There is the unity of membership, which is the union of things separately imperfect into a perfect whole; this is the great unity of which all other unities are but parts and means. In matter it is the consistency of bodies, the harmony of sounds;--with spiritual beings, it is their love, happiness, and life in God. But this unity cannot subsist between things _similar_ to each other. Two or more equal or like things cannot be members the one of the other, nor can they form one or a whole thing. _Two_ they must remain both in nature and in our conception unless they are united by a _third_. Thus the arms, which are like each other, remain always two arms in our conception, and could not be united by a third arm, but must be linked by something which is not an arm, and which, imperfect without them as they without it, will, with them, form one perfect body. Nor is unity even thus accomplished without a difference and opposition of direction in the setting on of members. Therefore, among things which are to have membership with each other, 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 very remarkable that this stricture appears rather characteristic of the lower creatures than the higher, as the many legs of the caterpillar, and the arms and suckers of Radiata seem to prove. As we rise in the order of being the number of similar members becomes less; their structure appearing based on the principle of two things united by a third;--a constant type even in matter of the Triune Existence. Out of the necessity of _unity_ arises that of _variety_, a necessity vividly felt, because it lies at the surface of things, and is assisted by our love of change and the power of contrast. It were a mistake to suppose that mere variety, without a linking principle of unity, is, necessarily, either agreeable or beautiful. 'All are needed by each one, Nothing is fair or good alone. I thought the sparrow's note from heaven, Singing at dawn on the alder bough; I brought him home in his nest at even; He sings the song, but it pleases not now, For I could not bring home the river and sky;-- He sang to my ear,--they sang to my eye. The delicate shells lay on the shore; The bubbles of the latest wave Fresh pearls to their enamel gave; And the bellowing of the savage sea Greeted their safe escape to me. I wiped away the weeds and foam, I fetched my seaborn treasures home; But the poor, unsightly, noisome things Had left their beauty on the shore With the sun, and the sand, and the wild uproar.'