Wireless Telephony

The Great Round World

At the recent annual session of the British Association for the Advancement of Science it was announced that experiments in wireless telephony have proved that it is possible to convey audible speech without wires six or eight miles over the sea. William H. Preece, who made the announcement, is consulting engineer to the British Post Office and the colonies. He has had a lifelong experience in electrical engineering, and is the author of text-books on telegraphy and telephony.

The wireless telephone is made practicable by the invention of Mr. Walker Moseley, a well-known English electrical engineer. The difficulty that has stood in the way of the use of the apparatus of wireless telegraphy for telephony is that wireless telegraphy requires an electric current much stronger than any telephone transmitter hitherto invented will stand. Mr. Moseley has made a transmitter that will utilize fifty times more current than any other now in use. "I take," he says, "a wooden hemisphere, like a salad bowl, and cut about twenty-five holes through through it, in each of which I fix a diaphragm two inches in diameter, each diaphragm having one of my new microphones in its centre." The electrical current for this new telephony is carried, not through the air as in the case of wireless telegraphy, but through the sea or the ground. From the transmitter a wire runs out for a hundred yards or more a few feet above the earth. This wire is the "base." Now, an electrical current always tends to return to its startingplace, either through the earth or through the air. The current engendered by speaking into Mr. Moseley's transmitter, after passing along the wire to the other end of the base, passes through the earth on its way back. "But," as Mr. Moseley explains it, "its way back is not wholly straight. Many waves describe parabolic curves, limited in circumference only by the length of the base. With a base of one hundred yards these electrical waves will reach considerably over a mile away, so that, if there is a receiving apparatus to tap them at that distance, I can speak to any person stationed there."

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