Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . not through both. A permanent magnet can be substituted for the electro-magnet in Fig. 242, as the same principles are wooden ring could belowered to the middleposition of the magnet andthe wire prolonged when agreater part of its fieldwould be in the magnetsfield. If the ring were locatedon the base, Fig. 242, andthe wire, AB, extended thewhole length of the magnet,one pole would tend to urge it in one direction and the otherpole in the opposite direction, so that if th
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . not through both. A permanent magnet can be substituted for the electro-magnet in Fig. 242, as the same principles are wooden ring could belowered to the middleposition of the magnet andthe wire prolonged when agreater part of its fieldwould be in the magnetsfield. If the ring were locatedon the base, Fig. 242, andthe wire, AB, extended thewhole length of the magnet,one pole would tend to urge it in one direction and the otherpole in the opposite direction, so that if the poles were ofequal strength the wire would not rotate. Another device to produce continuous rotation is illus-trated in Fig. 244, and called Barlows wheel. The edgeof a pivoted copper disc dips into a trough of mercury locatedbetween the poles of a horseshoe magnet. The magnets fieldacts at right angles to the currents field since the currentflows from the periphery of the disc to its axis, and the discrotates in the direction of the hands of a clock, Fig. 244, ascan be determined by the left-hand Fig. 244.—Barlows disc dynamo driven as a motor. 280 PRACTICAL ELECTRICITY. 268. Electrodynamics.—The term electrodynamics is ap-plied to the study of that part of electricity which treats ofthe force exerted by one current upon another. We havejust noted the reciprocal action between a current and a mag-net, and now in electrodynamics, the mutual action of thecurrents upon each other is to be considered. Every wirethrough which a current is flowing is surrounded by a mag-netic field, and the magnetic fields of two wires react uponeach other. This reaction may take place between two neigh-boring wires in the same circuit through which a current is
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