diate enquiry; but I must first lay the divisions of the
entire subject completely before you.

131. I have said that all objects detach themselves as masses of
colour. Usually, light and shade are thought of as separate from colour;
but the fact is that all nature is seen as a mosaic composed of gradated
portions of different colours, dark or light. There is no difference in
the quality of these colours, except as affected by texture. You will
constantly hear lights and shades spoken of as if these were different
in their nature, and to be painted in different ways. But every light is
a shadow compared to higher lights, till we reach the brightness of the
sun; and every shadow is a light compared to lower shadows, till we
reach the darkness of night.

Every colour used in painting, except pure white and black, is therefore
a light and shade at the same time. It is a light with reference to all
below it, and a shade with reference to all above it.

132. The solid forms of an object, that is to say, the projections or
recessions of its surface within the outline, are, for the most part,
rendered visible by variations in the intensity or quantity of light
falling on them. The study of the relations between the quantities of
this light, irrespectively of its colour, is the second division of the
regulated science of painting.

133. Finally, the qualities and relations of natural colours, the means
of imitating them, and the laws by which they become separately
beautiful, and in association harmonious, are the subjects of the third
and final division of the painter's study. I shall endeavour at once to
state to you what is most immediately desirable for you to know on each
of these topics, in this and the two following lectures.

134. What we have to do, then, from beginning to end, is, I repeat once
more, simply to draw spaces of their true shape, and to fill them with
colours which shall match their colours; quite a simple thing in the
definition of it, not quite so easy in the doing of it.

But it is something to get this simple definition; and I wish you to
notice that the terms of it are complete, though I do not introduce the
term "light," or "shadow." Painters who have no eye for colour have
greatly confused and falsified the practice of art by the theory that
shadow is an absence of colour. Shadow is, on the contrary, necessary to
the full presence of colour; for every colour is a diminished quantity
o