incompatibility which escaped the notice both of Aristotle and of many subsequent writers who wrote at a time when astronomical theories had been developed and compared with greater fulness. Even Ideler, a good astronomer as well as a good scholar, though he must surely have known that Plato asserted the rotation of the sidereal sphere (for no man can read the ‘Timæus’ without knowing it), ascribed to him also the other doctrine inconsistent with it, not noticing such inconsistency until M. Boeckh pointed it out.

It appears to me, therefore, that M. Boeckh has not satisfactorily made good his point — “Plato cannot have believed in the diurnal rotation of the earth, because he unquestionably believed in the rotation of the sidereal sphere as causing the succession of night and day.” For, though the two doctrines really are incompatible, yet the critics antecedent to M. Boeckh took no notice of such incompatibility. We cannot presume that Plato saw what Aristotle and other authors, even many writing under a more highly developed astronomy, did not see. We ought rather, I think, to presume the contrary, unless Plato’s words distinctly attest that he did see farther than his successors.

Now let us examine what Plato’s words do attest:— γῆν δὲ τροφὸν μὲν ἡμετέραν, εἱλλομένην (al. εἱλομένην, ἰλλομένην) δὲ περὶ τὸν διὰ παντὸς πόλον τεταμένον φύλακα καὶ δημιουργὸν νυκτός τε καὶ ἡμέρας ἐμηχανήσατο, πρώτην καὶ πρεσβυτάτην θεῶν, ὅσοι ἐντὸς οὐράνου γεγόνασι.

I explain these words as follows:—

In the passage immediately preceding, Plato had described the uniform and unchanging rotation of the outer sidereal sphere, or Circle of The Same, and the erratic movements of the sun, moon, and planets, in the interior Circles of the Diverse. He now explains the situation and functions of the earth. Being the first and most venerable of the intra-kosmic deities, the earth has the most important place in the interior of the kosmos — the centre. It is packed, fastened, or rolled, close round the axis which traverses the entire kosmos; and its function is to watch over and bring about the succession of night and day. Plato conceives the kosmic axis itself as a solid cylinder revolving or turning round, and causing thereby the revolution of the circumference or the sidereal sphere. The outer circumference of the kosmos not only revolves round its axis, but obeys a rotatory impulse emanating from its axis, like the spinning of a teetotum or the turning of a spindle. Plato in the Republic illustrates the cosmical axis by comparison with a spindle turned by Necessity, and describes it as causing by its own rotation the rotation of all the heavenly bodies (Republ. x. p. 616, c. 617 A). ἐκ δὲ τῶν ἄκρων τεταμένον Ἀνάγκης ἄτρακτον, δι’ οὗ πάσας ἐπιστρέφεσθαι τὰς περίφορας …, κυκλεῖσθαι δὲ δὴ στρεφόμενον τὸν ἄτρακτον ὅλον μὲν τὴν αὐτὴν φοραν …. στρέφεσθαι δὲ αὐτὸν ἐν τοῖς Ἀνάγκης γόνασιν.1

Now the function which Plato ascribes to the earth in the passage of the Timæus before us is very analogous to that which in the Republic he ascribes to Necessity — the active guardianship of the axis of the kosmos and the maintenance of its regular rotation. With a view to the exercise of this function, the earth is planted in the centre of the axis, the very root of the kosmic soul (Plato, Timæus, p. 34 B). It is even “packed close round the axis,” in order to make sure that the axis shall not be displaced from its proper situation and direction. The earth is thus not merely active and influential, but is really the chief regulator of the march of the kosmos, being the immediate neighbour and auxiliary of the kosmic soul. Such a function is worthy of “the first and eldest of intra-kosmic deities,” as Plato calls the earth. With perfect propriety he may say that the earth, in the exercise of such a function, “is guardian and artificer of day and night.” This is noway inconsistent with that which he says in another passage, that the revolutions of the outer sidereal sphere determine day and night. For these revolutions of the outer sidereal sphere depend upon the revolutions of the axis, which latter is kept in uniform position and movement by the earth grasping it round its centre and revolving with it. The earth does not determine days and nights by means of its own rotations, but by its continued influence upon the rotations of the kosmic axis, and (through this latter) upon those of the outer sidereal sphere.

It is important to attend to the circumstance last mentioned, and to understand in what sense Plato admitted a rotatory movement of the earth. In my judgment, the conception respecting the earth and its functions, as developed in the Platonic Timæus, has not been considered with all its points taken together. One point among several, and that too the least important point, has been discussed as if it were the whole, because it falls in with the discussions of subsequent astronomy. Thus Plato admits the rotation of the earth, but he does not admit it as producing any effects, or as the primary function of the earth: it is only an indirect consequence of the position which the earth occupies in the discharge of its primary function — of keeping the cosmical axis steady, and maintaining the uniformity of its rotations. If the cosmical axis is to revolve, the earth, being closely packed and fastened round it, must