329 and the natural heaviness is being acquired, it will stand to reason that all the contrary force will finally be lost, and that the natural heaviness will be resumed, and that, therefore, the cause having been removed, the acceleration will cease. And yet I would not say that the whole contrary force is consumed because I may happen to think that whatever is always diminished must finally be annihilated (for I am not unaware that this is not necessary, as will be said below); but I will only say that it is consumed because experience seems to me to show this. {1}For, in the first place, if we look at something that is not at all heavy coming from on high, a ball of wool or a feather or some such thing, we will see that it is moved more slowly at the beginning, but that nevertheless, a little latter, it will observe a uniform motion. Now the reason why this appears more manifest in things that are less heavy is that, when these things begin to be moved, since they have an amount of the contrary force equal to their proper heaviness, and they themselves are not very heavy, hence, the contrary impressed force will also be small, and thus it will be consumed more swiftly; when it has been consumed, these things will be moved with a uniform motion: and since they are moved slowly, it will be easier to observe the uniformity of such a motion in them than in the case of those that go down very swiftly.
Now in the case of heavier things, since a great amount of contrary force must be consumed in their descent, a greater time will be required for it to be consumed; in which time, since they are carried swiftly, they will descend a great distance: since we cannot avail ourselves of such great distances from which to release heavy things, it is not astonishing if the stone, released from merely the height of a tower, will seem to accelerate all the way to the ground; for this short distance and short time of motion are not sufficient to destroy the whole contrary force.
A second experience can be taken from other alterative motions in which at the end the contrary quality is completely lost; as when, after being white-hot, iron becomes very cold, and all the heat is entirely annihilated. One must, therefore, judge in the same way in the case of the stone which from light becomes heavy, that it loses all of its extrinsic lightness; when this happens, the intensification of the speed will cease. Thirdly, it can be confirmed by both reason and experience, not only that motion is not always accelerated when a mobile has receded from a state of rest; but also that, if at the beginning of the motion a great force which impels it downward is impressed by an external mover, it too will be destroyed. And the reason is because then the heaviness of the mobile would have the effect of lightness, since the heaviness by itself free and simple would go down more slowly than when joined with an impetus; and thus the proper and natural slowness [of the mobile] in going down would resist