John Roger Arnold, London c.1818 No.569

1 day marine chronometer in mahogany box

For notes on John Roger Arnold, see pp.xxx

Box/Mounting

Three-tier brass bound mahogany box measuring 140mm high, 152mm wide, and 143mm deep.

The lid has brass butt- hinges, opening to 90° to reveal a glazed panel retained with narrow wooden beading (now missing). The front of the upper half has a brass push-button lid catch with an inlaid brass ‘petal’-style escutcheon. 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 opens right over, seating flat on the table. There is a half baize covering running round the centre of the upper edge of the lower half, and forming a dust seal when closed. There is an ink inscription of the right hand box hinge, indecipherable, but possibly “165”.

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 narrow, silvered and lacquered brass gimbal ring supports a straight-sided brass bowl (cast tube with base soldered in), with a brass poising weight inside. The flat base of the bowl is stamped: “569”, has a circular brass winding shutter centred on the base, and a narrow brass bayonet-fitting bezel (2 prongs: 1 peg, 1 screw), with a thin convex glass over the dial. The interior fittings are otherwise of standard layout except that the J.R.Arnold-type heart-shaped winding key, which is stamped: “569”, is mounted on a shelf at the rear left corner. The gimbal lock, on the front right hand side in the box, consists of a curved brass swiveling bar with upstanding finger piece, mounted under a screwed knob on a triangular brass plate in the corner of the box. The underside of the box is plain and appears never to have had a baize covering.

Dial and hands

The 63.6 mm Ø, engraved and wax-filled, silvered-brass dial has three small riveted feet which fix to the pillar plate with pins and the dial itself 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 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/ 569”. The dial has “569” and two short lines scratched on the back. Blued steel spade and poker-hands with a fine, blued steel pointer seconds hand with polished steel slotted centre and a counter-poised tail. The minute hand boss has a circular hole locating on a cylindrical shoulder on the cannon pinion, secured and orientated with a side screw locating on a flat on the side of the cylinder.

Movement

Full-plate fusee movement with four pillars with flanges and fins at either end and one fin in the lower middle, pinned to the potence plate, except for one pillar, screwed with the head embraced by the barrel bridge. The blued steel set up ratchet wheel is dot marked for position. There are two small drilled dots on the barrel bridge by the ratchet wheel to mark set-up positions against a nick on one edge of the square, and there is one small hole plugged by the ratchet wheel. The potence plate is engraved on its upper surface: “Jno. R Arnold London Inv.t. et. Fecit. No.569”. The outside of the pillar plate, and the inside of the potence plate, the centre wheel, and the barrel bridge are marked with two engraved/scratched lines, and the underside of the set-up ratchet click, the potence foot, the train bar, the third wheel, fourth wheel, the barrel and balance cock have two dots drilled, The underside of the barrel is scratched: “569”, “Arnold & Dent”, “Arnold”, and something indecipherable. The underside of the barrel cap is scratched “569”, as is `the underside of the centre wheel, though the number is patially erased by the finishing of the pinion. The fusee cap is dot marked for the pin entry hole and the inside of the fusee is marked with “/”, “//” and “/ X”. The ratchet wheel is dot marked for correct positioning in the fusee (3 rivets) during manufacture. The later modern 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 (dot marked for position). 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, as well as the maintaining power detent.

Escapement, balance, spring and jewelling

Arnold-type spring detent escapement, the later, grey-finished detent with an elongated foot. The detent banks against the usual eccentrically mounted gold banking disc, recessed into a sink alongside on the potence plate. The rest of the escapement is probably the original, including the grey-finished impulse roller with its radial pink impulse jewel and the discharge roller, which also has a light pink stone inset. As currently adjusted, the escape wheel drops onto the pallet before the line of centres, and the tooth face meets the pallet half way down its curved impulse surface; the teeth bear the usual wear marks caused by the severe engaging friction.

The J.R.Arnold patent bimetal-arm, undersprung balance, has steel posts projecting down from the bimetal arm, with brass compensation nuts mounted on threaded ends of the steel posts, and brass meantime nuts screwed onto threaded ends of the arm. There is also a narrow steel ring, with two arms, mounted on the balance staff just below the bimetal arm, with two brass poising weights clamped to the rim. The blued steel helical balance spring has terminals on both ends, the lower terminal clamped to an L-shaped brass stud-piece, which is then clamped to a brass stud mounted on the potence plate. The jewelling, which is all in clear stones (except a facetted diamond in the balance cock) mounted in brass settings, 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 well patinated condition but with a number of knocks, dents andf scratches. There are particular areas of scratching and knocks round the edges of the lid and on the right hand side of the box. The glass under the lid, and all the beading, is now missing, as is part of the baize dust seal along the back and front left. The internal and external brasswork is now very nicely patinated, with a considerable amount of old (probably original) lacquer surviving. The steel parts of the \hinges and lock are now quite rusty (some mechanical cleaning done to reduce the corrosion products).

The dial silvering is sound, but thin and with brassy patches over signature and in seconds dial.

The movement is in generally sound clean condition, though it was found to be thick with old, solidified oil. The brass movements parts have some severe, blackened finger-printing in places. The movement has only been very lightly cleaned, and has been re-oiled, during inspection.

Commentary, Provenance, etc

The cylindrical cannon pinion boss prevents hand setting by use of a key.

Potence Plate Ø: 55.0

Pillar Plate Ø: 55.0

Plate distance: 10.3

Inside barrel Ø: 22.8

Arbor Ø: 7.9 steel, snailed.

Thickness: 0.25 untapered

Height: 7.2

(4 ½ full turns output from barrel)

Set up: 8 teeth (5 teeth as found).

TRAIN COUNT


Wheel / Pinion (+ext dia) Comment:

Fusee/Great: 60 / 25.8 No.of Turns: 6 (Chain 37.5cms, 127 links)

Ratchet: 44 / 10.6 Brass, 2 steel clicks

Maintaining Power: 112 / 23.7 Steel

Centre/2nd: 75 / 23.0 + 12 / 5.6 Solid wheel. Finely finished pinion

Third: 64 / 18.2 + 10 / 3.4 5 tapered crossings “

Fourth: 80 / 16.8 + 8 / 2.6 “

Escape: 15 / app.12.5 + 8 / 1.9 4 curved crossings

Balance Frequency: 18,000 vbs/ hr (5 beats in 2 seconds)

Hour: 60 / 15.8 Brass

Minute Wheel: 64 / 16.8 “

Minute Pinion: 20 / 5.8 Highly polished steel

Cannon: 16 / 4.7 Polished steel

Set up ratchet: 15 / 9.5 Blued steel

Impulse pallet tip Ø: 5.0

Discharge pallet tip radius: 1.4

Detent length: 20.0

Balance Ø (across posts): 23.0 Balance Mass (incl. b/spring & stud): 3.5g

Balance spring Ø: 12.3 Material: Blued steel

Turns incl. terminals: 13 ½ (c/w down)