Timaeus — Plato

and hence the obhqiie hne in which the planets are supposed to move becomes a spiral.

The motion of the same is said to be undivided, whereas the inner motion is split into seven unequal orbits — the intervals between them being in the ratio of two and three, three of either: — the Sun, moving in the opposite direction to Mercury and Venus, but with equal swiftness ; the remaining four, Moon, Saturn, Mars, Jupiter, with unequal swiftness to the former three and to one another.

Thus arises the following progression: — Moon i, Sun 2, Venus 3, Mercury 4, Mars 8, Jupiter 9, Saturn 27. This series of numbers is the compound of the two Pythagorean ratios, having the same intervals, though not in the same order, as the mixture which was originally divided in forming the soul of the world. Plato was struck by the phenomenon of Mercury, Venus, and the Sun appearing to overtake and be overtaken by one another.

The true reason of this, namely, that they lie within the circle of the earth's orbit, was unknown to him, and the reason which he gives — that the two former move in an opposite direction to the latter — is far from explaining the appearance of them in the heavens.

All the planets, including the sun, are carried round in the daily motion of the circle of the fixed stars, and they have a second or oblique motion which gives the explanation of the different lengths of the sun's course in different parts of the earth.

The fixed stars have also two movements — a forward movement in their orbit which is common to the whole circle ; and a movement on the same spot around an axis, which Plato calls the movement of thought about the same. In this latter respect they are more perfect than the wandering stars, as Plato himself terms them in the Timaeus, although in the Laws (loc. cit.) he condemns the appellation as blasphemous.

The revolution of thq world around the earth, which is accomplished in a single day and night, is described as being the most perfect or intelligent. Yet Plato also speaks of an * annus magnus ' or cyclical year, in which periods wonderful for their complexity are found to coincide in a perfect number, i. e. a number which equals the sum of its factors, as 6=1+ 2 + 3.

This, although not literally contradictory, is in spirit irreconcileable with the perfect revolution of twenty-four hours. The same remark may be applied to the complexity of the appearances and 2occultations of the stars, which, if the outer heaven is supposed Timaeus. to be moving around the centre once in twenty-four hours, must Introduc be confined to the effects produced by the seven planets. Plato ^'°^' seems to confuse the actual observation of the heavens with his desire to find in them mathematical perfection.

The same spirit is carried yet further by him in the passage already quoted from the Laws, in which he affirms their wanderings to be an appearance only, which a little knowledge of mathematics would enable men to correct. We have now to consider the much discussed question of the rotation or immobility of the earth.

Plato's doctrine on this subject is contained in the following words: — ' The earth, which is our nurse, compacted \or revolving] around the pole which is extended through the universe, he made to be the guardian and artificer of night and day, first and eldest of gods that are in the interior of heaven ' (40 B, C).

There is an unfortunate doubt in this passage (i) about the meaning of the word ITJiofihrjVy which is translated either 'compacted' or 'revolving,' and is equally capable of both explanations. A doubt (2) may also be raised as to whether the words * artificer of day and night ' are consistent with the mere passive causation of them, produced by the immobility of the earth in the midst of the circling universe.

We must admit, further, (3) that Aristotle attributed to Plato the doctrine of the rotation of the earth on its axis. On the other hand it has been urged that if the earth goes round with the outer heaven and sun in twenty-four hours, there is no way of accounting for the alternation of day and night ; since the equal motion of the earth and sun would have the effect of absolute immobility.

To which it may be replied that Plato never says that the earth goes round with the outer heaven and sun ; although the whole question depends on the relation of earth and sun, their movements are nowhere precisely described.

But if we suppose, with Mr. Grote, that the diurnal rotation of the earth on its axis and the revolution of the sun and outer heaven precisely coincide, it would be difficult to imagine that Plato was unaware of the consequence.

For though he was ignorant of many things which are familiar to us, and often confused in his ideas where we have become clear, we have no right to attribute to him a childish want of reasoning about very simple facts, or an 3inability to understand the necessary and obvious deductions from geometrical figures or movements. Of the causes of day and night the pre-Socratic philosophers, and especially the Pythagoreans, gave various accounts, and therefore the question can hardly be imagined to have escaped him.

On the other hand it may be urged that the further step, however simple and obvious, is just what Plato often seems to be ignorant of, and that as there is no limit to his insight, there is also no limit to the blindness which sometimes obscures his intelligence (cp. the construction of solids out of surfaces in his account of the creation of the world, or the attraction of similars to similars).

Further, Mr. Grote supposes, not that \llojievr]v means * revolving,' or that this is the sense in which Aristotle understood the word, but that the rotation of the earth is necessarily implied in its adherence to the cosmical axis.

But (a) if, as Mr. Grote assumes, Plato did not see that the rotation of the earth on its axis and of the sun and outer heavens around the earth in equal times was inconsistent with the alternation of day and night, neither need we suppose that he would have seen the immobility of the earth to be inconsistent with the rotation of the axis.

And (/3) what proof is there that the axis of the world revolves at all ? (y) The comparison of the two passages quoted by Mr. Grote (see p. 19 of his pamphlet on * The Rotation of the Earth ') from Aristotle or the writer De Caelo, Book II (c, 13, EVLOL — yeypaTTTai, and c.

14, i^/nslg — fieaov), clearly shows, although this is a matter of minor importance, that Aristotle, as Proclus and Simplicius supposed, understood VklEadai in the Timaeus to mean * revolving.

For the second passage, in which motion on an axis is expressly mentioned, refers to the first, but this would be unmeaning unless IXXeadai in the first passage meant rotation on an axis. (4) The immobility of the earth is more in accordance with Plato's other writings than the opposite hypothesis. For in the Phaedo the earth is described as the centre of the world, and is not said to be in motion.

In the Republic the pilgrims appear to be looking out from the earth upon the motions of the heavenly bodies ; in the Phaedrus, Hestia, who remains immovable in the house of Zeus while the other gods go in procession, is called the first and eldest of the gods, and is probably the symbol of the earth. The silence of Plato in these and in some other passages (cp. Laws x. 893 B) in which he