Instruments · Marine chronometer
Marine chronometer by Mercer, London, c. 1864
- Maker / attribution
- Mercer (maker)
- Date
- c. 1864
- Historical period
- Industrial Revolution (1850 – 1900)
- Country of origin
- England
- Place
- London
- Object type
- Marine chronometer
- Materials / technique
- rosewood
- Stock no.
- Product 613
- Credit line
- Dealer listing, P A Oxley (product 613)
- Catalogue title (original)
- Rare 19th century Chronometer by Mercer of London (English)
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Record summary
Catalogued by P A Oxley (dealer), Wiltshire (stock number Product 613), this is a marine chronometer by Mercer, made in London, England, dated c. 1864. The Atlas places it in the Industrial Revolution period (1850 – 1900) of its Instruments collection. Materials and techniques recorded by the source: rosewood. The record is illustrated with 5 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
Dealer description — P A Oxley
A very early Thomas Mercer 2 Day Marine Chronometer. The silvered brass dial is engraved with the makers name, Thomas Mercer, Maker to the Admiralty, London No 901. The exceptional movement features an Earnshaw spring-detent escapement and a compensated balance wheel. The dial also shows the current capacity of the mainspring via a wind up and wind down subsidiary dial. The Rosewood veneered case is also of the highest quality with brass bound edges and the retailers name to the front elevation. Also with a push button lid which reveals the glass covered Chronometer below. RESTORATION: This Chronometer has only just arrived, although currently in working order it will require a full service before delivery. NOTE: Based on Mercers numbering system we can date this Chronometer very accurately to 1864. This is extremely early for a Mercer Chronometer. Other known Chronometers of this date are mostly found in Museums. Thomas Mercer was an exceptional maker, later in the 19th century the Mercer company was producing huge numbers of Chronometers for the Admiralty and Merchant ships. According to records this was not used by the Admiralty which therefore means it was used on a Merchant ship. The research is currently ongoing to find out which ship that was.
Historical context
Industrial Revolution (1850 – 1900)
American interchangeable-parts manufacture; railroad time standards; Swiss and German factory systems.
Instruments spread into industry, science and sport: stopwatches, chronoscopes, metronomes, watchmen's clocks and time recorders.
Read the period in the timelineMore instruments from this periodEarlier: Precision & Scientific Horology
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.
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