On the percussion of dense bodies.

It seems that percussion, being made in indivisible time, cannot pass into the place, or body, that receives it without divisible time. For it is called indivisible when it is created on the surface of bodies, that is, at their contacts. But we shall call it divisible when such power penetrates through the body that receives it, because it goes distinguishing itself through all the parts of that body. And the farther it moves from its origin, the more it diminishes, because it divides into more parts. And certainly the part is less than its whole. And the more the parts are, the more they move away from the first power. Hence, the longer and thicker the bodies that receive it, the less harm they will give to the place that supports them when they are struck by the blow. And so conversely, when the struck bodies are smaller. And for this reason, if you strike with the same hammer upon 2 nails of various sizes and of equal sharpness and contact upon wood where they are to be fixed, certainly that nail which is of smaller shape will fix itself much deeper than the larger nail. But if the said smaller nail is attached to the face of the hammer with a little wax, and the blow is given with the point of that nail upon the said wood, that nail will be of marvelous penetration. But what shall we say of the knife, which cuts the peach in the air, with all its flesh, and stone, and kernel, which almost seems to be all of turnip or of some other soft and frangible thing, and the edge of the knife is not spoiled?

And what shall we say of the ball struck by the other ball, which imparts its own motion to that which is struck by it, and itself stays still in the place of that which flees before it? And certainly, if the ball that fled had been resistant, without any motion, that ball which struck it would rebound backward. But since that which is struck moves, and the ball that strikes had no fixity nor support to launch its leap — like one who stands upon this board and wants to leap forward, and the board, fleeing backward, does not await the building-up of the leap — hence such board flees, and the leaper falls back whence he rose.

United patient, of one pound in weight.

Disunited patient. Of one pound in weight.

Last degree of power, that is, in weakness of penetration.

First degree of power, that is, in the highest degree of penetration.