What is "thermophone"

Thermophone \Ther"mo*phone\, n. [Thermo- + phone.]

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.

n. 1 A form of transducer that generates sound waves of precise power. 2 (cx historical English) A portable telethermometer, using a telephone in connection with a differential thermometer. 3 (cx historical English) 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.