Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/55

 is corrupted, resides it in the same Earth or in some other bodie, which must either be the Air or Water? I believe you will grant, that like as the Motions upwards and downwards, and gravity and levity, which you make the first contraries, cannot be in the same Subject, so neither can moist and dry, hot and cold: you must therefore consequently acknowledg that when a bodie corrupteth, it is occasioned by some quality residing in another contrary to its own: therefore to make the Cœlestial Body become corruptible, it sufficeth that there are in Nature, bodies that have a contrariety to that Cœlestial body; and such are the Elements, if it be true that corruptibility be contrary to incorruptibility.

This sufficeth not, Sir; The Elements alter and corrupt, because they are intermixed, and are joyn'd to one another, and so may exercise their contrariety; but Cœlestial bodies are separated from the Elements, by which they are not so much as toucht, though indeed they have an influence upon the Elements. It is requisite, if you will prove generation and corruption in Cœlestial bodies, that you shew, that there resides contrarieties between them.

See how I will find those contrarieties between them. The first fountain from whence you derive the contrariety of the Elements, is the contrariety of their motions upwards and downwards: it therefore is necessary that those Principles be in like manner contraries to each other, upon which those motions depend: and because that is moveable upwards by lightness, and this downwards by gravity, it is necessary that lightness and gravity are contrary to each other: no less are we to believe those other Principles to be contraries, which are the causes that this is heavy, and that light: but by your own confession, levity and gravity follow as consequents of rarity and density; therefore rarity and density shall be contraries: the which conditions or affections are so amply found in Cœlestial bodies, that you esteem the stars to be onely more dense parts of their Heaven: and if this be so, it followeth that the density of the stars exceeds that of the rest of Heaven, by almost infinite degrees: which is manifest, in that Heaven is infinitely transparent, and the stars extremely opacous; and for that there are there above no other qualities, but more and less density and rarity, which may be causes of the greater or less transparency. There being then such contrariety between the Cœlestial bodies, it is necessary that they also be generable and corruptible, in the same manner as the Elementary bodies are; or else that contrariety is not the cause of corruptibility, &c.

There is no necessity either of one or the other, for that density and rarity in Cœlestial bodies, are not contraries to