One indication of increasing rarity in the air is to be found in the lowering of the point at which water boils. On the surface of the earth ebullition takes place, as is well known, at 212° Fahr.; but at the top of a mountain like Mont Blanc, where the pressure is so much lightened, and the liquid therefore encounters so much less resistance to its vaporous propensities, it will pass into steam at a temperature of about 178°. At still greater elevations this point becomes so ridiculously reduced—if the expression may be employed—that we might plunge our hand into the fluid when in full simmer, or drink it in the form of tea when absolutely boiling. Of course, under such circumstances, it would be impossible to extract the full flavour of that generous herb unless the process were carried on under artificial pressure, and therefore the most gentle and legitimate of all stimulants must lose much of its potency if decocted at 20,000 feet above the level of the sea.
Another little circumstance is very significant. In opening a flask of pure water at the earth's surface, we should not expect the cork to fly out with an explosion as if it were a flask of Clicquot's sprightliest champagne; but this is what occurs when we reach an altitude where the external pressure is slight compared with the spring of the imprisoned air. In dealing with a bottle of frisky porter or highly impatient soda-water, it may be well to act cautiously, lest the cork should go like a shot through the envelope of the balloon; and in drinking the contents it will be wise to wait till the effervescence has subsided, lest the same results should arise as those which were experienced by the Siamese king, when, instead of mixing his soda powders in his goblet, he put the acid and the alkali separately into his stomach, and left them to settle their affinities there.
Whilst urging his way aloft, therefore, the novice will probably call to mind some of the accounts he has read of poor animals which have been tormented and philosophically murdered in the receiver of an air-pump. He will remember how miserable butterflies and other insects have been unable to use their wings, and, after a few flutterings, have fallen motionless; or how helpless mice, after gasping for a time in hopeless distress, have expired, unwilling martyrs to science. And can he enter such an attenuated atmosphere as the one above him without undergoing some of their agonies, though in a milder and less fatal form? For, on ascending a lofty mountain, the traveller is soon reminded that his lungs are dealing with a much thinner fluid than they inhaled below. Long before he reaches the summit he finds that his drafts upon the atmosphere are increased in consequence of its tenuity, and that the requisite supply can only be obtained with much pulmonary toil. His head begins to ache, a feeling of nausea is frequently induced, and sometimes he experiences the taste of blood in the mouth, or the scent of the same fluid in the nostrils. With throbbing temples and tottering limbs, he drags himself to the peak, and then probably throws himself upon the rock utterly exhausted, his first sentiment being one of relief that the ascent is well over, and his next one of regret that the descent is not already accomplished.
But in estimating the results in such a case, we must remember the great physical exertion which has been incurred. Every traveller who plants himself upon the summit of the Dôme du Gouté must have lifted as many pounds avoirdupois as he weighs, to say nothing of his baggage and personal accoutrements, to a height of some 15,000 feet in the atmosphere by the sheer force of his own muscles. To carry one's own body about is scarcely regarded as porter's work, but what particularly stout man would ever dream of reaching the Grand Plateau, or even attempt to scale the Great Pyramid, without a troop of attendants to drag him to the top? In a balloon, however, all this expenditure of strength is spared. The aeronaut arrives at an elevation far higher than the tallest peak in Europe without squandering as much force as would be required to grind an ounce of coffee. Here, therefore, the influences of rarefied air may be tested without any of the complications arising from previous fatigue or present muscular exhaustion.
Now, the results, as noted by different voyagers, are by no means accordant. In his first ascent, Mr. Glaisher found his pulse throbbing at the rate of a hundred per minute, when he had reached a height of 18,844 feet. At 19,415 feet, his heart began to palpitate audibly. At 19,435, it was beating more vehemently, his pulse had accelerated its pace, his hands and lips were dyed of a dark bluish hue, and it was with great difficulty that he could read his philosophical instruments. At 21,792 feet (upwards of four miles), he seemed to lose the power of making the requisite observations, and a feeling analogous to sea-sickness stole over him, though there was no heaving or rolling in the balloon. Of course, we may well suppose that different individuals will be differently affected. There are some terrestrials who suffer little from sea-sickness, whilst there are others who can scarcely cross the bar of a river without incurring the agonies of that abominable complaint. But Mr. Glaisher seems to be of opinion that the balloon voyager may speedily master the maladie de l'air, and become quite at home at any elevation hitherto attained. It is a matter of simple acclimatization. In his own case, he found that he could breathe without inconvenience at a height of three or four miles, whereas his first sallies into that region, as we have seen, were productive of considerable discomfort; and though he regards an altitude of six or seven miles as the frontier line of natural respiration, with a possible reserve in favour of its extension, he hints that artificial appliances may, perhaps, be devised for freighting the aerostat with the fluid in suitable quantity, and so enlarging the sphere of atmospheric enterprise. We are not certain whether this hint has reference to an apparatus for condensing the air; but it is a pleasant fancy, whether practicable or not, to picture a couple of excursionists feeding their lungs by compressing the thin medium around them into pabulum of the needful density.
There is another enemy, however, to encounter, and it is probably to this more than to the attenuation of the air that the painful effects in question are attributable. We allude to the extreme cold of the upper skies. The atmosphere has its polar regions as well as the earth. There frost builds no solid barriers it is true, but his invisible ramparts are a surer defence against intrusion than bulwarks of granite. Even at a height of three or four miles, explorers are apt to find their extremities benumbed, and their faces turning purple or blue. In a night ascent in 1804, Count Zambeccari, who subsequently met his death in consequence of his balloon taking fire, was so severely handled by the frost that he lost the use of his fingers, and was compelled to have some of them amputated. On one occasion, Mr. Coxwell, having laid hold of the grapnel with his naked hand, cried out in pain that he was scalded, which is precisely the punishment inflicted by metallic objects upon all who grasp them incautiously in arctic latitudes, when the temperature is exceedingly low.
Combining, therefore, these two causes, the rarefaction of the upper air, and the crushing influences of frost, we may readily understand why so many bold adventurers have been smitten with asphyxia when pushing their way into such untrodden solitudes. When Andreoli and Brioschi ascended from Padua, in 1808, to a prodigious height, the latter sank into a state of torpor, and shortly afterwards the former found that he had lost the use of his left arm. In the instance already alluded to, when Zambeccari was so mangled by the cold, he and Dr. Grassetti both became insensible, and their companion alone retained the control of his faculties.
On one memorable occasion, Mr. Glaisher and Mr. Coxwell rose to a region which had certainly never been visited before, and most probably will not be speedily visited again. The precise elevation they reached could only be guessed, but it could scarcely be less than 35,000 feet, and might possibly extend to 37,000 feet, or seven miles. This famous ascent was made in 1862 from Wolverhampton. When the aeronauts had soared to a height of some 29,000 feet, about five-and-a-half miles, Mr. Glaisher suddenly discovered that one arm was powerless, and when he tried to move the other, it proved to have been as suddenly stripped of its strength. He then endeavoured to shake himself, but, strange to say, he seemed to possess no limbs. His head fell on his left shoulder, and on his struggling to place it erect, it reeled over to the right. Then his body sank backwards against the side of the car, whilst one arm hung helplessly downwards in the air. In a moment more, he found that all the muscular power which remained in his neck and back had deserted him at a stroke. He tried to speak to his companion, but the power of speech had departed as well. Sight still continued, though dimly; but this, too, speedily vanished, and darkness, black as midnight, drowned his vision in an instant. Whether hearing survived, he could not tell, for there was no sound to break the silence of those lofty solitudes. Consciousness certainly remained; but the mind had ceased to control the body, and the reins of power seemed to have slipped for ever from his grasp. Was this the way men died? And did one faculty after another desert the soul in its extremity, as servile courtiers steal away from the presence of royalty when its last hour has arrived? Soon afterwards consciousness itself disappeared.
Fortunately, this insensibility was not of long duration. He was roused by Mr. Coxwell, but, at first, could only hear a voice exhorting him to 'try.' Not a word could he speak, not an object could he see, not a limb could he move. In a while, however, sight returned; shortly afterwards he rose from his seat, and then found sufficient tongue to exclaim, 'I have been insensible!' 'You have,' was the reply; 'and I too, very nearly!'
At the time Mr. Glaisher was smitten with paralysis, Mr. Coxwell had climbed up to the ring of the balloon, in order to free the valve-rope, which had become entangled. There, his hands were so frozen that he lost the use of them, and was compelled to drop down into the car. His fingers were not simply blue, but positively black with cold, and it became necessary to pour brandy over them to restore the circulation. Observing on his return that Mr. Glaisher's countenance was devoid of animation, he spoke to him, but, receiving no reply, at once drew the conclusion that his companion was in a state of utter unconsciousness. He endeavoured to approach, but found that he himself was lapsing into the same condition. With wonderful presence of mind, however, he attempted to open the valve of the balloon, in order that they might escape from this deadly region, but his hands were too much benumbed to pull the rope. In this fearful extremity, he seized the rope with his teeth, dipped his head downwards two or three times, and found to his relief that the machine was rapidly descending into a more genial sphere. Fortunately, the voyagers reached the ground in safety, without feeling any lasting mischief from their audacious excursion; but it would be difficult to invent a scene better calculated to make the nervous shudder than that of a balloon floating at a height of nearly seven miles, with its occupants awaking from a state of insensibility to discover that their limbs were utterly powerless, that the rope which might enable them to descend was dangling beyond their reach, and that there they must remain until the cold, which had turned every drop of water into ice, should eat away the feeble relics of vitality from their frames.