94 THE POPULAR SCIENCE MONTHLY. 



across its broad end, made a successful receiver. "With tlie 

 small end made to fit the ear, and the diaphragm end only a 

 few inches below the water, the sound of a hand-bell has been 

 received nearly a mile distant. Colladon and Sturm used a 

 somewhat similar receiver, and heard a heavy bell ten miles 

 away. 



It was necessary to devise a better form of receiving appara- 

 tus. The Bell receiver and the Blake transmitter will not work 

 under water. The first success was obtained by a form of trans- 

 mitter resembling the Ader. 



With this Prof. Blake transmitted and received signals be- 

 tween boats half a mile apart on the Taunton River in 1883. 

 The transmitter was weighted to float at different depths, but in 

 all positions as regards the approaching sound-waves it received 

 equally well. Up to half a mile the signals from an ordinary 

 dinner-bell were distinctly heard. These experiments seemed to 

 indicate that a transmitter dependent upon a variable contact 

 might yet be made which would work with satisfaction. This 

 line was consequently followed up, and apparatus was devised 

 by which signals were transmitted between boats a mile distant 

 off Stone Bridge, near Newport, R. I., in the same summer of 

 1883 through a rough sea and in a dense fog. Various forms of 

 microphonic transmitters were constructed, and experiments on 

 Long Island Sound and on the Wabash River at Terre Haute, 

 Ind., were conducted as opportunity permitted. One form of 

 transmitter which worked fairly well consists merely of a dia- 

 phragm having within itself the elements of a microphone. It 

 is placed in simple voltaic circuit with a Bell receiver. This 

 diaphragm is made of hard carbon in granules about the size of 

 smallest shot. A paste is made of these with rubber cement, 

 and this in a mold and die under heat and pressure becomes a 

 hard, thin, elastic disk. This diaphragm takes up the sound- 

 vibrations quite well out of the water. The action is similar to 

 that of a multiple contact transmitter. On the river, however, 

 through a long distance these did not seem sufficiently satisfac- 

 tory. This difference in action between a long and short dis- 

 tance led to the thought that, as the advancing front of the 

 sound-wave is an arc, approaching in curvature nearer and 

 nearer the tangent to its circle, a large diaphragm would receive 

 more sonorous energy and thus probably prove more effective. 

 This is the point to which the experiments have now been car- 

 ried, and the next trials will be with a diaphragm eighteen 

 inches square. In October, 1885, signals were transmitted and 

 received one and a half mile on the Wabash River from a 

 locomotive-bell around three or four windings of the river, so 

 that the operators were out of each other's sight and the sound 



