This stanza could only have been written by someone with a definite geometrical diagram before his inward eye—a diagram which it has often been my business to demonstrate to mathematical classes. As evidence, note especially the last line which gives poetical imagery to the light surrounding night’s pyramid. This idea could not occur to anyone without the diagram. But the whole poem and other poems are permeated with touches of this kind. Now the poet, so sympathetic with science, so absorbed in its ideas, can simply make nothing of the doctrine of secondary qualities which is fundamental to its concepts. For Shelley nature retains its beauty and its colour. Shelley’s nature is in its essence a nature of organisms, functioning with the full content of our perceptual experience. We are so used to ignoring the implications of orthodox scientific doctrine, that it is difficult to make evident the criticism upon it which is thereby implied. If anybody could have treated it seriously, Shelley would have done so. Furthermore Shelley is entirely at one with Wordsworth as to the interfusing of the Presence in nature. Here is the opening stanza of his poem entitled _Mont Blanc_: “The everlasting universe of Things Flows through the Mind, and rolls its rapid waves, Now dark—now glittering—now reflecting gloom— Now lending splendour, where from secret springs The source of human thought its tribute brings Of waters,—with a sound but half its own, Such as a feeble brook will oft assume In the wild woods, among the Mountains lone, Where waterfalls around it leap for ever, Where woods and winds contend, and a vast river Over its rocks ceaselessly bursts and raves.” Shelley has written these lines with explicit reference to some form of idealism, Kantian or Berkeleyan or Platonic. But however you construe him, he is here an emphatic witness to a prehensive unification as constituting the very being of nature. Berkeley, Wordsworth, Shelley are representative of the intuitive refusal seriously to accept the abstract materialism of science. There is an interesting difference in the treatment of nature by Wordsworth and by Shelley, which brings forward the exact questions we have got to think about. Shelley thinks of nature as changing, dissolving, transforming as it were at a fairy’s touch. The leaves fly before the West Wind “Like ghosts from an enchanter fleeing.” In his poem _The Cloud_ it is the transformations of water which excite his imagination. The subject of the poem is the endless, eternal, elusive change of things: “I change but I cannot die.” This is one aspect of nature, its elusive change: a change not merely to be expressed by locomotion, but a change of inward character. This is where Shelley places his emphasis, on the change of what cannot die.