Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/358

 nor a lesse mutation being discerned in the fixed Stars, methinks that by this means the annual motion of the Earth is destroyed and overthrown.

You might very well so conclude, Simplicius, if we had nothing else to say in behalf of Copernicus: but we have many things to alledge that yet have not been mentioned; and as to that your reply, nothing hindereth, but that we may suppose the distance of the fixed Stars to be yet much greater than that which hath been allowed them, and you your self, and whoever else will not derogate from the propositions admitted by Piolomy's sectators, must needs grant it as a thing most requisite to suppose the Starry Sphere to be very much bigger yet than that which even now we said that it ought to be esteemed. For all Astronomers agreeing in this, that the cause of the greater tardity of the Revolutions of the Planets is, the majority of their Spheres, and that therefore Saturn is more slow than Jupiter, and Jupiter than the Sun, for that the first is to describe a greater circle than the second, and that than this later, &c. considering that Saturn v. g. the altitude of whose Orb is nine times higher than that of the Sun, and that for that cause the time of one Revolution of Saturn, is thirty times longer than that of a conversion of the Sun, in regard that according to the Doctrine of Ptolomy, one conversion of the starry Sphere is finished in 36000. years, whereas that of Saturn is consummate in thirty, and that of the Sun in one, arguing with a like proportion, and saying, if the Orb of Saturn, by reason it is nine times bigger than that of the Sun, revolves in a time thirty times longer, by conversion, how great ought that Orb to be, which revolves 36000. times more slowly? it shall be found that the distance of the starry Sphere ought to be 10800 semidiameters of the grand Orb, which should be full five times bigger than that, which even now we computed it to be, in case that a fixed Star of the sixth magnitude were equal to the Sun. Now see how much lesser yet; upon this account, the variation occasioned in the said Stars, by the annual motion of the Earth, ought to appear. And if at the same rate we would argue the distance of the starry Sphere from Jupiter, and from Mars, that would give it us to be 15000. and this 27000 semidiameters of the grand Orb, to wit, the first seven, and the second twelve times bigger than what the magnitude of the fixed Star, supposed equal to the Sun, did make it.

Methinks that to this might be answered, that the motion of the starry Sphere hath, since Ptolomy, been observed not to be so slow as he accounted it; yea, if I mistake not, I have heard that Copernicus himself made the Observation.