms
Beats per hour: 18,000
Cannon pinion 12 leaves, minute pinion 14 leaves
Hour wheel 42 teeth, minute wheel 48 teeth.
Provenance: Earl of Egmont, then Ilbert Collection, purchased by Ilbert at Christie's sale, 12 July, 1933, lot 4.
Note: This watch is in almost perfect mechanical condition, and is a good example of its kind with sugar tongs compensation. Although the working surfaces are well finished, the minimum of effort has been expended in finishing the rest of the movement.
- On display (G39/dc14/no55)
- Exhibition history
1998-1999 04 Dec-18 Apr, London, National Maritime Museum, Arnold & Earnshaw, Pioneers of the Chronometer
1992 4 Jun-8 Nov, Germany, Essen, Villa Hügel, London 1800-1838
- Latest: 3 (2016)
- 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.1731 (Ilbert Collection)
Previous owner/ex-collection number: N78 (Ilbert Ledger)