greatest invention in the history of therapeutics) will have pushed their way from surgery into medicine. There are numerous diseases which can be not merely cured, but ultimately abolished when we have once discovered how to use oxygen adequately. The readjustment of the conditions of life determined by the removal from the civilised world of the greater number of diseases, and perhaps of all diseases except those arising out of wilful misconduct (as improper diet) and even by the elimination of most of the evils of hurry and overwork (for what are medically and chemically known as fatigue products can almost certainly be eliminated from the system by the proper use, yet to be discovered, of oxygen) must inevitably have an enormous influence not merely upon the physical life of man, but also, and even more, upon his mental constitution. The rate of progress will thus in yet another way be vastly accelerated. Most likely the universal source of power, then, before the middle of the century, will be the recomposition of water--in other words, we shall get all the power we want by splitting up water into oxygen and hydrogen, and then allowing those gases to recombine, thereby returning to us the energy we have employed in the analysis. How we shall employ this power is largely for the future to decide, and certainly in the earlier future we shall employ it in the generation of etheric waves of various kinds. The world of science is visibly on the threshold of new and revolutionary discoveries on the nature and composition of matter, and whither these discoveries will lead us it is not usefully possible to conjecture. But certainly, after the usual incubation period of a scientific discovery--when it is merely a sort of wonderful toy, as argon and radium are at present--there will come the practical men, suckled at the large and noble breasts of disinterested, unremunerative truth, and ready to turn that nutriment into world-moving material usefulness: so, again, the rate of progress will receive a vast and valuable acceleration. Electricity, whose gift to the world has been so great, will probably not, until after several decades, approach the limits of its realm, and so long as electricity remains a considerable element in the utilisation of those stores of dissipating energy by which the planet lives, it is possible to foresee something of what will become of man during the next age.