Earth Inductor

Earth Inductor

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This instrument is marked "MAX KOHL Werkstätten für Prazisions Mechanick CHEMNITZ I.S." and "CENTRAL SCIENTIFIC CO. LABORATORY APPARATUS CHICAGO U.S.A." Kohl described it as an "Earth Inductor after Palmieri...with round frame 300 mm diameter, with 100 turns of 1 mm thick wire, with commutator." Luigi Palmieri was a physicist in Naples who, in the 1840s, developed an earth inductor with elliptical ring that rotated around its longer axis. The Palmieri apparatus with a circular ring, as in this example, seems to have originated in the 1860s.

Max Kohl was in business as a scientific instrument maker from 1876 to 1937. The Central Scientific Co. was established in 1900. This example belonged to Trinity College in Hartford, Conn., and came to the Smithsonian in 1981.

Ref: Max Kohl, Physical Apparatus (Chemnitz, 1926), p. 974.

Currently not on view
Max Kohl
Place Made
Deutschland: Sachsen, Chemnitz
Physical Description
wood (overall material)
metal (part material)
overall: 15 3/4 in; 40.005 cm
overall: 17 in x 19 1/4 in x 11 3/4 in; 43.18 cm x 48.895 cm x 29.845 cm
ID Number
accession number
catalog number
Credit Line
Trinity College, Department of Physics
Science & Scientific Instruments
Science & Scientific Instruments
See more items in
Medicine and Science: Physical Sciences
Science & Mathematics
Measuring & Mapping
Data Source
National Museum of American History


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