of motions going on at other places many feet away from that spot. But it is also a fact that he will immediately feel an inclination to shift his eyes in order to see any one of these motions more clearly. In making that shift he will, of course, have to move his eyeballs. Now, if that moving object changes its place, his eyeballs will continue to make the movements necessary to follow it. And, if the attention continues directed toward that object, his eyes will have to make great or small movements, according as the object makes a great or small change of place.
An interesting theory, which scientific tests support, is that, although the eye has to make a series of irregular, jerky movements when following any moving object, these movements become fewer and smaller as the smoothness and regularity of the observed motion increases.
What we have just said about eye movement explains, at least partly, why the aimless crawling of a house fly over a window pane is ugly, while the graceful flying of a sea gull is beautiful; why the clambering of a monkey is ugly, while the swimming of a fish is graceful, and why the zigzag falling of a sheet of paper thrown from a window is displeasing, while the smooth spiralling of an airplane is pleasing.
In some of the movements which we classify as beautiful, it is clear that the principle of repetition is at work, which, as we have said, makes seeing easy. Any task accomplished once and undertaken again becomes easier and easier with repetition. We have already shown how this makes the perception of rhythmical fixed lines or balanced composition of fixed lines easier for the mind, if not for the eye itself.
