Arnold and Son, London c.1788/1810 No.326

Small 1 day marine chronometer in mahogany box

For notes on Arnold and Son, see pp.xxx

Box/Mounting


Three-tier mahogany box measuring 95mm high, 93mm wide, and 92mm deep. The lid has ebony stringing to top edges, has butt hinges allowing it to open to 90° only, and originally opened to a glazed panel retained with narrow wooden beading. The front of the upper half has a push button brass lid catch. The lock on the lower half is inlaid with a ‘navette’-shaped ebony escutcheon. The box is of fine, visible, dovetailed construction at all four corners, and the upper half opens right over and rests on the table level with the lower half. Inside the back of the upper half is marked in ink: “Revd. G.Fisher / 3 (Private)”. On the upper surface of the edge at the back of the lower half is marked in ink: “155” and scratched on the right hand hinge, alongside, is: “1555”.

The box has the gimbal screws threaded directly into the wood of the sides, the narrow, lacquered silvered-brass gimbal ring locked via a gilt brass latch, pivoted on the gimbal ring and engaging in a slot under a triangular brass`plate in the usual position. The straight-sided bowl has a small circular brass winding shutter centred on the flat base, and has a narrow brass bayonet-fitting bezel (3 pins), with a thin convex glass over the dial. Inside the bowl is marked in ink: “286”, and there is a brass poising weight, with a small piece of paper trapped behind it, marked in pen: “July 22nd 1836”. , over-writing a faded inscription including “1825”. The underside of the box has a green baize covering.

Dial and hands

The 42.5 mm Ø, white enamel dial has three feet which pin to the brass edge, which 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 IV o’clock having Arabic ten-second figures with straight batons at alternate five-second intervals. The dial is signed below XII: “Arnold / 326”. The dial has no intentional marks on the counter-enamel. It is attached by pinning to the solid pillar plate of the movement directly with its three copper feet. Gold spade and poker-hands with a fine, blued steel pointer seconds hand with a gold centre and counter-poised tail. The hands are very nicely finished, the curved pointer to the minute hand also being polished and shaped on its underside and the spade of the hour hand being nicely shaped and bevelled.

Movement

Full-plate, gilt brass, fusee, pocket chronometer movement, with four pillars, the potence plate fixed with four taper pins, the barrel under the potence plate, without a bridge. The blued steel set up click on the underside of the pillar plate has an integral blued steel spring and the blued steel ratchet wheel and square are marked for orientation. The general level of finish of the movement is very fine, with all surfaces gilt, even under the dial. The potence plate is engraved on its upper surface: “John Arnold & Son / London” and: “No.326/627 Inv.t. et. Fec.t.”, and adjacent to the set-up square are five sets of ‘isochronising’ marks: one dot, two sets of two dots, one three dots and one ‘x’. Around the escapement opening in the potence plate is a shallow sink (all gilt) and two small holes, function unknown. The pillar plate, which has the brass edge integral with it, has the remains of the movement knuckle from the case joint, and a slot and holes for the bolt and two holes for the bolt spring. The fusee pipe is angled on its upper rim, to match the curved shape of the original metal case of the pocket chronometer. The underside of the pillar plate is marked: “JW 5 92” and with three straight scratch-marks by the centre pivot. The underside of the barrel is very lightly scratched: “Arnold & Dent / 326”. The undersides of the balance cock foot and the potence foot are marked: “627” (scratched with the points of tweezers – in one area the lines are doubled). The potence plate has a couple of raised burrs under the balance cock foot, suggesting a later balance staff at some stage. The blued steel, needle-type, maintaining power spring has been moved and its original hole filled with an ungilt plug. The maintaining power detent has also been reduced in size, or replaced. On the edge of the upper surface of the potence plate, just after “et Fec.t”, is a dull patch of gilding with a small dot, drilled through the gilding, purpose unknown, but possibly for clamping something in this position temporarily. The underside of the barrel also has a single dot, drilled into the gilding. The centre, third and fourth wheels all have three straight scratch marks under the gilding, by their pinions.

The blued steel mainspring, which may be the original, but has been rehooked, 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 a narrow, straight-sided fusee pipe screwed to the plate.The train wheels are gilt brass with the third and fourth 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. There are two small unthreaded holes in the potence plate under the balance, adjacent to the centre pivot, drilled through the gilding, the function of which is uncertain. The narrow ‘bridge’ of metal in the potence plate which supports the detent adjusting screw has been dovetailed in to the potence plate.

Escapement, balance, spring and jewelling

Arnold-type spring detent escapement with original, grey-finished, foot detent let into a slot in the potence plate and banking on a steel pin angled into the plate. The well made and finished steel detent has a steel passing spring running alongside the detent blade, the tip of the spring being polished where it acts on the discharging jewel, and the blade is set with a pink jeweled, rectangular locking stone. The plainly finished impulse roller has a radial, pink stone and the discharge roller also has a pink stone inset. The brass escape wheel has visible wear marks on the curved impulse faces where they engage the impulse pallet before the line of centres, dropping onto the edge of the pallet half way down the curved face of the impulse teeth.

The Arnold OZ-type balance has a polished steel, three-arm central wheel, with two bimetal rim segments are fixed to the upper surface of the steel wheel with blued steel brackets.arms each having a steel screws at the end for mean time adjustment. The Arnold-type bimetal rim segments, which have brass ‘bobbin’ type weights on the curved threads, are composed of blued steel inside, in combination with Arnold’s ‘Platina’ metal on the outside. At 90° to the mean time screws are holes in the rim segments where additional m/t screws could be fitted. The three-arm steel wheel has a small additional hole in the edge, function unknown, but perhaps originally to be part of an amplitude limiting device (maybe in association with whatever was clamped to the potence plate?). The blued steel helical balance spring has terminals on both ends, the upper terminal with a blued steel stud fixed to the cock table. The stud has a hole in the top, possibly originally for a pin for isochronal adjustments. The jewelling, which is all light pink stones mounted in brass settings, extends to the balance and escape wheel with endstones (balance with small faceted diamond in a blued steel setting), the fourth and third wheels, and the escapement parts as mentioned.

Alterations/condition

The wooden box is in sound and clean condition with only a few small knocks and dents. The rear string of ebony across the back edge of the lid is missing, as is the thin glass panel beneath the lid. The brasswork is generally well preserved though it has lost its lacquer in places and now has a stable brown tarnish in those areas.

The dial enamel is very clean, but with cracks running from ‘V’ to ‘II’ and ‘V’ to ‘60’ on the seconds dial. There is also some cracking between ‘X’ and just beyond ‘XII’.

The movement is in generally sound clean condition, though it was found to be thick with old, solidified oil.. There are burrs raised under the cock foot suggesting the balance has had a new staff or has had it repivoted. The movement has only been very lightly cleaned, and has been re-oiled, during inspection.

Commentary, Provenance, etc

The movement was created as a pocket chronometer and has survived in almost completely original state from that period. It was then removed from its metal (probably silver or gold) case and fitted to the current small mahogany box with gimbals about 1810, probably by J.R.Arnold’s workshops.



Potence Plate Ø: 40.0

Pillar Plate Ø: 43.0

Plate distance: 6.8

Inside barrel Ø: 17.3

Arbor Ø: 6.7 steel, unsnailed.

Thickness: 0.22 – 0.18

Height: 4.85

(5 ¼ full turns output from barrel)

Set up: (16 as found) 10 teeth (very close to fully wound spring).

TRAIN COUNT


Wheel / Pinion Comment:

Fusee/Great: 60 / 19.0 No.of Turns: 6 ½ (Chain 279mms, 162 links)

Ratchet: 37 / 9.2 Brass, 2 steel clicks

Maintaining Power: 106 / 17.5 Brass

Centre/2nd: 64 / 18.7 + 12 / 4.0 Solid wheel. V.finely finished pinion

Third: 60 / 16.3 + 8 / 2.6 4 curved crossings “

Fourth: 60 / 15.3 + 8 / 2.4 “ “

Escape:: 15 / appr.11.3 + 6 / 1.7 4 curved crossings (ungilt) “

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

Hour: 36 / 10.9 Gilt-brass

Minute Wheel: 40 / 11.5 “ and ungilt under

Minute Pinion: 12 / 4.1 Highly polished steel

Cannon: 10 / 3.4 Polished steel

Set up ratchet: 19 / appr.5.4 Blued steel

Impulse pallet tip Ø: 3.35

Discharge pallet tip radius: app. 0.9

Detent length: 20.5

Balance Ø: 20.1 Balance Mass (incl. b/spring & stud): 0.75g

Balance spring Ø: 7.1 Material: Blued steel

Turns incl. terminals: 8 (c/w down)