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