The eye adjusting to light, and muscles in exertion
With rules for the area of any triangle and any pyramid
This page opens with a note that limbs and muscles should be shown thickened only where they are actually at work, then turns to a longer argument about vision: why an eye adapted to bright open air sees the inside of a dwelling as dark. Leonardo explains this by the pupil contracting to bear the brightness of the air, so that less-lit interiors appear shadowy. A perspective sketch of a chamber lettered a b g and d f c accompanies the discussion, and at the foot are two mensuration rules, for the area of any triangle and of any pyramid.
On this page
Why the eye in bright light sees interiors as dark
Leonardo asks why an eye standing in a luminous place sees darkness inside a dwelling, though once inside it would find the room quite luminous. He answers that the pupil, offended by excess light in the bright air, closes and diminishes its opening to bear that splendour. With the pupil so reduced, the less-lit interior comes to look dark to such an eye.
Muscles thickening only where the limb is at work
Under the heading on the disposition of the limbs according to the forces, Leonardo directs that limbs and muscles be shown thickened where they are in operation at their fitting exertions. Those not in operation should be left simple and undefined.
Area of any triangle and any pyramid
A short mensuration rule states that the area of every triangle is made of the whole base with half its height. The area of every pyramid is made of the whole base and a third of its height.
Perspective diagram of a chamber (a b g, d f c, h)
Below the text a long chamber is drawn in perspective, lettered a b g along its near frame and d f c with a point h, set beside small triangular sketches. It accompanies the argument about how the eye, adapted to bright air, perceives the interior of a dwelling as dark.