Marine chronometer no. 4489 by Abraham Louis Breguet & Fils

Catalogue description — Royal Museums Greenwich

Breguet, Paris, c.1827 No.4489 8 day marine chronometer in mahogany box For biographical details of the firm of Breguet of Paris, see pp.xxx Box/Mounting Two-tier, plain mahogany box measuring 218mm high, 262mm wide, and 235mm deep. The top of the box has an inset dovetailed mahogany removable slide, probably originally with a recess at the front for gripping with the finger, now missing. The slide can thus be drawn forward and taken off, revealing an open, 112mmØ aperture, through which the dial can be viewed. The slide has in the centre of the top, an inlaid diamond-shaped brass tablet, engraved: “No.4489”. The lock on the lower half, is of the French, double-throw type, with two bolts engaging with two pins, and has an oval, brass escutcheon on the front. The box has a pair of plain hinges and a brass strut on the left hand side, restraining the upper half to 90°opening. There is a raised step running around the inside of the junction on the lower half, mating with a rebate in the junction of the upper half and forming a dust seal when closed. The construction of the box is of the ‘lapped-mitre’ type, with the junction of the corners appearing on the sides of the box. There appears to have been a label pasted inside the back of the upper half at some stage in the past, only a shadow remaining. The box fittings are similar to the standard French type, with brass drop handles on the sides and brass gimbals with a narrow bezel, fixed with three brass side screws, having a flat, beveled glass over the dial with a concave brass sight ring and hole in the glass for winding, the hole, protected from dust with a knurled brass stopper. The oval-section gimbal ring, which has straight front and back with curved sides, is without any form of locking, and the outer gimbal pivots are steel screws screwed straight into the wooden side of the lower half of the box. The heavy brass bowl has a flat base and inside has a lead weight fixed on one side, to counterbalance the spring barrel when the movement is in place. Set into the top of the bowl is a brass edge, fixed with two brass side-screws, and into which the dial seats to support the movement within the bowl. Over this is fixed the bezel. Dial and hands The 128.4 mm Ø, engraved and wax-filled, French-silvered matt-finish dial is attached to the pillar plate of the movement with four feet, pinned to the plate, and the movement as a whole seats in the bowl with the edge of the dial in the brass edge, fixed down with four brass counter-sunk screws. The subsidiary hours and minutes dial has roman hour numerals and Arabic ten-seconds figures, with the winding hole to the left, engraved with an arrow to show the anti-clockwise direction of winding. The large seconds dial below has arabic ten second figures and straight batons at five-second intervals. The dial is signed across the centre: “Breguet et Fils - No.4489”. The back of the dial is scratched: “4489”, and: “Brosse 1837 Fevrier”. Polished and blued steel spade and poker hands with a fine, blued steel pointer seconds hand. Movement Full-plate, going barrel movement with four plain straight pillars pinned to the rear plate. The escapement is mounted on a separate platform, standing on the rear plate. A brass post stands next to the platform, protecting the balance from accidental damage should the movement be placed movement-down on the table. The wheels are all brass, the fourth wheel is run on a cock on the front of the pillar plate and the 2nd (‘centre’) wheel and third wheel are under cocks on the rear plate. There is a steel endplate under the fourth wheel pivot on the rear plate. The general level of finish of the movement is high with most movement parts flat-polished. The front of the pillar plate is stamped: “4489”. The pillar plate was drilled for the four dial feet about 10 degrees anti-clockwise from their present positions, all neatly plugged probably during construction.The going barrel has a single click and a finely cut brass ratchet wheel. Continental type stopwork on the barrel cap, the stop wheel having a friction spring inset on its underside. The underside of the ratchet wheel is stamped with one dot. The inside of the barrel is scratched:”4489”. There is a meshing inspection hole by the great / 2nd pivot in the pillar plate, and an enlarged opening for the 2nd / 3rd in the rear plate. All the pivot holes have been re-planted during construction, the 4th rear pivot possibly moved twice. Escapement, balance, spring and jewelling The ‘Navette’-shaped platform of the escapement is fixed with three screws and located with three brass steady-pins. One of the fixing screws, when unscrewed, releases a spring detent into engagement with the fourth wheel preventing a ‘runaway’ should there still be power on the train. The platform is stamped on its lower surface: “100”. The underside of the platform is recessed with a sink to allow room for the steel endplate for the fourth wheel. Breguet-type spring detent escapement, the spring detent with a single spring blade, mounted on a Breguet-type brass mounting block, with a cam banking piece on its end, to adjust the depth of the detent locking with a brass screw. There is a gold passing spring screwed to a steel block on the side of the detent, and running at about 5 degrees to the detent blade, crossing over the horn of the detent at the end. The detent has with a clear locking stone inset. The undersprung, two-arm bimetal balance has straight blued-steel arms and the bimetal rims are of Breguet’s platina alloy and steel. There are brass meantime nuts mounted on fixed threads at the end of the arms and smaller compensation nuts at 90° on the rims. There are also additional brass meantime nuts mounted on the rims just to one side of the balance arms (with an additional threaded hole alongside), and a series of 11 holes at the ends of the rim segments , hole 5 having an auxiliary compensation screw. The impulse roller has a steeply raked, pi