A prism divided into equal pyramids
With notes on centres of gravity and on wind within flexible bodies
This recto is filled with drawings of three-dimensional prisms and wedges shown in perspective, cut by internal diagonals into pyramids. A demonstration below the figures proves that the pyramid a b c e is one third of the whole wedge, since two equal pyramids share the base a b c and a third is halved along the diameter b d. Marginal notes connect the solids to mechanics, observing how the centres of two natural gravities answer to their common centre, and remarking that wind cannot enter a flexible body where it has no way out.
On this page
A triangular prism divided into three equal pyramids
Upon the base a b c stand two equal pyramids, a b c e and a b c d, while a third pyramid a b c d f is halved by the diameter b d of its base into a b d c and a b d f. Because each of these parts is equal to a third, the pyramid a b c e is shown to be one third of the whole wedge.
Correspondence of natural and accidental centres of gravity
A note states that the centres of two natural gravities answer to their common centre in the same way that the two centres of accidental gravities answer to their common accidental centre. It ties the geometry of the solids to the mechanics of weight and balance.
Wind cannot enter a flexible body without an outlet
A short observation declares that the wind does not enter where it has no way out, and that every flexible body behaves in the same manner. It reads as a general remark on air enclosed within yielding forms.