Le Roy Marine clock - CnAM 1395

Record summary

Held and catalogued by Conservatoire national des Arts et Métiers (object number 01395-0000-), this is a marine chronometer by Pierre Le Roy, made in France, dated 1766. The Atlas places it in the Precision & Scientific Horology period (1750 – 1850) of its Instruments collection. Materials and techniques recorded by the source: wood, steel, brass. Recorded dimensions: length: 35 centimetre; width: 25 centimetre; height: 25 centimetre. The record is illustrated with 4 photographs.

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

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