Dip Circle
date: label: Date made
content: ca 1900
name: label: maker
content: Chasselon
notes: label: Description
content: 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.
label: Description
content: 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.
label: Description
content: Ref: E. Mascart and J. Joubert, <i>A Treatise on Electricity and Magnetism</i>, English transl. By E. Atkinson, (London, 1888), vol. II, pp. 591-593.
label: Description
content: E. Mascart, <i>Traité de Magnétism Terrestre</i> (Paris, 1900), pp. 168 and 214.
label: Description
content: Daniel Hazard, "Results of Magnetic Dip and Intensity Observations," <i>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</i>, Appendix No. 6, p. 350.
label: Location
content: Currently not on view
place: label: Place Made
content: France: Île-de-France, Paris
topic: label: Subject
content: Science & Scientific Instruments
setName: label: See more items in
content: Medicine and Science: Physical Sciences
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content: Science & Mathematics
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content: Measuring & Mapping
creditLine: label: Credit Line
content: U.S. Department of Commerce, Coast & Geodetic Survey
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: PH.316508
label: accession number
content: 225703
label: catalog number
content: 316508
objectType: label: Object Name
content: dip circle
physicalDescription: label: Physical Description
content: metal (overall material)
label: Measurements
content: verticle circle: 3 in; 7.62 cm
label: Measurements
content: overall; 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