THE THEORY OF THE FIRMAMENT.
we*t to east, which is attributed as peculiar to the planets, is not true, but only apparent, from the outstripping of the starry firmament toward the west, and the leaving behind of the planets towards the east, which being granted, it is evi dent that the velocity of that cosmical motion, by an unperturbed law of nature, as it descends, decreases, so that the nearer each planet ap proaches the earth, the slower it moves; whereas the received opinion overthrows and turns upside down that law ; and by attributing a motion of their own to the planets, falls into the absurdity, that the planets, the nearer they are to the earth, (which is, naturally, the place of rest,) in that ratio have their celerity increased ; which astro nomers, in the most trifling and unsuccessful manner, attempt to excuse, by a relaxation of the force of the primum mobile. But if it seem to any one a matter of wonder, that, in spaces so vast as interpose between the starry firmament and the moon, that motion should gradually de crease by portions so small, by less, to wit, than one hour, which is the twenty-fourth part of the diurnal motion ; it subsides when we consider that each planet, the nearer it is to the earth, completes lesser circles, revolving in a shorter circuit; so that, the decrement of the size of the circle being added to the decrement of the period ic time, that motion is perceived to decrease in a marked manner. Up to this time we have spoken of the velocity, absolutely and apart, as if the planets, placed, for example, in the plane of the equator, or of any of its parallels, were simply overtaken by the starry firmament, and by one another, but yet in that selfsame circle ; for this would be a mere leaving behind, without any respect to obliquity. But it is manifest, that the planets not only hasten on their course with unequal relative speed, but do not return to the same point of a circle, but decline towards the south and the north, the limits of which declina tion are the tropics ; which declination has pro duced a circle oblique to us, and its different polarity; after the same manner that that ine quality of velocity has caused the motion of an opposite action. Nor really is there need of this figment in the nature of things, since, by introduc ing spiral lines, (the thing that comes nearest to sense and fact,) the matter in dispute may be settled, and those points be safe and sound. Besides, (which is the sum and substance of the matter,) these spirals are nothing else than devia tions from a perfectly circular motion, which the planets cannot bear; for in proportion as the sub stances degenerate in purity and expansion, so also do their motions. But it happens, that as in point of celerity the higher planets are carried on quicker, and the inferior slower; so, also, that the superior planets form spires that approximate*
- Propiores, if not misprinted for propriores, must respect
ihe foci of the ellipses; which explains " dUjunctai " bul. and more nearly resemble circles, but the inferior curves more disjoined and i-ccmtrir- ; for, by de scending more and more, there is a perpetual departure both from that prime state of velocity and that perfect circular motion, by a law of nature nowhere interrupted. In this, however, the planets agree, (as bodies retaining much of a common nature, though in other respects differ ing,) that they have the same limits of declination. For neither doth Saturn return within the tropics, nor does the moon stray beyond the tropics, (and yet we must not dismiss from our consideration what has been handed down and remarked by some upon the wanderings of the planet Venus,) but all the planets, whether superior or inferior, after their arrival at the tropics, turn themselves, and recommence a course back again, weary of a lesser spiral range, such as they would have to undergo, if they did approach nearer the poles ; and dreading that loss of motion as destructive of their nature. For, howsoever it may be, in the starry firmament, both the stars near the poles, and those about the equinoctial, preserve their ranks and positions, reduced into order, one by another, with steadfastness and consummate uni formity ; nevertheless, the planets seem to be of that mixed nature, that they admit not willingly an ampler circuit, nor bear at all a shorter. Furthermore, these doctrines concerning the hea venly motions seem to us somewhat preferable to forced and opposite motions, and of a different polarity of the zodiac, and an inverted order of velocity, and such like, which in no way agree with the nature of things, though they may in a manner accord with calculations. Neither have eminent astronomers been blind to these matters, but, wrapped up in their craft, and reveries of perfect circles, catching at subtleties and the evil results of a fashionable philosophy, they have disdained to follow nature. Truly, how ever, is that despotic decretal against nature of wise men more mischievous, than the very simplicity and utter credulity of the uninformed, when any one, for instance, looks with scorn at truth, because it is manifest. And yet huge is that evil, and most widely extended, that the human intellect, whenever it finds itself unequal to subjects, has a predilection to soar above them. But now we must inquire whether that one and simple motion in a circle, and in a spiral curve, from east to west, upon certain south and north poles, cease and terminate with the heavens, or it also be conveyed down to things beneath. For it would not be ingenuous in us to feign here in this nether region such aphorism as they sup pose with respect to the heavens. Wherefore, if in these regions be also found that motion, it if Ihe Illustrious author did write propiores, why did he after- wards tautologize by saying "qus-que circulo* prop u* reff
