It is demonstrated what proportion the power of percussion has to the power of impetus with regard to the moving of heavy bodies.

What the moving body gains in height in its rebounding motion is born only from the power of the simple percussion; and what that rebounding motion gains in length is born only from the power of the simple impetus. Now I find that in the bounce drawn here its height d e goes into its length b e c exactly four times. Hence we shall conclude, from what is said above, that just as the height d e goes four times into the length b e c, so likewise the power that is the cause of the bounce b d c goes four times into the power of the impetus a b, which drove the said moving body to the percussion at the place b.

Therefore we shall say that by as much as the bounce is higher than it is long, by so much does the power of percussion exceed the power of impetus; and by as much as that bounce has its height exceeded by its length, by so much is the percussion exceeded by the impetus. Hence the natures of the causes are made manifest through the effects, and the natures of the effects through the causes, as will be shown in the cases below.

Given one degree of power of impetus and one degree of power of percussion, the figure of the arc made by the rebounding motion is sought.

In this case we shall divide the degrees of the impetus into 16 and the degrees of the percussion into 4. Each degree, both of impetus and of force, will turn out to be equal, because we say the impetus to be four times more powerful than the percussion; hence 4 degrees of impetus will be equal to 4 degrees of percussion; wherefore, by the question posed above, it is concluded that one degree of impetus and one of percussion will cause the arc of the rebounding motion to be as high as it is long.

That percussion will be of lesser power which is created upon a smaller angle.

Even though one and the same power moves one and the same moving body, through one and the same space, upon one and the same object, there can be caused by the aforesaid means percussions of infinitely variable power. And this happens because the angles upon which such percussions are generated can be infinitely variable from greater to smaller; and, as has been said, a greater or smaller angle generates a greater or smaller percussion. For if in the greater angle the moving body moves from a and descends to b, that moving body returns toward a, whence it descended. And this is the greatest blow that can be made by a fixed power. But if that same power moves the same moving body along the line d e, its percussion will be made upon the object e with as much less power than at b as the angle e is smaller than the angle b. So that the proportion of the percussions among themselves will be the same as that of the aforesaid angles among themselves.