That return journey constitutes one of the most delightful experiences of my life. Within a week of leaving the Base Camp, I had entirely regained my strength, although a certain tenderness in the soles of my feet made itself felt for some considerable time. For the most part the weather was warm, and everywhere the eye feasted on the riotous colouring of blossoms such as we had never before seen. The only fly in the ointment was the ever-present sense of defeat coupled with the knowledge that with only a little better luck we should have won through. In spite of our failure, however, I felt that we had learnt much; and perhaps the most important lesson of all was that we had been taught the real value of oxygen. Prior to the formation of the 1922 Expedition, the oxygen problem had already been the subject of much discussion round which two distinct schools of thought had arisen. The first, headed by Professor G. Dreyer, F.R.S., Professor of Pathology at the University of Oxford, was staunch to the belief that, without the assistance of a supply of oxygen carried in containers on the back of the climber, it would be impossible for a man to reach the summit of Mount Everest. The second body of scientific opinion held that, not only would it be possible for a man to attain the summit of Everest unaided by an artificial supply of oxygen, but that the weight of such a supply would only hamper the climber in his efforts, and thus completely counterbalance any advantages likely to accrue from its use. To arrive at an impartial conclusion as to the correctitude of these two divergent opinions, it is only necessary to give careful consideration to the results achieved on the two high climbs of May 22 and May 27 respectively. The former was made without an artificial supply of oxygen, the latter with. The first climbing party, consisting of Mallory, Morshead, Norton, and Somervell, left the North Col at 7 a.m. on the 20th of May, and that afternoon, at an altitude of 25,000 feet above sea-level, pitched a camp just off the great North ridge leading down from the shoulder. Morshead had suffered from the cold and was evidently unwell. One of Norton’s ears had been badly frostbitten, and Mallory had frostbitten finger-tips. Somervell alone was, to all intents and purposes, as yet untouched. Snow fell during the night, but they were untroubled by wind. At eight o’clock next morning they left their camp—all save Morshead, who, apparently at the end of his tether and unable to go farther, had to remain behind. After over six hours’ climbing, Mallory, Norton, and Somervell succeeded in reaching an altitude of 26,985 feet; so that, since their departure from their high camp, they had gained a vertical height of 1,985 feet at a rate of ascent of 330 feet per hour. The point at which they turned back lies below the shoulder on the great North ridge, and is, in horizontal distance, about 1⅛ miles from the summit, and rather over 2,000 feet