Optics: the images of bodies fill every point of the air
With a ray-bundle diagram and a theorem on a square inscribed in a right triangle
The main text sets out Leonardo's optics of the 'species' of bodies: the air is wholly filled with infinite rays carrying the images of every body within it, each indivisible point holding all those images at once without confusion, and the eye seeing only when it forms a pyramid answering the pyramid of rays. A short note attached to a diagram treats a double bundle of rays meeting at a point n. A second passage states a geometric theorem about a square inscribed in a right triangle, where the excesses of the triangle's sides multiplied together equal the inscribed square.
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The images of bodies fill every point of the air
The air is wholly interwoven and full of infinite rays carrying the images (species) of the bodies within it; every point of the air is indivisible yet holds all those images at once, united and distinct without confusion. Although the images reach the eye in pyramids, the eye perceives only when it forms a contrary pyramid toward the thing seen. A small diagram of a double bundle of rays notes that the point n will appear double, because the pyramids do not intersect upon it as they do upon the line a o.
Square inscribed in a right triangle
If a square is inscribed in a right triangle so that one angle touches the hypotenuse and the opposite angle covers the right angle, then the excesses by which the triangle's sides exceed the square's sides, multiplied one by the other, yield a surface equal to the inscribed square.