Besides his constant occupation in watching and cheering his invalid brother, who had a relapse just after he came down, Keats was busy during these Devonshire days seeing through the press the last sheets of _Endymion_. He also composed, with the exception of the few verses he had begun at Hampstead, the whole of _Isabella_, the first of his longer poems written with real maturity of art and certainty of touch. At the same time he was reading and appreciating Milton as he had never done before. With the minor poems he had been familiar from a boy, but had not been attracted by _Paradise Lost_, until first Severn, and then more energetically Bailey, had insisted that this was a reproach to him: and he now turned to that poem, and penetrated with the grasp and swiftness of genius, as his marginal criticisms show, into the very essence of its power and beauty. His correspondence with his friends, particularly Bailey and Reynolds, is during this same time unusually sustained and full. It was in all senses manifestly a time with Keats of rapidly maturing power, and in some degree also of threatening gloom. The mysteries of existence and of suffering, and the 'deeps of good and evil,' were beginning for the first time to press habitually on his thoughts. In that beautiful and interesting letter to Reynolds, in which he makes the comparison of human life to a mansion of many apartments, it is his own present state which he thus describes:-- "We no sooner get into the second chamber, which I shall call the Chamber of Maiden-thought, than we become intoxicated with the light and the atmosphere. We see nothing but pleasant wonders, and think of delaying there for ever in delight. However, among the effects this breathing is father of, is that tremendous one of sharpening one's vision into the heart and nature of man, of convincing one's nerves that the world is full of misery and heartbreak, pain, sickness, and oppression; whereby this Chamber of Maiden-thought becomes gradually darkened, and at the same time, on all sides of it, many doors are set open--but all dark--all leading to dark passages. We see not the balance of good and evil; we are in a mist, _we_ are in that state, we feel the 'Burden of the Mystery.'" A few weeks earlier, addressing to the same friend the last of his rhymed _Epistles_, Keats had thus expressed the mood which came upon him as he sat taking the beauty of the evening on a rock at the sea's edge:--