Dip Circle

Soon after becoming Superintendent of the U.S. Coast Survey in 1843, Alexander Dallas Bache ordered a dip circle from Henry Barrow (1790-1870), then the leading producer of geomagnetic instruments in England. The Survey went on to purchase several more Barrow circles of this sort and was still using them in the 1870s.

This example is marked "Henry Barrow & Co., 26 Oxendon Street, London" and "CS 9." It is based on the form that H. P. Gambey of Paris introduced in the 1830s. The needle is long, stretching from one side of the vertical circle to the other. The vertical circle is housed within the wood and glass box, graduated to about 15 minutes, and read by opposite magnifiers. The horizontal circle is graduated and read by vernier.

Ref: Charles A. Schott, "Terrestrial Magnetism," Report of the Superintendent of the U.S. Coast Survey for 1872, Appendix No. 14, p. 248 and plate 21.

Charles A. Schott, "Terrestrial Magnetism," Report of the Superintendent of the U.S. Coast Survey for 1875, Appendix No. 16, pp. 263-264 and plate 29.

Currently not on view
Object Name
dip circle
Henry Barrow & Co.
Physical Description
metal (overall material)
circle: 10 1/4 in; 26.035 cm
place made
United Kingdom: England, London
ID Number
catalog number
accession 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. Coast & Geodetic Survey

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