stant vibration in the blue; constant variety in the plane of
color,--a throb of color sensation which is not to be expressed by a
dead, flat tint.

Paint the sky loosely. Lay on the color as you will, with a broad,
flat brush, or with a loose, smudgy handling; put it on with
horizontal strokes, or with criss-cross touches, but never make it a
lifeless tone. Have variety in it; keep a pulsation between the warm
and cool color. You can work in the separate touches of half-mixed
color, warm and cool, all through the sky, so that the whole tone will
be flat and even, but not dense and dead. So far as the sky is
concerned, the atmosphere is essential, and is to be represented not
by dense color, but by free, loose, vibrating color.

=Clouds.=--If you have clouds to paint, do not draw them rigidly. Get
the effect of the mass and movement, and the lightness of them. As
they constantly change in form, any one form they may assume cannot be
characteristic. The type form is what you must get, and the suggestion
of the motion and lightness. You can suggest, too, the direction of
the wind by the way they mass and sway and flow. The direction of the
sun's rays, too, counts in the color of them. The outline of a cloud
mass is never hard, never rigid. The pitch and luminosity and subtlety
are what give you most of the effect of it.

Study the type of cloud, of course. It is a _cumulus_, _cirrus_,
_stratus_, or what not. This character is important; but the character
lies in the whole body of the cloud form, not in the accidental
outlines or the special position of it for the moment.

=Sky Composition.=--The massing of cloud forms is a very useful factor
in the composition of the landscape. The cloud bank or cloud line is
capable of giving accent or balance to the picture. As it is not
constant in position any more than in form, you can place it with
truth to nature pretty nearly always where it will do the most good as
an element in the composition. Make use of them, then, and study the
forms and the possible phases of them so as to make the best use of
them.

=Diffused Light.=--Much of the characteristic quality of out-door
light is the result of the diffusion of light due to both the
refraction and the reflection of the sky. The light which bathes the
landscape comes in all directions from the sky. Necessarily, then, the
sky will be in most cases far higher in value than anything under it.
Even the blue of the sky, which look