The picture plane and the visual pyramid
Perspective theory: the pariete as a pane of glass gathering the pyramids of sight
This mostly textual leaf sets out Leonardo's foundational theory of perspective. He defines the pariete, or picture plane, as a perpendicular line placed before the eye-point where the visual pyramids converge, comparing it to a flat pane of glass through which one might trace whatever is seen. Objects appear smaller than their originals in proportion to how far the plane cuts the pyramid, and equal planes meeting the perpendiculars at right angles diminish as they rise toward eye level. A closing note observes that the farther a spherical body recedes from the eye, the more of it is seen. A small pyramid figure is sketched at the lower right.
On this page
The wall (pariete) as picture plane
The wall is a perpendicular line figured before the point where the convergence of the pyramids joins. It performs for the eye the same office a flat glass would, upon which, fixing the eye, one could draw whatever the pyramids carry to it; objects appear smaller than their origin as the remainder of the pyramid enters the greater remainder.
Diminution of equal planes toward eye level
All planes whose extremities meet the perpendicular lines at right angles must, being of equal width, diminish the more they rise toward the height of the eye, and grow the more they pass above or below it.
Spherical bodies at a distance
A closing observation states that the farther a spherical body moves away from the eye, the more of its surface you see — a note on how vision embraces a curved solid.
Figure of the visual pyramid
A small tapering pyramid or funnel figure is drawn at the lower right, illustrating the cone of rays that the wall intercepts.