Marine chronometer
Cope, London c.1829 No.741
2 day marine chronometer in brass bound mahogany box
Cope,……………
Box/Mounting
Three-tier brass-bound mahogany box measuring 160mm high, 173mm wide, and 164mm deep.
The lid has a hollow-corner lozenge lacquered-brass plate inlaid in the top, with brass butt- hinges, opening to 90° to reveal a glazed panel retained with narrow wooden beading. The front of the upper half has a brass push-button lid catch with inlaid brass 'petal' escutcheon, and a small circular ivory tablet, engraved : "↑ / COPE / 741 / TWO DAYS", below. The lock on the lower half has an inlaid brass 'hollow-corner' lozenge escutcheon. The box is of fine, concealed dovetailed construction at all four corners, and the upper half has plain hinges, originally opening right over, but now limited to 90° owing to a later brass strut inside on the right hand side. There would almost certainly have been a baize covering running round the upper edge of the lower half, and forming a dust seal when closed, but this is now missing. The inside of the lower box has been strengthened with two pieces of mahogany quadrant running down the left and right hand side (3 brass`screws each side), and the top of the lid has been secured with 8 brass screws on top.
The box fittings are of the standard layout. There are brass drop handles on the sides, the gimbal screws threaded into bevelled brass blocks on the outsides of the box. The narrow, quite close-fitting lacquered brass gimbal ring has an adjustable curved plate for supporting the front gimbal pivot and adjustable curved plates on the bowl for the fixing the front and back pivot blocks themselves. The cast brass bowl has a slightly off-centre swiveling shutter on ther base, the underside of the shutter scratched: "741". The upper part of the bowl sweeps out to a somewhat larger diameter, threaded for the bezel. Narrow brass screwed bezel (2 turns) with a short, flat side and narrow mouldings, with thin convex glass over the dial, and scratched:"71" on the underside. The winding key is no\longer present,. The underside of the box has a green baize covering.
Dial and hands
The 82.8 mm Ø, engraved and wax-filled, silvered-brass dial small counter-sunk screws at
III and IX o'clock, which fix it into a recess in the brass edge. The pillar plate of the movement seats in a deep recess on the other side of the brass edge, with a pin in the brass edge to locate it and two blued steel dog-screws retaining it. The brass edge then seats in the recess in the bowl, a pin at XII and a notch in the bowl orientating it correctly. The dial has roman hour numerals and the seconds dial, below the centre, has arabic ten-second figures with straight batons at alternate five-second intervals. An up and down dial below XII is marked in 8 hour intervals and has "UP" next to "0", "WIND" next to "24" and "Down" next to "48". The main dial is signed across the centre: "CHAs. JNo. COPE / Rathbone Place LONDON / NO. 741". In side the seconds dial is engraved "↑".The brass edge is scratched "741" and "Set up 10 teeth". Blued steel spade and poker-hands with a fine, blued steel pointer seconds hand with a counter-poised tail, and blued steel pointer up and down hand.
Movement
Full-plate fusee movement with four pillars with flanges and fins at either end and one fin in the lower middle, screwed to the potence plate with blued steel screws. The potence plate is engraved: "↑ / CHAs. JNo. COPE, Rathbone Place LONDON 741". The table of the balance cock is also engraved: "↑". The underside of the blued steel set up ratchet wheel is scratch-marked for position against a nick on the edge of the square, and it also has two triangular dots (polishing points?). The double-nose set-up click is in blued steel. There is a small drilled dot on the barrel bar by the ratchet wheel to mark set-up positions against a dot on the top surface of the wheel, and a one dot and a two dot set-up / isochronising marks on the underside of the pillar plate, corresponding with a dot on the end of the barrel arbor pivot. There is a polishing point on the inside of the maintaining power detent, and the inside of the potence plate, the train bar, the fusee bar and the undersides of the pillar plate, the barrel bar, the barrel, the balance cock foot, the potence, the maintaining power wheel and the great wheel, are marked with one dot. The great wheel is scratched "29/10/59" under the blued steel cap, and: "H A July 1856", "H A October 1859", "w e c", and "H J A / Cleaned 8 March 1864". The brass ratchet wheel is scratched: "741". The straight sided fusee pipe is dot-marked for position and the fusee cap is dot marked for the pin entry hole. The later, signed blued steel mainspring has a steel square hooking in the barrel. There is a five-wheel train including great wheel, the fusee with Harrison's maintaining power and with a straight-sided fusee pipe push-fitted to the square. The train wheels are brass with the third, fourth and escape wheels run on a bar on the pillar plate with the lower fusee pivot run on a separate bar. All train holes have been plugged and re-pitched from new, including the maintaining power detent.
Escapement, balance, spring and jewelling
Earnshaw-type spring detent escapement, the fine grey-finished foot detent with gold passing spring screwed to the side, and pink locking stone in a pipe. The detent banks against a gilt-brass banking piece, fixed alongside the detent and there is a small viewing/locking hole directly above, for viewing the dcepth of engagement of the locking stone, and possibly for blocking the train with a pin into the escape teeth. Bright, grey-finished impulse roller with polished edge and polished impulse face, and discharge roller with a light pink stone inset.
The standard, oversprung bimetal balance, has round brass compensation weights mounted on the rim segments at 90° to the arms. Brass mean time nuts are mounted on threads at the ends of the arms, and there are spare threaded holes on the small pieces of rim segment beyond the arms and also at the other ends of the rim segments, beyond the compensation weights. The bright steel helical balance spring has terminals on both ends, the upper terminal pinned to a brass pointer stud on the balance cock. The jewelling, is all in pink stones, except for clear stones for the fourth wheel and a facetted diamond in a blued steel setting in the balance cock, all otherwise mounted in brass settings. It extends to both pivots of the fourth wheel, and the escapement parts as mentioned.
Alterations/condition
The box is in sound and clean condition but with a number of slight knocks and scratches. The box has been rather heavily re-finished at some stage. The rosewood key-shelf and the green baize on the base are probably both later replacements. The brass furniture in general is well patinated, with a certain amount of old (probably not original) lacquer surviving.
The dial silvering is sound and clean.
The movement is in generally sound clean condition, though it was found to be thick with old, solidified oil. Several screws were seized solid in the holes and had to be oil-soaked to release. The detent has been roughly treated at some stage and the spring is somewhat bent, but still perfectly functional. The brass movement parts have some light finger-printing in places. The movement has only been very lightly cleaned, and has been re-oiled, during inspection. The upper turn of the fusee was evidently turned too thin and has broken away, the chain running into a rough groove on the last turn, but the fusee is still sound.
Commentary, Provenance, etc
Potence Plate Ø: 66.2
Pillar Plate Ø: 66.8
Plate distance: 15.8
Inside barrel Ø: 28.6
Arbor Ø: 8.8 steel, unsnailed.
Thickness: 0.30 - 0.24
Height: 14.0
(7 ¼ full turns output from barrel)
Set up: 18 teeth (31 teeth as found).
Signature: (?) "T Lan Se.r 10th 50 CF" (22cms from outer end)
TRAIN COUNT
Wheel / Pinion (+ext dia) Comment:
Fusee/Great: 90 / 33.0 No.of Turns: 8 (Chain 56.5cms, 141 links)
Ratchet: 30 / 14.0 Brass, 2 steel clicks
Maintaining Power: 120 / 31.6 Brass
Centre/2nd: 90/ 26.1 + 14 / 5.3 Solid wheel. Very finely finished pinion
Third: 80 / 21.0 + 12 / 3.6 5 tapered crossings "
Fourth: 80 / 17.8 + 10 / 2.8 " "
Escape: 13 / ap.11.0 + 8 / 2.0 3 curved crossings "
Balance Frequency: 15,600 vbs/ hr (130 beats per minute)
Hour: 54 / 18.9 Brass
Minute Wheel: 56 / 20.1 "
Minute Pinion: 18 / 5.6 Polished steel
Cannon: 14 / 5.5 "
Up & down pinion: 8 / 2.5 "
Up & down transmission wheel: 80 / 19.8 Brass
Up & down wheel: 80 / 19.7 "
Set up ratchet: 16 / 8.3 Blued steel + double nose click
Impulse pallet tip Ø: 6.0
Discharge pallet tip radius: 1.5
Detent length: 23.0
Balance Ø (length of arm): 25.5 Balance Mass (incl. b/spring & stud): 5.2g
Balance spring Ø: 10.5 Material: bright steel
Turns incl. terminals: 10 (c/w down)
Credit: National Maritime Museum, Greenwich, London