ian ink or water-colour the outline of
whatever view there happens to be outside, being careful to keep the eye
always in the same place by means of a rest; when this is dry, place a
piece of drawing-paper over it and trace through with a pencil. Now we
will rub out the tracing on the glass, which is sure to be rather
clumsy, and, fixing our paper down on a board, proceed to draw the scene
before us, using the main lines of our tracing as our guiding lines.

If we take pains over our work, we shall find that, without troubling
ourselves much about rules, we have produced a perfect perspective of
perhaps a very difficult subject. After practising for some little time
in this way we shall get accustomed to what are called perspective
deformations, and soon be able to dispense with the glass and the
tracing altogether and to sketch straight from nature, taking little
note of perspective beyond fixing the point of sight and the
horizontal-line; in fact, doing what every artist does when he goes out
sketching.

[Illustration: Fig. 6.
This is a much reduced reproduction of a drawing made on my studio
window in this way some twenty years ago, when the builder started
covering the fields at the back with rows and rows of houses.]

THE THEORY OF PERSPECTIVE

DEFINITIONS

I

Fig. 7. In this figure, _AKB_ represents the picture or transparent
vertical plane through which the objects to be represented can be seen,
or on which they can be traced, such as the cube _C_.

[Illustration: Fig. 7.]

The line _HD_ is the +Horizontal-line+ or +Horizon+, the chief line in
perspective, as upon it are placed the principal points to which our
perspective lines are drawn. First, the +Point of Sight+ and next _D_,
the +Point of Distance+. The chief vanishing points and measuring points
are also placed on this line.

Another important line is _AB_, the +Base+ or +Ground line+, as it is on
this that we measure the width of any object to be represented, such as
_ef_, the base of the square _efgh_, on which the cube _C_ is raised.
_E_ is the position of the eye of the spectator, being drawn in
perspective, and is called the +Station-point+.

Note that the perspective of the board, and the line _SE_, is not the
same as that of the cube in the picture _AKB_, and also that so much of
the board which is behind the picture plane partially represents the
+Perspective-plane+, supposed to be perfectly level and to extend from