John Roger Arnold, London c.1822 No.548

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 156mm high, 168mm wide, and 154mm deep. The box is constructed with concealed, lapped mitred joints and brass binding. The lid has butt hinges and opens to 90° to glass viewing panel showing the dial below. Screwed inside the lid is a small brass plate engraved: “Presented to / The Royal astronomical Society / by John James hall / A Fellow / A.D.1932”.

The lid has 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 an inlaid brass ‘petal’-style escutcheon. The lock on the lower half has an inlaid brass ‘hollow-corner’ lozenge escutcheon, immediately below which is inlaid an unsigned, round ivory tablet. There is a hole on the front of the lower tier, to the left of the lock, to accommodate a knotted string to tie the key for the box. The box is of fine, concealed dovetailed construction at all four corners, with brass binding, the inside of the box having a sliding brass strut (apparently original), preventing the upper half from opening more than 90°. 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.

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, gold-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: “548”, has a circular brass winding shutter centred on the base, and a narrow brass bayonet-fitting bezel (2 prongs: 1 peg, 1 screw, now missing), with a thin convex glass over the dial. The interior fittings are otherwise of standard layout except that the (probably later, Arnold and Dent-type?) rising ratchet winding key is mounted on a shelf at the rear left corner (shelf now missing). The gimbal lock, on the front right hand side in the box, consists of a curved brass swinging fork, mounted under a screwed knob on a triangular brass plate in the corner of the box, the fork swing over and engaging with a gate/block on the bowl, one ‘tyne’ of the fork through a slot in the gimbal ring. The underside of the box has a baize covering.

Dial and hands

The 77.4 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/ 548”, and: “With Airy’s Compensation” and “ONE DAY” across the centre. The dial has “S 4-31” scratched on the back. Blued steel spade and poker-hands with a fine, blued steel pointer seconds hand with 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 in a dimple on a small 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. A slightly ill-fitting foot suggests the current balance cock, which is engraved: “Restored by / Chas. Frodsham / A.D. 1846”, is a later replacement. The pinned, blued steel set up ratchet wheel has on its underside a drilled dot at the corner of the hole for correct orientation with a small nick on the square. There is also a drilled dot by the ratchet wheel on the bridge, to mark set-up positions against two further nicks on one edge of the square. A brass pin, originally standing next to the tail of the set-up click on the barrel bridge, has now been cut and smoothed off. The general level of finish of the movement is of a reasonably fine polish, over slight vestigial scratching from the preparatory stoning, and with later, probably mid 19th century, circular hand spotting and quite a lot of later over-polishing. The position of the scape wheel has been moved slightly and the jewelling holes plugged and re-positioned, probably when the escapement was converted from Arnold to Earnshaw, and the fourth wheel and escape pinion replaced, to have higher numbers, at the same time. The potence plate is engraved on its upper surface: “Jno. R Arnold London Inv.t. et. Fecit. No.549”. The inside of the pillar plate, the potence plate, the potence foot and the underside the train bar the fusee ratchet wheel, the great wheel and barrel bridge all have one dot, and the underside of the potence foot has one engraved line, the underside of the pillar plate has two engraved lines and the great wheel and the maintaining power spring each have one scratched line. The underside of the barrel is scratched: “Arnold No.548”. The fusee cap is dot marked for the pin entry hole, and there is a punched dot on the inside of the maintaining power click. 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 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. A new banking piece has been fixed to the underside of the potence plate to accommodate the later arrangement of the escapement. There is a threaded hole, two empty steady holes and two drilled depressions (to clear the ends of screws) in the potence plate where there was an earlier stud for an undersprung balance.

Escapement, balance, spring and jewelling

Earnshaw-type spring detent escapement with grey-finished, foot detent screwed under the potence plate and banking on a gold screw mounted on a small brass potence on the plate. The well made and finely finished detent has a gold passing spring running alongside the detent blade, and a pink jeweled, round section locking stone. The escapement, balance and spring have been converted at some stage, probably by Charles Frodsham in 1846, the slot remaining in the plate for the original Arnold detent, with the circular banking screw sink, and the holes remaining in the potence plate for the original undersprung balance spring stud. The polished and grained impulse roller is unjewelled and the discharge roller has a light pink stone inset.

The special, compound bimetal balance, of Frodsham’s early type, has straight bimetal arms, angled up from the centre at about 3°. The bimetal rim segments extend fully, just short of the opposite arm, where a short piece of rim segment runs from the arm in the other direction with a single screw hole for attaching an additional mean time screw. The rim segments have (later) circular brass weights mounted about 75° from the arms, and brass meantime nuts are attached at the end of the arms. An Airy’s bar with small brass circular weights on sprung blades, has been fitted within the balance, friction mounted under the balance spring collet in the usual way. The blued steel helical balance spring has terminals on both ends, the upper terminal with a brass stud fixed to the balance cock. The underside of the stud has a drilled dimple, probably intended to locate with a brass pin projecting up from the cock table, but this pin appears to have been smoothed off flush. The jewelling, which is all in light pink stones mounted in brass settings, extends to the balance and escape wheel with endstones (later faceted diamond in steel for the balance upper pivot) and the lower fourth wheel, and the escapement parts as mentioned.

Alterations/condition

The box is in sound and clean condition with a few small knocks and dents, but has a fine fracture across the lid at the back. One piece of beading is missing from the glass panel under the lid, and the corner piece for the winding key is missing. The screw from the bayonet fitting for the bezel is now missing, as is the thin veneer covering for the lid catch, inset in the inside front of the upper half.

The dial silvering is clean, with two small patches of green corrosion at ‘5 seconds’ (area scraped clean with pegwood). The dial has been re-silvered several times in the past, and the engraving is now getting a little thin.

The movement is in generally sound clean condition, though it was found to be thick with old, solidified oil. The balance cock and jewelling has been replaced, probably also in 1846, and the circular balance weights were probably fitted in the 1870s at the same time as the Airy’s bar., The movement has only been very lightly cleaned, and has been re-oiled, during inspection.

Commentary, Provenance, etc

Mainspring evidently a replacement and has broken in two places and been re-hooked at its outer end (old hooking and second piece held in collection). Balance and spring, and the balance cock, have been altered at least once during the chronometers life. Originally the balance would have been undersprung, the spring studded on the plate, and was then converted (perhaps in 1846 by Frodshams?) to oversprung probably at the same time as the escapement was converted. The cylindrical cannon pinion boss prevents hand setting by use of a key. The height of the upper half is significantly less than the lower half, and it would seem therefore that the strut inside the box is original and that the upper half cannot ever have been intended to open right over and lie flat on the table.


Potence Plate Ø: 64.8

Pillar Plate Ø: 65.5

Plate distance: 13.4

Inside barrel Ø: 28.7

Arbor Ø: 9.3 steel, snailed.

Thickness: 0.27 - 0.37

Height: 11.75

(6 ¾ full turns output from barrel)

Set up: 24 teeth (12 teeth as found).

Signature: “Geo Cotton April 1889” (scratched on inside of spring, 20cms from end)

TRAIN COUNT


Wheel / Pinion (+ext dia) Comment:

Fusee/Great: 70 / 33.8 No.of Turns: 6 (Chain 48cms, 121 links)

Ratchet: 46 / 15.6 Brass, 2 steel clicks

Maintaining Power: 120 / 32.0 Brass

Centre/2nd: 75 / 26.6 + 14 / 7.2 Solid wheel. Finely finished pinion

Third: 64 / 21.1 + 10 / 3.9 4 curved crossings “

Fourth: 80 / 17.7 + 8 / 3.0 “

Escape: 15 / app.12.8 + 10 / 2.4 4 curved crossings

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

Hour: 60 / 16.2 Brass

Minute Wheel: 64 / 17.2 “

Minute Pinion: 20 / 5.6 Highly polished steel

Cannon: 16 / 4.5 Polished steel

Set up ratchet: 25 / 10.0 Blued steel (7 teeth cutaway)

Impulse pallet tip Ø: 6.1

Discharge pallet tip radius: 1.3

Detent length: 22.0

Balance Ø: 30.5 Balance Mass (incl. b/spring & stud): 7.3g

Balance spring Ø: 12.0 Material: Blued steel

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