On air resistance: air densest under the heaviest weight
Two bodies a and b of equal thickness compress the air beneath them
A heading declares the subject "on air resistance": the air pressed by the greatest weight becomes the densest. A small diagram of two upright bodies of equal thickness, the shorter labelled a and the taller b, illustrates the point. The text argues that because b is twice as heavy as a, it makes the air escaping beneath it twice as dense, while the air above grows proportionally more rarefied.
On this page
The air pressed by the greatest weight becomes densest
The folio opens with a rule on air resistance: the air that is compressed by the heaviest weight is the one that becomes densest. This frames the falling-body studies of the surrounding pages, where the surrounding air is the resisting medium.
Body b, twice as heavy, doubles the density of the air below
Though b is as thick as a, its being twice as heavy makes the air escaping beneath it twice as dense; the denser it becomes below, the more rarefied it becomes above, in proportion. The two bodies a and b are shown side by side.