‎"BELL, ALEXANDER GRAHAM. - ""THE GREATEST INVENTION I HAVE EVER MADE"": THE PHOTOPHONE.‎
‎On the Production and Reproduction of Sound by Light. (Read before the American Association for the Advancement of Science, in Boston, August 27, 1880).‎

‎(New Haven), 1880. 8vo. Modern plain wrappers. In: American Journal of Science"", Third series, Vol. XX, No. 118, October 1880. Frontispiece-plate. Pp. 257-352 (entire issue offered). Bell's paper: pp. 305-324 and 11 textillustrations. A small stamp to verso of plate and the first leaf.‎

Reference : 46951

‎First printing of this important paper in which Bell describes his and Charles Sumner Tainter's, his assistent, invention of the Photophone or Radiophone, THE PROGENITOR OF MODERN FIBER OPTICS. This invention made possible the world's FIRST WIRELESS TELEPHONE MESSAGE, and the first call was sent from the Franklin Scool to the window of Bell's laboratory, some 213 meter away.""On June 3, 1880, Alexander Graham Bell transmitted the first wireless telephone message on his newly invented ""photophone."" Bell believed the photophone was his most important invention. The device allowed for the transmission of sound on a beam of light. Of the eighteen patents granted in Bell's name alone, and the twelve he shared with his collaborators, four were for the photophone. Bell's photophone worked by projecting voice through an instrument toward a mirror. Vibrations in the voice caused similar vibrations in the mirror. Bell directed sunlight into the mirror, which captured and projected the mirror's vibrations. The vibrations were transformed back into sound at the receiving end of the projection. The photophone functioned similarly to the telephone, except the photophone used light as a means of projecting the information, while the telephone relied on electricity."" (Mary Bellis).The first successful attempts were based upon the properties of selenium: ""The electric resistance of which varies with the degree of illumination to which it is exposed. Hence, given a transmitting instrument, such as a flexible mirror, by which the vibrations of a sound could throw into vibrations a beam of light, a receiver, consisting of sensitive selenium, forming part of an electric circuit with a battery and a telephone, should suffice to translate the varying intensities of light into corresponding varying intensities of electric current, and finally into vibrations of the telephone disk audible once more as sound."" (Prescott, George. Bell's Electric Speaking Telephone. 313 p.).‎