different in _quality_; and that quality by which the illuminated dead
color would be felt in nature different from the unilluminated bright
one, is what artists are perpetually aiming at, and connoisseurs talking
nonsense about, under the name of "tone." The want of tone in pictures
is caused by objects looking bright in their own positive hue, and not
by illumination, and by the consequent want of sensation of the raising
of their hues by light.

Sec. 3. Difference between tone in its first sense and aerial perspective.

The first of these meanings of the word "tone" is liable to be
confounded with what is commonly called "aerial perspective." But aerial
perspective is the expression of space, by any means whatsoever,
sharpness of edge, vividness of color, etc., assisted by greater pitch
of shadow, and requires only that objects should be detached from each
other, by degrees of intensity in _proportion_ to their distance,
without requiring that the difference between the farthest and nearest
should be in positive quantity the same that nature has put. But what I
have called "tone" requires that there should be the same sum of
difference, as well as the same division of differences.

Sec. 4. The pictures of the old masters perfect in relation of middle tints
to light.

Now the finely toned pictures of the old masters are, in this respect,
some of the notes of nature played two or three octaves below her key;
the dark objects in the middle distance having precisely the same
relation to the light of the sky which they have in nature, but the
light being necessarily infinitely lowered, and the mass of the shadow
deepened in the same degree. I have often been struck, when looking at a
camera-obscuro on a dark day, with the exact resemblance the image bore
to one of the finest pictures of the old masters; all the foliage coming
dark against the sky, and nothing being seen in its mass but here and
there the isolated light of a silvery stem or an unusually illumined
cluster of leafage.

Sec. 5. And consequently totally false in relation of middle tints to
darkness.

Now if this could be done consistently, and all the notes of nature
given in this way an octave or two down, it would be right and necessary
so to do: but be it observed, not only does nature surpass us in power
of obtaining light as much as the sun surpasses white paper, but she
also infinitely surpasses us in her power of shade. Her de