Text-book of general physics, for the use of colleges and scientific schools (1899)
Hastings, Charles Sheldon · Boston: Ginn & company · leaf 503
the dia-phragm is set in vibration and emits a succession of sound-waves almost exactly the counterpart of those which originallyfell on the transmitter. 447. Microphone. — In 1878 Hughes made the discoverythat, if one portion of a conducting circuit rested lightlyagainst another, very slight… … TRANSMITTER. 493 bon resting lightly in small holes in the two carbon supportsA, B, carried by a light sounding board, I). Any slightvibration experienced byD will vary the contactresistance at the points of(7, and give rise to soundsof considerable intensityat the telephone T.
Physics
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