The initial consideration was that of extent. If any literary work is too long to be read at one sitting, we must be content to dispense with the immensely important effect derivable from unity of impression—for, if two sittings be required, the affairs of the world interfere, and everything like totality is at once destroyed. But since, _ceteris paribus_, no poet can afford to dispense with _anything_ that may advance his design, it but remains to be seen whether there is, in extent, any advantage to counterbalance the loss of unity which attends it. Here I say no, at once. What we term a long poem is, in fact, merely a succession of brief ones—that is to say, of brief poetical effects. It is needless to demonstrate that a poem is such only inasmuch as it intensely excites, by elevating the soul; and all intense excitements are, through a psychal necessity, brief. For this reason, at least one-half of the “Paradise Lost” is essentially prose—a succession of poetical excitements interspersed, _inevitably_, with corresponding depressions—the whole being deprived, through the extremeness of its length, of the vastly important artistic element, totality, or unity of effect. It appears evident, then, that there is a distinct limit, as regards length, to all works of literary art—the limit of a single sitting—and that, although in certain classes of prose composition, such as “Robinson Crusoe” (demanding no unity), this limit may be advantageously overpassed, it can never properly be overpassed in a poem. Within this limit, the extent of a poem may be made to bear mathematical relation to its merit—in other words, to the excitement or elevation—again, in other words, to the degree of the true poetical effect which it is capable of inducing; for it is clear that the brevity must be in direct ratio of the intensity of the intended effect—this, with one proviso—that a certain degree of duration is absolutely requisite for the production of any effect at all. Holding in view these considerations, as well as that degree of excitement which I deemed not above the popular, while not below the critical taste, I reached at once what I conceived the proper _length_ for my intended poem—a length of about one hundred lines. It is, in fact, a hundred and eight.