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

The Road Ahead the white beside it. It is easy to see that with twentyfive hundred letters and thirty images per second, several million "dots" or electrical impulses are required each second in a television system. If the telegraph dot consists of a momentary burst of current, it can be seen that an ordinary alternating electrical current consists of a continuous series of such bursts, these being twice as many as the current has "cycles per second." Only about ten thousand impulses a second are required to produce speech quite well, so telephone lines are only made to carry that many. It costs a great deal to make the special circuits required to carry the millions of impulses needed for television, but a few have been constructed for experimental purposes. Because of the nature of radio equipment it is necessary that the radio waves in use be composed of several — usually at least from five to ten — times as many impulses as the signal to be sent. Since the shortest radio broadcast waves themselves have only about three million impulses each second, they could not be expected easily to carry a television signal of about that same amount. As a result radio waves having about one hundred million impulses are used to carry a three million impulse signal. It can be seen that if a broadcast transmitter can send for five hundred miles, and a television transmitter only fifty miles, a great many television transmitters would be needed for everyone in the country, as well as the cities, to see television programs as they now hear vocal broadcasts. In addition these transmitters and the neces [283]