JOH. AL. BORELLI

...per se habens... as the previous page concludes: "having no motive force of its own"... it would fall perpendicularly to the surface of the earth as a heavy object, yet because it is surrounded on all sides by air previously agitated and set in motion, it happens that the stone is carried by the air surrounding it as if by a rapid river, until the agitation of the air languishes and finally is extinguished together with the motion of the same carried stone. Others of the same Peripatetic school later say that the air, following the projectile with the greatest rapidity and force, returns to fill the space abandoned by the projectile, lest a vacuum—which nature abhors—should follow, and thus, by continuously pressing the rear part of the stone most vehemently, it promotes it, not otherwise than boys expel fruit pits far away by squeezing them from behind with their fingers.

If a projectile were carried by impelled air, the air would also have to be impelled by other air, and so on to infinity.

But in order for the vanity of this opinion to be shown, it must first be observed that if a fluid medium, such as water or air, carries a projectile body like a river after it has been abandoned by the thrower, it must also be granted that the impelled air or water was itself impelled by the same thrower, since such a fluid medium is also a movable object to which motion is newly impressed, which it previously lacked. Therefore, when the propulsion of the thrower ceases, unless we wish to admit the migration of a motive virtue from one subject into another—namely, from the thrower into the fluid itself—we are forced to assign a cause by which the subsequent motion of the same fluid is continued. Therefore, there must be found another fluid body surrounding the air or water hitherto projected and impelled, by which its flow can be continued, and with it, it may also carry the included projectile. That same exterior fluid would also have to be impelled by another surrounding fluid, and thus successively to infinity. Wherefore a stone could not be thrown through the air unless the entire world were agitated at once; how vain and impossible this is, is sufficiently clear by itself. But if someone should effect a projection inside a vial full of water and closed on all sides, if indeed the stone were promoted by the water surrounding it after it is abandoned by the thrower, even if one grants that the whole water is moved and carried around as far as the surface of the containing vessel, then certainly the outermost surface of the water contiguous to the glass, if it lacked motive virtue, would have to be carried and propelled by the surface of the glass itself, which is entirely immobile, which is surely most vain. Add to this that the evidence of the senses confirms that air or water but little distant from the projectile is not moved at all, but persists in the most tranquil rest; this can be most evidently observed

The falsity of this opinion is proven by experience.