Instruments · Marine chronometer
Marine chronometer no. 5421 by William Webb
- Maker / attribution
- William Webb (maker)
- Date
- 1860
- Historical period
- Industrial Revolution (1850 – 1900)
- Country of origin
- Unrecorded in source
- Object type
- Marine chronometer
- Dimensions
- Overall: 185 x 185 x 185 mm
- Holding institution
- Royal Museums Greenwich
- Accession / object no.
- ZAA0094
- Credit line
- National Maritime Museum, Greenwich, London
- Catalogue title (original)
- 5421 (English)
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Record summary
Held and catalogued by Royal Museums Greenwich (object number ZAA0094), this is a marine chronometer by William Webb, dated 1860. The Atlas places it in the Industrial Revolution period (1850 – 1900) of its Instruments collection. Recorded dimensions: Overall: 185 x 185 x 185 mm. 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
Catalogue description — Royal Museums Greenwich
This chronometer was purchased by the Admiralty from William Webb on December 6 1860. In 1869 it was sent to the Cape of Good Hope, probably for issue to a ship there rather than to the Observatory, returning three years later. In 1870 it was sent to the destroyer HMS Wolverine and in 1886 was issued to the second rate Victor Emmanuel. In 1902 it went to the cruiser HMS Charybdis for three years and served on the tanker HMS Birchol in 1924. In 1932 the chronometer was on board the light cruiser HMS Cairo for five years, then going to Colombo in 1940. In 1946 it served on the trawler HMS Sursay and then on Royal Fleet Auxiliary ship Belgol. In 1965 the chronometer was presented to the NMM by the Astronomer Royal. It was loaned to the Physics Exhibition at Alexandra Palace in March 1972 [56th Exhibition of Scientific Instruments and Apparatus (Institute of Physics) at Alexandra Palace in London from March 13-16, 1972]. On 10 February 1978, the instrument was loaned, with a number of others, to the BBC at Ealing Studios, to take part in the filming of the six-part BBC miniseries The Voyage of Charles Darwin.
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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