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

The Road Ahead had been photographed in motion pictures and projected like them on a screen. Let us watch a television eye "read" our page. It cannot read the words, as our eye reads them. It cannot even read individual letters all at once. (By "read" is meant to set up a series of electrical impulses which will reproduce the image of the letter in the receiver.) It must be done by a method similar to looking at the letter through a tiny hole which is being moved back and forth across the paper on which the letter is printed. This is done in a continuous succession of sweeps such as one would use in removing leaves from the sidewalk. As it moves, at one moment one sees the white paper through the hole, and the next the black ink of the printing. The light reflected from the tiny hole then can be thrown on a photoelectric cell similar to that we have seen used in reproductions photographed on motion picture film. As the light through the hole varies, the electric current generated by the cell varies and the television signal is formed. The little moving hole can be replaced, as in systems at present most popular, by a device known as an "iconoscope." In this device a tiny stream of invisible electricity sweeps or scans a picture thrown on a small screen by an ordinary camera lens — much as you would water the rows of flowers in your garden, one after another, with a hose. The screen consists of many tiny photoelectric cells, each of .which develops electricty proportional to the light thrown upon it. These are connected to the transmitter, one after another, by the sweeping stream of electricity. [281 ]