p at the bottom of this jar is connected with one wire of the battery E, the other going to the ground. At the receiving station the wire simply passes over an electro-magnet H, thence to the ground. Close to H is placed the diaphragm D, properly provided at its center with a metal plate which serves as armature for the electro-magnet, and fastened at its circumference in the holder T. The action of the instrument
Fig. 2.
is as follows: The person sending the message speaks into the mouthpiece T1 thus causing the diaphragm D1 with the plunger N, to vibrate. The greater the amplitude of vibration the deeper the rod N descends into the liquid, and therefore the thinner the stratum of liquid through which the current will have to pass; thus the resistance to the passage of the current is varied inversely as the intensity of the sound. At the receiving station the current magnetizes the electro-magnet H, and thus reproduces in the diaphragm D the vibrations of the diaphragm D1.
A number of telephones have since been invented, differing from each other in method of application and details of construction, but all embodying the scientific principle used by Gray.
Using the instrument invented by Reis, and the suggestions which Gray's experiments afforded, Thomas A. Edison began his attempts to construct a new form of telephone. Inasmuch as his experiments in this direction "cover many thousand pages of manuscript," only a few of the more characteristic ones will be given.
In the Reis transmitter a platinum screw was made to face the diaphragm, and a drop of water was put between them. The only result, however, was the decomposition of the water and the deposit of a sediment on the platinum. Two disks of platinum, one on the diaphragm and the other on the screw, so placed as to hold several drops of water by capillary attraction, were then tried. Acidulated solutions were substituted for water; paper and other materials, saturated with various solutions, were tried; sharp edges were substituted for disks. The result of all these experiments was complete failure, on
