colours vary with the intensity of light. There is no colour peculiar
to any object, but only more or less rapid vibration of light upon its
surface. The speed depends, as is demonstrated by optics, on the degree
of the inclination of the rays which, according to their vertical or
oblique direction, give different light and colour.

The colours of the spectrum are thus recomposed in everything we see. It
is their relative proportion which makes new tones out of the seven
spectral tones. This leads immediately to some practical conclusions,
the first of which is, that what has formerly been called _local colour_
is an error: a leaf is not green, a tree-trunk is not brown, and,
according to the time of day, _i.e._ according to the greater or smaller
inclination of the rays (scientifically called the angle of incidence),
the green of the leaf and the brown of the tree are modified. What has
to be studied therefore in these objects, if one wishes to recall their
colour to the beholder of a picture, is the composition of the
atmosphere which separates them from the eye. This atmosphere is the
real subject of the picture, and whatever is represented upon it only
exists through its medium.

[Illustration: DEGAS

THE GREEK DANCE--PASTEL.]

A second consequence of this analysis of light is, that shadow is not
absence of light, but light of _a different quality_ and of different
value. Shadow is not a part of the landscape, where light ceases, but
where it is subordinated to a light which appears to us more intense. In
the shadow the rays of the spectrum vibrate with different speed.
Painting should therefore try to discover here, as in the light parts,