<s id="id.1.2.6.01.02">However, while I was on and off investigating the cause of this effect, which I would not call astonishing but necessary (for the cause which is reported by Aristotle never appealed to me), for a long time I was troubled, and I found nothing that was fully satisfying. </s>
<s id="id.1.2.6.01.03">But, once the very true cause (at least in my own judgment) had been found, at first I rejoiced: but, when I examined it with more application, I was suspicious because it appeared free from any difficulty: but, finally, all difficulty having been progressively cleared away with the passage of time, I will now bring out for everyone to see which is assuredly finished and very certain. </s>
<s id="id.1.2.6.01.04">But first of all, according to our custom, we will consider with care what strength there is in the cause which is expressed by Arsitotle. </s>
</p>
<p>
<s id="id.1.2.6.02.00"/>
<s id="id.1.2.6.02.01">And, in the first place, it must be known that certain recent authors assert that Aristotle attributes this cause to the parts of the air, which hit the back of the mobile, rushing back to fill in the void: by this striking, they themselves say, the natural motion is increased. </s>
<s id="id.1.2.6.02.02">But that Aristotle did not think this can clearly be concluded from the things that are read in De Caelo, Book I, [ch.8], text #89, [277b1-9], where he says in clear words: Natural motion is not helped by extrusion, as some have believed; for in that case it would be a violent motion, which is weakened at the end, not increased, like the natural.</s>
<s id="id.1.2.6.02.03">It is thus evident that Aristotle not only does not hold this opinion, but that he rejects it: and indeed it deserves to be rejected. </s>
<s id="id.1.2.6.02.04">For, from what they say concerniing the void, either a void is left behind in back of the mobile, or not; if not, why do they say that the air rushes back to fill in the void? and if it is left, why do they not say that the mobile also moves back to fill in the void, and that thus the motion is rather retarded by such a cause, and not helped?</s>
<s id="id.1.2.6.02.05">In the second place: let a mobile be taken, concerning which there can be no doubt that it is not impelled from behind by the air; such as a solid rhombus made up of two cones, both tapering out into a very sharp point. </s>
<s id="id.1.2.6.02.06">Surely this thing will not be able to be impelled by the air, since its shape has nothing against which the air could hit. </s>
<s id="id.1.2.6.02.07">In the third place, things that are moved by violence, are not moved more swiftly than that by which they are moved; but the air, while it is moved towards the back of the mobile, is moved by force (for in its natural region it is at rest): hence it cannot be moved more swiftly than that by which it is moved. </s>
<s id="id.1.2.6.02.08">Now it is moved by that body going down; hence the air will not be moved faster than the mobile going down: but if it is not moved faster, it certainly will not be able to impel that body; </s>
