On Natural Motions Depending on Gravity

...reached, and this desire original: "desiderium." Borelli uses "desire" to describe the inherent physical tendency of matter to seek its natural place, a common concept in early modern physics. of theirs cannot be fulfilled except through motion. Therefore, when the goal ceases, the means necessarily ceases as well. Specifically, when a heavy body can no longer get closer to the center of the earth than it was before, it will not move at all. From this it follows that the aforementioned bodies remain at rest. If they were to move, they would either have to recede and be moved away from the center of the earth, or be carried sideways. In the first case, the action would be contrary to the natural instinct of heavy bodies, which is impossible. In the second case, the action would be empty and useless. The heavy body would gain nothing further since it could no longer get closer to the center of the earth by hypothesis. It is absurd and contrary to reason for nature to act by chance and without a goal. Therefore, it is impossible for bodies that cannot get closer to the center of the earth to be moved in any way. For this reason, it is necessary that they remain fixed at rest in the same position where they were previously.

SUPPOSITION IV.

Furthermore, Archimedes assumed as a first principle, known through itself, that the parts of the same consistent fluid that are continuous in the same horizontal plane and are less pressed must be ejected and expelled upward perpendicularly by the parts of the same fluid that are more compressed. This principle, although it is very true, still has some obscurity. It is not at all evident why parts of the same fluid can be compressed more or? less. Nor is it equally evident

A