The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 99
eased and through the other decreased. As,however, the currents are arranged to pass in opposite direc-tions through the two primary coils, a double effect in thesame direction is induced in the secondary. Pencil Microphones.—These are generally various com-binations of Hughes carbon pencil… … Fig. 65 in the loose carbon contacts when subjected to slight jars.They are rather more powerful than the Blake, but not so goodas the granular type. The Crossley was the first pencil microphone brought intopractical use. As shown in Fig. 65, it consisted of four carbonblocks b, b, b, and b,…
Telephone
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