tain amount of knowledge of necessary preliminaries--technical
matters which are not strictly painting, but without which good painting
is impossible.

It is all well enough to put paint on canvas, but there must be a
knowledge on which to base the where and the why of laying it on, as
well as the knowledge of how to lay it on. If anything, the where and
why are more important than the how. There are almost infinite methods
and processes of getting the paint onto the surface. Every painter may
select or invent his own way, and provided it accomplishes the main
purpose--the bringing about of combinations of form, relative color
and pitch, the expression of an idea--it is all right. But there are
laws which govern the positions of the different spots of paint, and
the reasons for placing them in certain relations. These laws are back
of personal idiosyncrasy. They are a part of the laws which control
all material things. The painter may no more go contrary to them in
painting than he may go contrary to physical laws in any of the
practical matters of life. If pigments are not used in accordance with
the laws governing their chemical composition, they will not stand. If
the laws of proportion are not observed in composition, the picture
will not balance. The laws of color harmony are as mathematically
fixed as the law of gravity. So, too, the relations of size, which
give the impression of nearness or distance to objects, rest on the
laws of optics. You have infinite scope for individual expression
inside of those laws, but you cannot go outside of them.

=Scientific Knowledge not Necessary.=--It is not necessary that you
should have any special knowledge of all these laws nor even of the
application of them; but you must recognize their existence, and have
some practical notions about them and their effect on your work.

You can of course carry the study as far as you are interested to go.
The farther the better. The more you study them the more you will find
them interesting, and the easier will it be for you to work freely
within their limitations. But this is not the place for special study.
There are books which treat particularly of these things, and you must
go to them.

But a superficial consideration of these subjects cannot be left out
of any book which would be really helpful to the student of painting.
I can go into the theory of things only so far as to give you that
amount of practical knowledge which is