OF THE SPACES [SHOWING THE SKY] IN TREES THEMSELVES.

The spaces between the parts in the mass of trees, and the spaces
between the trees in the air, are, at great distances, invisible to
the eye; for, where it is an effort [even] to see the whole it is
most difficult to discern the parts.--But a confused mixture is the
result, partaking chiefly of the [hue] which predominates. The
spaces between the leaves consist of particles of illuminated air
which are very much smaller than the tree and are lost sight of
sooner than the tree; but it does not therefore follow that they are
not there. Hence, necessarily, a compounded [effect] is produced of
the sky and of the shadows of the tree in shade, which both together
strike the eye which sees them.

OF TREES WHICH CONCEAL THESE SPACES IN ONE ANOTHER.

That part of a tree will show the fewest spaces, behind which a
large number of trees are standing between the tree and the air
[sky]; thus in the tree _a_ the spaces are not concealed nor in _b_,
as there is no tree behind. But in _c_ only half shows the spaces
filled up by the tree _d_, and part of the tree _d_ is filled up by
the tree _e_ and a little farther on all the spaces in the mass of
the trees are lost, and only that at the side remains.