When expositors in Plutarch's day, and since his day, enquired whether or not the Platonic Timæus affirmed the rotation of the earth, they meant to designate the rotation of the earth in the sense of Aristarchus, and in the sense in which modern astronomy understands that capital fact. Now speaking the language of modern astronomy, I think it certain that the rotation of the earth is _not_ to be found affirmed in the Platonic Timæus; and I agree with M. Boeckh when he says (Untersuch. p. 77), "Granting that Aristotle ascribed to Plato the doctrine of the rotation of the earth, he at least did not ascribe to him the doctrine as Gruppe assumes, and as now understood." As between Gruppe--who holds that the Platonic Timæus affirms the rotation of the earth, and that Aristotle ascribes it to him, in our sense of the words--and M. Boeckh, who denies this--I stand with the latter for the negative. But when M. Boeckh assumes that the only alternative doctrine is the immobility of the earth, and tries to show that this doctrine is proclaimed in the Platonic Timæus--nay, that no opposite doctrine _can_ be proclaimed, because the discourse expressly announces the rotation of the sidereal heaven in twenty-four hours--I am compelled to dissent from him as to the conclusion, and to deny the cogency of his proof. M. Boeckh has hardly asked himself the question, whether there was not some other sense in which Plato might have affirmed it in the Timæus. I have endeavoured to show that there was another sense; that there are good analogies in Plato to justify the belief that he intended to affirm the doctrine in that other sense; and that the comments of Aristotle--while thoroughly pertinent, if we thus understand the passage in the Timæus--become either irrelevant, dishonest, or absurd, if we construe the passage as signifying either what is maintained by M. Boeckh or what is maintained by Gruppe.