iancy of light in sky and in
sunlighted things: and the second, that among the tints which you can
imitate, those which you thought the darkest will continually turn out
to be in reality the lightest. Darkness of objects is estimated by us,
under ordinary circumstances, much more by _knowledge_ than by sight;
thus, a cedar or Scotch fir, at 200 yards off, will be thought of darker
green than an elm or oak near us; because we know by experience that the
peculiar colour they exhibit, at that distance, is the _sign_ of
darkness of foliage. But when we try them through the cardboard, the
near oak will be found, indeed, rather dark green, and the distant
cedar, perhaps, pale gray-purple. The quantity of purple and grey in
Nature is, by the way, another somewhat surprising subject of discovery.

Well, having ascertained thus your principal tints, you may proceed to
fill up your sketch; in doing which observe these following particulars:

1. Many portions of your subject appeared through the aperture in the
paper brighter than the paper, as sky, sunlighted grass, &c. Leave these
portions, for the present, white; and proceed with the parts of which
you can match the tints.

2. As you tried your subject with the cardboard, you must have observed
how many changes of hue took place over small spaces. In filling up your
work, try to educate your eye to perceive these differences of hue
without the help of the cardboard, and lay them deliberately, like a
mosaic-worker, as separate colours, preparing each carefully on your
palatte, and laying it as if it were a patch of coloured cloth, cut out,
to be fitted neatly by its edge to the next patch; so that the _fault_
of your work may be, not a slurred or misty look, but a patched
bed-cover look, as if it had all been cut out with scissors. For
instance, in drawing the trunk of a birch tree, there will be probably
white high lights, then a pale rosy grey round them on the light side,
then a (probably greenish) deeper grey on the dark side, varied by
reflected colours, and over all, rich black strips of bark and brown
spots of moss. Lay first the rosy grey, leaving white for the high
lights _and for the spots of moss_, and not touching the dark side. Then
lay the grey for the dark side, fitting it well up to the rosy grey of
the light, leaving also in this darker grey the white paper in the
places for the black and brown moss; then prepare the moss colours
separately for each spot, and