Marine chronometer by Henri Robert

Description — British Museum

Marine chronometer; pivoted detent escapement; movement in brass bowl gimballed in mahogany box; winding key; flat silvered engraved brass dial; blued steel 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 Henri Robert, c. 1849 Marine Chronometer Signature: On the dial only 'HRI. Robert Paris 58' (the number within the seconds circle).(1) Box: The movement contained in a brass bowl with a friction-tight glazed bezel.… There was once an escutcheon plate with an eccentric winding hole on the bottom of the bowl. The movement is fitted into a very thick flanged ring the edges of which are turned to fit into the bowl and which is screwed to the bowl. This ring also takes the bezel. The bowl is gimballed in a mahogany box, the gimbal ring having adjustments to level the chronometer and with a lock in the near right-hand corner of the box. The box has a glazed panel in the top, with a hinged lid and catch, it also has a lock but no carrying handles. The winding key fits in a hole in a gusset in the near left-hand corner, and around the edge of the top of the lower half of the box is glued a strip of green baize to exclude dust. Base 169 mm square; sides 161 mm square; h. 178 mm. Dial and hands: Flat silvered engraved brass dial with a granular surface finish, the engraving filled with black wax. The chapter ring is not central with respect to the bezel. Hands of blued steel. Movement: Movement ring flange diam. 91.0mm (reduced to 84.0mm); overall ht. 23.2mm; dial and dial plate diam. 78.2mm; front plate diam. 78.2 mm; frame th. over barrel cock 34.4 mm. Frame: A most unusual construction in which the lower pivots of the going train run in the dial plate. The latter has three turned pillars passing into the front plate, held by pins. The dial is secured to the dial plate by two screws from the back and is hollowed out for the motion work; this is carried on a separate plate screwed to the inside. The barrel cock, balance cock and the other smaller cocks on the front plate are made of a red brass. Removal of the balance cock screw causes a steel rod carried on a springy steel arm to rise into the path of the escape wheel teeth thus locking the train. The balancers also protected by a stout pin set in the bezel ring. The movement is fitted into a thick turned ring of brass with the dial resting against a shoulder and secured by three eccentric brass plates each held with a shoulder screw on the front plate and passing into slots in the ring. There is also a positioning peg in the edge of the front plate and a corresponding slot in the ring. The visible brass parts are spotted. Going barrel: Fitted with an eight-turn Geneva stop-work on the cover end. The cover is prevented from rotating by a steel piece held with a screw so that it overlaps the edge and passes into a slot in the barrel wall. The barrel arbor has a snailed brass boss with a steel hook passing into it. The mainspring is hooked at its outer end to a small steel piece screwed and steady pinned to the barrel wall. There is also a bride. The spring is signed 'Bourquin Mars 1849' and is of exceptionally fine quality, beautifully blued and finished and with a slight taper, getting thinner towards the inner end. Going train: Well made, the pinions and arbors well finished and polished, the brass wheels circular grained. Jewelling: The pivots of the fourth and escape pinion arbors and balance staff in pierced jewels. Diamond endstones are used for the balance cock and the rear fourth bearings, and ruby for the rear escape pinion and the lower balance staff bearings. The detent pivots are run in holes in the brass, with a steel endpiece on the rear cock. Escapement: Pivoted detent escapement, the brass escape wheel with arms and rim sunk out on the underside and held with two screws on a brass collet. The detent with a spiral return spring, cylindrical locking stone with a ground locking surface, and banked by its tail against a brass peg set eccentrically in a screw head. The steel impulse roller with its edge and notch polished, secured by a single screw to a flange on the extended collet on which the balance is fixed. The impulse jewel is set leaning towards a radial to the tip. The steel discharge roller has two adjusting flats and a flat-sided jewel. Balance: Bimetallic two-armed balance with screws and segment weights, and quarter screws in brass pieces screwed to the inside of the rim and set above the level of the other screws. It is secured to a brass collet on the staff by two screws. Diam. 27.2 mm, h. 2.6 mm. Balance spring: Blued steel helical spring of 11¼ turns, with terminal curves, pinned to a rectangular steel collet, and clamped to a steel stud which is itself clamped under a steel plate on the end of the balance cock by two screws. Going-train counts: Great wheel (barrel) 112 teeth, 8 turn stop-work Centre pinion 16 leaves, wheel 96 teeth, 5 arms Third pinion 12 leaves, wheel 90 teeth, 5 arms Fourth pinion 12 leaves, wheel 90 teeth, 5 arms Escape pinion 12 leaves, wheel 15 teeth, 4 arms Beats per hour: 13,500 Motion work: Cannon 'pinion' 25 leaves, being a brass wheel on a steel cannon, minute pinion 10 leaves Hour wheel 60 teeth, minute wheel 50 teeth Provenance: Ilbert Collection; in his inventory notebook Ilbert records the acquisition of this chronometer in 1932 from Collen. Presented by Mr Gilbert Edgar C.B.E. in 1958. Note: (1) Henri Robert's dates, as recorded by Tardy 1971, are 1794-1874; an eminent maker, he published a number of papers on different aspects of Horology. Bibliography: M. J. Berlioz, 'Rapport sur d'horlogerie a l'exposition de 1878', Paris, 1878, 14 figs in pl. 1.