Dip Circle


This Kew pattern dip circle is marked "U.S.C.&G.S. No. 23" and was probably made in the instrument shop of the U.S. Coast and Geodetic Survey. The vertical circle is silvered, graduated to 30 minutes, and read by opposite verniers and magnifiers to single minutes. The horizontal circle is graduated to 30 minutes and read by vernier to single minutes. On top of the box there is a compass needle in a box with peep sights that measures magnetic variation.

A brass housing on the front of the instrument holds an auxiliary needle (now missing) that serves as a deflector for the determination of total intensity; this technique was introduced by Humphrey Lloyd, professor of natural philosophy at Trinity College, Dublin, in the early 1840s.

Ref: Daniel Hazard, Directions for Magnetic Measurements (Washington, D.C., 1911), pp. 66-69.

Humphrey Lloyd, "On a New Magnetical Instrument, for the Measurement of the Inclination, and Its Changes," Proceedings of the Royal Irish Academy 2 (1840-1844): 210-217, 226-232.

Maker: U.S. Coast and Geodetic Survey

Location: Currently not on view

Place Made: United States: District of Columbia, Washington

Subject: Science & Scientific Instruments


See more items in: Medicine and Science: Physical Sciences, Science & Mathematics, Measuring & Mapping


Exhibition Location:

Credit Line: U.S. Coast & Geodetic Survey

Data Source: National Museum of American History

Id Number: PH.314632Accession Number: 208213Catalog Number: 314632

Object Name: dip circle

Physical Description: metal (overall material)Measurements: overall: 10 1/2 in; 26.67 cmoverall in case: 12 in x 9 3/8 in x 8 1/4 in; 30.48 cm x 23.8125 cm x 20.955 cm

Guid: http://n2t.net/ark:/65665/ng49ca746a8-e5e1-704b-e053-15f76fa0b4fa

Record Id: nmah_1029361

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