Dip Circle

Description:

This type of unusually small dip circle was designed by Emile Brunner in Paris in the 1880s and widely used by the French Magnetic Survey. The vertical circle is movable, located inside the box, and equipped with two small concave mirrors. The center of curvature of these mirrors is in the plane of the needle, and so the mirrors give real and inverted images of the points of the needle. To take a reading, the viewer rotates the circle until these two images are brought into contact with the points themselves. The vertical is graduated to 30 minutes and read by vernier to single minutes. The horizontal circle is silvered and graduated.

This example was made by Victor Chasselon, a French instrument maker who took over the Brunner shop in the 1890s. The inscriptions read "Chasselon a Paris No. 40" and "USC&GS NO 24." It belonged to the U.S. Coast and Geodetic Survey, which found impurities in the brass of which it was constructed.

Ref: E. Mascart and J. Joubert, A Treatise on Electricity and Magnetism, English transl. By E. Atkinson, (London, 1888), vol. II, pp. 591-593.

E. Mascart, Traité de Magnétism Terrestre (Paris, 1900), pp. 168 and 214.

Daniel Hazard, "Results of Magnetic Dip and Intensity Observations," Report of the Superintendent of the United States Coast and Geodetic Survey Showing the Progress of the Work from July 1, 1901, to June 30, 1902, Appendix No. 6, p. 350.

Date Made: ca 1900

Maker: Chasselon

Location: Currently not on view

Place Made: France: Île-de-France, Paris

Subject: Science & Scientific Instruments

Subject:

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

Exhibition:

Exhibition Location:

Credit Line: U.S. Department of Commerce, Coast & Geodetic Survey

Data Source: National Museum of American History

Id Number: PH.316508Accession Number: 225703Catalog Number: 316508

Object Name: dip circle

Physical Description: metal (overall material)Measurements: verticle circle: 3 in; 7.62 cmoverall; dip circle: 6 1/4 in x 4 5/8 in x 4 3/8 in; 15.875 cm x 11.7475 cm x 11.1125 cm

Guid: http://n2t.net/ark:/65665/ng49ca746a8-f7ad-704b-e053-15f76fa0b4fa

Record Id: nmah_1029365

Our collection database is a work in progress. We may update this record based on further research and review. Learn more about our approach to sharing our collection online.

If you would like to know how you can use content on this page, see the Smithsonian's Terms of Use. If you need to request an image for publication or other use, please visit Rights and Reproductions.