But the working out of the revelations promised by radiology belongs rather to this end of the century than to the other. During the interval there can be no doubt that electricity, already man's chief handmaid, will have increased and perhaps completed her services to the race. When, as I ventured to suggest in a former chapter, inexhaustible and cheap "current" is yielded to us by some method of utilising the electrical reciprocity of the hydrogen and oxygen gases derived from water, doubtless all machinery will be electrically driven, all transport electrically propelled. Perhaps this discovery lies so far in the foreground of the future as to be irrelevant to any anticipations of the world's condition a hundred years hence. The full development of electrically-driven machinery lies in the middle distance, and the duration of the electrical age can hardly be precalculated with any greater exactness than the suggestion that it will probably have reached, or at all events approached, its end in about a century's time. The most important problem connected with this subject is to imagine, if we can, how electrical power will be applied. It is quite evident that the device of long conductors, either overhead or below ground--the "live wires" of alarmed America--is too clumsy and too dangerous to be long tolerated. It is indeed a public scandal that cables carrying an electrical charge capable of killing or paralysing at a touch should be suspended over the heads of the citizens, exposed to momentary breakage by snowfall, high wind, or the inevitable wear which careless inspectors may overlook: and the mere fact that a horse can occasionally set foot on a ground plate and fall dead from the contact shows that even the vaunted "conduit system" must not be regarded as anything but a strictly-temporary device. Some of the dangers of the underground electric wires arise out of the use of our present illuminating gas, when a pipe leaks into a manhole or inspection chamber, forming an explosive mixture of gas and air, which presently becomes ignited by an electric spark and blows up the whole affair. No doubt coal gas is within easily measurable distance of its end as a convenience of civilisation. But it is extremely probable that hydrogen and oxygen will be conveyed by mains to houses and public buildings during a long time: and it is hardly possible to believe that the mains will not sometimes leak and be capable of letting out mixtures far more dangerous on ignition than the mixture of coal gas and air, and still more dangerous because neither of the gases, nor the mixture of them, has any smell, unless indeed we should take the precaution of giving them one artificially. Whatever we may do, and we shall do much, to minimise the dangers of highly-evolved civilisation, accidents will always occur, and their violence will probably increase. We must pay our toll to the conveniences of life,