understand that we should very commodiously salve all the Phænomena of these two Planets, with two Circles, in like manner, drawn about the Sun, and this first for Jupiter, marking it EL, and another above that for Saturn marked FM.
Salv.You have behaved your self bravely hitherto.The approximation and recession of the three superiour Planets, importeth double the Suns distance. And because (as you see) the approach and recession of the three Superiour Planets is measured with double the distance between the Earth and Sun, this maketh greater difference in Mars than in Jupiter, the Circle DI,The difference of the apparent magnitude lesse in Saturn, than in Jupiter, an dn Jupiter than in Mars, and why. of Mars, being lesser than the Circle EL, of Jupiter, and likewise because this EL, is lesse than this Circle FM, of Saturn, the said difference is also yet lesser in Saturn than in Jupiter, and that punctually answereth the Phænomena. It remains now that you assign a place to the Moon.
Simpl.Following the same Method (which seems to me very conclusive) in regard we see that the Moon cometh to conjunction and opposition with the Sun,The Moons Orb invironeth the Earth, but not the Sun. it is necessary to say, that its circle encompasseth the Earth, but yet doth it not follow, that it must environ the Sun, for then at that time towards its conjunction, it would not seem horned, but alwayes round and full of Light. Moreover it could never make, as it often doth, the Eclipse of the Sun, by interposing betwixt it and us; It is necessary therefore to assign it a circle about the Earth, which should be this NP, so that being constituted in P, it will appear from the Earth A, to be in conjunction with the Sun, and placed in N, it appeareth opposite to the Sun, and in that position it may fall under the Earths shadow, and be obscured.
Salv.Now, Simplicius, what shall we do with the fixed stars? Shall we suppose them scattered through the immense abisses of the Universe, at different distances, from any one determinate point; or else placed in a superficies spherically distended about a centre of its own, so that each of them may be equidistant from the said centre?
Simpl.I would rather take a middle way;The probable situation of the fixed stars. and would assign them an Orb described about a determinate centre and comprized within two spherical superficies, to wit, one very high, and concave, and the other lower,Which ought to be accounted the sphere of the Universe. and convex, betwixt which I would constitute the innumerable multitude of stars, but yet at divers altitudes, and this might be called the Sphere of the Universe, conteining within it the Orbs of the planets already by us described.
Salv.But now we have all this while, Simplicius, disposed the mundane bodies exactly, according to the order of Copernicus, and we have done it with your hand; and moreover to each of them you have assigned peculiar motions of their own, except to the Sun, the Earth, and starry Sphere; and to Mercury with Venus, you have ascribed the circular motion about the Sun,with
