CHAPTER XV. Telegraphing Without Wires

TELEGRAPHING WITHOUT WIRES

THE telegraph pole is one of the signs of civilisation. Along every railway the telegraph poles, with their insulating cups and strands of wires, stand like a military guard, connecting each station with all the rest, and preserving the necessary communication with headquarters. Along the high roads also, and sometimes over hill and dale, these outposts of civilisation stretch their long arms. They resemble human beings in this respect that they suffer from heat and cold and exposure to the weather. In hot weather the wires expand, in cold weather they contract, and in stormy weather they groan and howl. Sometimes they are blown down, and then they are as useless for purposes of telegraphy as a fallen soldier is useless for war. When protection from storm is specially necessary, the wires are sometimes buried in the ground. They are insulated properly and twisted together into a cable, which looks very much like a wire rope; and the cable is laid in the ground surrounded by a leaden tube. Such cables are used when we want to connect two stations across the sea, and when that sea is the Atlantic Ocean, the cables have to be very stout and strong.

All this trouble would be saved if there were some way of telegraphing without wires. We do not use wires in communicating with each other by speech or sign, and there is no reason why a similar system should not be invented for great distances. This has really been accomplished, after long-sustained efforts, and now we have systems of wireless telegraphy by which ships in mid-ocean can keep in constant communication with the land, and even print a daily newspaper containing all the latest news.

We have seen that when an electric current is sent through a coil of wire wound round a piece of soft iron we get an electromagnet. The electromagnet is capable of turning a magnetic needle at some distance. If we could make the needle turn at a distance of a mile, we should have a simple system of wireless telegraphy. It would be sufficient to send the current into the electric magnet now in one direction and now in another. The needle would then turn towards the West or the East, and we could arrange with our friend who observes the magnet as to what we mean by the various signals. The action of the magnet is felt all over the world, but it is felt much less at a great distance from us than within a few feet or inches. In fact, when the distance becomes more than a few yards, the effect is so small that it is quite invisible. That is why this simple system cannot succeed. We want a system the power of which is not confined to close quarters. Our success will depend upon the rate at which the power of our instrument diminishes when the resistance is increased.

If we drop a stone into water, it sends out circular waves which become gradually feebler and feebler as the distance increases. At a distance of twenty feet they are twice as feeble as they are at a distance of ten feet. Their crests only reach half the height. Bad as this is, it is much worse in the case of light, and very much worse in the case of magnetism. In the case of light only a quarter of the strength remains when we double the distance, and in the case of magnetism only one-eighth remains. If, however, we could have some system of telegraphy resembling water waves it would be a great deal better than any other kind. And this is precisely the way in which the inventors of wireless telegraphy attained their triumph.

The first man to produce waves of electricity, and to prove that they were waves of electricity, was a German professor of the name of Hertz. He lived at Bonn on the Rhine, and spent a great deal of time trying to prove that electric force does not spread out into space instantly, but takes time to reach a distant point. He found that this time was very short indeed. He found, in fact, that the speed of electricity is the same as the speed of light. He proved that if electricity is made to surge up and down an electric wire, a wave of electric force travels out in all directions. If such a wave falls upon a sheet of metal, it is reflected just as light is reflected from a mirror. A similarity to light also appeared in many other properties of the electric waves or radiations. These could be concentrated by a curved mirror, and refracted by a large prism of pitch. These waves of electric force are indeed a kind of light waves. But whereas light waves are so short that some fifty thousand of them go to the inch, the waves which Hertz discovered were each several yards long.

The first practical system of wireless telegraphy was invented and carried out by a young Italian engineer of the name of Marconi. Strictly speaking, it may be said that Marconi discovered nothing. What he did was to apply the scientific discoveries of his predecessors and make them practically useful. Marconi made the electric discharge pass between two round knobs, and to these two knobs he attached two wires. One of the wires went high into the air, and the other went down into the ground. The consequence was that when the discharge passed between the two knobs, electricity was in turn thrown up into the air and thrown down into the ground. The effect was very much like that produced by throwing a stone into water. A wave of electric force started from the wire and spread out all around it. As soon as any electricity was thrown into the earth, it spread out along the surface in great waves, which travelled over the ground at an incredible speed. As soon as electricity was thrust up along the wire, a want of electricity was produced in the earth, and this electric vacuum, as we might call it, spread out along the ground in the same way as the first pulse. It was indeed a process resembling the crest and the valley of a wave of water.

This was, therefore, the state of things likely to produce the best results. Any other vertical wire at a distance along the surface of the earth would experience the effect of such waves. The electricity would surge up into the wire when the crest of the wave readied it, and would rush down again as the wave subsided.

Now, every such motion of electricity constitutes an electric current. It remained to discover this current, and to devise a delicate instrument for discovering it even when it is very weak.

The instrument which Marconi used for this purpose was called a “coherer.” It was a little glass tube filled with some metallic powder. When an electric wave passes through such powder, the particles cohere or stick together, and then the powder conducts the current easily. That being the case it was only necessary to have a battery in readiness to take advantage of the new state of affairs. That battery was connected to both the end wires of the coherer, and as soon as the wave reached the wire and the coherer began to conduct it, a current from the battery passed through and worked an ordinary telegraph apparatus. When the coherer was shaken or tapped with a little hammer, it lost its conductivity and was ready to receive the next wave. Marconi had a little hammer tapping the coherer at very short intervals, so that it was always ready to receive any wave that might be sent out from the sending station as a signal.

That is, in a few words, the principle of Marconi’s system of wireless telegraphy. It was first tried at a regatta on the Thames, being fixed up on board a steam launch which followed the racing boats and sent news of the exact position of the boats to the receiving station on the shore. It was next tried on the open sea during a regatta off Kingstown, in Ireland. Later it was used to send messages a distance of forty miles over Salisbury Plain. For this purpose the wire had to be taken very high into the air, and this was done by means of kites.

Wireless telegraphy was also tried on board an Italian war vessel which sailed from Italy to Gibraltar, and round the coasts of France, Denmark, and Germany as far as Russia. The war-ship remained all the time in telegraphic communication with a wireless telegraphic station in Cornwall. But the greatest triumph of all was when Marconi succeeded in establishing communication between Cornwall, and Connemara, on this side of the Atlantic, and Canada on the other side. To cover this great distance large sending stations had to be erected and several thousand horse-power had to be used. But this system had the enormous advantage over the cable system of being free from any dangers threatened by the Atlantic Ocean.

Wireless telegraphy has been the means of preventing great disasters at sea by enabling vessels in distress to summon the aid of other vessels, notably during the sinking of the Republic off Nantucket and stranding of the Slavonia on Flores Island, Azores.