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 or both of them? The difficulty is still more apparent when we find that admitting what Ptolemy said as regards the epicycle of the moon, and its inclination towards a point different both from the centre of the Universe and from its own centre, the calculations according to these hypotheses are perfectly correct, within one minute: that their correctness is confirmed by the most accurate calculation of the time, duration, and extent of the eclipses, which is always based on these hypotheses. Furthermore, how can we reconcile, without assuming the existence of epicycles, the apparent retrogression of a star with its other motions? How can rotation or motion take place round a point which is not fixed? These are real difficulties.

I have explained to you already viva voce, that these difficulties do not concern the astronomer: for he does not profess to tell us the existing properties of the spheres, but to suggest, whether correctly or not, a theory in which the motion of the stars is circular and uniform, and yet in agreement with our observation. You know that Abu-bekr al-Zaig, in his treatise on Physics, expresses a doubt whether Aristotle knew the excentricity of the sun but ignored it, and only discussed the effect of the inclination, because he saw that the effect of the excentricity was identical with that of the inclination; or whether he did not perceive it. The truth is that he did not notice it or hear of it: the science was not perfect in his age. If he had heard of it, he would have strongly opposed it; if he had been convinced of its correctness, he would have been greatly embarrassed as regards all that he said on the question. What I said before (ch. xxii.) 1 will repeat now, namely, that the theory of Aristotle, in explaining the phenomena in the sublunary world, is in accordance with logical inference: here we know the causal relation between one phenomenon and another; we see how far science can investigate them, and the management of nature is clear and intelligible. But of the things in the heavens man knows nothing except a few mathematical calculations, and you see how far these go. I say in the words of the poet," The heavens are the Lord's, but the earth He hath given to the sons of man" (Ps. cxv. 16): that is to say, God alone has a perfect and true knowledge of the heavens, their nature, their essence, their form, their motions, and their causes; but He gave man power to know the things which are under the heavens: here is man's world, here is his home, into which he has been placed, and of which he is himself a portion. This is in reality the truth. For the facts which we require in proving the existence of heavenly beings are withheld from us: the heavens are too far from us, and too exalted in place and rank. Man's faculties are too deficient to comprehend even the general proof the heavens contain for the existence of Him who sets them in motion. It is in fact ignorance or a kind of madness to weary our minds with finding out things which are beyond our reach. without having the means of approaching them. We must content ourselves with that which is within our reach, and that which cannot be approached by logical inference let us leave to him who has been endowed with that great and divine influence, expressed in the words:" Mouth to mouth do I speak with Him" (Num. xii. 8).

This is all I can say on this question; another person may perhaps be able to establish by proof what appears doubtful to me. It is on account of my great love of truth that I have shown my embarrassment in these matters and