Many investigators had succeeded before Marconi in sending telegraphic messages several miles through the air or ether between two points not directly connected by wires. Marconi has extended the distance by employing a much higher electro-motive force at the sending station and using the feeble inductive effect at a distance to set in action a local battery.
It is evident that wires are needed at the sending station from every point of which magnetic and electric waves are sent out, and wires at the receiving station which embrace, so to speak, these waves in the manner shown by our photographs. These waves produce minute sparks in the receiving instrument, which act like a suddenly drawn flood gate in allowing the current from a local battery to flow through the circuit in which the spark occurs, and thus produce a click on a telegraphic instrument.
We have said that messages had been sent by what is called wireless telegraphy before Marconi made his experiments. These messages had also been sent by induction, signals on one wire being received by a parallel and distant wire. To Marconi is due the credit of greatly extending the method by using a vertical wire. The method of using the coherer to detect electric pulses is not due, however, to Marconi. It is usually attributed to Branly; it had been employed, however, by previous observers, among whom is Hughes, the inventor of the microphone, an instrument analogous in its action to that of the coherer. In the case of the microphone, the waves from the human voice shake up the particles of carbon in the microphone transmitter, and thus cause an electrical current to flow more easily through the minute contacts of the carbon particles.
Fig. 5.—Magnetic whirls about the receiving wire.
The action of the telephone transmitter, which also consists of minute conducting particles in which a battery terminals are immersed, and the analogous coherer is microscopic, and there are many theories to account for their changes of resistance to electrical currents. We can not, I believe, be far wrong in thinking that the electric force breaks down the insulating effect of the infinitely thin layers of air between the particles, and thus allows an electric current to flow. This action is doubtless of the nature of an electric spark. An electric spark, in the case of wireless telegraphy, produces magnetic and electric lines of force in space, these reach out and embrace the circuit containing the coherer, and produce in turn minute sparks. Similia similibus—one action perfectly corresponds to the other.
The Marconi system, therefore, of what is called wireless telegraphy is not new in principle, but only new in practical application. It had been used to show the phenomena of electric waves in lecture rooms. Marconi extended it from distances of sixty to one hundred feet to fifty or sixty miles. He did this by lifting the sending-wire spark on a lofty pole and improving the sensitiveness of the metallic filings in the glass tube at the receiving station. He adopted a mechanical arrangement for continually tapping the coherer in order to break up the minute bridges formed by the cohering action, and thus to prepare the filings for the next magnetic pulse. The system of wireless telegraphy is emphatically a spark system strangely analogous to flash-light signaling, a system in which the human eye with its rods and cones in the retina acts as the coherer, and the nerve system, the local battery, making a signal or sensation in the brain.
