Instruments · Deck watch
Deck watch no. 6485 by A. Johannsen & Co
- Maker / attribution
- A. Johannsen & Co (maker)
- Date
- c. 1894
- Historical period
- Industrial Revolution (1850 – 1900)
- Country of origin
- Unrecorded in source
- Object type
- Deck watch
- Materials / technique
- metal: brass; metal: steel; wood: mahogany
- Dimensions
- Watch: 56 x 70 x 16 mm; Box: 95 x 62 x 120 mm
- Holding institution
- Royal Museums Greenwich
- Accession / object no.
- ZAA0220
- Credit line
- National Maritime Museum, Greenwich, London
- Catalogue title (original)
- 6485 (English)
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Record summary
Held and catalogued by Royal Museums Greenwich (object number ZAA0220), this is a deck watch by A. Johannsen & Co, dated c. 1894. The Atlas places it in the Industrial Revolution period (1850 – 1900) of its Instruments collection. Materials and techniques recorded by the source: metal: brass; metal: steel; wood: mahogany. Recorded dimensions: Watch: 56 x 70 x 16 mm; Box: 95 x 62 x 120 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
Catalogue description — Royal Museums Greenwich
Deck watch in a silver open-face case, in a wooden deck box. Three-quarter plate movement, signed and numbered and marked with a broad arrow, with lever escapement and compensation balance. The watch has a white enamel dial, signed and numbered and marked with a broad arrow, with Roman numerals and steel spade and poker hands, and a sunken subsidiary seconds dial below centre with a steel hand. It is contained in a silver open-face case, with the dome and back numbered and hallmarked for London, 1893-94, and the back marked with a broad arrow. The case has no glass. The watch is housed under screw-down glass in a brass canister in a wooden signed and numbered deck box.
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.
Read next:Spring detent (chronometer) escapementFuseeBalance spring (hairspring)Detent escapement
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