No visible object can be well understood and comprehended by the
human eye excepting from the difference of the background against
which the edges of the object terminate and by which they are
bounded, and no object will appear [to stand out] separate from that
background so far as the outlines of its borders are concerned. The
moon, though it is at a great distance from the sun, when, in an
eclipse, it comes between our eyes and the sun, appears to the eyes
of men to be close to the sun and affixed to it, because the sun is
then the background to the moon.
252.
A luminous body will appear more brilliant in proportion as it is
surrounded by deeper shadow. [Footnote: The diagram which, in the
original, is placed after this text, has no connection with it.]
253.
The straight edges of a body will appear broken when they are
conterminous with a dark space streaked with rays of light.
[Footnote: Here again the diagrams in the original have no
connection with the text.]
254.
Of several bodies, all equally large and equally distant, that which
is most brightly illuminated will appear to the eye nearest and
largest. [Footnote: Here again the diagrams in the original have no
connection with the text.]
255.
If several luminous bodies are seen from a great distance although
they are really separate they will appear united as one body.
256.
If several objects in shadow, standing very close together, are seen
against a bright background they will appear separated by wide
intervals.
257.
Of several bodies of equal size and tone, that which is farthest
will appear the lightest and smallest.
258.
Of several objects equal in size, brightness of background and
length that which has the flattest surface will look the largest. A
bar of iron equally thick throughout and of which half is red hot,
affords an example, for the red hot part looks thicker than the
rest.
259.
Of several bodies of equal size and length, and alike in form and in
depth of shade, that will appear smallest which is surrounded by the
most luminous background.
260.
DIFFERENT PORTIONS OF A WALL SURFACE WILL BE DARKER OR BRIGHTER IN
PROPORTION AS THE LIGHT OR SHADOW FALLS ON THEM AT A LARGER ANGLE.
The foregoing proposition can be clearly proved in this way. Let us
say that _m q_ is the luminous body, then _f g_ will be the opaque
body; and let _a e_ be the above-mentioned plane on which the said
angles fall, showing [plainly] the nature and character of their
bases. Then: _a_ will be more luminous than _b_; the base of the
angle _a_ is larger than that of _b_ and it therefore makes a
greater angle which will be _a m q_; and the pyramid _b p m_ will be
narrower and _m o c_ will be still finer, and so on by degrees, in
proportion as they are nearer to _e_, the pyramids will become
narrower and darker. That portion of the wall will be the darkest
where the breadth of the pyramid of shadow is greater than the
breadth of the pyramid of light.
At the point _a_ the pyramid of light is equal in strength to the
pyramid of shadow, because the base _f g_ is equal to the base _r
f_. At the point _d_ the pyramid of light is narrower than the
pyramid of shadow by so much as the base _s f_ is less than the base
_f g_.
Divide the foregoing proposition into two diagrams, one with the
pyramids of light and shadow, the other with the pyramids of light
[only].
261.
Among shadows of equal depth those which are nearest to the eye will
look least deep.
262.
The more brilliant the light given by a luminous body, the deeper
will the shadows be cast by the objects it illuminates.
_V._
_Theory of colours._
_Leonardo's theory of colours is even more intimately connected with
his principles of light and shade than his Perspective of
Disappearance and is in fact merely an appendix or supplement to
those principles, as we gather from the titles to sections_ 264,
267_, and _276_, while others again_ (_Nos._ 281, 282_) are headed_
Prospettiva.
_A very few of these chapters are to be found in the oldest copies
and editions of the Treatise on Painting, and although the material
they afford is but meager and the connection between them but
slight, we must still attribute to them a special theoretical value
as well as practical utility--all the more so because our knowledge
of the theory and use of colours at the time of the Renaissance is
still extremely limited._
The reciprocal effects of colours on objects placed opposite each
other (263-272).
263.