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.
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