The capital argument of Boeckh is as follows: "The Platonic Timæus affirms, in express and unequivocal terms, the rotation of the outer celestial sphere (the sidereal sphere or Aplanes) in twenty-four hours, as bringing about and determining the succession of day and night. Whoever believes this cannot at the same time believe that the earth revolves round its own axis in twenty-four hours, and that the succession of day and night is determined thereby. The one of these two affirmations excludes the other; and, as the first of the two is proclaimed, beyond all possibility of doubt, in the Platonic Timæus, so we may be sure that the second of the two cannot be proclaimed in that same discourse. If any passage therein seems to countenance it, we must look for some other mode of interpreting the passage." This is the main argument of M. Boeckh, and also of Messrs. Cousin and Martin. The latter protests against the idea of imputing to Plato "un mélange monstrueux de deux systêmes incompatibles" (Études sur le Timée, vol. ii. p. 86-88). As applied to any person educated in the modern astronomy, the argument is irresistible. But is it equally irresistible when applied to Plato and to Plato's time? I think not. The incompatibility which appears so glaring at present, did not suggest itself to him or to his contemporaries. To prove this we have only to look at the reasoning of Aristotle, who (in the treatise De Coelo, ii. 13-14, p. 293. b. 30, 296. a. 25) notices and controverts the doctrine of the rotation of the earth, with express reference to the followers of the Platonic Timæus--and who (if we follow the view of Martin) imputes this doctrine with wilful falsehood to Plato, for the purpose of contemptuously refuting it "pour se donner le plaisir de la réfuter avec dédain." Granting the view of M. Boeckh (still more that of Martin) to be correct, we should find Aristotle arguing thus:--"Plato affirms the diurnal rotation of the earth round the centre of the cosmical axis. This is both incredible, and incompatible with his own distinct affirmation that the sidereal sphere revolves in twenty-four hours. It is a glaring inconsistency that the same author should affirm both the one and the other." Such would have been Aristotle's reasoning, on the hypothesis which I am considering; but when we turn to his treatise we find that he does not employ this argument at all. He contests the alleged rotation of the earth upon totally different arguments--chiefly on the ground that rotatory motion is not natural to the earth, that the kind of motion natural to the earth is rectilineal, towards the centre; and he adds various corollaries flowing from this doctrine which I shall not now consider. At the close of his refutation, he states in general terms that the celestial appearances, as observed by scientific men, coincided with his doctrine.