And thus we see how the mechanical production of cold has assisted in the pursuit of pure science. The newly-found gases are not of any great use at present. They are so inactive that possibly they never will be, with one exception, and that is neon. If an electric discharge be made to pass through a tube filled with this gas, a beautiful glow is the result, and it is just possible that neon tubes may become the electric light of the future. That is only a prediction, however, and a hesitating one at that. The inactive elements may become of value in explosives. We have seen how important nitrogen is in these dangerous substances, the chief feature of which is their instability--their readiness, that is, to change into something else--which instability is due to the reluctance with which nitrogen enters into them. Now nitrogen, though inactive, is much less so than these others, and if a way should ever be found of inducing them to enter into a compound, that compound will probably be an extremely powerful explosive. CHAPTER VI SCIENTIFIC INVENTIONS AT SEA The safety of our fellow-creatures has always been a strong stimulus to our inventive faculties. The occurrence of a bad railway accident, and, roughly, its nature, can be inferred from the files of the Patent Office, for such an event brings men's thoughts to devising ways and means of preventing a recurrence, and an avalanche of such inventions descends upon the patent department in consequence. In like manner a particularly distressing accident to a lifeboat some years ago brought out many inventions for the improvement of those romantic craft. Many of the inventions which arise under these conditions are, of course, utterly worthless, but some of them "come to stay." It is not surprising, therefore, when we think of the almost innumerable wrecks which happen, even with modern shipping, that human ingenuity has been extremely busy in devising ways for bringing more of safety and less of risk into the lives of those who go down to the sea in ships. Of these perhaps none is more fascinating than the modern lighthouse, with its tall tower, its brightly flashing light, standing undisturbed in the wildest storm, quietly and persistently sending forth its guiding rays, no matter how the elements may be buffeting it. There is something specially attractive in this perfect embodiment of quiet strength and devotion to duty. Of course, its origin is very ancient. One of the earliest inventions, no doubt, was the bright thought of a very primitive man who lit a fire on a hill to serve as a guide to some belated friends out in their fishing canoes. From some such beginning the modern lighthouse, a magnificent product of the science of civil engineering and the science of optics, has arisen.