The expressiveness of lines is determined by several--at least three-- factors. In the first place, the perception of lines is an active process. In order to get a line we have to follow it with the eye; and if we do not now follow it with our fingers, we at least followed similar lines thus in the past. Now this process of the perception of a line requires of us an energy of attention to the successive elements of the line as we pass over them and a further expenditure of energy in remembering and synthesizing them into a whole. This energy, since it is evoked by the line and is not connected with any definite inner striving of the self, is felt by us to belong to the line, to be an element in its life, as clearly its own as its shape. For example, a line with many sudden turns or changes of direction is an energetic and exciting line because it demands in perception a constant and difficult and shifting attention; a straight line, on the contrary, because simple and unvarying in its demands upon the attention, is monotonous and reposeful; while the curved line, with its lawful and continuous changes, at once stimulating yet never distracting attention, possesses the character of progressive and happy action. This, the primary source of the vital interpretation of lines is supplemented by elements derived from association. Lines suggest to us the movements of our bodies along paths of similar form, and we interpret them according to the feeling of these movements; in the imagination, we may seem to move along the very lines themselves as paths. Every skater or runner knows the difficulty of moving along a path full of sudden turns and angles, a difficulty which, if he is in good trim, may nevertheless afford him pleasure in the overcoming; the delightful and various ease of moving along curved lines; the monotony of a long, straight path, but the quick triumph of going right to the end along a short and terminal line of this character. But lines suggest to us not only the movements, but also the attitudes of our bodies. They may be straight and rising,--rigid or dignified or joyously expanding; they may be horizontal and lie down and rest; they may be falling and sorrowful; or the shapes whose outlines they form may be heavy or light, delicate or ungainly or graceful, as bodies are. Finally, the interpretation of lines may be further enriched as follows: The sight of a line suggests the drawing of it, the sweep of the brush that made it; we ourselves, in the imagination once more, may re-create the line after the artist, and feel, just as he must have felt, the mastery, ease, vigor, or delicacy of the execution into the line itself. Few can fail to get this effect from the paintings of Franz Hals, for example, where the abounding energy of the artist is apparent in each stroke of the brush. Artists feel this life in execution most strongly; yet, since almost every one has had some practice in drawing lines,