Marine chronometer by Lego

Description — British Museum

Marine chronometer; constant force escapement; grained and lacquered brass case; flat enamel dial, subsidiary hours, minutes and seconds; blued steel moon hands.

Curator's comments — British Museum

Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990) Made by Lego, c. 1818 Marine Chronometer Signature: On the dial 'No 15 Inventé et fait par Lego à Lorient'.(1) Box: The movement contained in a grained and lacquered brass canister, the bottom weighted with a disc of brass,… offset, and a levelling weight of lead, and fitted with a bayonet catch in the bottom. The knurled flat glazed bezel fitting friction tight on the outside of the edge of the drum. The glass is drilled for winding through the dial. The canister is gimballed in a well-made wooden box. There is no provision for locking the gimbal ring and the key once fitting in a slot in the right-hand side panels of the box is missing. There is the usual lock, and a sliding panel in the top over a circular aperture. There are no carrying handles. Box base 158 mm square, h. 133.5 mm. Dial and hands: Flat enamel dial with subsidiary indications of hours and minutes and seconds, and with a hole for the squared winding-arbor, the dial with hair cracks. There are two rectangular-section dial feet with their ends passing into slots in the front plate, the dial is held by screws through the sides of the feet into brackets on the front plate. There is no dial plate. The back of the dial signed in the enamel 'Lucard'.(2) (See registration nos 1958,1201.1587; 1958,1201.1153; 1958,1201.1154 and 1958,1201.1928.) Blued steel moon hands. Movement Front plate diam. 76.5 mm; back plate diam. 71.2 mm; frame h. 18.0 mm; frame h. over the barrel bridge 30.9 mm. Frame: Built up on the front plate, two long turned pillars carry a bridge over the barrel. The going train arbors are pivoted in the front plate and in a detachable crescent-shaped bridge carried on three short turned pillars. The complete escapement and balance assembly is also planted on both sides of the crescent-shaped bridge. Going barrel: Very large compared with size of balance, wound through the dial, with the ratchet and click on the dial side of the front plate. The well-made mainspring hooked with an eye to a steel hook in the brass unsnailed boss of the arbor. The outer end solid hooked to a slot in the barrel wall. The mainspring signed 'Vincent Mai 1818 20 Francs'. There is a five-turn stop-work on the end of the barrel. Going train: The offset centre arbor drives the train in the usual way. The centre wheel meshes with a brass pinion driving a wheel turning once per hour and with the cannon pinion on its arbor. The pinions and arbors are well finished and polished, the brass wheels circular grained. The lower pivots of the third and fourth arbor are supported on steel friction rollers. Jewelling: All the pivots in the escapement run in pierced jewels except the detent locking the escape wheel. The balance bearings have endstones, a diamond in the balance bridge. The pivoted remontoire detent pivots have steel endplates. Escapement: A type of constant force escapement in which impulse to the balance is given by a helical spring via a pivoted impulse detent. The helical spring is then rewound by the escape wheel. This occurs at each alternate swing of the balance. The impulse detent is released at the correct moment so as to impulse correctly. A pivoted jewelled roller, carried on an arm on the impulse detent arbor, lands on a polished steel pallet on the balance staff to give this impulse. The impulse detent arbor carries a second smaller pivoted roller which releases the escape wheel via another pivoted detent at the end of impulse, so that the impulse detent can be rewound. This whole complicated system is most beautifully and carefully made and shows evidence of the greatest care, resource and skill in its construction. There is provision for altering the set up of the helical impulsing spring so as to adjust the amount of impulse, its fixed end is connected to an arm like an index, with a pointer moving over a scale. The principle of the mechanism is similar to that of Breguet as fitted in his No. 428, registration no. 1958,1201.2121, except that the escape wheel teeth are locked directly on a detent. In Breguet's mechanism the locking force is demultiplied by a wheel and fly, the latter being locked on a detent. Balance: Bimetallic four-armed balance with brass com¬pensation weights closely resembling that of Louis Berthoud as fitted in his No. 127, registration no. 1958,1201.1941. There are even tapped holes in the ends of the brass weights towards the free ends of the rim but no screws have been fitted. Note also the similar balance bridge with its bearing, and the balance spring stud. Diam. of rim 23.9 mm, h. 1.7 mm. Balance spring: Blued steel helical spring of 10½ turns clamped concentrically to both collet and stud, without terminal curves. The steel stud has three levelling screws and closely resembles that used by Louis Berthoud. Going-train counts: Great wheel (barrel) 84 teeth, 5 turn stop work Offset centre pinion 12 leaves, wheel 80 teeth, 4 arms Third pinion 10 leaves, wheel 75 teeth, 4 arms Fourth pinion 10 leaves, wheel 100 teeth, 4 arms Escape pinion 10 leaves, wheel 15 teeth, 4 arms Beats per hour: 18,000 A brass pinion of 30 leaves meshes with the centre wheel, and drives a wheel of 80 teeth, 4 arms, turning once per hour and carrying the motion work. Motion work: Cannon pinion 12 leaves, minute pinion 10 leaves Hour wheel 40 teeth, minute pinion 36 teeth Provenance: Ilbert Collection ; purchased from Clowes by Ilbert in 1939. Presented by Mr. Gilbert Edgar C.B.E. in 1958. Notes: (1) There is a port called Lorient on the coast of France, south of Brest on the Bay of Biscay. There is also a village in Switzerland called L'Orient in the Vallée de Joux, Canton of Vaud, an area that became famous for repeating and complicated watch manufacture in the nineteenth century. (2) Lucard is given in Tardy 1971 as Place de Thionville, 1806-1820. Bibliography: Bertele 1981, pp. 182, 183.