has not been bought for a
high price. All the knowledge an artist needs, will, in these days, come
to him almost without his seeking; if he has far to look for it, he may
be sure he does not want it. Prout became Prout, without knowing a
single rule of perspective to the end of his days; and all the
perspective in the Encyclopaedia will never produce us another Prout.

Sec. XX. And observe, also, knowledge is not only very often unnecessary,
but it is often _untrustworthy_. It is inaccurate, and betrays us where
the eye would have been true to us. Let us take the single instance of
the knowledge of aerial perspective, of which the moderns are so proud,
and see how it betrays us in various ways. First by the conceit of it,
which often prevents our enjoying work in which higher and better things
were thought of than effects of mist. The other day I showed a line
impression of Albert Durer's "St. Hubert" to a modern engraver, who had
never seen it nor any other of Albert Durer's works. He looked at it for
a minute contemptuously, then turned away: "Ah, I see that man did not
know much about aerial perspective!" All the glorious work and thought
of the mighty master, all the redundant landscape, the living
vegetation, the magnificent truth of line, were dead letters to him,
because he happened to have been taught one particular piece of
knowledge which Durer despised.

Sec. XXI. But not only in the conceit of it, but in the inaccuracy of
it, this science betrays us. Aerial perspective, as given by the modern
artist, is, in nine cases out of ten, a gross and ridiculous
exaggeration, as is demonstrable in a moment. The effect of air in
altering the hue and depth of color is of course great in the exact
proportion of the volume of air between the observer and the object. It
is not violent within the first few yards, and then diminished
gradually, but it is equal for each foot of interposing air. Now in a
clear day, and clear climate, such as that generally presupposed in a
work of fine color, objects are completely visible at a distance of ten
miles; visible in light and shade, with gradations between the two.
Take, then, the faintest possible hue of shadow, or of any color, and
the most violent and positive possible, and set them side by side. The
interval between them is greater than the real difference (for objects
may often be seen clearly much farther than ten miles, I have seen Mont
Blanc at 120) caused by the ten mile