78 THE POPULAR SCIENCE MONTHLY. 



that there are three distinguishable moments or aspects in this unity 

 namely, continuity of parts one with another ; then common correla- 

 tion 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 com- 

 pleteness.* The special aesthetic value of contour is seen in the cus- 

 tom of accentuating it in decorative designs by means of ornamental 

 appendages. It is evident that this feeling for the aesthetic 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.f 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 pleas- 

 ing 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 cen- 

 tral 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 sup- 

 plied 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 



* This is strictly analogous to the satisfaction which the ear derives from melodic 

 movement, setting out from a given note (the tonic) and returning to the same. 



f It is a distinguishing peculiarity of movements of the eye from the primary position 

 outward, that they are attended by no rolling of the eye about the axis of vision. As a 

 consequence of this, the eye, in tracing lines which radiate from the center of the field 

 (exactly opposite to it), continues to receive the image of the line on the same retinal 

 meridian or series of retinal points, so that at any two successive movements the images 

 partly overlap. This fact speaks for the supreme importance of estimating direction 

 and distance in relation to the center.. 



