he sky, but a
single cloud: sometimes a round cumulus will stay five or six minutes
quite steady enough to let you mark out his principal masses; and one or
two white or crimson lines which cross the sunrise will often stay
without serious change for as long. And in order to be the readier in
drawing them, practice occasionally drawing lumps of cotton, which will
teach you better than any other stable thing the kind of softness there
is in clouds. For you will find when you have made a few genuine studies
of sky, and then look at any ancient or modern painting, that ordinary
artists have always fallen into one of two faults: either, in rounding
the clouds, they make them as solid and hard-edged as a heap of stones
tied up in a sack, or they represent them not as rounded at all, but as
vague wreaths of mist or flat lights in the sky; and think they have
done enough in leaving a little white paper between dashes of blue, or
in taking an irregular space out with the sponge. Now clouds are not as
solid as flour-sacks; but, on the other hand, they are neither spongy
nor flat. They are definite and very beautiful forms of sculptured mist;
sculptured is a perfectly accurate word; they are not more _drifted_
into form than they are _carved_ into form, the warm air around them
cutting them into shape by absorbing the visible vapor beyond certain
limits; hence their angular and fantastic outlines, as different from a
swollen, spherical, or globular formation, on the one hand, as from that
of flat films or shapeless mists on the other. And the worst of all is,
that while these forms are difficult enough to draw on any terms,
especially considering that they never stay quiet, they must be drawn
also at greater disadvantage of light and shade than any others, the
force of light in clouds being wholly unattainable by art; so that if we
put shade enough to express their form as positively as it is expressed
in reality, we must make them painfully too dark on the dark sides.
Nevertheless, they are so beautiful, if you in the least succeed with
them, that you will hardly, I think, lose courage.

150. Outline them often with the pen, as you can catch them here and
there; one of the chief uses of doing this will be, not so much the
memorandum so obtained, as the lesson you will get respecting the
softness of the cloud-outlines. You will always find yourself at a loss
to see where the outline really is; and when drawn it will always look
h