8 THEORY OF THE FIRMAMENT. 



decrement of the periodic 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 

 declination are the tropics; which declination has produced 

 a circle oblique to us, and its different polarity ; after the 

 same manner, that that inequality 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 

 introducing 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 deviations from a perfectly circular mo 

 tion, which the planets cannot bear ; for in proportion as 

 the substances degenerate in purity and expansion, so also 

 do their motions. But it happens, that as in point of cele 

 rity the higher planets are carried on quicker, and the 

 inferior slower; so, also, that the superior planets form 

 spires that approximate * and more nearly resemble cir 

 cles, but the inferior curves more disjoined and eccentric ; 

 for, by descending 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 no where 

 interrupted. In this however the planets agree, (as bodies 

 retaining much of a common nature, though in other 

 respects differing,) that they have the same limits of decli 

 nation. 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 



Propiores, if not misprinted for propriores, must respect the foci of the 

 ellipses ; which explains &quot; disjunctas : &quot; but, if the illustrious author did write 

 propiores, why did he afterwards tautologize by saying &quot; quaiquc circulos propius 

 referant 1 &quot; 



