Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/325

 motion straight forwards, it goeth to the matutine conjunction; and moreover it being true, that when it appeareth bigge it shews with a corniculate figure, and when it appeareth little, it seems perfectly round, these appearances, I say, being true, I do not see how one can choose but affirm the said star to revolve in a circle about the Sun, for that the said circle cannot in any wise be said to encompasse or to contain the Earth within it, nor to be inferiour to the Sun, that is between it and the Earth, nor yet superiour to the Sun. That circle cannot incompasse the Earth, because Venus would then sometimes come to opposition with the Sun; it cannot be inferiour, for then Venus in both its conjunctions with the Sun would seem horned; nor can it be superiour, for then it would alwayes appear round, and never cornicular; and therefore for receit of it I will draw the circle CH, about the Sun, without encompassing the Earth.

Having placed Venus, it is requisite that you think of Mercury, which, as you know, alwayes keeping about the Sun, doth recede lesse distance from it than Venus; therefore consider with your self, what place is most convenient to assign it.

It is not to be questioned, but that this Planet imitating Venus, the most commodious place for it will be, a lesser circle within this of Venus, in like manner about the Sun, being that of its greatest vicinity to the Sun, an argument, an evidence sufficiently proving the vigour of its illumination, above that of Venus, and of the other Planets, we may therefore upon these considerations draw its Circle, marking it with the Characters BG.

But Mars, Where shall we place it?

Mars, Because it comes to an opposition with the Sun, its Circle must of necessity encompass the Earth; But I see that it must necessarily encompass the Sun also, for coming to conjunction with the Sun, if it did not move over it, but were below it, it would appear horned, as Venus and the Moon; but it shews alwayes round, and therefore it is necessary, that it no less includeth the Sun within its circle than the Earth. And because I remember that you did say, that when it is in opposition with the Sun, it seems 60 times bigger than when it is in the conjunction, me thinks that a Circle about the Centre of the Sun, and that taketh in the earth, will very well agree with these Phænomena, which I do note and mark DI, where Mars in the point D, is near to the earth, and opposite to the Sun; but when it is in the point I, it is at Conjuction with the Sun, but very far from the Earth. And because the same appearances are observed in Jupiter and Saturn, although with much lesser difference in Jupiter than in Mars, and with yet lesse in Saturn than in Jupiter; me thinks I