And now for the great mountain itself. First of all, it is a rock peak. All the upper part is a great pyramid of stone, with three main _arêtes_--the West, the South-West, and the North-East. It lies exactly on the frontier between Tibet and Nepal, and from the Nepalese side and the plains of India it is hard to get a good view of it, for only a wedge of white is seen peeping between and over other peaks. On the Tibetan side, however, it stands clear, and its pre-eminence over its neighbours is patent. Now, in all attacks upon a great peak the first question is how to get to it--a problem most difficult in the case of other Himalayan summits like K2, and of peaks like Mount McKinley in Alaska and Mount Robson in Canada. It is not only the question of the climbers getting there, but of transporting the food and tents and accessories required by a well-equipped expedition. Had the only route to Everest lain through the deep-cut gorges of Nepal, the transport problem might have been insuperable. But here came in the value of Tibet, which is a high plateau, averaging twelve or thirteen thousand feet. It was possible to take a large party, with baggage animals, up through the passes of Sikkim to the Kampa Dzong (Kampa Jong), and then westwards along the north side of the range to a base camp at Tingri Dzong, due north of the mountain. Everest itself would be forty or fifty miles from such a base camp, but there was a clear road to it by the upper glens and glaciers of the Arun, which flows north and east before it turns south and cuts its way through the Himalayan wall. The problem of access to the base was, therefore, not a hard one. The problem of the ascent was two-fold--part physiological, part physical. Could human beings survive at an altitude of 29,000 feet--human beings who were forced to carry loads and to move their limbs? Aviators, of course, had risen to greater heights, but they had not been compelled to exert themselves. Could a man in action support life in that rarified air? Above 20,000 feet a cubic foot of air contains less than half the oxygen which it holds at sea-level. As the working of the body depends upon the oxygen supplied through the lungs, this fact was bound to lessen enormously man's physical energy. On the other hand, it had been found that the human frame could adapt itself to great altitudes by increasing the number of red blood corpuscles. Dr. Kellas had been able to climb 600 feet an hour above 21,000 feet, and Mr. Meade had camped in comparative comfort at 23,600 feet. Still, the highest altitude yet reached had been only 24,600 feet, and no one could say what difference the extra 4,500 feet might make. Clearly, before the final climbing began it would be necessary to acclimatize the party. In the last resort oxygen might be artificially supplied to the climbers. The physiological problem was of the kind which could only be solved in practice.