On things that descend through the air. The air condenses in front of the bodies that penetrate it with speed, with the greater or lesser density according as the speed is of greater or lesser fury.

The board of uniform width, length, depth and weight will not keep its initiated oblique motion, amid the air it penetrates, for a long stretch, but will turn back and then forward, and so with a winding motion will finish its descent. And this arises because the air corrupts its uniform natural thickness, since it condenses beneath the right angle of its front, which front strikes and opens that air. But at the opposite front of such a board it does the contrary, rarefying itself, wherefore the rarefied air is of less resistance, and for this reason that front shows itself heavier. Much greater is the rarity that the air behind the said board acquires than the density generated at the front of that board. It is proved because the air condenses. The air condenses around the bodies that penetrate it, because he who pushes one part of it does not push the whole, and that which is in front of it. And this the flooding teaches us, which is generated before the front of the ship. On the weight the cord feels. The cord always feels double the weight of the load suspended by it. Which weight is wholly in act at the front of the cord joined to it, and is wholly in potentiality at the opposite end of the same cord, with which potentiality it resists the descent of the actual weight. Proved in the margin.

Every cord feels twice the weight that is supported by it, or else weight on one side and force on the other.

d g - e f

a d - b - c

m - n o. The cord n m resists the descent of the weight o in every part of its length, and the opposite cord does the same.