rial things with which we are at present
concerned, there is this necessary to be observed, that it cannot exist
between things similar to each other. Two or more equal and like things
cannot be members one of another, nor can they form one, or a whole
thing. Two they must remain, both in nature and in our conception, so
long as they remain alike, unless they are united by a third different
from both. Thus the arms, which are like each other, remain two arms in
our conception. They could not be united by a third arm, they must be
united by something which is not an arm, and which, imperfect without
them as they without it, shall form one perfect body; nor is unity even
thus accomplished, without a difference and opposition of direction in
the setting on of the like members. Therefore among all things which are
to have unity of membership one with another, there must be difference
or variety; and though it is possible that many like things may be made
members of one body, yet it is remarkable that this structure appears
characteristic of the lower creatures, rather than the higher, as the
many legs of the caterpillar, and the many arms and suckers of the
radiata, and that, as we rise in order of being, the number of similar
members becomes less, and their structure commonly seems based on the
principle of the unity of two things by a third, as Plato has it in the
Timaeus, Sec. II.

Sec. 5. Variety. Why required.

Hence, out of the necessity of unity, arises that of variety, a
necessity often more vividly, though never so deeply felt, because lying
at the surfaces of things, and assisted by an influential principle of
our nature, the love of change, and the power of contrast. But it is a
mistake which has led to many unfortunate results, in matters respecting
art, to insist on any inherent agreeableness of variety, without
reference to a farther end. For it is not even true that variety as
such, and in its highest degree, is beautiful. A patched garment of many
colors is by no means so agreeable as one of a single and continuous
hue; the splendid colors of many birds are eminently painful from their
violent separation and inordinate variety, while the pure and colorless
swan is, under certain circumstances, the most beautiful of all
feathered creatures.[14] A forest of all manner of trees is poor, if not
disagreeable in effect,[15] a mass of one species of tree is sublime. It
is therefore only harmonious and chordal va