Dodge, Mary Mapes, 1830-1905 · [New York : Scribner & Co.] · leaf 283
either with mines or with naturalobstacles. His method consisted, in brief,of laying an electric cable along the channelto be followed, and having it extend into thesea to any necessary distance from the shore.This ingenious device was described in St.Nicholas for December, 1920, by Mr. A.Russell… … APPARATUS POR MEASURING THE MAGNETIC FIELDS one on each side of the ship—these are flatspirals four feet in diameter called pancakecoils. The signals are transmitted from thecable to these coils by what is known as in-duction. This is based on the principle thatwhen an alternating current passes…
Children's literature
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