John Roger Arnold, London c.1811 No.379

1 day marine chronometer in mahogany box

For notes on John Roger Arnold, see pp.xxx

Box/Mounting


Three-tier mahogany box measuring 125mm high, 135mm wide, and 122mm deep. The lid has ebony stringing to top edge, has butt hinges allowing it to open to 90° only, and opens 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, a green baize lining to the upper edge of the lower half forming a dust seal when closed.

The box fittings are standard, with brass drop handles on the sides, the gimbal screws threaded directly into the wood of the sides. The narrow lacquered brass gimbal ring supports a straight-sided bowl which 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 a poised annular lead weight, and the base is marked in pen: “march 1836”, over-writing a faded inscription including “1825”.The interior fittings are otherwise of standard layout except that the rising ratchet winding key, which is probably a later replacement, is mounted on a shelf at the rear left corner, and the gimbal lock, on the front right hand side in the box consists of a small rectangular swiveling plate mounted on the gimbal ring and locating simultaneously in slots in brass pieces on the bowl and in the corner of the box, the latter piece being stamped on its upper surface: “379”.The underside of the box has a green baize covering.

Dial and hands

The 63.3 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 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 IV o’clock having Arabic ten-second figures with straight batons at alternate five-second intervals and is marked: “379” below 60. The dial is signed below XII: “ARNOLD / London”. The dial has been scratched: “W REID DUNDALK 1 / 6 / 08” on the back, the mark almost completely obliterated. Blued steel spade and poker-hands with a fine, blued steel pointer seconds hand with a counter-poised tail.

Movement

Full-plate fusee movement with four pillars with flanges and fins at either end and one fin in the lower middle, 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 potence plate has a blued steel spring and the blued steel ratchet wheel has on its underside a drilled dot (meaning uncertain) and a punched dot at the corner of the square for correct orientation on the square. There is also a drilled dot by the ratchet wheel on the plate, purpose uncertain.The general level of finish of the movement is fine, with a high polish, over slight vestigial scratching from the preparatory stoning. The potence plate is engraved on its upper surface: “Jn.o. R. Arnold London Inv.t. et. Fecit. No.379”. The underside of the balance cock foot, the potence foot, the train bar, the great wheel, the third wheel and the pillar plate are all scratched with a “V”. The underside of the pillar plate is scratched: “RER / 1840”, “RF 1868”, “1/2 T” (by the barrel pivot) and “J Gibson 1864”, the latter under a train bar foot. The inside of the great wheel is also scratched: “HGWS…(indecipherable)…D 1848”. There are also two neat scratched circles where the holes for the m/p spring might have been. The later signed blued steel mainspring has a blued 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 bell-mouthfusee pipe pinned to the square. 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. There is a tiny hole in the pillar plate under the balance centre, and there are viewing holes in the potence plate for the meshing of great/centre and centre/third. The balance aperture in the potence plate has been opened out and a new steady inserted in the potence foot (one of the original steadies half removed by the opening) to accommodate a later arrangement of the escapement. There is a plugged hole by the present stud on te potence plate where there was probably an earlier stud for the current undersprung balance. The balance cock table has a cutaway and has a plugged screw-hole, both for the stud originally associated with the oversprung balance. Burrs under the balance cock foot and the potence foot indicate a new or repivoted balance staff at some stage.

Escapement, balance, spring and jewelling

Arnold-type spring detent escapement with grey-finished, foot detent let into a slot in the potence plate and banking on a slightly eccentric gold disc inset 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 having a short piece of gold halved onto it to form the acting tip. There is also a clear jeweled, rectangular locking stone. The escapement has been rebuilt at some stage, the original Arnold escape wheel now only performing the function of locking on the detent, the impulse being given by a second, Earnshaw-type wheel mounted below the original, and necessitating the lowering of the impulse roller on the balance staff. The plainly finished impulse roller has a raked, clear stone and the discharge roller also has a clear stone inset. As found, impulse is arranged to occur on the line of centres.

The Arnold Z-type, two-arm bimetal balance has narrow, slightly tapered brass arms. The rim segments are fixed to the arms with a pair of screws` at each end and the steel element is blued. They extend to within 20° of the opposite arm and have Arnold-type circular gold nuts (probably mean-time nuts from a later balance)on the threaded ends. Small gold meantime screws are attached at the end of the arms, and brass meantime screws are attached on short pieces of rim segment extending on the other side of the arms.. The blued steel helical balance spring has terminals on both ends, the upper terminal with a brass stud fixed to a secondary stud on the potence plate. The jewelling, which is all light pink stones mounted in brass settings, extends to the balance and escape wheel with endstones, the lower fourth and the escapement parts as mentioned.

Alterations/condition

The wooden box is in sound and clean condition with a few small knocks and dents, and has been rather heavily refinished, inside and out, in recent years. There is a fracture on top of the lid across the back from the left. The ebony escutcheon has a piece missing on the left of the opening. The right hand side gimbal screw had stripped the thread from the wooden side and this has been ‘bushed’ with mahogany and re-threaded (starting with a 3 BA tap and then using the gimbal screw to finish the thread. The drop handles and outer brasswork are reasonably clean and sound and the inner brasswork is well preserved though it appears to have been fairly coarsely re-grained and lacquered in the recent past. The current arrangement of a steel squared control of the gimbal lock is probably a 20th century alteration; this part would probably originally have been fixed with a central shoulder screw and had an upstanding post for swinging the latch in/out of engagement. The lead counter-weighting inside the bowl may also be a later addition to lower the centre of gravity of the bowl.

The dial silvering is very clean, with slight darkening at the edges. The dial has probably been re-silvered several times in the past, as the engraving is now getting a little thin in places.

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, though the upper pivot of the staff is currently broken (Cock packed with a sliver of paper to ensure staff is safely retained for the time being). The movement has only been very lightly cleaned, and has been re-oiled, during inspection.

Commentary, Provenance, etc

Mainspring evidently a replacement. Balance and spring have been altered at least twice during the chronometers life. Originally the balance would have been oversprung, the spring studded on the cock. It was then converted to JRA’s suspended (undersprung) balance (to relieve the pressure on the lower balance pivot in use), with the spring studded directly on the potence plate, and this stud then appears to have been altered to the current adjustable stud arrangement. It was probably at this stage that the original escapewheel was augmented with the second, Earnshaw-type locking wheel and the balance was re-staffed, the opening in the potence plate perhaps being enlarged at that time, and the later balance weights perhaps being fitted then too, as part of a major refit. This re-design of Arnold’s escapement is quite an interesting improvement, providing the benefit of Arnold’s type (locking in tension) with that of Earnshaw’s (less friction in impulsing).



Potence Plate Ø: 54.5

Pillar Plate Ø: 54.8

Plate distance: 10.4

Inside barrel Ø: 22.3

Arbor Ø: 7.5 steel, unsnailed.

Thickness: 0.25 untapered

Height: 7.0

(4 ½ full turns output from barrel)

Set up: (5 as found) 8 teeth.

Signature: “Meredith May 865” (scratched on inside of spring, 20cms from end)

TRAIN COUNT


Wheel / Pinion (+ext dia) Comment: Crossings? Marks?Jewelled?

Fusee/Great: 60 / 25.6 No.of Turns: 6 (Chain 35cms, 134 links)

Ratchet: 27 / 11.5 Brass, 2 steel clicks

Maintaining Power: 96 / 23.5 Brass

Centre/2nd: 75 / 22.8 + 12 / 5.6 Solid wheel. V.finely finished pinion

Third: 64 / 18.2 + 10 / 3.2 4 curved crossings “

Fourth: 80 / 17.0 + 8 / 2.6 “

Escape (both): 12 / 12.3 + 8 / 2.8 4 curved crossings

Balance Frequency: 14,400 vbs/ hr (half seconds)

Hour: 48 / 13.7 Brass

Minute Wheel: 48 / 14.4 “

Minute Pinion: 16 / 4.8 Highly polished steel

Cannon: 12 / 4.1 Polished steel

Set up ratchet: 16 / 9.6 Blued steel

Impulse pallet tip Ø: 6.2

Discharge pallet tip radius: 1.3

Detent length: 21.0

Balance Ø: 23.5 Balance Mass (incl. b/spring & stud): 2.7g

Balance spring Ø: 11.5 Material: Blued steel

Turns incl. terminals: 6 ¼ (c/w down)