The second was the physical. A man might live and even move slowly above, say, 26,000 feet, but it was quite certain that no human being would be capable of the severe exertions required by difficult climbing. If the last stage of Everest proved to be like the last stages of many Himalayan mountains, then the thing was strictly impossible. The hope was that on the Tibetan side the _arêtes_ might be easy going. It all depended upon finding an easy route, and being able to make an ultimate camp at some point like 26,000 feet. There was good hope that the first might be possible, judging from Rawling's survey at a distance of sixty miles and the known geographical features of the Tibetan side of the range. The other physical difficulties would be the gigantic scale of Himalayan obstacles, the hugeness of the ice-fields and glaciers, the immensity of the rock-falls and avalanches. Also at a great height there would be the bitter cold to lower vitality, and the likelihood of violent winds. Much would depend on the weather, which was still an unknown quantity. Indeed, all the physical factors were in the region of speculation; only a reconnaissance could determine them. It might be that the expedition would have to turn back at once, confessing its task impossible. General Bruce, who was the chief living authority on Himalayan travelling, was unable to accompany the party, so Colonel Howard-Bury was selected as leader. An elaborate scientific equipment was prepared, and steps were taken to get the full scientific value out of the journey. But the primary object was mountaineering: first a reconnaissance, and then, if fortune favoured, an effort to reach the summit. The four climbers chosen were Mr. Harold Raeburn, who, in 1920, had done good work on the spurs of Kanchenjunga; Dr. Kellas, who had reached 23,400 feet on Kamet; and two younger men, Mr. George Leigh Mallory and Mr. Bullock, distinguished members of the Alpine Club, who had been together at Winchester. In India they were to be joined by Major Morshead and Major Wheeler, of the Indian Survey. Early in May 1921, the party assembled at Darjeeling. II The start from Darjeeling was on 18th May. The first stage through Sikkim, and by way of the Chumbi valley to the Tibetan plateau, was over familiar ground, which need not be described. There was a good deal of trouble with the mules, which had been badly chosen, but no incident of importance happened till Dochen was reached, the point where their road left the main road to Lhasa. At Kampa Dzong, Dr. Kellas died suddenly from heart failure--an irreparable loss to the expedition, for he had been one of the mountaineers from whom most was looked for, and he was the only member of the party qualified by his medical knowledge to carry out experiments in oxygen and blood pressure. There, too, Mr. Raeburn fell sick, and had to return to Sikkim. [Illustration: The Route of the Mount Everest Expedition.]