The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 76
:V777ZZ&2Z^ Fig. 37 On the same day that Bell filed his patent, Prof. E. Gray 54 PRACTICAL TELEPHONE HANDBOOK also filed one with very similar suggestions for producing varia-tions in the resistance of an electric circuit. Edisons Carbon Transmitter.—Edison, in 1878, was the firstto produce a…
Telephone
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