Wireless Telegraphy and Telephony

134 WIRELESS TELEGRAPHY rod to a second diaphragm, which is provided with a mouthpiece. The water normally flows out of the jet in a smooth, unbroken column, breaking into drops at about the point A. As soon as it is disturbed in any way, how- ever, the distance from the outlet of the tube and the point where the drops commence becomes shortened. The vibra- tions of the voice, thrown into the mouthpiece and striking the diaphragm, are transmitted to the membrane through the medium of the little rod, and so cause corresponding changes in the pressure of the fluid in the tube. Each variation or disturbance in the pressure increases or de- creases the length of the stream before it breaks into drops. A pair of fine wires are inserted in the stream where the contractions are the strongest. Connection is estab- lished between the wires by the liquid. If the stream is narrow its resistance will be greater than if it were ex- panded at that point. The contracted portion of the liquid will jump up and down with the vibrations of the voice, and thus alter the amount of current flowing. The receiving apparatus consists of some form of detector and a telephone receiver and battery. The usual form of detector employed is the electrolytic. The currents gener- ated in the receiving aerial by the incoming waves vary in amplitude with those of the transmitting aerial, and, be- ing in perfect accordance with the vibrations conveyed into the transmitter, cause the detector and telephone trans- mitter to reproduce the speech perfectly. Experiments in wireless telephony have developed an in- teresting type of detector, known as the “Audion.” This consists of a six-volt, low-candlepower, incandescent lamp, having a small, nickel plate fastened a short distance from the filament, and a “grid” bent from wire placed midway between the two. When the filament is lighted from a battery, it throws off a stream of extremely small particles