Marine chronometer by John Roger Arnold

Description — British Museum

Marine chronometer; eight-day movement; two-arm balance; steel spring; mahogany case bordered with satinwood stringing.

Curator's comments — British Museum

Comment from Anthony G. Randall and Richard Good, Catalogue of Watches in the British Museum. Vol. VI (1990) Made by John R. Arnold, 1804 Marine Chronometer (8-day) Signature: on the back plate: 'John R Arnold Invt et Fecit No 223'. On the dial: 'Arnold London' across the centre and 'No. 223 ' in the upper part of the second ring. Box: Octagonal mahogany box similar to those of registration no. 1958,1201.2067 but well-made and finished in polished mahogany veneer. The fittings for a gimbal ring still remain. The edge of the box lid has stringing of a lighter wood. Numbered in ink inside the bottom 223 and EJW 4/98, on paper glued in, 28 October 1813. A key to the lock. The movement is protected by a brass drum with a glazed brass bezel secured to the underside of the wooden movement surround by two brackets and screws. A rotating brass disc as a dust cover to the winding hole with a large red arrow indicating direction of wind. There is also a label (partly missing) with 'wind slowly' please turn key from left to right. The winding and setting-up squares project through holes in the bottom of the drum. Box 167 mm across the flats, h. 94 mm. Dial and hands: Engraved, silvered brass dial, the engraving filled with black wax, secured to the front plate by three screws near the edge. In the upper part of the dial is an Up and Down sector with eight divisions for the eight-day going period. On the reverse of the dial repair marks 'Cleaned R E Burreto (?) ap 95' and 'Cleaned Sept 1932'. Blued steel hands, the minute hand held by a screw in its boss to a square on the cannon pinion. The seconds hand screwed to a pipe having a blind hole. There was once a collet and pin to secure the cannon pinion friction tight on the extended centre arbor. Movement: Front plate diam. 118.1 mm, reduced to 105.5 rnm; back plate diam. 105.4 mm; frame h. 36.5 mm. Frame: Full plate construction with a high detachable barrel bridge. Four turned pillars, the back plate retained by blued steel screws, two having turned brass washers and two recessed in the back plate. Otherwise similar in construction and execution to registration no. 1958,1201.1952. Fusee: Reversed and fitted with Harrison's maintaining power and the usual stop-work. The maintaining ratchet wheel brass. On the squared winding arbor is pinned a brass dust-excluding cup. On the inside of the great wheel, under the blued steel maintaining spring, is marked '1804' and 'Wm F Rattray Septr 12'. The fusee has been turned out on the inside breaking into the chain groove. Setting-up work for the mainspring is planted on top of the barrel bridge and has a set screw to lock the tail of the click. The barrel arbor is squared on that end only. The mainspring is not tapered, and is hooked by an eye to a hook in the barrel wall and to a hook passing through the brass snailed boss and barrel arbor. Going-train: With an intermediate wheel and pinion so as to achieve the eight days of running. All the wheels except the fourth and escape are riveted to their pinions, the latter two being mounted on brass collets. The pinions and arbors are polished all over except the undercuts. Jewelling: The pivots of the fourth and escapement arbors in pierced jewels, those of the fourth rear and escapement with endstones, that on the balance cock a diamond set in a brass ring. The jewels themselves are set in plain brass discs and not double sunk in their settings in the frame. Where an endstone is fitted the pierced jewel is almost flat on the side remote from the endstone and convex curved towards the endstone. Oil sinks are cut on both sides of these pierced jewels which appear to touch the endstone on their convex sides. Escapement: Arnold spring detent escapement, the brass wheel soldered to its collet and showing signs of both bending and filing. The cycloidal impulse faces slightly marked by contact with the corner of the impulse jewel but also with file marks. The detent fitted with a steel passing spring held by two rivets, its jewel replaced with a piece of polished steel. The two rollers polished in the usual way. Banking for the detent provided by a brass screw set in the edge of the detent slot. Balance: 'z' type bimetallic balance with a brass cross bar and central boss fixed to a brass collet on the balance staff by two screws. The blued steel and brass bimetallic rims attached by screws to blocks left integral with the ends of the arms. Steel timing screws are fitted in slotted holes in the blocks to which the rims are screwed, the rims having clearance holes. There is also a tapped hole near the free end of each rim for poising screws, now removed. Brass compensation nuts are on a threaded portion integral with the free ends of the rims. Diam. 31.7 mm over rim, h. 3.8 mm. Balance spring: An undersprung helical blued steel spring of 5½ turns, with terminal curves, fitted between the balance and the back plate. The collet is a rectangular block of brass with square hole and peg to clamp the spring. The stud, screwed and steady pinned to the back plate, has an adjustable plate with a clamp for the end of the spring, the clamp being arranged to grip the spring concentric with the terminal curve. Going-train counts: Great wheel (fusee) 80 teeth (similar to that used in the two-day chronometers, registration nos 1958,1201.2067 and 1958,1201.1952) Intermediate pinion 20 leaves, wheel 80 teeth, 6 arms (wheel similar to great wheel) Centre pinion 10 leaves, wheel 80 teeth, 4 arms Third pinion 10 leaves, wheel 75 teeth, 4 arms Fourth pinion 10 leaves, wheel 80 teeth, 4 arms Escape pinion 10 leaves, wheel 15 teeth, 4 arms Beats per hour: 14,400 Motion work: Cannon pinion 14 leaves, minute pinion 14 leaves (brass) Hour wheel 42 teeth, minute wheel 56 teeth Up-and-down work: A lantern pinion of 5 pins on the great wheel arbor meshes with a sector carrying the indicating hand. Provenance: Ilbert Collection - purchased by Ilbert from Malcolm Gardner in 1930. Presented by Mr Gilb.