[f. as prec. + Gr. φωνή voice, sound, after TELEPHONE.] An apparatus in which sonorous vibrations of a diaphragm are produced by heat-rays.
1878. Th. Wiesendanger, in Engineer, XLVI. Nov., 335. The Thermophone. A new source of sound for the telephone.
1881. A. G. Bell, in Nature, 12 May, 44/1. We have decided to adopt the term ‘radiophone’ … limiting the words thermophone, photophone, and actinophone to apparatus for the production of sound by thermal, luminous, or actinic rays respectively.
1902. Sloane, Stand. Electr. Dict., 537. Thermophone, an apparatus for reproducing sounds telephonically by the agency of heat; a receiving-telephone actuated by heat.
