backplate - from catalog card: 2 29/32 in; 7.366 cm
overall: 2 1/8 in x 4 1/2 in; 5.3975 cm x 11.43 cm
box chronometer, without case
United Kingdom: England, London
This instrument is a specialized timekeeper for finding longitude at sea. It was made by the firm Robert Molyneux & Sons of London, England, between 1832 and 1845. The U.S. Navy Bureau of Ships transferred it to the Smithsonian in 1953.
To find longitude at sea, a chronometer would be set to the time of a place of known longitude, like Greenwich, England, the prime meridian. That time, carried to a remote location, could be compared to local time. Because one hour of difference in time equals 15 degrees difference in longitude, the difference in time between the chronometer and local time would yield local longitude. The instruments require careful handling to keep precise time. Although the original box for this instrument has not survived, most chronometers are fitted in a wooden box in a gimbal to remain level and compensate for the movement of a ship at sea.
Robert Molyneux was a maker of chronometers and precision clocks in England. He was trained by Thomas Earnshaw and went into business for himself in the 1820s. In 1832 he moved his London business from 44 Devonshire Street to 30 Southampton Row and partnered with his son Henry in 1835. In 1842 the chronometer firm Birchall & Appleton moved to that address.
Escapement: Earnshaw spring detent
Power source: Spring drive with chain and fuse
Balance spring: helical, blued steel
Engraved and silvered brass
Indicates hours, minutes, seconds, and winding level up and down
Inscription: “Molyneux & Sons / 30 Southampton Row, London / No 1436 / U.S. Army.”
Blued steel spade hands
Brass bowl with fittings to insert in gimbal
No winding key
1. Britten, Frederick James. <i>Old Clocks and Watches & Their Makers.</i> London: E. & N. Spon Limited, 1922.
2. Gould, Rupert T. <i>The Marine Chronometer.</i> London: Holland Press, 1960.
3. Mercer, Tony. <i>Chronometer Makers of the World.</i> Essex: N.A.G. Press, 1991.
4. Whitney, Marvin. <i>The Ship’s Chronometer.</i> Cincinnati: American Watchmakers Institute Press, 1985.