The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 82
as lifted out of a reservoir, t, containing the electro-lyte solution, and brought into contact with the chalk. When properly adjusted, the instrument was a powerfulone, giving out sounds that could be heard all over a largehall. The tone of the instrument, however, being verynasal, left much to be… … Fig. 43 instruments have since been invented, such as the GrahamBell and Tainters Photophone (1879), in which advantageis taken of the fact that the resistance of some substances,especially a preparation of selenium, is affected by light.At the transmitting station a parallel ray of light is…
Telephone
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