In all mountainous regions the permanent habitations of men cease at a limit far below the most elevated points reached by the mountain-climber. St. Veran and Gargl, the highest villages of France and Germany, are situated at the respective heights of 6,591 and 6,197 feet; but the Hospice of St. Bernard, in Switzerland, built centuries ago to shelter travellers when benumbed with the cold, is much more elevated, its height being 8,110 feet above sea-level. The most elevated cluster of houses in the world is the convent of Hanle, inhabited by twenty Thibetan priests; its height is 14,976 feet. None of the villages of the Andes, except perhaps that of Santa Anna, in Bolivia, have been built at so great a height. Travellers who venture to ascend lofty mountains not only have to suffer all the rigours of cold and run the risk of being frozen on their route, but they may also experience painful sensations owing to the rarefaction of the air. It would naturally be supposed that at an elevation at which the pressure of the atmosphere is reduced to one half, or even to one fourth that of the plains below, a certain uneasiness should be caused by the change, the more so since other conditions, such as warmth and moisture, are different. Undaunted climbers, like Professor Tyndall, who have never felt the effect of this "mountain-sickness" (_mal de montagne_), deny that the sensations proceed from anything else than mere fatigue. In the Himalayas, the traveller does not begin to suffer from the attacks of this ailment until he has reached a height of 16,500 feet; while on the Andes a large number of persons are affected by it at an altitude of 10,700 feet. In the South American mountains, the symptoms are much more serious: to the fatigue, head-ache, and want of breath are added giddiness, sometimes fainting-fits, and bleeding from lips, gums, and eyelids. The aeronaut, however, who is spared all the fatigue of climbing, rarely suffers any inconvenience except from cold, at such elevations. But on rising to greater heights, 30,000 or 40,000 feet, the malady shows itself; and if the balloon continued to rise, the aerial voyager would infallibly perish. Professor Bonney says:-- "I have occasionally seen persons singularly affected on high mountains; and as the barometer stands at about sixteen inches on Mont Blanc, and at thirty at sea-level, one would expect this great difference to be felt. Still, I do not think it easy to separate the inconveniences due to atmosphere from those caused by unwonted fatigue, and am inclined to attribute most of them to the latter." But the fact that the aeronaut suffers seems conclusive.