hand, they have their own revolutions with varying angular velocities from west to east, but they are also carried along by the diurnal revolution from east to west. Apparently this was expressed by saying that the motions of the planetary orbits, which are oblique to the celestial equator, are mastered (κρατεῖται) by the diurnal revolution. The Ionians, down to the Demokritos, never accepted this view. They clung to the theory of the vortex, which made it necessary to hold that all the heavenly bodies revolved in the same direction, so that those which, on the Pythagorean system, have the greatest angular velocity have the least on theirs. On the Pythagorean view, Saturn, for instance, takes about thirty years to complete its revolution; on the Ionian view it is "left behind" far less than any other planet, that is, it more nearly keeps pace with the signs of the Zodiac.[1]
For reasons which will appear later, we may confidently attribute to Pythagoras himself the discovery of the sphericity of the earth which the Ionians, even Anaxagoras and Demokritos, refused to accept. It is probable, however, that he still adhered to the geocentric system, and that the discovery that the earth was a planet belongs to a later generation (§150).
The account just given of the views of Pythagoras is, no doubt, conjectural and incomplete. We have simply assigned to him those portions of the Pythagorean system which appear to be the oldest, and it has not even been possible at this stage to cite fully the evidence on which our discussion is based. It will only appear in its true light when we have examined the second part of the poem of Parmenides and the system of the later Pythagoreans.[2]
- ↑ See the account of the theory of Demokritos in Lucretius, v. 621 sqq., and cf. above, p. 70. The technical term is ὑπόλειψις. Strictly speaking, the Ionian view is only another way of describing the same phenomena, but it does not lend itself so easily to a consistent theory of the real planetary motions.
- ↑ See Chap. IV. §§ 92-93, and Chap. VII. §§ 150-152.
