Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book (1902)
Swoope, Coates Walton. [from old catalog] · New York, D. Van Nostrand company · leaf 58
Fig. 53.^PolarizedArmature. Fig. 54.—HorseshoeJIagnet with Keeper. The magnetism induced in the keeper reacts on the magnet,and not only helps to maintain the strength of the magnet,but also serves to augment it. A magnet deprived of itskeeper gradually loses its magnetism. Steel is much…
Electricity · Magnetism
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