There have been several attempts to solve the problem of directing torpedoes by means of wireless telegraphy. The great drawback, however, has been that the receiving apparatus which the torpedo had to carry was outside it and must appear above the surface of the water, and was, therefore, liable to be sighted and shot away. The same objection has been raised to the equipment of submersible torpedo boats with “wireless.” Of recent years a torpedo has been contrived which the inventors claim can be directed by wireless telegraphy, and as there seems no reason why the principle applied cannot be improved and extended to submarines and submersibles, the utility of these under-water craft may be augmented to an inconceivable degree. The “Actinaut” is the name of the torpedo, and the jet of salt water which it ejects serves not only to indicate the position of the torpedo, but is an “indestructible receiver for the electric waves.”[58] SUBMARINES Submarine warfare and exploration are no new ideas, but in the past as in the present, the great difficulties have been to ensure the provision of sufficient power for rapid propulsion, and to keep the air pure enough for the crew to breathe for a long journey under water. Efforts at submarine warfare seemed to have been made many centuries ago, but none of the contrivances then used had any fighting value, and were more interesting as freaks than in any other capacity. It is unnecessary to attempt even to summarise all the schemes which early and late inventors evolved to render possible under-water attacks upon an enemy’s fleet. The problem was as fascinating seven or eight hundred years ago as at the present time. Most of the alleged mediæval inventions probably never got beyond the imaginative or paper stage, and however wonderful the inventors’ theories or written descriptions may have been, even when embellished with weird illustrations showing the contrivance at the bottom of the sea, it is not recorded that any of the submarines achieved any actual success whatever. One of the earliest submarine descents which is supposed to have been made was that of Alexander the Great, who is mendaciously represented to have been lowered to the bottom of the sea in a glass barrel, too small for him to stand up in, with a smoky oil lamp or two, and an animal which might have been a dog or a cat (it is difficult to say which the artist intended) for company, the circumstances being such that he could not have failed to be asphyxiated in a very short space of time. It appears, too, that he wore a crown and his royal robes on that occasion, so that he evidently visited Neptune in state.