Thomas Earnshaw marine chronometer no. 509
Record status
Individual type · partial
Period
1795-1805
This one-day marine chronometer was made around 1795 to 1805 by Thomas Earnshaw in London. Housed in a brass bowl mounted within a brass gimbal system, it sits inside a rectangular mahogany box lined with green baize.
The movement features Earnshaw's spring-detent escapement, a split-bimetallic balance, a helical blued-steel balance spring, fusee, and maintaining power. The silvered brass dial displays Roman hour numerals, an outer minute ring, and a subsidiary seconds track above the VI numeral, bearing the signature 'Thos Earnshaw INVT ET FECIT NO 509 ONE DAY'. Historically, it saw service across several Royal Navy vessels, notably including HMS Beagle under Captain Robert FitzRoy.
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
- One-day marine chronometer
- Maker
- Thomas Earnshaw (Senior)
- Duration
- One-day
- Escapement
- Earnshaw spring-detent escapement
- Ship Service
- HMS Beagle
- Museum Number
- 1958,1006.1957
- Place recorded
- United Kingdom
- Dial Inscription
- Thos Earnshaw INVT ET FECIT NO 509 ONE DAY
- Maker / attribution
- Thomas Earnshaw (Senior)
Design
- Visible features
- • Silvered dial with Roman numerals I through XII and a subsidiary seconds dial located above the six o'clock position. • Blued steel hour, minute, and seconds hands. • Gimballed brass mounting ring holding the cylindrical chronometer bowl inside a hinged mahogany box. • Mahogany box lid with glazed aperture and circular ivory inlay on the exterior.
- Dial and Mechanism
- The silvered brass dial bears the signature 'Thos Earnshaw INVT ET FECIT NO 509 ONE DAY'. It features Roman numerals I-XII and a subsidiary seconds dial located above the VI numeral. The dial is attached to the movement via two screws, one of which is currently missing. The one-day spring-driven movement includes a fusee, Harrison's maintaining power, and an Earnshaw spring-detent escapement. It utilizes a split-bimetallic balance and a helical blued-steel balance spring, which is noted as a later replacement. The brass escape wheel contains thirteen teeth.
- Service and Provenance
- The chronometer served on various Royal Navy ships, including HMS Hecla, before being sent to Robert Molyneux for overhaul in July 1830. In December 1831, it was placed into service on HMS Beagle for the voyage involving Captain Robert Fitzroy and Charles Darwin. The object was part of the Ilbert Collection, purchased in 1931 from Lilley & Son, and was subsequently presented to the British Museum by Gilbert Edgar in 1958.
- Construction and Housing
- The chronometer is housed in a rectangular mahogany box with dovetailed base corners and brass carrying handles. The lid, which features a round glazed aperture and a mahogany sliding cover, includes an internal brass slide to limit its opening. The box is lined with green baize, excluding two triangular wooden inserts at the corners that contain brass spring locking pieces. The exterior of the case features a small empty hole in the front of the lower section. An ivory disc recess is present in the front of the top lid, though the disc itself is missing. The underside of the sliding cover is lined with dark purple leather.
Identification
- Serial number
- 509
- 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: Source notes conflicting details regarding the ivory disc: described as an 'inserted plain ivory disc' in one section, but later noted as 'Ivory disc recess in the front of the top but with the engraved(?) disc now missing'.
- Research required: Movement interior, balance spring, and back plate inscriptions are not visible in the provided exterior photographs.