OF PAINTING.

In landscapes which represent [a scene in] winter. The mountains
should not be shown blue, as we see in the mountains in the summer.
And this is proved [Footnote 5. 6.: _Per la_ 4_a di questo_. It is
impossible to ascertain what this quotation refers to. _Questo_
certainly does not mean the MS. in hand, nor any other now known to
us. The same remark applies to the phrase in line 15: _per la_ 2_a
di questo_.] in the 4th of this which says: Among mountains seen
from a great distance those will look of the bluest colour which are
in themselves the darkest; hence, when the trees are stripped of
their leaves, they will show a bluer tinge which will be in itself
darker; therefore, when the trees have lost their leaves they will
look of a gray colour, while, with their leaves, they are green, and
in proportion as the green is darker than the grey hue the green
will be of a bluer tinge than the gray. Also by the 2nd of this: The
shadows of trees covered with leaves are darker than the shadows of
those trees which have lost their leaves in proportion as the trees
covered with leaves are denser than those without leaves--and thus
my meaning is proved.

The definition of the blue colour of the atmosphere explains why the
landscape is bluer in the summer than in the winter.