[567] _Par._ x. 1-12. ------------------------------------------------------------------------ Dante knew that great men in ancient days had speculated on the possibility that it was Earth, and not the skies, that moved in the diurnal period, but the balance of authority was against them, and they had been confuted by the Master of those who KNOW,[568] that glorious philosopher to whom Nature most fully revealed her secrets,[569] Aristotle. In Treatise III. of the _Convivio_ he gives a clear and concise account of the theory of Philolaus, and of what he understood to be the theory of Plato.[570] In the former he seems to have been struck with the deduction that, if Fire were at the centre of the Universe, the real motion of fire on Earth, which to us appears always to ascend, would in reality be a descent towards its own place at the centre. ------------------------------------------------------------------------ [568] _Inf._ iv. 131. [569] _Conv._ III. v. 54-56. [570] _Conv._ III. v. 29-52. See Part I. of this book _Pythagoras and his Followers_, and _Plato_, for a description of their astronomical systems. ------------------------------------------------------------------------ Both these hypotheses he had evidently learned from Aristotle’s _De Cælo_,[571] and when thus presented they seem entirely fanciful; so although Dante had reverence for both Pythagoras and Plato it is not surprising that he rejected the systems of both. He adds that it is not his intention to recount here the arguments by which Aristotle confutes them and establishes the truth: it is enough for his readers to know, on so great an authority, that the earth is fixed, and does not revolve, and is at the centre of the World. Dante has to confess reluctantly that Aristotle made two mistakes in his astronomy: he said that there were only eight spheres, those of the seven planets, and that of the stars, “e che di fuori da esso non fosse altro alcuno;”[572] also he placed the heaven of the sun immediately above that of the moon, that is to say second in order, counting from Earth outward. Aristotle’s loyal admirer hastens to add that these serious mistakes “questa sua sentenza così erronea”[573] are explicable and excusable because, as Aristotle himself shows in the _Metaphysics_, when he treated of astrology he was merely following the opinions of others. That is to say, he took his facts from others, and they cannot all be depended upon, but his philosophical deductions are his own, and are never in error. In the above question of the possible movements of Earth, we saw (pp. 101-2) that Aristotle’s arguments were almost entirely drawn from metaphysics. ------------------------------------------------------------------------ [571] See Part I. “Aristotle.” [572] “And that outside the latter there was no other.” _Conv._ II. iii. 24, 25. [573] “This entirely mistaken opinion of his.” _Ibid._ 28. ------------------------------------------------------------------------