Page:Popular Science Monthly Volume 17.djvu/88

 that there are three distinguishable moments or aspects in this unity—namely, continuity of parts one with another; then common correlation with some one dominant element, which is usually the central one; and, finally, similarity and equality of parts. A word or two must suffice in illustrating each of these aspects:

1. We have found a reason for introducing continuity of lines into pleasing form in the nature of ocular movement. Over and above the feeling of smooth transition thus given, a continuous as opposed to a broken arrangement is at once felt to be a unity. The movement of the eye around a contour, to the point from which it set out, yields a peculiar feeling of gratification which may be called a sense of completeness. The special æsthetic value of contour is seen in the custom of accentuating it in decorative designs by means of ornamental appendages. It is evident that this feeling for the æsthetic value of continuity in form will be developed by experience, which leads us to look on continuity of parts and contour as an essential factor in the unity of objects.

2. Another mode of unity in form closely related to continuity is common connection with one principal element of form, and more particularly with a dominant central feature. For the resting eye, as for the moving, the arrangement of parts about a center has a special value as supplying the most natural mode of percipient activity. Owing, indeed, to the structure of the retina, the center of an object or group of objects is naturally raised to a place of honor. The eye is instinctively disposed to connect all parts of a design with some central element, and the recognition of such a common connection with a center gives to a design the artistic charm of unity. The most natural central element is, of course, a point, and there are many pleasing forms both in nature and in art which owe a part of their aesthetic value to the presence of such a connecting point. The circular and stellar or radiating forms, the scroll or volute, clearly have this central dominating factor. In many cases, however, the central element is a line or even some simple figure. Thus, all arrangements about an axis, as the forms of trees, flowers, and stems, and all like patterns, are pleasing. In decorative art, again, a central feature is frequently supplied in the shape of some small circle or rectilinear figure.

3. The third aspect of unity, similarity of parts, includes likeness of direction, equality of magnitudes, proportion, etc. All pleasing