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. [Illustration: Fig. 70.—Section of Transatlantic Cable. C, core; G, gutta-percha; J, jute fibres; F, steel wires embedded in hemp.] 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.