It is honourable to the penetration of M. Boeckh that he should have pointed out, what so many previous critics had overlooked, that these two opinions are scientifically incompatible. He wonders, and there may be good ground for wondering, how it happened that none of these previous writers were aware of the incompatibility. But the fact that it did not occur to them, is not the less certain, and is of the greatest moment in reference to the question now under debate; for we are not now inquiring what is or is not scientifically true or consistent, but what were the opinions of Plato. M. Boeckh has called our attention to the fact, that these two opinions are incompatible; but can we safely assume that Plato must have perceived such incompatibility between them? Surely not. The Pythagoreans of his day did not perceive it; their cosmical system included both the revolution of the earth and the revolution of the sidereal sphere round the central fire, ten revolving bodies in all (Aristotel. Metaphysic. i. 35, p. 96 a. 10. De Coelo, ii. 13, p. 293 b. 21). They were not aware that the revolutions of the one annulled those of the other as to effect, and that their system thus involved the two contradictory articles, or "mélange monstrueux," of which Martin speaks so disdainfully. Nay, more, their opponent, Aristotle, while producing other arguments against them, never points out the contradiction. Since it did not occur to them, we can have no greater difficulty in believing that neither did it occur to Plato. Indeed, the wonder would rather be if Plato _had_ seen an astronomical 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.