ELD4840708: Acoustic: a test session on deaf-and-dumb people of the audiphone of Colladon, designed by the Swiss physicist, specialist in acoustics, Jean-Daniel (Jean Daniel) Colladon (1802-1893) on deaf-and-dumb people of the audiphone of Colladon. On, a type of hearing aid consisting of a diaphragm that, when placed against the upper teeth, conveys sound vibrations to the inner ear Engraving from “Popular Science” 1880 Private collection / Bridgeman Images