Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/33

 if not so, then the supposion of Aristotle is defective. It appears moreover that Aristotle hinteth but one circular motion alone to be in the World, and consequently but one onely Center, to which alone the motions of upwards and downwards, refer. All which are apparent proofs, that Aristotles aim is, to make white black, and to accommodate Architecture to the building, and not to modle the building according to the precepts of Arthitecture: for if I should say that Nature in Universal may have a thousand Circular Motions, and by consequence a thousand Centers, there would be also a thousand motions upwards, and downwards. Again he makes as hath been said, a simple motion, and a mixt motion, calling simple, the circular and right; and mixt, the compound of them two: of natural bodies he calls some simple (namely those that have a natural principle to simple motion) and others compound: and simple motions he attributes to simple bodies, and the compounded to the compound; but by compound motion he doth no longer understand the mixt of right and circular, which may be in the World; but introduceth a mixt motion as impossible, as it is impossible to mixe opposite motions made in the same right line, so as to produce from them a motion partly upwards, partly downwards; and, to moderate such an absurdity, and impossibility, he asserts that such mixt bodies move according to the simple part predominant: which necessitates others to say, that even the motion made by the same right line is sometimes simple, and sometimes also compound: so that the simplicity of the motion, is no longer dependent onely on the simplicity of the line.

How? Is it not difference sufficient, that the simple and absolute are more swift than that which proceeds from predominion? and how much faster doth a piece of pure Earth descend, than a piece of Wood?

Well, Simplicius; But put case the simplicity for this cause was changed, besides that there would be a hundred thousand mixt motions, you would not be able to determine the simple; nay farther, if the greater or lesse velocity be able to alter the simplicity of the motion, no simple body should move with a simple motion; since that in all natural right motions, the velocity is ever encreasing, and by consequence still changing the simplicity, which as it is simplicity, ought of consequence to be immutable, and that which more importeth, you charge Aristotle with another thing, that in the definition of motions compounded, he hath not made mention of tardity nor velocity, which you now insert for a necessary and essential point. Again you can draw no advantage from this rule, for that there will be amongst the mixt bodies some, (and that not a few) that will move swiftly,