Structural line, or that which stands for the initial form of the picture and conjunctive line, or that which joins itself naturally to such form are the two phases of line which engage the scientific study of the artist. Line for line’s sake is an opportunity offered him quite apart from structural considerations. Line has a distinct æsthetic value no less than one contributive to picture mechanics. Thus pictures conceived in vertical lines bespeak dignity, solemnity, quietude ; pillars, trees of straight shaft, ascending smoke and other vertical forms all voice these and allied emotions. With slightly less force does a series of horizontals affect us and with a kindred emotion. But when the line slants and ceases to support itself, or becomes curved, movement is suggested and another set of emotions is evoked. The diagonal typifies the quick darting lightning. The vertical curved line is emblematic of the tongue of flame; the horizontal curve, of a gliding serpent. In the circle and ellipse we feel the whirl and fascination of continuity. The linear impulse in composition therefore plays a part in emotional art independent of the subject itself.
Pictorial art owes a large and increasing debt to decorative art and no small part of this is its simple beauty of line. It is rare however to find the painter governed in his first conception by any positive linear form. The outlines of great compositions only hint of decorative structure and give no evidence that they were planned as linear designs. The requirement of linear design that she beautifully fill a space is met by pictorial composition through the many correlative opportunities which in her broader range are open to her, by which she adds to the fundamental forms of construction (which often prove bad space fillers) such items as connect their outlines with the encasement or frame. With some ingenuity advocates of pure design as the basis of pictorial structure, point out the similarity of certain compositions to formal, ornamental design or type forms of plants, flowers, etc., yet omit to state how many of the best compositions they reject in their search for the happy hit or to allow for the fact that in those which they cite, cruel disturbance of the beautiful scheme could easily be wrought by slight reconstruction, leaving the work quite as good. The author’s contention is directly opposed to the notion that pictorial art is dependent on the flat plan of the design, which is only contributory, but that its essence is known by an apprehension of balance through the depth of the picture. Pictorial art is not an art of two dimensions but of three.