Light through a window, the eye's inner sense, and hair recipes
Why images reverse passing a wall; the impressiva must lie in the eye; two cosmetic recipes
The left folio (171v) studies light and vision: a thicker wall admits less light, and images passing through a window into a walled chamber are cast in reversed position, so that a thing moving east to west appears to move the contrary way. Leonardo argues that the 'impressiva,' the receptive power of sight, must lie within the eye itself, describing the optic nerve running to the brain and the common sense, and notes that opaque objects look dark beside a luminous one. Optical diagrams of the eye and of rays through an aperture accompany the text. The right folio (170r) is unrelated household matter: two recipes, one distilled to remove freckles and lighten hair, another a walnut-and-vinegar hair dye.
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Images reverse passing through a window
The thicker the wall, the smaller the light that passes. All the images of things that pass through a window from the free air into the air constrained by a wall are seen in contrary position; a thing that in the free air moves from east to west will appear, by shadow, on the walls lit by the constrained air, moving the contrary way.
The impressiva must lie within the eye
Were the impressiva (the receptive faculty) outside the eye, straight lines would have no place; for though b comes by a straight line to the eye f and from f goes to d, the line to the impressiva stays straight and oblique. Therefore the impressiva must be in the eye. When the eye has a luminous object, opaque objects appear dark.
The optic nerve to the brain and common sense
The nerve that departs from the eye and goes to the brain is like perforated cords that with infinite branches weave the skin of the body, and through their voids the impression is carried to the common sense. The reasoning binds the geometry of sight to the anatomy of the optic nerve conducting vision inward.
Recipes for freckles and for coloring hair
Tartar, powdered sugar and honey in equal parts, distilled in an alembic: the first product drives away freckles, the second turns hair from black to yellow, applied 'alla fiorentina' after washing and drying the head. A second recipe boils litharge of lead, quicklime, gall, green or dried walnut husks and strong vinegar at a slow fire, strained hot through felt, its water used to bathe the hair.