Such comparisons indicate not only that there is a necessary association of ideas with certain lines and forms, but also that certain relations and associations of line of a similar character are necessary to produce a harmonious composition, and one which conveys a definite and pervading sentiment or emotion, just as we saw that the controlling lines of structural curves, spirals, and angles require to be in relation, and to be re-echoed by the character of the design they inclose or which is built upon them.
The same law holds true in figure composition. The sense of repose and restfulness necessary to sitting or reclining groups depends upon the gentle declivities of the curves and their gradual descent to the horizontal.
Draw a figure sitting rigid, tense, and alert, and you destroy the sense of repose at once, and you are obliged also to resort to angles, still more emphatic where strong action is to be expressed; while to express continual or progressive movement, a choice of associated lines of action in different stages of progress leading up to the crescendo of the final one (as in a group of mowers) would be necessary (see illustrations, p. [161]). We cannot, then, in any composition have too definite a conception. We must, at any sacrifice of detail, bring out the main expression and meaning. Every group of figures must be in the strictest relation to each other and to the central interest or expression of the design. You cannot, for instance, in a procession of figures, make your faces turn all sorts of ways without stopping the onward movement which is essential to the idea of a procession. This would not preclude variety, but the general tendency must be in one direction. Every line in a composition must lead up to the central idea, and be subordinated or contributory to it (see illustration, Nos. 1 and 2, p. [163]).
The same with masses: you cannot put a number of forms together without some sort of relation, either of general character and contour or some uniting line. We may learn this principle from nature also. Look at a heap of broken stones and débris, which in detail may contain all sorts of varieties of form, as we find them tumbled down a steep place, as the rocky bed of a mountain stream, a heap of boulders upon a hillside, or the débris from a quarry or mine; in each case the law of gravity and the persistence of force working together arrange the diverse forms in masses controlled by the lines, which express the direction and degree of descent, and the pressure of force. The same thing may be seen on any hilly ground after heavy rain; the scattered pebbles are arranged in related groups, combined and composed by the flow of miniature streams, which channel the face of the ground and form hollows for their reception (see Nos. 3 and 4, p. [163]). The force of the tides and currents upon the sea-shore illustrates the same principle and affords us magnificent lessons in composition, not only in the delicate lines taken by the sculptured sand, but in the harmonious grouping of masses of shingle and shells, weeds and drift, arranged by the movement of the waves.