Instruments · Marine chronometer; fric rest
Marine chronometer by Sully, Henry, France, 1724
- Maker / attribution
- Sully, Henry (maker)
- Date
- 1724
- Historical period
- Early Modern Horology (1600 – 1750)
- Country of origin
- France
- Place
- Paris, Ville de Paris, Ile-de-France, France, Paris
- Object type
- Marine chronometer; fric rest
- Holding institution
- Science Museum Group, London
- Accession / object no.
- L2015-3478
- Credit line
- Lent by the Worshipful Company of Clockmakers
- Catalogue title (original)
- Marine timekeeper by Henry Sully, Paris, 1724
Record summary
Held and catalogued by Science Museum Group, London (object number L2015-3478), this is a marine chronometer; fric rest by Sully, Henry, made in Paris, Ville de Paris, Ile-de-France, France, Paris, dated 1724. The Atlas places it in the Early Modern Horology period (1600 – 1750) of its Instruments collection. 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
Science Museum Group description
The prototype of two later clocks, it was demonstrated in Paris at the Academie Royale. Although tested vigorously on land; it was transported over cobble streets in a berline carriage, it unfortunately failed at sea. Clockmakers' Museum No. 597
Historical context
Early Modern Horology (1600 – 1750)
Huygens' pendulum and balance spring transform accuracy; English makers develop the anchor and deadbeat escapements.
Pocket sundials, Butterfield dials and sandglasses remained essential companions to imperfect clocks; navigators used sandglasses and the log line; observatories began to combine telescopes with pendulum clocks.
Read the period in the timelineMore instruments from this periodEarlier: Renaissance 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 escapementFuseeBalance spring (hairspring)Detent escapement
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