The history of thought should warn us against concluding that because the scientific theory of the world is the best that has yet been formulated, it is necessarily complete and final. We must remember that at bottom the generalizations of science or, in common parlance, the laws of nature, are merely hypotheses devised to explain that ever-shifting phantasmagoria of thought which we dignify with the high-sounding names of the world and the universe. In the last analysis magic, religion, and science are nothing but theories of thought; and as science has supplanted its predecessors, so it may hereafter be itself superseded by some more perfect hypothesis, perhaps by some totally different way of looking at the phenomena—of registering the shadows on the screen—of which we in this generation can form no idea. The advance of knowledge is an infinite progression toward a goal that forever recedes. Great things will come of that pursuit, though we may not enjoy them. Brighter stars will rise on some voyager of the future—some great Ulysses of the realms of thought—than shine on us. The dreams of magic may one day be the waking realities of science. But a dark shadow lies athwart the far end of this fair prospect. For however vast the increase of knowledge and of power which the future may have in store for man, he can scarcely hope to stay the sweep of those great forces which seem to be making silently but relentlessly for the destruction of all this starry universe in which our earth swims as a speck or mote. In the ages to come, man may be able to predict, perhaps even to control, the wayward courses of the winds and clouds, but hardly will his puny hands have strength to speed afresh our slackening planet in its orbit or rekindle the dying fire of the sun.