Of the wind. Many are the times that the course of one wind is transmuted into the course of another, and this arises from the percussions they make in the encounters of their courses; for, not being able to penetrate one another, necessity constrains them to rebound to opposite sides. But if the said winds are not of equal power among themselves, their reflex motions will not follow the motion of their striker; rather, the angle of percussion of the more powerful will be greater than that of the lesser power by as much as the greater power exceeds the lesser.

Winds that run toward one same quarter may be simple or mixed with other winds; that is, along one part of its breadth it may be entirely of the narrow wind that strikes the broad wind and rebounds backward at equal angles, but never against its own origin, because it would have to re-enter into itself, and the motion of two bodies cannot penetrate one within the other. It follows, then, that the part of the greater wind which is struck by the lesser wind would turn back and follow the line of the lesser wind, its striker; but it collides with the remainder of its own breadth, which little by little curves it until it has brought it back into its first course. Therefore a wind striking within itself generates diverse motions and diverse qualities of power, because that part of its breadth which drives forward the part that was fleeing also itself takes a reflex motion upon the wind struck by it; and so, successively, does that part which, being struck, makes the second flight; and the fourth that strikes the third, in such a way that in these places the wind comes to be made denser. But the first density is greater than the last, in the likeness of two waters that strike together, as I have shown in the 4th proposition of the seventh book of the mechanical elements, which forms an angle at the place of its first percussion, an angle that makes the water which first strikes leap up higher than any other part of it.

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