our recent experiences having shown that the greatest altitude at which acclimatisation takes place is about 22,000 feet above sea-level, it may be reasonably assumed that, from the climber’s point of view, high altitude on mount everest begins at that height. incidentally, also, on approaching the north col over the east rongbuk glacier, the snow and ice conditions met with up to this level approximate very closely to summer conditions in the alps. above 22,000 feet, however, such conditions, particularly the state of the snow, resemble those met with in the alps in mid-winter. this high-altitude zone may be further divided into two sub-zones—the first, from 22,000 feet (the foot of the steep snow and ice slopes leading up to the north col) to 23,000 feet, in which climatic conditions are by no means severe, as the north col affords protection from the prevailing west wind; and the second, from 23,000 feet onwards, of which extreme cold and strong wind are the predominant characteristics.
it is therefore evident that the climber must be equipped according to the zone in which he finds himself. in the first zone clothing somewhat warmer than that 263used in the alps in the summer is practically sufficient. owing to the marked intensity of the sun’s rays, however, it is advisable to cover the trunk with at least one layer of sunproof material, such as a sunproof shirt with spine pad, while a solar topee and suitable snow-glasses constitute the best form of headgear. crookes’ glasses of smoke-blue colour proved superior to other varieties; they afford complete protection from glare and do not cause eye-strain and subsequent headache. as sunburn, even very superficial and involving only a small area, is invariably followed by conditions of feverishness which must impair one’s fitness, a veil should be worn over the face and gloves on the hands. oxygen should be employed from the foot of the north col slopes onwards, for no useful purpose can be served by tiring oneself through not using it, when, as we have seen elsewhere, full recovery from fatigue is no longer possible at 23,000 feet. the second zone (from 23,000 feet onwards), where a radical change in climatic conditions is manifest, demands more complicated preparation. wind is seldom absent, and the degree of intensity of the cold is comparable with that met with at the poles, and indeed probably often exceeds it. also, owing to the rarefied state of the atmosphere, the cold is felt much more severely than would be the case at sea-level. a far greater volume of air is expelled from the climber’s lungs, and this air, at blood heat and under a low pressure approximating to one-third of an atmosphere, is saturated with moisture drawn from the body via the 264lungs. the result is a proportionately far greater loss of animal heat. further, the partial pressure of oxygen contained in a normal atmosphere becomes so low at altitudes over 23,000 feet that, unless the climber has recourse to a supply of oxygen carried by himself, his climbing efficiency is enormously reduced. the climbing equipment of the mountaineer in this second zone of high altitude should therefore include, firstly, a supply of oxygen; secondly, warm and windproof clothing and foot-gear; thirdly, plenty of food and drink, as the use of oxygen has a most stimulating effect upon the appetite.
the oxygen equipment has already been fully described by mr. unna in the alpine journal, vol. xxxiv., page 235. the apparatus is, in principle, quite simple. it consists of a frame carried on the shoulders of the climber, at whose back, in a rack attached to the frame, are four steel cylinders filled with oxygen compressed to 120 atmospheres. from the cylinders the oxygen is taken by means of copper tubes over to an instrument arm in front of the climber. this instrument arm, also attached to the frame, carries the pressure gauges and so forth which indicate how much oxygen the climber is left and how rapidly the supplies are being used up. close to the instrument arm and readily accessible are the valves necessary for controlling the rate of flow of oxygen from the apparatus. from the instrument arm the oxygen passes through a flexible rubber tubing up to a mask covering the face of the climber. the two types of mask 265supplied to the expedition proved useless, partly owing to their stifling effect upon the wearer, and partly to the fact that saliva and moisture collected rapidly under them and froze. both, therefore, had to be discarded, but fortunately i was able to make a substitute which functioned successfully. this mask consists of a rubber tube into which is let a rubber bladder by means of a glass t-piece, or by means of two straight pieces of glass tube let in at opposite ends of the bladder. one end of the rubber tube is fastened to the tube of the apparatus out of which the oxygen flows, the other end being held in the climber’s mouth. on exhaling, the climber closes the rubber tube by biting upon it, and the oxygen issuing from the apparatus, instead of being wasted, is stored up in the rubber bladder. on inhaling, the pressure of the teeth is released sufficiently to allow the rubber tube to open, thus permitting the oxygen stored up in the bladder to flow into the climber’s mouth, whence, mixing with the air exhaled, it is drawn into the lungs. the chief advantages of this mask are that, firstly, it economises oxygen to the greatest possible extent, and secondly, the swelling and the shrinking of the bladder during each exhalation and inhalation respectively give the climber a fair idea as to how rapidly the oxygen is flowing from the apparatus, and thus enables him to keep a check upon the readings of the flow-meter, or instrument which indicates the rate of flow of gas. in actual practice it was found that in the space of a few minutes the climber used the mask quite automatically. 266the biting upon and closing the rubber tube and subsequent opening were performed without mental effort.
a certain amount of breathing takes place via the pores of the skin. as, however, the best clothing for a climber on mount everest is windproof, there is a likelihood of the air surrounding the body becoming stale, in which case the process of skin-breathing is seriously impeded. this difficulty could be easily surmounted by flushing out the stale air by means of a tube inserted inside the climber’s clothes, the flushing-out process being done at intervals by temporarily fixing this tube to the orifice of the oxygen apparatus. it is not known definitely whether the advantage gained would be worth the trouble, but there is every reason for believing so. in any case it is a matter which might well be critically tested on the next expedition.
cigarette-smoking proved of great value at high altitudes. geoffrey bruce, tejbir, and i, after pitching camp at 25,500 feet, settled down inside our little tent about 2.30 in the afternoon. from then until seven o’clock the following evening we used no oxygen at all. at first we noticed that unless one kept one’s mind on the question of breathing—that is, made breathing a voluntary process instead of the involuntary process it ordinarily is—one suffered from lack of air and a consequent feeling of suffocation—a feeling from which one recovered by voluntarily forcing the lungs to work faster than they would of their own accord. there is a physiological explanation 267for this phenomenon. at normal altitudes human blood holds in solution a considerable quantity of carbon dioxide, which serves to stimulate the nerve centre controlling one’s involuntary breathing. at great altitudes, however, where, in order to obtain a sufficiency of oxygen, the climber is forced to breathe enormous volumes of air, much of this carbon dioxide is washed out of the blood, and the nerve centre, no longer sufficiently stimulated, fails to promote an adequately active involuntary breathing. a voluntary process must be substituted, and this throws a considerable strain upon the mind, and renders sleep impossible. on smoking cigarettes we discovered after the first few inhalations it was no longer necessary to concentrate on breathing, the process becoming once more an involuntary one. evidently some constituent of cigarette smoke takes the place and performs the stimulating function of the carbon dioxide normally present. the effect of a cigarette lasted for about three hours. clothing is a most important matter. it would be difficult to exaggerate the intensity of the cold encountered at high altitudes on mount everest. several layers—the innermost of which should be of silk, the others wool of moderate weight—form a much better protection against cold than one or two heavy layers. the chief item of clothing, however, should consist of a jumper and trousers made of windproof material. two of these windproof suits should be worn one above the other, and every precaution taken to reduce the circulation of the air to the 268smallest possible extent. the hands must be protected in accordance with the same principles, and the head. i used a r.n.a.s. pattern flying helmet and found it most satisfactory. helmet and snow-glasses should completely cover the head and face, leaving no skin exposed. boots were a source of trouble to all, but fortunately we had so many different designs which we could test out thoroughly that we are now able to form a very shrewd idea as to which kind is the most suitable. leather conducts heat too well for reliance to be placed upon it for the preservation of warmth. the uppers of the boots should be of felt, strengthened where necessary to prevent stretching, by leather straps covered by duroprened canvas. toe and heel caps must be hard and strong, and the former especially should be high, so that the toes are given plenty of room. the sole of the boot should be composed of a layer of thin leather attached to a layer of three-ply wood, hinged in two sections at the instep. a thin layer of felt should form the inside of the sole. the boots should be large enough to accommodate in comfort two pairs of thick socks, or, even better still, two pairs of thin socks and one pair of thick socks. nails used in the boots should penetrate through the leather into the three-ply wood, but not through the latter.
in conclusion, i should like to thank the governing body of the imperial college of science and technology for granting me the necessary leave to enable me to take part in the 1922 mount everest expedition, and also for 269granting me facilities for carrying out a considerable number of investigations in the laboratory of the department of chemical technology upon questions relating, amongst others, to oxygen equipment, fuels, and vacuum flasks. these last were required in order to enable us to keep foods liquid at heights over 23,000 feet, and the flasks obtained on the market proved quite useless for this purpose in view of the fact that they had not been sufficiently well evacuated.
