Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/56

 each other, as in Elementary bodies; for that they depend not on the primary qualities, cold and heat, which are contraries; but on the more or less matter in proportion to quantity: now much and little, speak onely a relative opposition, that is, the least of oppositions, and which hath nothing to do with generation and corruption.

Therefore affirming, that density and rarity, which amongst the Elements should be the cause of gravity and levity, which may be the causes of contrary motions sursum and deorsùm, on which, again, dependeth the contrarieties for generation and corruption; it sufficeth not that they be those densnesses and rarenesses which under the same quantity, or (if you will) mass contain much or little matter, but it is necessary that they be densnesses and rarenesses caused by the primary qualities, hot and cold, otherwise they would operate nothing at all: but if this be so, Aristotle hath deceived us, for that he should have told it us at first, and so have left written that those simple bodies are generable and corruptible, that are moveable with simple motions upwards and downwards, dependent on levity and gravity, caused by rarity and density, made by much or little matter, by reason of heat and cold; and not to have staid at the simple motion sursum and deorsùm: for I assure you that to the making of bodies heavy or light, whereby they come to be moved with contrary motions, any kind of density and rarity sufficeth, whether it proceed from heat and cold, or what else you please; for heat and cold have nothing to do in this affair: and you shall upon experiment find, that a red iron, which you must grant to have heat, weigheth as much, and moves in the same manner as when it is cold. But to overpass this also, how know you but that Cœlestial rarity and density depend on heat and cold?

I know it, because those qualities are not amongst Cœlestial bodies, which are neither hot nor cold.

I see we are again going about to engulph our selves in a bottomless ocean, where there is no getting to shore; for this is a Navigation without Compass, Stars, or Rudder: so that it will follow either that we be forced to pass from Shelf to Shelf, or run on ground, or to sail continually in danger of being lost. Therefore, if according to your advice we shall proceed in our main design, we must of necessity for the present overpass this general consideration, whether direct motion be necessary in Nature, and agree with some bodies; and come to the particular demonstrations, observations and experiments; propounding in the first place all those that have been hitherto alledged by Aristotle, Ptolomey, and others, to prove the stability of the Earth, endeavouring in the next place to answer them: and producing in