American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 424
THE PHONE. FIG. 268 … MAGNETIC COIL. 355^ AMERICAN TELEGRAPHY. The Gray Harmonic 1 elegraph. It is known that a steel rod or a tuning-fork lieicl at one end will vibrate at agiven rate when hit a smart blow, or moved out of the normal position and quicklyset free. This rate of vibration of the rod or fork is termed the…
Telegraph
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