tight within a wheelwork of revolving spheres. It was compendious, complete, ingenious, like a toy in a crystal box. Beyond the outer shell nothing existed. The heavens were incorruptible. No change could occur in the whole system, save on the earth alone. The universe was created for the sole use of man. It was small and finite. To us, the awful infinitudes of space are only to be faintly imagined after a series of conceptions, each one so overwhelming that it fades after the briefest instant of realization. Human attention can not grasp the whole series in one view. Each one of the myriad stars is a sun like our own, subjected, as it is, to prodigious physical alterations and catastrophies. Each one is, perhaps, surrounded by a train of planets, like those we know, that must forever remain invisible to our vision. The condition of every celestial body is perpetually changing in a long progress of evolution. Each separate star is situated as far from every other as our own sun from the very nearest of them all. Every star is in motion. The sun, so mighty and all-powerful to us, is but a feeble light among thousands of millions of others scattered so sparsely throughout the never-ending expanse that centuries are needed even for their light to traverse the intervening spaces. In the feeble light of that sunbeam, vital to us, the earth, our mother, shines like the merest mote. Its past is limited, its future insecure. With its finite history the fate of mankind is bound up.
We must not forget that the modern view of the universe is very different from that of Copernicus. Before his day the earth was motionless in the center of the world. After it the earth was in perpetual motion about the sun. Copernicus conceived the sun as fixed. But under Newton's law of universal gravitation there can be no fixed bodies. All are in motion. Our sun with its train of planets is speeding through space towards a goal as yet unknown. Newton's law of gravitation banished rest from the universe. To Copernicus as to Ptolemy rest was the natural state to which all bodies tended. They moved only when perpetually urged. The science of mechanics founded by Galileo and Newton changed all this. The real reformation of science dates from the acceptance of the new conception.