Marine chronometer, United States, 1942

Record summary

Held and catalogued by Royal Museums Greenwich (object number LOA0143 5050 ROG018 LOA0143 L5497 L5511 F1182 F1183), this is a marine chronometer, made in Lancaster, PA, United States, dated 1942. The Atlas places it in the Golden Age of Mechanical Watchmaking period (1900 – 1945) of its Instruments collection. Materials and techniques recorded by the source: mahogany mahogany mahogany mahogany mahogany mahogany mahogany mahogany. Recorded dimensions: Overall: 190 x 210 x 200 mm. 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.

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.

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