egree, we shall first declare the water
to be cold, and then to be warm; but the water has a definite heat
wholly independent of our sensations, and accurately ascertainable by a
thermometer. So it is with light and shade. Looking from the bright sky
to the white paper, we affirm the white paper to be "in shade,"--that
is, it produces on us a sensation of darkness, by comparison. But the
hue of the paper, and that of the sky, are just as fixed as temperatures
are; and the sky is actually a brighter thing than white paper, by a
certain number of degrees of light, scientifically determinable. In the
same way, every other color, or force of color, is a fixed thing, not
dependent on sensation, but numerically representable with as much
exactitude as a degree of heat by a thermometer. And of these hues, that
of open sky is one not producible by human art. The sky is not blue
_color_ merely,--it is blue _fire_, and cannot be painted.

Sec. 4. Next, observe, this blue fire has in it _white_ fire; that is, it
has white clouds, as much brighter than itself as _it_ is brighter than
the white paper. So, then, above this azure light, we have another
equally exalted step of white light. Supposing the value of the light of
the pure white paper represented by the number 10, then that of the blue
sky will be (approximately) about 20, and of the white clouds 30.

But look at the white clouds carefully, and it will be seen they are not
all of the same white; parts of them are quite grey compared with other
parts, and they are as full of passages of light and shade as if they
were of solid earth. Nevertheless, their most deeply shaded part is
that already so much lighter than the blue sky, which has brought us up
to our number 30, and all these high lights of white are some 10 degrees
above that, or, to white paper, as 40 to 10. And now if you look from
the blue sky and white clouds towards the sun, you will find that this
cloud white, which is four times as white as white paper, is quite dark
and lightless compared with those silver clouds that burn nearer the sun
itself, which you cannot gaze upon,--an infinite of brightness. How will
you estimate that?

And yet to express all this, we have but our poor white paper after all.
We must not talk too proudly of our "truths" of art; I am afraid we
shall have to let a good deal of black fallacy into it, at the best.

Sec. 5. Well, of the sun, and of the silver clouds, we will not talk for