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n.1.A portable form of telethermometer, using a telephone in connection with a differential thermometer.
2.A telephone involving heat effects, as changes in temperature (hence in length) due to pulsations of the line current in a fine wire connected with the receiver diaphragm.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
Crandall [2] studied the thermoacoustic effect and the thermophone as a source of sound theoretically and experimentally in 1917.
Arnold and Crandall [2] obtained the temperature variation over the surface of the thermophone and pressure in the far field by applying the current through themoacoustic source.
The next 20 years saw the development of the thermophone, a calculable source of sound for calibrating microphones [12], substantial expansion of the theory underlying microphone calibrations [13-17], and the development of improved condenser microphone designs suitable for mass production [18,19].