Marine chronometer Rectangular mahogany box, lined with green beize, with brass carrying handles at the sides. Hinged lid with glazed viewing aperture and sliding mahoganny cover. A key-operated lock at the front. There is an inserted plain ivory disc in the lid front. Silvered brass dial with Roman hours I-XII within a minutes circle. Subsidiary seconds dial above VI. Plain blued-steel hour, minute and seconds hands. Movement contained in a lacquered brass bowl. One-day spring-driven movement, with fusee and Harrison's maintaining power. Jewelled bearings for train wheels in screwed settings. Earnshaw spring-detent escapement with Earshaw split-bimetallic temperature compensation balance and free-sprung helical blued-steel balance spring.
- Made in: London (119 High Holborn)
- (Europe,British Isles,England,London)
- Height: 17.6 centimetres
- Width: 20.8 centimetres
- Depth: 20.8 centimetres
Inscription ContentThomas Earnshaw, No.509 Invent. et fecit
Inscription ContentLONDON No.2853
Inscription ContentThos. Earnshaw
INVT ET FECIT
Text from 'Clocks', by David Thompson, London, 2004, p. 132.
Marine chronometer no. 509
London, c. 1800
Height 17.6 cm, width 20.8 cm, depth 20.8 cm
John Arnold's rival in the protracted argument over who first invented the spring-detent escapement was Thomas Earnshaw. Born in Ashton-under-Lyne in 1749, Earnshaw served an apprenticeship in London which he completed in 1770; he then worked as a trade watch-finisher and escapement maker of extraordinary ability. In contrast to John Arnold, who had a somewhat privileged early career, Earnshaw came up the hard way. He married before he had finished his apprenticeship and within four years had three sons. By 1774 he was facing the debtors' prison and fled to Ireland, but in the end his conscience overcame him and he returned to the Fleet Prison in December 1774. By 1780 he had seemingly cleared his debts and was running a successful business which allowed him to concern himself with improvements to the pivoted detent escapement. From this work came his version of the spring-detent escapement. In May 1782, however, Arnold was granted a patent that included his version of the spring-detent escapement and it was not until February 1783 that Earnshaw's escapement received a patent in the name of Thomas Wright, who registered the design on Earnshaw's behalf.
An Earnshaw chronometer is simplicity itself with a movement comprised of a spring-barrel and fusee driving a four-wheel gear train and an escapement consisting of escape wheel, spring-detent, gold passing spring and jewelled impulse and discharge rollers. The operation of the escapement is controlled by a temperature-compensated balance with split rims on which are screwed two moveable weights which provide temperature compensation. The balance also has a helical blued-steel balance spring. The dial indicates hours, minutes and seconds and the whole machine is housed in a simple wooden box with gimbal mounts to keep it level irrespective of the motion of the ship.
This one-day chronometer, made in about 1800, is signed 'Thos Earnshaw Invt et Fecit No. 509 London No. 2853.During its illustrious history it served on a number of Royal Navy ships until June 1830 when it returned on HMS 'Hecla' with Captain J. Bolder after a period of seven years in service. In July 1830 it went to Robert Molyneux for cleaning and overhaul and was back at Greenwich ready for use again in November that same year. It was not issued to any ship until March 1831 when it was delivered to Devonport, where its rate was checked. In December ofthat year it went into service, along with a number of other chronometers, on HMS 'Beagle's' momentous voyage with Captain Robert Fitzroy and Charles Darwin.
Ilbert CollectionComment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990)
Made by Thomas Earnshaw, c. 1800
Signature: On the back plate 'Thos. Earnshaw Inv' et Fecit No 509'. On the barrel bridge 'London No 2853'. On the dial 'Thos Earnshaw INVT ET FECIT NO 509 ONE DAY'.
Box: Rectangular mahogany box with two brass carrying handles, locking lid with round glazed aperture in the top and mahogany sliding cover. The inside of the box lined with green baize, except for two triangular wooden (oak?) inserts to front right and rear left corners which have brass spring locking pieces screwed to them. The lid also has a brass slide which limits the opening to slightly more than vertical. One small empty hole in the front of the lower case. Ivory disc recess in the front of the top but with the engraved(?) disc now missing. The sliding cover is made from a darker mahogany veneer than the rest of the case and has been made from two pieces with different grain pattern. The underside of this cover is lined with dark purple leather. One key to lock, and one winding key. The corners of the base are dovetail jointed. Brass gimbal mountings carrying a brass canister which houses the movement. Sides 198 mm square, base 208 mm square, overall h. 176 mm.
Dial and hands: Silvered brass dial. Scratched on the back ' 509 ' and 'JB 2/6/86'. Dial attached to movement by two screws which pass through the front plate and screw into the back of the dial. One screw now missing.
Dial plate diam. 76.1 mm; dial plate th. 5.1 mm; front plate diam. 62.9 mm; back plate diam. 60.2 mm; frame h. 16.3 mm.
Frame: Similar to registration no. 1958,1201.1960 except that there is no dust-excluding tube for the winding arbor. The balance potence has a moulded edge to the foot.
Fusee: Similar to 1958,1201.1960. The maintaining detent is returned by a piece of steel wire set in a hole in the back plate and pointing down. The barrel is waisted at the closed end to miss the great wheel, and the rectangular hole for the original solid mainspring hooking has been carefully filled. The present mainspring, unsigned, is hooked by hook and eye at both ends.
Going train: Similar to 1958,1201.1960.
Jewelling: Similar to 1958,1201.1960, but without any separate bushes for the train pivots.
Escapement: Similar to 1958,1201.1960 but with a brass escape wheel of thirteen teeth, showing signs of marking on their acting faces. The discharge roller is smaller in proportion. The gold passing spring is pinned in a block on the side of the detent. The foot of the detent overlaps the edge of the back plate, and banking is against a steel screw.
Balance: Similar to 1958,1201.1960, riveted to a brass collet, but without the brass poising screws; the arms a different shape. The steel part of the bimetallic rim blued. Diam. of rim 28.0 mm, h. 2.8 mm.
Balance spring: Later closely coiled blued steel helical spring of 11 turns, with terminal curves, pinned to a brass collet, and stud on the balance cock.
Great wheel (fusee) 63 teeth, groove of 6¾ turns
Centre pinion 14 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 13 teeth, 4 arms
Beats per hour: 15,600
Cannon pinion 12 leaves, minute pinion 14 leaves, brass
Hour wheel 42 teeth, minute wheel 48 teeth.
Provenance: Ilbert Collection; in his inventory notebook Ilbert records the purchase of this chronometer in 1931 from Lilley & Son. Presented by Mr Gilbert Edgar C.B.E. in 1958.
Bibliography: Britten 1982, p. 222, pl. 139a and b.
Exhibited: 2015-2016 May-May, HOTW, tbc. PROMISED
2014-2015 Dec-Mar, HOTW, tbc. PROMISED
2014 Mar-Jun, HOTW, tbc. PROMISED
2010-2011, London, BM/BBC, 'A History of the World in 100 Objects'
2002 Dec 06-2004 Jan 25, London, National Maritime Museum, 'The Beagle Voyages: from Earth to Mars'
The Ilbert Collection of clocks, prints and other related material was destined to be sold at Christie's auction house on 6th-7th November 1958. As a result of the generous donation of funds by Gilbert Edgar CBE the sale was cancelled and the material purchased privately from the beneficiaries of the Ilbert Estate.NL1Ilbert's watches were then acquired with further funds from Gilbert Edgar CBE, public donations and government funds. These were then registered in the series 1958,1201.
Prehistory and Europe
- CAI.1957 (Ilbert Collection)
- L210 (Ilbert Ledger)
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Object reference number: MCC3194
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