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Description: | John Roger Arnold, London c.1810 No.356
1 day marine chronometer in mahogany box
For notes on John Roger Arnold, see pp.xxx
Box/Mounting
Three-tier plain mahogany box measuring 179mm high, 185mm wide, and 178mm deep.
The plain mahogany lid has brass butt-hinges, opening the lid to 90� to reveal a glazed panel retained with narrow wooden beading. The inside of the lid has pasted in a label for chronometer maker James Pyott, and the glass has pasted ona cutting from an auction catalogue, the en try reading: ?An Old English ship?s chronometer, taken by Sir William Parry upon his Arctic expedition in 1818?. The front of the upper half has a push button brass lid catch and the lock on the lower half has an inlaid narrow, diamond-shaped ebony escutcheon. The box is of fine, visible dovetailed construction at all four corners, and opens right over, the upper half resting on the table level with the lower half. There is a coarse green baize lining covering the whole of the inside of the box, including half the upper and lower edges of the opening, forming a dust seal when the box is closed.
The box fittings are standard, with brass drop handles on the sides, the gimbal screws threaded directly into the wood of the sides with domed washers behind. The square-section lacquered brass gimbal ring supports a straight-sided brass bowl (tube with base soldered in), with poising weight inside (moved round once), and which has a small circular brass winding shutter off-centre on the flat base, and a narrow, moulded, brass bayonet-fitting bezel (3 prongs and 1 internal peg to stop bezel at correct position), with holes for securing bezel with two screws at 1 o?clock and 7 o?clock positions (screws now missing), the holes running right through the bezel, bowl edge, and into the edge of the dial. There is a thin convex glass over the dial. The shelf for the winding key is at the rear left corner, and the gimbal lock, on the front right hand side in the box consists of a small curved brass swiveling bar mounted on the gimbal ring and locating simultaneously in slots in a brass piece on the bowl and under a thumb screw, mounted on a triangular brass plate in the corner of the box. The underside of the box has a green baize covering.
Dial and hands
The 80.3 mm �, engraved and wax-filled, silvered-brass dial has four small riveted feet which fix to the pillar plate with pins and the dial itself seats in the recess in the bowl, a notch at XII and a pin in the bowl orientating it correctly.. The dial has roman hour numerals and there is a large seconds dial at VI o?clock having Arabic ten-second figures with straight batons at alternate five-second intervals. The dial is signed below XII: ?Arnold / LONDON?, and ?356? in the seconds dial. The dial has ?356? scratched on the back, and has a ?knocking out? on the back, near the centre, where a casting fault has needed erasing on the front. Blued steel spade and poker-hands, the minute hand probably an early replacement and now a push fit on the square of the cannon pinion, though the square has a dimple for an Arnold-type minute hand with a side-screw. Fine, blued steel pointer seconds hand with polished steel slotted centre and a counter-poised tail.
Movement
Full-plate going barrel movement with four pillars with flanges and fins at either end and one fin in the lower middle, pinned to the potence plate. The pinned, blued steel ratchet wheel (dot marked for position on its underside) is mounted directly on the potence plate, which does not have a barrel bridge. The potence plate is engraved on its upper surface: ?John R Arnold London Inv.t. et. Fecit. No.356?. The outside of the pillar plate, and the inside of the potence plate, the potence foot, the train bar, the third and the fourth wheels, are all marked with one dot and one short, scribed line. The underside of the barrel is scratched: ?Arnold Dent? and the underside of the potence foot is scratched: ?356?. The going barrel has a rim of teeth sweated onto the barrel, and has the cap, which is dot-marked for position, arranged to be upper most when the chronometer is in use, retaining the oil. The other end of the barrel has steel 5-turn stop work inset in sinks, the 1-tooth indexing piece on the square also forming the steel bearing for the arbor. The square is cross-drilled for a pin for the stop-finger (now plugged) and for the ratchet wheel and the pipe. The later, signed blued steel mainspring has an outer hole, hooking on a round hook in the barrel wall. There is a five-wheel train including great wheel. The train wheels are brass with the third, fourth and escape wheels run on a bar on the pillar plate. All train holes have been plugged and re-pitched from new. There is a small hole in the pillar plate opposite the balance centre.
Escapement, balance, spring and jewelling
The Earnshaw-type spring detent escapement is a later replacement of the original Arnold-type. It has a foot detent fitted to the potence plate and banking on a brass block with a brass screw (there is a large plugged hole under the foot of the banking block, perhaps for an aborted earlier banking). The grey-finished detent has a gold passing spring screwed alongside the detent blade, and a pink jeweled, D-section locking stone mounted in a pipe on the detent. The impulse roller has a clear radial impulse jewel and the discharge roller also has a clear stone inset.
The Arnold-type bimetal undersprung balance, has very slightly tapered brass arms, the bimetal rim segments of Arnold?s type, with his special ?platina? alloy on the outside, in conjunction with steel. The rim segments extend just beyond 90� and have brass compensation nuts mounted on the curved threaded ends of the rims, and a small brass screw just behind these, in the rim. There are brass meantime screws attached at the end of the arms and short threaded extensions to the rims on the other side of the arms, now with no weights attached. The flat-section, blued steel helical balance spring, which is probably a later replacement, has terminals on both ends, the lower terminal with a brass stud with an elongated slot, fixed with a steel plate and two screws onto a small brass plate screwed to the potence plate (slight tendency to lift balance as stud is fixed, a la Arnold?s design). There is a large threaded hole nearby which may have been for fixing an earlier stud plate. The jewelling, which is all in clear or light pink stones mounted in brass settings (upper balance pivot on a later faceted diamond endstone in the cock), extends to the balance and escape wheel with endstones and the lower fourth wheel, and the escapement parts as mentioned.
Alterations/condition
The box is in sound and clean condition with a few knocks and dents, but the whole surface has been covered with a dark red, ?treacly? varnish. The lock screws have penetrated to the outside of the box at some stage. The baize lining of the box is probably a later addition, the seal on the junction probably originally being the only part to be baize covered. The lid catch is very tight and the woodwork around it has been repaired in the past.
The dial silvering is clean, but generally a little grey.
The movement is in generally sound clean condition, though it was found to be thick with old, solidified oil. The balance cock has had its foot burred up at the edge and in several places underneath to accommodate a new balance staff. The detent banking block has had its arm bent to increase the depth of the detent (uncertain why the screw simply wasn?t screwed in further). The movement has only been very lightly cleaned, and has been re-oiled, during inspection.
Commentary, Provenance, etc
In this unusual calibre, Arnold places the going barrel where the fusee would be, and runs the train closer to where the barrel would have been, leaving more space where the escapement would normally appear. The slot in the potence plate for the original Arnold-type detent, cuts right across the engraved signature, revealing that the chronometer was engraved before it was sent to the escapement maker. The Earnshaw escapement and balance spring were probably fitted as an upgrade to the movement by Arnold and Dent in late 1830s, re-using the original balance but, to keep the same frequency, lightening it to match the finer balance spring by removing the additional nuts by the arms. There appears to be no evidence to support the claim that this chronometer was with Parry on his Arctic voyage of exploration with John Parry in 1818.
Potence Plate �: 64.8
Pillar Plate �: 65.5
Plate distance: 15.8
Inside barrel �: 29.2
Arbor �: 9.1 steel, snailed.
Thickness: 0.30 - 0.34
Height: 11.25
(6 � full turns output from barrel)
Set up: 2 turns (1 turn as found).
Signature: ?Geo Cotton June 1883? (scratched on inside of spring, 18cms from end)
TRAIN COUNT
Wheel / Pinion (+ext dia) Comment:
Great: 80 / 34.1 5 turns from stopwork
Ratchet: 20 / 9.9 Blued steel
Centre/2nd: 75 / 26.3 + 10 / 4.7 Solid wheel. Finely finished pinion
Third: 64 / 21.2 + 10 / 3.9 4 curved crossings ?
Fourth: 84 / 20.4 + 8 / 3.0 ?
Escape: 12 / 12.3 + 7 / app.2.0 3 curved crossings
Balance Frequency: 17,280 vbs/hr (12 beats in 5 secs)
Hour: 48 / 18.4 Brass
Minute Wheel: 56 / 19.6 ?
Minute Pinion: 16 / 6.8 Highly polished steel
Cannon: 14 / 5.6 Polished steel
Impulse pallet tip �: 6.4
Discharge pallet tip radius: 1.5
Detent length: 24.3
Balance �: 30.2 Balance Mass (incl. b/spring & stud): 4.2g
Balance spring �: 10.5 Material: Blued steel
Turns incl. terminals: 10 (c/w down)
AQN: Caird, James, Sir (owner).
caption: Marine Chronometer - Overall
caption: Marine Chronometer - Movement | Publisher: | "http://collections.rmg.co.uk/" | Rights holder: | "Royal Museums Greenwich" | Subjects: | William Edward Florence Isabelle Marine chronometer chronometers Pugh Parry | Source: | Royal Museums Greenwich | Identifier: | http://collections.rmg.co.uk/collections... | Go to resource |
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