As preparatory to the consideration of the beauty of form, it will be necessary to give an explanation of the _gracefulness of motion_. Although this has been vaguely and in part referred to ease of execution, yet, the physiological principle on which ease of execution depends, not having been clearly understood and distinctly stated, the gracefulness of _all_ motions could not be referred to their true source. Thus, writers on taste have been under the necessity of admitting, as a distinct and independent source of gracefulness, the _curvilinear direction_ of motions, and have been able to generalize this fact no farther than by referring it to the beauty of curved forms, which beauty was considered an _ultimate_ fact. In applying the principles above developed, to the explanation of the pleasure or pain attending the contemplation of particular motions, we shall defer for the present the investigation of the intrinsic beauty of curved motions, which is the same as that of curved lines, and assume that in general those motions which are physically pleasurable to the agent are agreeable to the observer. The pleasure or pain of the agent will engage the sympathy of the observer; for he associates the observed action with his own experience. To make a single application, suppose a public speaker extend his arm horizontally and move it slowly in a horizontal position, through one third of a circle. This motion would not appear graceful. That it would not be performed with perfect ease, any one might prove by experiment. The principal difficulty is in preserving for a long time the horizontal position." "In the ordinary state of the muscular system, and within certain limits, the motion of the eye in any direction is pleasurable. Whenever the power of directing the eye is acquired, the tracing of a line will, to a certain extent and for a certain time, afford some degree of positive pleasure; in other words, any short line will possess some degree of positive beauty, and the infant becomes conscious of an emotion of which he was previously ignorant--the emotion of beauty of form. A point awakens no such emotion; it never will; it can possess no beauty. It must be recollected, that this has been restricted to minute points of inappreciable form. Circular dots will be considered under the head of figures. The colorific property of a dot as compared with that of the ground on which it is placed, may afford that kind of ocular pleasure which is foreign to the present inquiry. "From points as compared with lines, we naturally proceed to _lines as compared with each other_.