Even if the fall of heavy bodies results from blows and impulses delivered by the inner motive virtue of the heavy body itself, it is, however, surprising how different this internal percussion is from that which is diffused in projectiles. The force of projection delivers a blow once at the beginning and then is inactive whereas the force of gravity is always active and delivers a blow again and again which results in an acceleration of the movement. Moreover, they differ from each other for another more wonderful reason. The force impelling a projectile creates in one instant a well-determined degree of impetus in the projectile. This impetus is not indivisible but is quantifiable and has a linear magnitude. The virtue of gravity does not create in one instant a quantifiable but an absolutely indivisible impetus. The impulses multiplied then by an unutterable multitude of instants of elapsed time finally result in a quantifiable and linear velocity.