John Arnold Marine Chronometer No. 12
Record status
Individual type · partial
Period
1778 or 1779 (also dated 1782)
This marine chronometer by John Arnold is housed in an octagonal mahogany box with a glazed brass bezel and lock. Museum documentation dates the piece to 1778, 1779, or 1782 and notes it as likely the first marine chronometer built with Arnold's spring detent escapement and a double-T transverse compensation balance.
The movement features a full-plate design with fusee maintaining power, a blued steel helical balance spring, and a white enamel dial signed 'John Arnold, London No 12'. Formerly in the Courtenay Adrian Ilbert Collection, it was donated to the British Museum by Gilbert Edgar in 1958.
Evidence at a glance
- Linked sources
- 1
- Photograph views
- 1
- Catalogue references
- 0
Counts describe this entry’s documentation, not authenticity, rarity or completeness. Photographs may show one specimen; check each caption and licence.
Technical characteristics
- Type
- Box marine chronometer
- Box Type
- Octagonal mahogany box
- Escapement
- Spring detent escapement
- Museum Number
- 1958,1006.2067
- Dial Signature
- John Arnold, London No 12.
- Place recorded
- United Kingdom
- Maker / attribution
- John Arnold
- Back Plate Signature
- John Arnold Inv' et Fecit London N° 12
Design
- Balance and Dial
- The balance is a bimetallic two-armed steel design, identified as a 'double T' type. It incorporates bimetallic strips of steel and brass with a corrugated appearance and wire trammels for rod stabilization. Tapped holes for timing screws are present on the rim, though the screws are missing. The flat white enamel dial features Roman hour numerals and Arabic five-minute markings. It is signed 'John Arnold, London No 12.' The back plate is inscribed 'John Arnold Inv' et Fecit London N° 12'.
- Visible features
- • Octagonal dark mahogany case with front lock keyhole • Circular white enamel dial showing hairline cracks, Roman hour numerals, and outer Arabic five-minute numerals • Large subsidiary seconds ring at the 6 o'clock position • Glazed aperture secured within a turned brass bezel ring • Blued steel hands for hours, minutes, and subsidiary seconds
- Case Construction
- The marine chronometer is contained in an octagonal mahogany box. The lid is glazed and secured with a single five-knuckle hinge and a lock. The exterior shows marks indicating previous suspension in gimbals. The base of the box features a brass-lined winding hole protected by an eccentric shutter. Inside, a brass plate with a projecting tube aligns with a brass dust-excluding cup on the movement's winding square. The glass is noted as likely original, exhibiting a greenish tint and bubbles.
- Movement and Escapement
- The movement uses a full-plate design with Harrison's maintaining power. Curatorial records indicate the spring detent escapement is a crude, unoriginal replacement. Observations suggest the original layout was intended for a pivoted detent but was altered during early construction. The escape pinion arbor shows evidence of relocation toward the balance, with holes filled and the potence foot raised with a section of brass. Jewelling on the fourth arbor and balance staff is consistent with nineteenth-century English standards and is considered a later addition.
Identification
- Reference
- 1958,1006.2067
- Serial number
- 12
- Source note
- Facts transcribed from the linked source listing or collection record. Attribution and specifications are source-reported and have not been independently authenticated.
Catalogue references
No catalogue numbers recorded. Numbers are only published once transcribed from a verified edition of a standard catalogue — they are never inferred.
Research required
- Research required: Dating varies in museum records between 1778–1779 and 1782
- Research required: Curatorial comments note the spring detent is an unoriginal replacement and jewelling was added or altered later
- Research required: Internal movement features are not directly visible in the closed exterior view