Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/322

 figure; and moveth circularly, hath necessarily, and in respect of its figure a centre; and we being moreover certain, that within the starry Sphere there are many Orbs, the one within another, with their stars, which likewise do move circulary, it is in dispute whether it is most reasonable to believe and to say that these conteined Orbs do move round the said centre of the World, or else about some other centre far remote from that? Tell me now Simplicius what you think concerning this particular.

If we could stay upon this onely supposition, and that we were sure that we might encounter nothing else that might disturb us, I would say that it were much more reasonable to affirm that the Orb containing, and the parts contained, do all move about one common centre, than about divers.

Now if it were true that the centre of the World is the same about which the Orbs of mundane bodies, that is to say, of the Planets, move, it is most certain that it is not the Earth, but the Sun rather that is fixed in the centre of the World. So that as to this first simple and general apprehension, the middle place belongeth to the Sun, and the Earth is as far remote from the centre, as it is from that same Sun.

But from whence do you argue that not the Earth, but the Sun is in the centre of the Planetary revolutions?

I infer the same from most evident, and therefore necessarily concludent observations, of which the most palpable to exclude the Earth from the said centre, and to place the Sun therein, are, the seeing all the Planets one while neerer and another while farther off from the Earth with so great differences, that for example, Venus when it is at the farthest, is six times more remote from us, than when it is neerest, and Mars riseth almost eight times as high at one time as at another. See therefore whether Aristotle was not somewhat mistaken in thinking that it was at all times equidistant from us.

What in the next place are the tokens that their motions are about the Sun?

It is argued in the three superiour planets Mars, Jupiter, and Saturn, in that we find them alwayes neerest to the Earth when they are in opposition to the Sun, and farthest off when they are towards the conjunction, and this approximatian and recession importeth thus much that Mars neer at hand, appeareth very neer 60 times greater than when it is remote. As to Venus in the next place, and to Mercury, we are certain that they revolve about the Sun, in that they never move far from him, and in that we see them one while above and another while below it, as the mutations of figure in Venus necessarily argueth. TonchingTouching [sic] the Moon it is certain, that she cannot in any way