And we are just at the moment when a thousand new reasons for having confidence in the destinies of our kind are being born around us. For hundreds and hundreds of centuries we have occupied this earth; and the greatest dangers seem past. They were so threatening that we have escaped them only by a chance that cannot occur more than once in a thousand times in the history of the worlds. The earth, still too young, was poising its continents, its islands and its seas before fixing them. The central fire, the first master of the planet, was at every moment bursting from its granite prison; and the globe, hesitating in space, wandered among greedy and hostile stars ignorant of their laws. Our undetermined faculties floated blindly in our bodies, like the nebulæ in the ether; a mere nothing could have destroyed our human future at the groping hours when our brain was forming itself, when the network of our nerves was branching out. To-day, the instability of the seas and the uprisings of the central fire are infinitely less to be feared; in any case, it is unlikely that they will bring about any more universal catastrophes. As for the third peril, collision with a stray star, we may be permitted to believe that we shall be granted the few centuries of respite necessary for us to learn how to ward it off. When we see what we have done and what we are on the point of doing, it is not absurd to hope that one day we shall lay hold of that essential secret of the worlds which, for the time being and to soothe our ignorance (even as we soothe a child and lull it to sleep by repeating to it meaningless and monotonous words), we have called the law of gravitation. There is nothing mad in supposing that the secret of this sovereign force lies hidden within us, or around us, within reach of our hand. It is perhaps tractable and docile, even as light and electricity; it is perhaps wholly spiritual and depends upon a very simple cause which the displacing of an object may reveal to us. The discovery of an unexpected property of matter, analogous to that which has just disclosed to us the disconcerting qualities of radium, may lead us straight to the very sources of the energy and the life of the stars; and from that moment man's lot would be changed and the earth, definitively saved, would become eternal. It would, at our pleasure, draw closer to or further from the centres of heat and light, it would flee from worn-out suns and go in search of unsuspected fluids, forces and lives in the orbit of virgin and inexhaustible worlds. XII