Talking pictures : how they are made, how to appreciate them (c. 1937)

Talking Pictures sary receivers are more costly than the vocal sort. These factors, plus the small image, make it seem improbable to most observers that television will enjoy a wide use for some time to come. Having transmitted this television signal as though it were a telephone or telegraph signal, it is now necessary to change it back from electricity into light. This might be done with a large number of tiny electric lamps lying beside each other like cells in a comb of honey. If it were practical to connect each of these lights by a separate wire or radio set to the corresponding little photoelectric cell in the sending device, the image would then be formed in the pattern of these lights, without any other mechanism. This would require thousands of wires or radio sets, and hence it would be impractical. It is necessary therefore to switch each light, one after another, to the receiver just at the exact speed and in the exact manner that the little photoelectric cells are switched to the transmitter. But for television so many thousands of lights would be required, one being like a single dot in a coarse newspaper illustration, that this use of individual lights is impracticable. Instead, in most of the modern systems, a device is used in the receiver which makes use of another tiny electrical stream. This is like the one in the sending apparatus, and it is caused to move in exactly the same manner or simultaneously with the one in the sending device. This stream varies in strength as that of a hose when the valve is opened and closed. The valve for the electrical stream is the light thrown into the sending device by its lens. As this stream strikes a special kind of screen, [284]