ON PAINTING.

The comparison of the various qualities of shadows and lights not
infrequently seems ambiguous and confused to the painter who desires
to imitate and copy the objects he sees. The reason is this: If you
see a white drapery side by side with a black one, that part of the
white drapery which lies against the black one will certainly look
much whiter than the part which lies against something whiter than
itself. [Footnote: It is evident from this that so early as in 1492
Leonardo's writing in perspective was so far advanced that he could
quote his own statements.--As bearing on this subject compare what
is said in No. 280.] And the reason of this is shown in my [book on]
perspective.