Connection is established between the wires by the liquid. If the stream is narrow its resistance will be greater than if it were expanded 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 generated in the receiving aerial by the incoming waves vary in amplitude with those of the transmitting aerial, and, being in perfect accordance with the vibrations conveyed into the transmitter, cause the detector and telephone transmitter to reproduce the speech perfectly.
Experiments in wireless telephony have developed an interesting 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 charged with electricity and called "ions."
These ions pass through the grid and discharge against the plate. When the aerial is connected to the "grid," and the plate to the ground, the stream of ions carries that part of the alternating current in the aerial which flows in the same direction, across, but does not allow the current tending to pass in the opposite direction. In reality it is a valve, or "rectifier," opening one way and closing the other; thus changing the current into an intermittent, direct current, capable of manifesting itself in a telephone receiver.
FIG. 149.—Showing the brush discharge from a Marconi transatlantic aerial at night.
The Audion is a very sensitive device, and is much employed for wireless telephone purposes.
With such a system it has been found possible to transmit speech and music to a distance of two hundred miles. In fact, even greater distances have been covered, and there does not seem to be any good reason why it is limited to any range.
Transmission by wireless telephone is considerably more distinct than by wire line, and the fine inflections of the voice are brought out much better.
Unlike the ordinary line telephone, no rumbling or roaring noises are heard which confuse the speech, and there is absolute silence in the wireless telephone receiver, except when talking is going on. Any noises or sounds produced in the transmitting station, such as walking about the room, or the breathing of the person speaking into the transmitter, are reproduced faithfully at the receiving station many miles away.