A second principle might be named the law of centrality. The artist must carefully distinguish between the accidental and the essential, and be sure to remember that art is the emphasis of the essential; that emphasis is the manifestation of what is of fundamental importance and the subordination of what is of secondary value. Careless and inartistic minds always find the accidental first; the accidental is to them always more interesting. But when an accidental is made an essential, the result is a one-sided effect; and while a temporary impression may be produced upon an audience, it is never permanently valuable. The reader who emphasizes accidents will himself grow weary of his monologue in a short time and not know the reason. Only a thing of beauty is a joy forever. Only that which is natural and in accordance with the laws of nature will stand forever as an object of interest. A third law is consistency. As the oak-leaf is consistent with the whole tree, so in art, the degree of literalness in one direction must be justified by a corresponding degree in another. If Mrs. Caudle is to have a night-cap, then an old-fashioned curtain bed, a stuffed image for Caudle, and a phonograph for his snore are equally requisite. The temptation to be literal would hardly lead a monologue interpreter to place Caliban in the position Browning suggests in the poem, since it is impracticable to have a pool on the stage and let Caliban lie in the cool slush. In the very nature of the case, accessories are suggestive, and the degree of suggestion in one direction must determine the degree in others. These three suggestive principles of unity, centrality, and consistency show that what may be done on the stage should not be a standard for the interpretation of a monologue. In the very nature of the case, the interpreter of the monologue cannot have all the means of producing an optical illusion which are available on the stage. His illusion must be mental and imaginative. Circumstances, however, change, though the laws will be found to apply. Because the speaker is supposed to be sitting in a grocery store on a barrel, it is not necessary for the reader to sit upon a table and swing his feet. We are not interested in the barrel, but in the one who sits upon it, and he would be as interesting if sitting upon something else, or even standing. The fundamental centre of interest in all expression is the mind, and whatever cannot reinforce that is not only useless, but a hindrance. The old age of Rabbi Ben Ezra is purely accidental. To present him as weak and enfeebled would destroy for us the vigorous mind, and strong convictions of the old man.