HOW GUGLIELMO MARCONI TELEGRAPHS WITHOUT WIRES

His father's farm was his first field of operations, the small beginnings of experiments that were later to stretch across many hundreds of miles of ocean. Set up on a pole planted at one side of the garden, he rigged a tin box to which he connected, by an insulated wire, his rude transmitting apparatus. At the other side of the garden a corresponding pole with another tin box was set up and connected with the receiving apparatus. The interest of the young inventor can easily be imagined as he sat and watched for the tick of his recording instrument that he knew should come from the flash sent across the garden by his companion. Much time had been spent in the planning and the making of both sets of instruments, and this was the first test; silent he waited, his nerves tense, impatient, eager. Suddenly the Morse sounder began to tick and burr-r-r; the boy's eyes flashed, and his heart gave an exultant bound—the first wireless message had been sent and received, and a new marvel had been added to the list of world's wonders. The quiet farm was the scene of many succeeding experiments, the place having been put at his disposal by his appreciative father, and in addition ample funds were generously supplied from the same source. Different heights of poles were tried, and it was found that the distance could be increased in proportion to the altitude of the pole bearing the receiving and transmitting tin boxes or “capacities”—the higher the poles the greater distance the message could be sent. The success of Marconi's system depended largely on his receiving apparatus, and it is on account of his use of some of the devices invented by other men that unthinking people have criticised him. He adapted to the use of wireless telegraphy certain inventions that had heretofore been merely interesting scientific toys—curious little instruments of no apparent practical value until his eye saw in them a contributory means to a great end.

Though Hertz caught the etheric waves on a wire hoop and saw the answering sparks jump across the unjoined ends, there was no way to record the flashes and so read the message. The electric current of a wireless message was too weak to work a recording device, so Marconi made use of an ingenious little instrument invented by M. Branly, called a coherer, to hitch on, as it were, the stronger current of a local battery. So the weak current of the ether waves, aided by the stronger current of the local circuit, worked the recorder and wrote the message down. The coherer was a little tube of glass not as long as your finger, and smaller than a lead pencil, into each end of which was tightly fitted plugs of silver; the plugs met within a small fraction of an inch in the centre of the tube, and the very small space between the ends of the plugs was filled with silver and nickel dust so fine as to be almost as light as air. Though a small instrument, and more delicate than a clinical thermometer, it loomed large in the working-out of wireless telegraphy. One of the silver plugs of the coherer was connected to the receiving wire, while the other was connected to the earth (grounded). To one plug of the coherer also was joined one pole of the local battery, while the other pole was in circuit with the other plug of the coherer through the recording instrument. The fine dust-like silver and nickel particles in the coherer possessed the quality of high resistance, except when charged by the electric current of the ether waves; then the particles of metal clung together, cohered, and allowed of the passage of the ether waves' current and the strong current of the local battery, which in turn actuated the Morse sounder and recorder. The difficulty with this instrument was in the fact that the metal particles continued to cohere, unless shaken apart, after the ether waves' current was discontinued. So Marconi invented a little device which was in circuit with the recorder and tapped the coherer tube with a tiny mallet at just the right moment, causing the particles to separate, or decohere, and so break the circuit and stop the local battery current. As no wireless message could have been received without the coherer, so no record or reading could have been made without the young Italian's improvement.

In sending the message from one side of his father's estate at Bologna to the other the young inventor used practically the same methods that he uses to-day. Marconi's transmitting apparatus consisted of electric batteries, an induction coil by which the force of the current is increased, a telegrapher's key to make and break the circuit, and a pair of brass knobs. The batteries were connected with the induction coil, which in turn was connected with the brass knobs; the telegrapher's key was placed between the battery and the coil. It was the boy scarcely out of his teens who worked out the principles of his system, but it took time and many, many experiments to overcome the obstacles of long-distance wireless telegraphy. The sending of a message across the garden in far-away Italy was a simple matter—the depressed key completed the electric circuit created by a strong battery through the induction coil and made a spark jump between the two brass knobs, which in turn started the ether vibrating at the rate of three or four hundred million times a minute from the tin box on top of a pole. The vibrations in the ether circled wider and wider, as the circular waves spread from the spot where a stone is dropped into a pool, but with the speed of light, until they reached a corresponding tin box on top of a like pole on the other side of the garden; this box, and the wire connected with it, caught the waves, carried them down to the coherer, and, joining the current from the local battery, a dot or dash was recorded; immediately after, the tapper separated the metal particles in the coherer and it was ready for the next series of waves.