The Theory and Practice of Perspective | Page 8

the perspective of the ancients, in the mediaeval painters, in the Japanese and Chinese, but are we always right ourselves? Even in celebrated pictures by old and modern masters there are occasionally errors that might easily have been avoided, if a ready means of settling the difficulty were at hand. We should endeavour then to make this study as simple, as easy, and as complete as possible, to show clear evidence of its correctness (according to its conditions), and at the same time to serve as a guide on any and all occasions that we may require it.
To illustrate what is perspective, and as an experiment that any one can make, whether artist or not, let us stand at a window that looks out on to a courtyard or a street or a garden, &c., and trace with a paint-brush charged with Indian 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 the base line to the horizon. Of this we shall speak further on. In nature it is not really level, but partakes in extended views of the rotundity of the earth, though in small areas such as ponds the roundness is infinitesimal.
[Illustration: Fig. 8.]
Fig. 8. This is a side view of the previous figure, the picture plane K being represented edgeways, and the line SE its full length. It also shows the position of the eye in front of the point of sight S. The horizontal-line HD and the base or ground-line AB are represented as receding from us, and in that case are called vanishing lines, a not quite satisfactory term.
It is to be noted that the cube C is placed close to the transparent picture plane, indeed touches it, and that the square fj faces the spectator E, and although here drawn in perspective it appears to him as in the other figure. Also, it is at the same time a perspective and a geometrical figure, and can therefore be measured with the compasses. Or in other words, we can touch the square fj, because it is on the surface of the picture, but we cannot touch the square ghmb at the other end of the cube and can only measure it by the rules of perspective.
II
THE POINT OF SIGHT, THE HORIZON, AND THE POINT OF DISTANCE
There are three things to be considered and