James Adam, The Republic of Plato

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τὸν δὲ τοῦ δευτέρου καὶ πέμπτου κτλ. The second and fifth are Saturn and Mercury, or Φαίνων and Στίλβων, as they were sometimes called, with reference to their brightness or colour. See the de mundo 2. 392^{a} 23 ff. Yellow, according to Plato, is a mixture of white and red (Tim. 68 B). The third (τρίτον δέ) or Jupiter was known also as Φαέθων, and the fourth, or Mars, as Πυρόεις. Venus, which is the sixth, and comes next to Jupiter in whiteness, had the name Φωσφόρος (de mundo l. c.). Cf. [Epin.] 986 E ff. and Diels Dox. Gr. 344.

κυκλεῖσθαι δὲ δὴ κτλ. Cf. Tim. 36 C, D. The whorl of the fixed stars revolves from East to West, bearing with it in its revolution the other seven whorls. In this way Plato portrays the apparent daily revolution of the stars and planets. In order to represent the movements of the Sun, Moon and planets in their own particular orbits, Plato says that each of the seven inner whorls is all the while pursuing on its own account a motion in the opposite direction, viz. from West to East. The revolving whorls in the words of Proclus, ‘carry round the stars’ (περιάγουσι τοὺς ἀστέρας l. c. p. 226. 12) which are situated in their rims.

Would the mechanism of Plato's picture really produce the movements which it is intended to portray? The question may be interesting, but is irrelevant. Imaginary machines have imaginary properties; and Plato himself invokes the assistance of supernatural beings to carry on the movements (617 C). The important point to keep in mind, as Professor Cook Wilson observes, is that “Plato has realised that the apparent phenomena are what we call a composition of movements (or velocities). This composition of movements he is not attempting to explain, by giving the sort of machinery which he thought really produced it, but he is endeavouring to make us understand what the movements are (not how they originate), by putting the objects concerned in an imaginary machine, the movements of which we can represent to the senses, and which would produce such movements in the objects as they actually have.” For similar reasons it is impossible to draw any inference from this passage as to the question whether Plato believed in the daily revolution of the earth. In the Timaeus, according to Grote (Plato on the Earth's Rotation, pp. 13 ff.), the cosmical axis is “a solid cylinder revolving or turning round, and causing thereby the revolution of the circumference or the sidereal sphere,” and necessarily also carrying round with itself the Earth, which is massed or globed round the axis of the whole (εἰλλομένην περὶ τὸν διὰ παντὸς πόλον τεταμένον Tim. 40 B. ‘Massed’ or ‘packed’ is Boeckh's interpretation of εἰλλομένην, with which Grote also agrees; but whether the word really bears this meaning, is another question, which we need not here discuss.) In support of his explanation of the passage in the Timaeus, Grote appeals to the myth of the Republic; and the appeal would be justified if Plato's figure of Necessity's spindle were intended to explain the cause, and not merely to represent the form, of the celestial motions. As it is, the Republic does not warrant any conclusion either way. Cf. 616 D, E note

τάχιστα μὲν κτλ. Cf. Tim. 38 C, D, 39 C, 40 B and [Epin.] 986 E ff.