After installing, on apparatus, Professor Rankine then left the theatre, the only contact between him and the theatre being a beam of light-passing through an aperture it. the wall and falling on to jo land speaker. Speaking into; the transmitter of his instru iment outside the theatre by was able to make his voice heard with ease, and then counted the numbers from one to twenty. During the counting an assistant from time to time intercepted the beam with a screen, when the sound absolutely atid dramatically ceased. The success of the experiment can be gathered from the fact that even when the beam was intercepted his natural voice could still be faintly j heard going on counting while when the beam fell on to the selenium the effect was so loud that the natural oice, different in tone, was completely drowned Another use had been found for ing fell accurately on to similar, the photophone, namely, the record-gaps of the second grating, with the/ing automatically of the human result that the maximum amountj{voice. In the gramophone the of light passed through.
The! waves of sound took the forms of tiniest deflection of the mirror that wavy lines much like a hospital occurred when the waves of speech temperature chart, but with the made the diaphragm vibrate slight- photophone the principle was differjy changed the direction of the rays, ent, and what was recorded directly with the result that part of the! were the rea] longitudinal waves light was cut off by the second grat-which can perhaps -be compating, and the issuing beam of light}ed roughly with the variations varied according to the movemenis; in pressure that would occur of the diaphragm. The selenium at!in a cylinder full of air the receiving end thus intercepted in which a piston was being light of varying intensity and modi-moved to and fro. These could be fied accordingly the current passing through the telephone, so that the sound from the transmitting station was reproduced, Selenium was most sensitive to the intrinsic brilliancy of the source of light used, and consequently sunlight was the best possible source, as it was some 250 times as brilliant as artificial light. With proper apparatus there was comparatively photographed by a form of cinema-camera, and when light was passed through them and thrown on to the selenium the sound that had produced them was reproduced. This also Professor. Rankine. very effectively demonstrated. The chief difficulty at present was to get satisfactory loud speakers, but some day this would doubtless be overcome.
Text read from the printed page and cleaned; old type leaves the occasional error.