Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book (1903)
Swoope, Coates Walton. [from old catalog] · New York, D. Van Nostrand company · leaf 61
here, such as is usedin roller bearings, by placing it between the unlike poles oftwo bar electromagnets so that its diameter and the axis ofthe magnets form a straight line. When plunged into filingsthe poles are readily observed. Cut a hole, equal to the di-ameter of the ball, in a sheet of… … Fig. 56.—The Earths Magnetic Polesand Equator. EARTHS MAGNETISM. 43
Electricity · Magnetism
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