Radio Broadcast (May-Oct 1922)

What Everyone Should Know About Radio History 20 1 second wire. When the sending switch was closed it sent current through the river water from one plate on the sending bank to the other. The current spread throughout the river and some of it strayed to the opposite bank, flowing through the opposite plates and wire and thus through the receiving instrument. Although but a small part of the current reached the opposite bank it was sufficient to actuate the galvanometer used for receiving, and thus wireless telegraphy was an accomplished fact. It may be noted that quite long wires were necessary on the two banks of the stream so it could not logically be called wireless communication, but it must be remembered that such is always the fact with our present radio stations. In a modern radio transAtlantic station the sending antenna may contain 50 miles of wire in the overhead net work and perhaps even more buried underground. The essential point in wireless communication is that there must be no wires connecting one station with the other. BRITISH SCIENTISTS WHO CONTRIBUTED In 1859, in Dundee, Lindsay was working along the same lines that Morse had followed, apparently unacquainted with Morse's experiments. He made many tests and endeavored to find the laws of transmission distance in terms of the size of plates used, length of land wires, size of galvanometer coil, etc. He came to the conclusion that if two plates were immersed in the ocean, one off the most northerly part of Scotland and the other off the southern coast of England, if a powerful set of batteries was used for sending, and if a galvanometer coil weighing two hundred pounds were used at the receiving station, it would be possible to send messages from England to America through the ocean water. We know now that the laws he deduced were not quite correct and that such a scheme is MICHAEL 1. PUPIN not feasible. The idea of a receiving coil weighing two hundred pounds is interesting when we consider that the coil of the galvanometer actually used to-day weighs less than an ounce. In 1845 Wilkins, in England, suggested that Morse's scheme be used in establishing wireless communication with France, across the English Channel, the same feat that was to make Marconi famous fifty years later, using a different and more effective form of transmission. Many more experimenters than the few mentioned here worked in this field, endeavoring to eliminate the connecting wire between the two stations, among them Professor Trowbridge, of Harvard. He reached the conclusion that transAtlantic communication by Morse's scheme might be possible if the two plates to be submerged in the ocean were as far apart as are Nova Scotia and Florida. The wire thus required to connect the two plates would be as long as the distance to be traversed, a statement which gives the approximate range for this type of wireless transmission. The laws of the spreading of current were better known to Trowbridge than they were to Lindsay when he first put out his project, and furthermore the telephone receiver had been invented in the mean time which gave to the scheme a receiver much more sensitive than anticipated by Lindsay. Trowbridge also put forth the quite feasible scheme of fitting a ship with submerged plates in bow and stern (or bow plate and a trailing insulated wire astern, carrying the second plate at its end) and sending out into the ocean an interrupted current which would spread out all around the ship; another ship similarly equipped with plates and a telephone receiver for listening, would be able to detect the presence of the first ship, thus rendering collision in case of fog much less likely. If the