Professor Trowbridge also revived the idea of telegraphing across the Atlantic by utilizing the conductivity of the sea-water to carry the currents. In working out the plan theoretically he discovered that the terminals on the American side would have to be widely separated--one in Nova Scotia and the other in Florida--and that they would have to be connected by an insulated cable. Two widely separated points on the coast of France were suggested for the other terminals. He also calculated that very high voltages would be necessary, and the practical difficulties involved made it seem certain that such a system would cost far too much to construct and to operate to be profitable.
Trowbridge suggested the possibility of using such a system for establishing communication between ships at sea. Ship could communicate with ship, over short distances, during a fog. A trailing wire was to be used to increase the sending and receiving power, and Trowbridge believed that with a dynamo capable of supplying current for a hundred lights, communication could be established at a distance of half a mile.
Not satisfied with the earth or the sea as a medium for carrying the current, Trowbridge essayed to use the air. He believed that this was possible, and that it would be accomplished at no distant date. He believed, however, that such a system could not be operated over considerable distances because of the curvature of the earth. He endeavored to establish communication through the air by induction. He demonstrated that if one coil of wire be set up and a current sent through it, a similar coil facing it will have like currents induced within it, which may be detected with a telephone receiver. He also determined that the currents were strongest in the receiving coil when it was placed in a plane parallel with the sending coil. By turning the receiving coil about until the sound was strongest in the telephone receiver, it was thus possible to determine the direction from which the messages were coming. Trowbridge recognized the great value of this feature to a ship at sea.
But these induced currents could only be detected at a distance by the use of enormous coils. To receive at a half-mile a coil of eight hundred feet radius would have been necessary, and this was obviously impossible for use on shipboard. So these experiments also developed no practical improvement in the existing means of communication. But Professor Trowbridge had demonstrated new possibilities, and had set men thinking along new lines. He was the pioneer who pointed the way to a great invention, though he himself failed to attain it.