We must remember that Plato had been actually present at the trial of Sokrates. He had heard the stress laid by the accusers on astronomical heresies, analogous to those of Anaxagoras, which they imputed to Sokrates — and the pains taken by the latter to deny that he held such opinions (see the Platonic Apology). The impression left by such a scene on Plato’s mind was not likely to pass away: nor can we be surprised that he preferred to use propositions which involved and implied, rather than those which directly and undisguisedly asserted, the heretical doctrine of the earth’s rotation. That his phraseology, however indirect, was perfectly understood by contemporary philosophers, both assentient and dissentient, as embodying his belief in the doctrine — is attested by the two passages of Aristotle.
Upon these reasons alone I should dissent from M. Cousin’s sixth argument. But I have other reasons besides. He rests it upon the two allegations that the doctrine of the earth’s motion was the subject of much controversial debate in Plato’s time, and of great importance in itself. Now the first of these two allegations can hardly be proved, as to the time of Plato; for Aristotle, when he is maintaining the earth’s immobility, does not specify any other opponents than the Pythagoreians and the followers of the Platonic Timæus. And the second allegation I believe to be unfounded, speaking with reference to the Platonic Timæus. In the cosmical system therein embodied, the rotation of the earth round the cosmical axis, though a real part of the system, was in itself a fact of no importance, and determining no results. The capital fact of the system was the position and function of the earth, packed close round the centre of the cosmical axis, and regulating the revolutions of that axis. Plato had no motive to bring prominently forward the circumstance that the earth revolved itself along with the cosmical axis, which circumstance was only an incidental accompaniment.
I have thus examined all the arguments adduced by M. Cousin, and have endeavoured to show that they fail in establishing his conclusion. There is, however, one point of the controversy in which I concur with him more than with Boeckh and Martin. This point is the proper conception of what Plato means by the cosmical axis. Boeckh and Martin seem to assume this upon the analogy of what is now spoken of as the axis of the earth: M. Boeckh (p. 13) declares the axis of the kosmos to be a prolongation of that axis. But it appears to me (and M. Cousin’s language indicates the same) that Plato’s conception was something very different. The axis of the earth (what astronomers speak of as such) is an imaginary line traversing the centre of the earth; a line round which the earth revolves. Now the cosmical axis, as Plato conceives it, is a solid material cylinder, which not only itself revolves, but causes by this revolution the revolution of the exterior circumference of the kosmos. This is a conception entirely different from that which we mean when we speak of the axis of the earth. It is, however, a conception symbolically enunciated in the tenth book of the Republic, where the spindle of Necessity is said to be composed of adamant, hard and solid material, and to cause by its own rotation the rotation of all the verticilli packed and fastened around it. What is thus enunciated in the Republic is implied in the Timæus. For when we read therein that the earth is packed or fastened round the cosmical axis, how can we understand it to be packed or fastened round an imaginary line? I will add that the very same meaning is brought out in the translation of Cicero — “trajecto axe sustinetur” (terra). The axis, round which the earth is fastened, and which sustains the earth, must be conceived, not as an imaginary line, but as a solid cylinder, itself revolving; while the earth, being fastened round it, revolves round and along with it. The axis, in the sense of an imaginary line, cannot be found in the conception of Plato.
Those contemporaries of Plato and Aristotle, who all agreed in asserting the revolution of the celestial sphere, did not all agree in their idea of the force whereby such revolution was brought about. Some thought that the poles of the celestial sphere exercised a determining force: others symbolised the mythical Atlas, as an axis traversing the sphere from pole to pole and turning it round. (Aristotel. De Motu Animal. 3. p. 699 a. 15-30.) Aristotle himself advocated the theory of a primum movens immobile acting upon the sphere from without the sphere. Even in the succeeding centuries, when astronomy was more developed, Aratus, Eratosthenes, and their commentators, differed in their way of conceiving the cosmical axis. Most of them considered it as solid: but of these, some thought it was stationary, with the sphere revolving round it — others that it revolved itself: again, among these latter, some believed that the revolutions of the axis determined those of the surrounding sphere — others, that the revolutions of the sphere caused those of the axis within it. Again, there were some physical philosophers who looked at the axis as airy or spiritual — τὸ διὰ μέσου τῆς σφαίρας διῆκον πνεῦμα. Then there were geometers who conceived it only as an imaginary line. (See the Phaenomena of Aratus 20-25 — with the Scholia thereon; Achilles Tatius ad Arati Phaenom. apud Petavium — Uranolog. p. 88; also Hipparchus ad Arat. ib. p. 144.) I do not go into these dissentient opinions farther than to show, how indispensable it is, when we construe the passage in the Platonic Timaeus, περὶ τὸν διὰ παντὸς πόλον τεταμένον, to enquire in what sense Plato understood the cosmical axis: and how unsafe it is to assume at once that he must have conceived it as an imaginary line.
Proklus argues that because the earth is mentioned by Plato in the Phædon as stationary in the centre of the heaven, we cannot imagine Plato to affirm its rotation in the Timæus. I agree with M. Boeckh in thinking this argument inconclusive; all the more, because, in the Phædon, not a word is said either about the axis of the kosmos, or about the rotation of the kosmos; all that Sokrates professes to give is τὴν ἰδέαν τῆς γῆς καὶ τοὺς τόπους αὐτῆς (p. 108 E). No cosmical system or theory is propounded in that dialogue.
When we turn to the Phædrus, we find that, in its highly poetical description, the rotation of the heaven occupies a prominent place. The internal circumference of the heavenly sphere, as well as its external circumference or back (νῶτον), are mentioned; also its periodical rotations, during which the gods are carried round on the back of the heaven, and contemplate the eternal Ideas occupying the super-celestial space (p. 247, 248), or the plain of truth.[5] But the purpose of this poetical representation appears to be metaphysical and intellectual, to illustrate the antithesis presented by the world of Ideas and Truth on one side — against that of sense and appearances on the other. Astronomically and cosmically considered, no intelligible meaning is conveyed. Nor can we even determine whether the rotations of the heaven, alluded to in the Phædrus, are intended to be diurnal or not; I incline to believe not (μέχρι τῆς ἑτέρας περιόδου — p. 248 — which can hardly be understood of so short a time as one day). Lastly, nothing is said in the Phædrus about the cosmical axis; and it is upon this that the rotations of the earth intimated in the Timæus depend.
[5] Whether Ἐστία in the Phædrus, which is said “to remain alone stationary in the house of the Gods,” can be held to mean the Earth, is considered by Proklus to be uncertain (p. 681).
Among the different illustrations, given by Plato in his different dialogues respecting the terrestrial and celestial bodies, I select the tenth book of the Republic as that which is most suitable for comparison with the Timæus, because it is only therein that we learn how Plato conceived the axis of the kosmos. M. Boeckh (Untersuchungen, p. 86) wishes us to regard the difference between the view taken in the Phædon, and that in the Republic, as no way important; he affirms that the adamantine spindle in the Republic is altogether mythical or poetical, and that Plato conceives the axis as not being material. On this point I dissent from M. Boeckh. The mythical illustrations in the tenth book of the Republic appear to me quite unsuitable to the theory of an imaginary, stationary, and immaterial axis. Here I much more agree with Gruppe (p. 15, 26-29), who recognises the solid material axis as an essential feature of the cosmical theory in the Republic; and recognises also the marked difference between that theory and what we read in the Phædon. Yet, though Gruppe is aware of this important difference between the Republic and the Phædon, he still wishes to illustrate the Timæus by the latter and not by the former. He affirms that the earth in the Timæus is conceived as unattached, and freely suspended, the same as in the Phædon; but that in the Timæus it is conceived, besides, as revolving on its own axis, which we do not find in the Phædon (p. 28, 29). Here I think Gruppe is mistaken. In construing the words of Timæus, εἱλομένην (ἰλλομένην) περὶ τὸν διὰ παντὸς πόλον τεταμένον, as designating “the unattached earth revolving round its own axis,” he does violence not less to the text of Plato than to the expository comment of Aristotle. Neither in the one nor the other is anything said about an axis of the earth; in both, the cosmical axis is expressly designated; and, if Gruppe is right in his interpretation of εἱλομένην, we must take Plato as affirming, not that the earth is fastened round the cosmical axis, but that it revolves, though unattached, around that axis, which is a proposition both difficult to understand, and leading to none of those astronomical consequences with which Gruppe would connect it. Again, when Gruppe says that εἱλομένην περὶ does not mean packed or fastened round, but that it does mean revolving round, he has both the analogies of the word and the other commentators against him. The main proof, if not the only proof, which he brings, is that Aristotle so construed it. Upon this point I join issue with him. I maintain that Aristotle does not understand εἱλομένην or ἰλλομένην περὶ as naturally meaning revolving round, and that he does understand the phrase as meaning fastened round. When we find him, in the second passage of the treatise De Cœlo, not satisfied with the verb ἴλλεσθαι alone, but adding to it the second verb καὶ κινεῖσθαι, we may be sure that he did not consider ἴλλεσθαι as naturally and properly denoting to revolve or move round.
Agreeing as I do with Gruppe in his view, that the interpretation put by Aristotle is the best evidence which we can follow in determining the meaning of this passage in the Timæus, I contend that the authority of Aristotle contradicts instead of justifying the conclusion at which he arrives. Aristotle understands ἰλλομένην as meaning packed or fastened round; he does not understand it as meaning, when taken by itself, revolving round.
The two meanings here indicated are undoubtedly distinct and independent. But they are not for that reason contradictory and incompatible. It has been the mistake of critics to conceive them as thus incompatible; so that if one of the two were admitted, the other must be rejected. I have endeavoured to show that this is not universally true, and that there are certain circumstances in which the two meanings not only may come together, but must come together. Such is the case when we revert to Plato’s conception of the cosmical axis as a solid revolving cylinder. That which is packed or fastened around the cylinder must revolve around it, and along with it.