The best means of generating the waves and the best means of detecting them at a distance--that is the whole problem, and all the workers in it will sooner or later come to much the same conclusions as to which are the best ways. Patents may do a little to delay this, but not much. For one thing, patents only last a few years. For another, a patent only covers a particular way of doing a particular thing. A machine that is termed "patent" is often the subject of a hundred patents, each covering a particular little point. It is well-nigh impossible to patent a whole machine. A general principle cannot be patented, only a particular application of that principle, and so there are in a great many cases little variations of a patented method which are quite as good as the patented one, and which can be used freely. So even patents will not have much effect, in all probability, upon this unification process. But, however that may be, there is no doubt that the whole world owes a deep debt of gratitude to the men who have worked out this most beneficent of inventions. It is difficult to think of a single one which has ever brought such a load of benefits to poor, struggling humanity as this has. The ship in distress, the lighthouse man on his lonely islet, the explorer in the Polar regions, the pioneer settler in the new lands--in fact, just those who most need some connecting link with their fellows--are the people to whom the wireless telegraph brings aid and comfort. All honour to the men who have done it. CHAPTER XIII HOW PICTURES CAN BE SENT BY WIRE The sending of a message by telegraph is easily understandable. Various combinations of two simple signs, such as short sounds and long sounds, can readily be made to indicate letters by which the words can be spelt out. Nor does the sending of sound over a wire make a very great demand upon the credulity. We all know that sound consists of innumerable little waves in the air, and by the simplest of devices these can be converted into variations in an electric current, which variations, by means equally simple, can be made to re-convert themselves back into sound waves at the other end. But to transmit a picture is another matter altogether. It seems barely possible in the case of a drawing such as a pen-and-ink sketch, which consists of a comparatively small number of definite lines; but with a shaded sketch or a photograph, with its gradations of light and shadow--to transmit such would seem to be beyond the bounds of possibility, did we not know that it has been done. The description of the methods will therefore constitute a not uninteresting subject for a chapter. It is worthy of remark that an attempt along these lines was made many years ago by a man named Caselli, and a description of this pioneer apparatus will form a good introduction to the later developments.