Another electrical apparatus for recording speech may be mentioned. This rejoices in the uncouth name of the Photographophone, and it is the invention of Ernst Ruhmer, a German. Its working is based upon the fact that the intensity of the light of the electric arc may be varied by sound vibrations, each variation in the latter producing a corresponding variation in the amount of light. In the photographophone the light of an arc lamp is passed through a lens which focuses it upon a moving photographic film. By speaking or singing, the light is made to vary in brilliance, and proportionate effects are produced in the silver bromide of the film. On developing the film a permanent record of the changes in the light intensity is obtained, in the form of shadings of different degrees of darkness. The film is now moved forward from end to end in front of a fairly powerful lamp. The light passes through the film, and falls upon a sort of plate made of selenium. This is a non-metallic substance which possesses the curious property of altering its resistance to an electric current according to the amount of light falling upon it; the greater the amount of light, the more current will the selenium allow to pass. The selenium plate is connected with a telephone receiver and with a battery. As the film travels along, its varying shadings allow an ever-changing amount of light to pass through and fall upon the selenium, which varies its resistance accordingly. The resulting variations in the current make the receiver diaphragm give out a series of sounds, which are exact reproductions of the original sounds made by the voice. The reproduction of speech by the photographophone is quite good, but as a rule it is not so perfect as with the telegraphone. About ten years ago a German inventor, Professor A. Korn, brought out the first really practical method of telegraphing drawings or photographs. This invention is remarkable not only for what it accomplishes, but perhaps still more for the ingenuity with which the many peculiar difficulties of the process are overcome. Like the photographophone, Korn’s photo-telegraphic apparatus utilizes the power of selenium to alter its resistance with the amount of light reaching it.