That wind which descends grazing the parts of the mountains that slope toward the sea penetrates to the bottom and makes waves whose flanks resemble the shore down which they descend; and therefore such waves are often of narrow and deep intervals, as I said in the book of the motion of waters. And such a storm lasts little after the striking of that wind, because, once it has struck, it rises again into the air until it meets the other wind and, striking upon it, condenses it, and again takes up the leap downward, in the likeness of rivers that beat against their banks.

Such are the motions of the winds, along all lines.

On the peaks of the mountains the wind becomes of great density, and [likewise] at the mouths of the valleys, when the mountains that enclose those valleys are of great height.
That opposite winds enter one beneath the other by contrary motions can happen for 2 reasons, namely either by the reflected motion of the wind that returns backward after the blow it has struck against the mountains, or, when contrary winds collide, by their striking with their more powerful parts upon their weaker parts.
The whirlwinds, or eddies, of the winds arise in the winds that open in the embrace of the mountains, or of some building, and then, on rejoining, strike one another with force; and their reflected motions are not made along a straight line, because [the wind] is impeded within its own sphere, where it moves, by matter like itself, which has the power to impede the straight impetus and bend it; whence such a wind, being unable to spread out, goes on consuming its impetus with mo[tion] ... It goes upward to consume its impetus, because it is compelled to for 3 reasons: the first is that it cannot in the same time return along the proper lines of its incidence; the second, because they have struck one another at angles less than right, and cannot rebound along lines equal to the incident ones.