Critics so justly esteemed as Mr Robert Bridges and Professor de Selincourt have sought a key to the organic structure of the poem in the supposition that each of its four books is intended to relate the hero's probationary adventures in one of the four elements, the first book being assigned to Earth, the second to Fire, the third to Water, the fourth to Air. I am convinced that this view is mistaken. The action of the first book passes on earth, no doubt, and that of the second beneath the earth. Now it is true that according to ancient belief there existed certain subterranean abodes or focuses of fire,--the stithy of Vulcan, the roots of Etna where the giants lay writhing, the river of bale rolling in flames around the city of the damned. But such things did not make the under-world, as the theory of these critics assumes, the recognized region of the element fire. According to the cosmology fully set forth by Ovid at the beginning of his first book, and therefore thoroughly familiar to Keats, the proper region or sphere of fire was placed above and outside that of air and farthest of all from earth.[5] Not only had Keats therefore no ancient authority for thinking of the under-world as the special region of fire, he had explicit authority to the contrary. Moreover, if he had meant fire he would have given us fire, whereas in his under-world there is never a gleam of it, not a flicker of the flames of Phlegethon nor so much as a spark from the anvil of Vulcan; but instead, endless shadowy temple corridors, magical cascades spouting among prodigious precipices, and the gardens and bower of Adonis in their spring herbage and freshness. It is true, again, that the third book takes us and keeps us under sea. But the reason is the general one that Endymion, typifying the poetic soul of man in love with the principle of essential Beauty, has to leave habitual things behind him and wander far In other regions, past the scanty bar To mortal steps, in order to learn secrets of life, death, and destiny necessary to his enlightenment and discipline. Where else should he learn such secrets if not in the mysterious hollows of the earth and on the untrodden floor of ocean? 'Our friend Keats,' Endymion is made to say in one of the poet's letters from Oxford, 'has been hauling me through the earth and sea with unrelenting perseverance': and in like manner in the poem itself the hero asks, Why am I not as are the dead, Since to a woe like this I have been led Through the dark earth, and through the wondrous sea?