Instruments · Marine chronometer
Marine chronometer, United States, 1947
- Maker / attribution
- Unrecorded in source
- Date
- 1947
- Historical period
- Modern Mechanical Horology (1945 – 1969)
- Country of origin
- United States
- Place
- Lancaster, United States
- Object type
- Marine chronometer
- Materials / technique
- Wood, brass, nickel, steel, aluminium, glass, jewels, textiles, plastic
- Dimensions
- Guard box: H.240 W.310 D.260 Chron.Box: H.195 W.210 D.205
- Holding institution
- Royal Museums Greenwich
- Accession / object no.
- ZBA4526 ZBA4526 L5000-001 L5000-002 L5000-003 L5000-004
- Credit line
- Royal Museums Greenwich
- Catalogue title (original)
- No. 4E109 (English)
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Record summary
Held and catalogued by Royal Museums Greenwich (object number ZBA4526 ZBA4526 L5000-001 L5000-002 L5000-003 L5000-004), this is a marine chronometer, made in Lancaster, United States, dated 1947. The Atlas places it in the Modern Mechanical Horology period (1945 – 1969) of its Instruments collection. Materials and techniques recorded by the source: Wood, brass, nickel, steel, aluminium, glass, jewels, textiles, plastic. Recorded dimensions: Guard box: H.240 W.310 D.260 Chron.Box: H.195 W.210 D.205. The record is illustrated with 1 photograph.
Assembled from the source record's structured fields. Dates and attributions are given as the source states them; where a field is missing the Atlas leaves it blank rather than estimating.
Catalogue description
The source record does not include a narrative description. The structured fields above are reproduced from it.
Historical context
Modern Mechanical Horology (1945 – 1969)
Tool watches for divers, pilots and astronauts; electric watches anticipate the electronic age.
Electronic instruments, quartz frequency standards and the first atomic clocks transformed precision timing in laboratories and broadcasting.
Read the period in the timelineMore instruments from this periodEarlier: Golden Age of Mechanical Watchmaking
Atlas type guide
Marine chronometers
A marine chronometer is a precision timekeeper carried at sea to find longitude: the navigator compares local noon, observed with a sextant, with the time at a reference meridian kept by the chronometer. Each hour of difference corresponds to fifteen degrees of longitude. John Harrison proved the method in the 1760s; Pierre Le Roy, Ferdinand Berthoud, John Arnold and Thomas Earnshaw then developed the detent escapement and the compensation balance that made chronometers practical to manufacture.
By the nineteenth century London, Liverpool, Le Locle and Glashütte supplied navies and merchant fleets. A typical box chronometer has a spring-detent escapement, a fusee to equalise mainspring torque, a bimetallic compensation balance with a helical balance spring, and is mounted in gimbals inside a wooden box so that it stays level.
What to look for
- Gimbals and a three-tier wooden box with a glazed inner lid.
- A power-reserve ('up and down') indicator on the dial, usually showing 56 hours on two-day instruments.
- Spring-detent escapement and a cylindrical (helical) balance spring visible through the movement.
- Admiralty or navy marks (broad arrow), and rating certificates from observatories.
- The maker's number on the dial and movement; many makers' registers survive, allowing dating.
Dating clues
- Earnshaw-type spring-detent chronometers became standard after about 1800.
- Auxiliary compensation devices on the balance appear from the mid-nineteenth century.
- Quartz and radio time signals ended routine use of mechanical chronometers in the 1970s and 1980s.
General guidance written by the Atlas editors about this kind of object. It is not a statement about this particular piece; for that, rely on the source record above and on physical examination.
Read next:Spring detent (chronometer) escapementFuseeBalance spring (hairspring)Detent escapement
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