Aesthetic harmony exists whenever some identical quality or form or purpose is embodied in various elements of a whole--sameness in difference. The repetition of the same space-form in architecture, like the round arch and window in the Roman style; the recurrence of the same motive in music; the use of a single hue to color the different objects in a painting, as in a nocturne of Whistler: these are simple illustrations of harmony. An almost equally simple case is gradation or lawful change of quality in space and time--the increase or decrease of loudness in music of saturation or brightness of hue in painting, the gentle change of direction of a curved line. In these cases there is, of course, a dynamic or dramatic effect, if you take the elements in sequence; but when taken simultaneously and together, they are a harmony, not a development. Simplest of all is the harmony between like parts of regular figures, such as squares and circles; or between colors which are neighboring in hue. Harmonious also are characters in a story or play which are united by feelings of love, friendship, or loyalty. Thus there is harmony between Hamlet and Horatio, or between the Cid and his followers. Aesthetic balance is the unity between elements which, while they oppose or conflict with one another, nevertheless need or supplement each other. Hostile things, enemies at war, business men that compete, persons that hate each other, have as great a need of their opponents, in order that there may be a certain type of life, as friends have, in order that there may be love between them; and in relation to each other they create a whole in the one case as in the other. There is as genuine a unity between contrasting colors and musical themes as there is between colors closely allied in hue or themes simply transposed in key. Contrasting elements are always the extremes of some series, and are unified, despite the contrast, because they supplement each other. Things merely different, no matter how different, cannot contrast, for there must be some underlying whole, to which both belong, in which they are unified. In order that this unity may be felt, it is often necessary to avoid absolute extremes, or at least to mediate between them. Among colors, for example, hues somewhat closer than the complementary are preferred to the latter, or, if the extremes are employed, each one leads up to the other through intermediate hues. The unity of contrasting colors is a balance because, as extremes, they take an equal hold on the attention. The well-known accentuation of contrasting elements does not interfere with the balance, because it is mutual. A balanced unity is also created by contrasts of character, as in Goethe's _Tasso_, or by a conflict between social classes or parties, as in Hauptmann's _Die Weber_. Balanced, finally, is the unity between the elements of a painting, right and left, which draw the attention in opposite directions. The