John Roger Arnold Box Chronometer

This instrument, made by John Roger Arnold about 1825, is a specialized timekeeper for finding longitude at sea. The chronometer was part of the James Arthur Collection at New York University, and the university donated a portion of the collection, including the chronometer, to the Smithsonian in 1984.
To find longitude at sea, a chronometer was set to the time of a place of known longitude, like Greenwich, England. 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.
John Roger Arnold (1769-1843) learned watchmaking from his father, chronometer pioneer John Arnold, and Abraham Louis Breguet. The Arnolds were in business as Arnold & Son between 1787 and 1799, when the father died. In 1805 John Roger Arnold accepted the English Board of Longitude’s posthumous award to his father for improvements to the marine chronometer, which included simplifications that permitted others to undertake batch production of chronometers—a detached escapement, a helical balance spring and a temperature-compensated balance. The younger Arnold continued the business and between 1830 and 1840 took in partner Edward John Dent. In that decade, the firm made about 600 chronometers.
Mechanism details:
Escapement: Arnold, spring detent
Duration: 8-day
Power source: Spring drive with chain and fusee
Balance spring: helical, blued steel
Balance: J. R. Arnold with built-in aux. comp. Patented in 1821 (#4531)
Inscription: "Jn. R. Arnold _ London. Invt et Fecit No 491" on backplate
Dial details:
Engraved and silvered brass
Indicates hours, minutes, seconds
Inscription: “ARNOLD. / London / No 491" on dial
Blued steel spade hands
Brass bowl; bayonet-fitted bezel; convex, plain crystal
No box
No winding key, sprung dust cover over winding work
1. Gould, Rupert T. The Marine Chronometer. London: Holland Press, 1960.
2. Mercer, Tony. Chronometer Makers of the World. Essex: NAG Press, 1991.
3. Mercer, Vaudrey. John Arnold & Son, Chronometer Makers, 1762-1843. London: The Antiquarian Horological Society, 1972.
4. Mercer, Vaudrey. The Life and Letters of Edward John Dent, Chronometer Maker and some account of his Successors. London: The Antiquarian Horological Society, 1977.
5. Whitney, Marvin E. The Ship's Chronometer. Cincinnati: American Watchmakers Institute Press, 1985.
date made
ca 1825
John Roger Arnold
place made
United Kingdom: England, London
Physical Description
brass (overall material)
glass (part: material)
overall: 2 1/2 in x 3 3/4 in; 6.35 cm x 9.525 cm
ID Number
accession number
catalog number
See more items in
Work and Industry: Mechanisms
Measuring & Mapping
Time and Navigation
Time and Navigation, National Air and Space Museum
Data Source
National Museum of American History, Kenneth E. Behring Center


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