American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 139
le wire would produce a very limited deflection of the magnetic needle, unlessthe current in the wire were quite strong, or the needle very sensitive, or both, it iscustomary, in the construction of ordinary galvanometers, to arrange the wire in theform of a coil, or ring, of many convolutions, in… … If the earths magnetic influence upon a magnetic needle should be temporarilyeliminated while the needle is at the center of a coil of wire carrying an electriccurrent, what has been said relative to the effect of the earths magnetic influenceupon the needle would be true of the effect of the…
Telegraph
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