But, as leaves come before flowers, it would be best to begin with leaf forms and try to express the character of oak and beech, lime and chestnut leaves, for instance, by means of outline. Probably at first we shall feel dissatisfied with our outline as not being full enough: it may look meagre in quality and small in definition of form. This probably arises from not allowing enough space—from setting the outline too much within the boundary of the form. To correct this one cannot do better than block in the form of the object we are drawing (leaf, flower, or figure) with a full brush in black silhouette, placing the object against the light or white paper, so that its true boundary may be seen uninterfered with by surface markings or shadows, and, concentrating our attention upon the edge, follow it as carefully as possible with the solid black. Then, if we compare the result with our outline, it will help to show where it has failed; and the practice of thus blocking in with the brush in solid silhouette will tend to encourage a larger style of drawing, since good outline means good perception of mass; and as a general principle in drawing, it may be recommended to place one's outline outside the silhouette boundary of the form rather than within it; that is to say, when the figure or object is relieved in light against dark, as the line in that case defines the edge against the background. When the figure or object appears as dark upon a light ground, however, the outline should be within the silhouette, obviously, or its delicate boundary is lost.
Linear Expression of Movement
Another important attribute of line is its power of expressing or suggesting movement. By a law of inseparable association, undulating lines approaching the horizontal, or leading down to it, are connected with the sense of repose; whereas broken curves and rectangular lines always suggest action and unrest, or the resistance to force of some kind.
The recurrence of a series of lines in the same direction in a kind of crescendo or wave-like movement suggests continuous pressure of force in the same direction, as in this series of instantaneous actions of a man bowling, where the line drawn through or touching the highest points in each figure takes the line of the curve of a wave. The wave-line, indeed, may be said not only to suggest movement, but also to describe its direction and force. It is, in fact, the line of movement. The principle may be seen in a simpler way, as Hogarth points out in his "Analysis of Beauty," by observing the line described along a wall by the head of a man walking along the street. Or, as we may see sometimes near the coast, trees exposed to the constant pressure of the wind illustrate this recurrence of lines in the same direction governing their general shape; and as each tree is forced to spread in the direction away from the wind, the effect is that of their being always struggling against its pressure even in the calmest weather; and this is entirely due to our association of wind-movement with this peculiar linear expression.