The book of impetus comes before this one, and before impetus comes motion.

d e - b g - a - c - f. No percussion made by a sphere counts for the whole weight of that sphere unless it is made with the front of the diameter of that sphere, when the diameter lies on the central line of the motion of that sphere. The percussion made by the sphere will be the more powerful the nearer its diameter is to the central line of its motion. The percussion made by the sphere will be of so much less power the more the central line of its motion is remote from the diameter of that sphere. The power of the percussion made outside the central line of the motion is always worth twice the smaller part of the sphere that remains outside the course of the part.

a - b. Of every sphere struck outside the central line of its motion, there is a part that reflects and a part that follows the first motion and...

Of every sphere struck outside the central line of its motion, there is a part that reflects back and one that follows the contrary motion. Of every spherical body that strikes with a part remote from the central line of its motion, a rotating motion is generated; and this is proved by the preceding. All spheres that strike with the central line of the motion rebound back with the whole body without rotating motion; and this arises because the struck parts are of equal weight around the struck place. Of every sphere struck outside the central line of its motion, the percussion is worth, at the struck place, the smaller part which is from the line of the percussion toward the struck place. Of the unequal mover of the sphere, like the fire in the bombard, which makes the ball rotate. The percussion made by the reflected part of the rotating sphere is worth next to nothing, because the part of the rotating body that reflects is swifter in returning back than the whole sphere is in going forward. The percussion made by the incident part of the rotating sphere is more powerful than the opposite part of the same body that reflects.

The sphere reflected by rotating motion will always be of brief course. And this arises when the struck body is of more powerful motion than the percussor, because then the percussor does not reflect like the struck body; but the struck body, not being beaten along its central line, acquires no power in reflecting except unequal power, whence its motion is composed of straight and rotating motion. This arises because the struck moving body was not struck in the middle of its power, but slantwise, that is obliquely; and because the percussions are fugitive, then the motion becomes rotating, because the power of the percussor was disposed to make the struck body turn about its own centre and there consumed great power, and the power of the struck body was in great part annulled, that is, by as much as was converted into rotation, and for this its straight motion was brief.

Of the immobile struck body. Of the struck body as fast as the percussor. Of the struck body less fast than the percussor. Of the percussion of the rotating body with the incident part. Of the percussion of the rotating body with the reflected part.

a - c b - d.

a; b. a and b are equal.

(a) - a - c; (b) - b - d. a and b are double one to the other, that is, b is double a.

c.

a - d; b; c - e. Here b is taken away by c equal to it; c remains equal to b. And if you take a from d, d remains equal to e c.

d; c - e.

n; o a. The portion n is worth a o.

b is one-sixteenth of its circle.

1509 - 1269 = 240.