The Korn transmitter for photographs is quite different, although the receiver is practically the same as what has just been described. The basis of it is a peculiar power possessed by the metal selenium when in a certain state. This, like all metals, is a conductor of electricity, but of course offers resistance in some degree. Now the special feature of selenium is that its resistance is reduced if light shine upon it. Suppose, then, that current be flowing through a mass of selenium and that the latter be suddenly illuminated brightly, the resistance will at once fall and the current increase. On the other hand, should the light falling upon the selenium diminish, its resistance will increase and the current flowing through it will decrease. In short, given a suitable arrangement, the current flowing in a circuit of which a selenium "cell" forms a part will increase or decrease with the increase or decrease in the light falling upon the cell. A while ago the papers were telling striking stories of a way by which blind people, so it was said, were to be recompensed for the loss of their sight--a new sense, as it were, was to be given them by which they could "hear" light, even if they could not see it. All this had reference to this curious property of selenium, it being, of course, an undoubted fact that it will vary an electric current in accordance with the variations in the light, and if that current be led through a telephone receiver a man, by holding that to his ear, could, in a sense, hear the variations in the light. [Illustration: THE TELEWRITER This remarkable instrument transmits actual writing and drawings, the receiving pen copying precisely the movements of the sending pen] In the Korn transmitter for photographs selenium is employed as follows:--A transparent photograph is made, on a celluloid or gelatine film, and this is fixed upon a glass cylinder mounted as already described. A pencil of light falls upon this in much the same way as in the case of the receiver just described, and, as the cylinder revolves, describes a fine spiral line all round and round it. Moreover, the light passes right through the photograph and falls upon a mirror inside, off which it is reflected on to a selenium cell. At every moment, then, the light is falling upon some small part of the photograph, and the amount of it which gets through and ultimately reaches the selenium depends upon the density of that part. Current, meanwhile, is flowing from a battery through the selenium, and thence over the main wire to the distant station. As the light pencil traces its spiral path over the rolled up photograph every variation in the density of the picture is reproduced as a variation in the current through the selenium. This, at the remote end, operates the Einthoven galvanometer, the movements of which vary the shade of the spiral line being drawn upon the photographic paper.