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JAIN PHILOSOPIIY & MODERN SCIENCC
our own, and all in motion relative to our own galaxy as also to one another. No one of all these galaxies. has a better claim than any other to constitute a standard 'rest from which the 'motions' of the others can be measured Nevertheless, many complications are avoided by imagining that the sun and not the earth is at rest. Neither the sun nor the earth is at rest in any absolute sense and yet it is, in a sense, nearer to the truth to say that the earth moves round. a fixed sun than to say that the sun moves round a fixed earth
Copernicus had still to retain a few minor epicycles to make his system agree with the facts of observation Thus, as we now know, was the inevit-, able consequence of his assumption that the planetary orbits were circular. Neither he nor any one else had so far dared to challenge Aristotle's dictum that the planets must necessarily move in circular orbits, because the circle was the only perfect course. As soon as Kepler substituted eclipses for the Coperni. cian circles, epicycles were seen to be unnecessary; and the theory of planetary motions assumed an ex ceedingly simple form—the form it was to retain for more than three centuries until an even greater simplicity was imparted to it by the relativity theory of Einstein, to which we shall come in a moment"
From the above mentioned link between the eas and the west we come to the conclusion that the main purpose is not to find whether the earth is 3"
