But that circulation is the first of lations is evident: for every lation, as we have before observed, is either in a circle or in a right line, or mixed from both these. It is necessary, however, that those should be prior to these: and the motion in a circle is prior to that which is in a right line; for it is simple and more perfect: for it is not possible for any thing to be moved through an infinite right line; since that which is thus infinite does not exist. Nor if it did could any thing be moved through it; since that which is impossible cannot take place. But to pass through the infinite is impossible; and the motion which is made upon a right line, if it returns, is a composite, and becomes two motions; but if it does not return, is imperfect and corruptible. The perfect, however, is prior by nature, by reason, and by time to the imperfect, and the incorruptible to the corruptible. Farther still, the lation which may be perpetual, is prior to that which cannot. Circulation, therefore, may be perpetual; but of other motions neither lation nor any other can be perpetual: for in these there must necessarily be standing still; but if there is standing still the motion is corrupted.
