can use them thus for the production of almost every kind of energy that man at present needs. We can use them for heat by burning them together. We can use them for light by burning them in the presence of any substance capable of being made incandescent. We shall be able to use them to generate electricity by some sort of contrivance akin to the accumulator of the present day {a highly rudimentary invention); and it would be even now a very simple matter to utilise their explosive recombination for the direct production of power as motion. Utilised apart, the constituent gases of water have many other uses and possible uses. Hydrogen, under suitable treatment, yields the greatest obtainable cold, as oxygen and hydrogen together yield the greatest heat. If our flying-machines need a sort of ballast to reinforce their mechanical lifting apparatus, hydrogen is the best possible assistant. And the probable uses of oxygen are yet more numerous. So long as we still burn anything at all except a mixture of oxygen and hydrogen—and ultimately we shall have nothing else left to burn—oxygen is capable of multiplying the efficiency of ail combustion, One of the greatest problems of our own day is the disposal of waste products of ail sorts—the sources of inconvenience, disease and dirt. Oxygen, if readily and copiously obtainable, is
