In the position of the eye which sees that portion of a tree
illuminated which turns towards the light, one tree will never be
seen to be illuminated equally with the other. To prove this, let
the eye be _c_ which sees the two trees _b d_ which are illuminated
by the sun _a_; I say that this eye _c_ will not see the light in
the same proportion to the shade, in one tree as in the other.
Because, the tree which is nearest to the sun will display so much
the stronger shadow than the more distant one, in proportion as one
tree is nearer to the rays of the sun that converge to the eye than
the other; &c.
You see that the eye _c_ sees nothing of the tree _d_ but shadow,
while the same eye _c_ sees thè tree _b_ half in light and half in
shade.
When a tree is seen from below, the eye sees the top of it as placed
within the circle made by its boughs[23].
Remember, O Painter! that the variety of depth of shade in any one
particular species of tree is in proportion to the rarity or density
of their branches.
[Footnote: The two lower sketches on the left of Pl XXVIII, No. 3,
refer to lines 21-23. The upper sketch has apparently been effaced
by Leonardo himself.]
The distribution of light and shade with reference to the position
of the spectator (441-443).
441.
The shadows of trees placed in a landscape do not display themselves
in the same position in the trees on the right hand and those on the
left; still more so if the sun is to the right or left. As is proved
by the 4th which says: Opaque bodies placed between the light and
the eye display themselves entirely in shadow; and by the 5th: The
eye when placed between the opaque body and the light sees the
opaque body entirely illuminated. And by the 6th: When the eye and
the opaque body are placed between darkness and light, it will be
seen half in shadow and half in light.
[Footnote: See the figure on the right hand side of Pl. XXVIII, No.
3. The first five lines of the text are written below the diagram
and above it are the last eight lines of the text, given as No.
461.]
442.