This instrument, a lighter and more robust version of the standard unifilar magnetometer used at the Kew Observatory, was designed by H. A. Denholm Fraser for the Magnetic Survey of India. Features include scales graduated on optical glass, and a phosphor-bronze ribbon to suspend the magnet. This example is marked "T. COOKE & SONS LTD. LONDON & YORK. No. 26" and "U.S.C.& G.S. No. 40." It was used at the U.S. Coast and Geodetic Survey's magnetic observatory in Honolulu from 1927 to the 1950s. The U.S. Geological Survey acquired it in 1973, when it took over the geomagnetic program of the federal government, and transferred it to the Smithsonian in 1982.
Thomas Cooke began in business in York, England, in 1837. The firm became T. Cooke & Sons in 1868, and T. Cooke & Sons Ltd. in 1897. A merger with Troughton & Simms Ltd. in 1922, led to the formation of Cooke, Troughton & Simms Ltd.
Photograph 82-15291 shows this magnetometer fitted with the induction apparatus developed by J. H. Nelson in 1938.
Ref: H. A. Denholm Fraser, "The Unifilar Magnetometer of the Magnetic Survey of India," Terrestrial Magnetism 6 (1901): 65-69.
T. Cooke & Sons, Illustrated Catalogue of Surveying Instruments, etc. (London, 1907), pp. 62-63.

Anita McConnell, Instrument Makers to the World. A History of Cooke, Troughton & Simms (York, 1992), pp. 69-70.

Currently not on view
Object Name
T. Cooke & Sons Ltd.
Physical Description
metal (overall material)
wood (part material)
horizontal circle: 6 in; x 15.24 cm
Place Made
United Kingdom: England, London
United Kingdom: England, York
ID Number
accession number
catalog number
Science & Scientific Instruments
Science & Scientific Instruments
See more items in
Medicine and Science: Physical Sciences
Measuring & Mapping
Science & Mathematics
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
U.S. Department of the Interior, U.S. Geological Survey
Additional Media

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