Theodolite magnetometers were designed for observations in the field, and so are relatively light, compact, of simple construction, and easily handled. Their tri-leg base can hold either the magnetometer or the theodolite that is used for astronomical alignment. The U.S. Coast and Geodetic Survey designed this particular form in the early 1890s, basing it on the instrument that the Survey had been using since the early 1880s but adding several new features. One is the octagonal shape of the collimating magnets. Another is the black velvet screen that connects the telescope with the suspension box: this cuts off stray light,and eliminates the problems caused by the glass window in the earlier form.
This example is marked "C. & G. S. NO. 18." The Survey produced it in 1892-1893 and made it available for L.A. Bauer's magnetic survey of Maryland at the end of the century. The base—marked "Bausch, Lomb, Saegmuller Co., ROCHESTER, N.Y. 2690"—must be a replacement, made after the formation of that firm in 1905.
The U.S. Geological Survey acquired this magnetometer in 1973 when it assumed control of the geomagnetic program of the federal government, and it transferred it to the Smithsonian in 1982.
Ref: Edwin Smith, "Notes on Some Instruments Recently Made in the Instrument Division of the Coast and Geodetic Survey Office," Report of the Superintendent of the United States Coast and Geodetic Survey for the Year 1894, Appendix No. 8, p. 275.
L. A. Bauer, Maryland Geological Survey (Baltimore, 1897), p. 433.
Currently not on view
Object Name
Date made
U.S. Coast and Geodetic Survey
Physical Description
metal (overall material)
overall: 22 1/4 in x 16 1/4 in x 7 1/2 in; 56.515 cm x 41.275 cm x 19.05 cm
Place Made
United States: District of Columbia, Washington
ID Number
accession number
catalog number
Measuring & Mapping
Science & Mathematics
Science & Scientific Instruments
Science & Scientific Instruments
See more items in
Medicine and Science: Physical Sciences
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
U.S. Department of the Interior, U.S. Geological Survey

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