Marine chronometer by A. Johannsen and Co., London, 1897

Record summary

Catalogued by Howard Walwyn Fine Antique Clocks (dealer), London (stock number SKU 105), this is a marine chronometer by A. Johannsen and Co., made in London, England, dated 1897. The Atlas places it in the Industrial Revolution period (1850 – 1900) of its Instruments collection. Recorded dimensions: Height 22 cm. The record is illustrated with 2 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:FuseeBalance spring (hairspring)Detent escapement