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. CHAPTER XVI THE NEW RAYS IT is not given to many men to make such a wonderful discovery as fell to the lot of Professor Röntgen in the year 1895. If anyone wishes to mention something very new and wonderful, some great revelation of science during the nineteenth century, he usually puts the Röntgen Rays or X-rays in the first place. This is very natural, for these rays give men powers of vision which they could hardly expect ever to possess. They enable us to see through many dark bodies, and even through the human body itself. The discovery of these rays forms one of the most romantic chapters in the history of science. The discovery was made in the course of some work with a vacuum tube. A vacuum tube is a bulb of glass from which all the air has been pumped. An electric lamp is a kind of vacuum tube, but it would not be suitable for the experiments of Professor Röntgen unless the filament were removed and nothing but the two platinum wires remained. If the current were sent through the bulb as usual, it would have some difficulty in passing from one platinum wire to the other, and indeed it could not pass at all unless some slight trace of air remained in the bulb. [Illustration: Fig. 72.--Professor W. C. Röntgen.]