air was at this time twelve degrees below zero." This certainly does not suggest that life on the earth would be pleasant, if the air were reduced in quantity to that above the level reached by Coxwell and Glaisher on this occasion. But the barometer still stood nearly seven inches high when they began to descend, at which time Glaisher was nearly two miles above his fainting level, while Coxwell was all but powerless. And then it is to be remembered, as Flammarion well remarks, that in balloon ascents "the explorer remains motionless, expending little or none of his strength, and he can therefore reach a greater elevation before feeling the disturbance which brings to a halt at a far lower level the traveller who ascends by the sole strength of his muscles the steep sides of a mountain." What would be the state of a traveller having to exert himself in an atmosphere reduced to five-sevenths of the density of the air in which Coxwell was just able to save his own life and Glaisher's, literally "by the skin of his teeth ?"

To show the effect of active exertion in increasing the unpleasant results of great atmospheric tenuity, we may quote the experience of De Saussure, in his ascent of Mont Blanc, noting however that recent Alpine travellers seem to have been more favored, while the guides would appear to have become more inured to the hardships of high places than they were in 1787. We learn that "at 13,000 feet, upon the Petit-Plateau, where he passed the night, the hardy guides, to whom the previous marching was absolute child's play, had only removed five or six spades-full of snow in order to pitch the tent, when they were obliged to give in and take a rest, while several felt so indisposed that they were compeiled to lie upon the snow to prevent themselves from fainting. The next day," says De Saussure, "in mounting the last ridge which leads to the summit, I was obliged to halt for breath at every fifteen or sixteen paces, generally remaining upright and leaning on my stock; but on more than one occasion I had to lie down, as I felt an absolute need of repose. If I attempted to surmount the feeling, my legs refused to perform their functions; I had an initiatory feeling of faintness, and was dazzled in a way quite independent of the action of the light, for the double crape over my face entirely sheltered the

eyes.

The only thing which refreshed me and augmented my strength was the fresh wind from the north. When, in mounting, I had this in my face, and could swallow it down in gulps, I could take twenty-five or twenty-six paces without stopping."

It must not be overlooked, however, that some of the effects thus experienced appear to be due to the presence of impure air. For experiments made by De Saussure showed that air near the surface of snow contains less oxygen than the surrounding air; and Boussingault points out respecting "certain hollows and enclosed valleys of the higher part of Mont Blanc

a

There are, indeed, parts of the earth where at an elevation nearly as great as that at which De Saussure experienced such unpleas int effects, the inhabitants of considerable cities enjoy health and strength. As Boussin gault well remarks, "When one has seen the activity which goes on in towns like Bogota, Micuipampa, Potosi, &c., which have height of from 8,500 feet to 13,000 feet; when one has witnessed the strength and agility of the torreadors in a bull-fight at Quito (9,541 feet); when one has seen young and delicate women dance for the whole night long in localities almost as lofty as Mont Blanc; when one remembers that a celebrated combat, that of Pichincha, took place at a height as great as that of Monte Rosa (15,000 feet), it will be admitted that man can become habituated to the rarefied air of the highest mountains." These places are, however, tropical, and it is manifest that cold plays an important part in producing the unpleasant sensations which are experienced in elevated regions. Since in Mars (according to our present assumption) we have not only a much greater atmospheric rarity than at the highest peak of the Himalayas, but also a much greater degree of cold than at such a height even in high latitudes, it is manifest that absolute uninhabitability by human beings must re

sult. Nay, since no living things except microscopic animalcules exist above certain elevations, or when a certain degree of cold is experienced, it remains clear that Mars cannot possibly be inhabited by creatures resembling any of the higher forms of living beings with which we are familiar on earth. "Beyond the last stage of vegetation, beyond the extreme region attained by the insect and mammifers, all becomes silent and uninhabited," says Flammarion," though the air is still full of microscopic animalcules which the wind raises up like dust and which are disseminated to an unknown height."

But the reader may be led to ask, at this stage, what is actually taking place in Mars when our astronomers perceive signs as of clouds forming and dissolving, of morning and evening mists, and other phenomena, not compatible, it should seem, with the idea of extreme cold. Nay, it is to be remembered that even the presence of ice and snow implies the action of heat. "Cold alone," says Tyndall, "will not produce glaciers. You may have the bitterest north-east winds here in London throughout the winter without a single flake of snow. Cold must have the fitting object to operate upon, and this object-the aqueous vapor of the air-is the direct product of heat." It is manifest, then, that the sun exerts enough heat on Mars to raise the vapor of water into the planet's atmosphere (as indeed spectroscopic analysis has taught us), and it is also clear that this vapor must be conveyed in some way to the Martial arctic regions, there to be precipitated in the form of snow. And then this difficulty is introduced: According to our ideas the whole surface of Mars is above the snow-line; any region on our earth where so great a degree of cold prevailed accompanied by so great an atmospheric tenuity would be far above the snow-line even at the equator. How is it then that the snow ever melts, as it manifestly does, since we can see the ruddy surface of the planet?

An explanation, first suggested, we believe, in Mr. Mattien Williams's ingenious book called The Fuel of the Sun, removes this difficulty. The snow actually falling on Mars must be small in quantity, simply because the sun's heat is not competent to raise up any great quantity of water vapor. There cannot, then, be any NEW SERIES.-VOL. XVIII., No. 3

thing like the accumulation of snow which gathers in regions above our snow-line; but instead of this there must exist over the surface of Mars except near the poles a thin coating of snow, or rather there will be ordinarily a mere coating of hoar frost. Now the sun of Mars, though powerless to raise great quantities of vapor into the planet's tenuous atmosphere, is perfectly competent to melt and vaporize this thin coating of snow or hoar frost. The direct heat of the sun, shining through so thin an atmosphere, must be considerable wherever the sun is at a sufficient elevation; and of course the very tenuity of the air renders vaporization so much the easier, for the boiling point (and consequently all temperatures of evaporation at given rates) would be correspondingly lowered.* Accordingly, during the greater part of the Martian day, the hoar frost and whatever light show might have fallen on the preceding evening would be completely dissolved away, and thus the ruddy earth or the greenish ice-masses of the so-called oceans would be revealed to the terrestrial obser

ver.

We may picture the result by conceiving one of those Martial globes which Captain Busk has recently caused Messrs. Malby to make from Mr. Proctor's charts, to be first coated with thin hoar frost, and then held before a fire just long enough to melt the hoar frost on the part of the globe nearest to the fire, leaving the features of the rest of the globe concealed from view under their snow-white veil.

Those who have seen Mars under good telescopic "power" will at once recognise the exact agreement between this hypothetical process and the actual appearance of the planet. All round the border of the disc there is a white light completely concealing all the features of the Martian continents and oceans. Of this peculiarity no satisfactory explanation has

* Amongst other disadvantages presented by Mars, regarded as an abode for beings like ourselves, is the circumstance that if his atmosphere be in proportion to his mass, as we have assumed, it must be impossible to boil food properly on the ruddy planet. For water would boil at a temperature about seventy degrees below our boiling point, so that it would barely be heated enough to parboil. A cup of good tea is an impossibility in Mars, and equally out of the question is a well-boiled potato. It does not make matters more pleasant that the tea-plant and the potato are impossible, of themselves, on Mars, and that therefore the possibility of boiling them may be regarded as a secondary consideration.

20

hitherto been advanced. Mr. Proctor, indeed, has shown how the peculiarity would present itself if the Martian atmosphere were loaded with rounded clouds resembling our summer woolpack clouds; but it is a little difficult to believe that all over Mars such clouds as these are prevalent. Moreover, it is to be noticed that these woolpack clouds are morning and forenoon phenomena on our earth; towards noon they either vanish or become modified in shape, and as evening approaches the clouds ordinarily assume a totally different aspect, being extended in long flat sheets, the stratus cloud of the meteorologist. Even when rounded clouds are present in the evening sky, they are not the separate small white clouds absolutely essential, as it appears to us, for the theory advanced by Mr. Proctor; but the great heavy cloud is seen

That rises upward always higher,

And onward drags a laboring breast, And topples round the dreary west A looming bastion fringed with fire. According to the views here suggested we have as the principal feature of Martian meteorology the melting of the coating of hoar frost (or of light snow, perhaps) from the ruddy soil of the planet and from the frozen surface of his oceans in the forenoon, and the precipitation of fresh snow or hoar frost when evening is approaching. Throughout the day the air remains tolerably clear, so far as can be judged from the telescopic aspect of the planet, though there is nothing to prevent the occasional accumulation of light cirrus or snow-clouds, especially in the forenoon. We believe, in fact, that the phenomena which have commonly been regarded as due to the precipitation of rain from true nimbus clouds over Martian oceans and continents must be ascribed to the dissipation of cirrus clouds by solar heat.

But we must not fall into the mistake of supposing that because the Martian atmosphere is at so low a pressure that Martian barometers (mercurial) probably stand at only four or five inches, the atmosphere is, therefore, exceedingly shallow. Even on our earth an atmosphere producing this amount of pressure would extend many miles above the sea-level, for as a matter of fact we know that at the height of eight or nine miles, only, the atmospheric pressure is thus reduced, and even

the lowest estimates assign to the atmosphere a height of fifty miles, or roughly. some forty miles above the height where the pressure corresponds to five inches of the common barometer. But in the case of Mars the atmospheric pressure diminishes much more slowly with altitude than on our own earth. We have only to climb to a height of three-and-a-half miles to find the pressure reduced to one-half (no matter what the height we start from); at seven miles it is reduced to one-fourth; and so on. But owing to the relatively small attraction of gravity in Mars a height of nine miles must be attained from his sea-level before the atmospheric pressure is reduced to one-half, and a height of eighteen miles before it is reduced to one fourth, and so on. And instead of forty miles (which, as we have seen, is the lowest estimate of our air's height above the level where its pressure is like that of the Martian air), we find a height of fully seventy-five miles as the minimum. We may fairly assume that the Martian atmosphere extends to a height of at least 100 miles from the planet's surface.

In such an atmosphere there is ample scope for air-currents, and it is probable that owing to the tenuity of the air the winds in Mars would have a high velocity. They would not necessarily be violent winds, since the force of wind depends on the quantity of air which is in motion. quite as much as on the velocity. So that we need not entertain the theory which was advanced some years since in the Spectator, that trees in Mars must be small in consequence of the great violence of Martian hurricanes by which all lofty trees would be destroyed. Even at a velocity of a hundred miles per hour, Martian winds would be less destructive than gales on earth blowing at the moderate rate of twenty miles per hour. But on a globe so small as that of Mars, compared at least with the earth's, swift air-currents would be very effective in carrying off from the central heated regions the moisture-laden air. In this way probably the polar snows of the planet are recruited. The polar regions must, in fact, act the part of veritable condensers, if the circulation of the Martian atmosphere is as brisk as it may well be believed to be. There must in that case be a continual gathering of fresh snows at the poles, and a continual downward motion of the glaciers thus formed,

accompanied necessarily by a very active abrasion and erosion of the planet's polar regions. It seems by no means improbable, moreover, that as Mr. Mattien Williams opines, there may be from time to time great catastrophes in these polar regions, produced by the toppling over or the rapid downward sliding of great glacial masses. For many considerations suggest that there must be an activity in the process of snow-gathering at the Martian poles altogether unlike anything known on our earth. It is noteworthy also that according to reliable observations changes have taken place in the aspect of the Martian snow-caps which imply catastrophes affecting ice-masses of enormous dimensions. Assuredly none of the changes taking place in our own polar regions could be discerned at so great a distance as separates us from Mars, save only the gradual increase and diminution of the extent of the snow-covering as winter or summer is in progress. An icemass as large as Spitzenbergen or Nova Zembla would not be separately discernible from so great a distance, and therefore the complete destruction of such a mass by collision or downfall would be quite imperceptible at that distance, though it would be an inconceivably stupendous terrestrial catastrophe. But masses of Martian ice, quite readily discernible with good telescopes, have been found to disappear in a few hours, suggesting the most startling conceptions as to the effects which must have been produced on the comparatively small planet where these remarkable events have taken place.

The following observation, for instance, made by the late Professor Mitchel with the fine refractor of the Cincinnati observatory, indicates the occurrence of an event which must have been accompanied by an inconceivable uproar,—

A wrack

As though the heavens and earth would mingle.

"I will record," he says, "a singular phenomenon connected with the snow-zone, which, so far as I know, has not been noticed elsewhere. On the night of July 12th, 1845, the bright polar spot presented an appearance never exhibited at any preceding or succeeding observation. In the very centre of the white surface was a dark spot, which retained its position during several hours, and was distinctly seen

Let

by two friends who passed the night with me in the observatory. It was much darker, and better defined than any spot previously or subsequently observed here; and indeed after an examination of more than eighty drawings, I find no notice of a dark spot ever having been seen in the bright snow-zone. On the following evening no trace of a dark spot was to be seen, and it has never since been visible." Does not this observation suggest that a great mass of ice had shipped away, leaving an intervening dark space, which in a few hours was snowed over, the gap remaining thereafter invisible? No other explanation, indeed, seems possible. But how tremendous a catastrophe to be discernible from a station some forty millions of miles away! Granting even that Mitchel used a power of 1,200 (which we find given in Loomis's Practical Astronomy as the highest power of the Cincinnati telescope), Mars was still viewed as from a distance of 40,000 miles with the naked eye. any one who has observed the aspect of an Alpine region, as seen with the naked eye from a distance of forty miles (that region being known, so that he could estimate the degree by which distance reduced even the most imposing mountain features) consider what would be the effect of removing the point of view to a distance one thousand times greater. Not merely would a mountain-range, but a whole country, be invisible at such a distance. But add to these considerations the fact that the most stupendous mountain catastrophes are reduced apparently to utter insignificance at a distance of a few miles, and are altogether undiscernible at a distance of thirty or forty miles, and we shall be able to understand, though we remain utterly unable to conceive, the vastness of the catastrophe on Mars, the effects of which could be discerned when viewed as by the naked eye from a distance of 40,000 miles. One would imagine that the very frame of the small planet must have been shaken.

It does not appear to us altogether unlikely that the varying accounts which astronomers have given respecting the polar flattening of Mars may find their true explanation in the theory we have been considering. It is certainly remarkable that eminent astronomers, like Sir W. Herschel, Arago, Dawes, Bessel, Hind, Main, and others, should have arrived at

the most conflicting results on an observational matter of such extreme simplicity. We have values of the compression varying from Sir Wm. Herschel's, who made the polar diameter of the planet a full sixteenth less than than the equatorial diameter, to Dawes's result, that the planet is not flattened at all. Nay, some observations have even suggested that the planet is elongated at the poles. If great changes of elevation take place at the poles of Mars, owing to the rapid process of accumulation of the Martian snows, these discrepancies would be accounted for.

But whatever opinion we form on details of this sort, it appears tolerably clear that in all its leading features the planet Mars is quite unlike the earth, and unfit to be the abode of creatures resembling those which inhabit our world. Neither

animal nor vegetable forms of life known to us could exist on Mars. To the creatures which thrive in our arctic regions or near the summits of lofty mountains, the torrid zone of Mars would be altogether too bleak and dismal for existence to be possible there. Our hardiest forms of vegetable life would not live a single hour if they could be transplanted to Mars. Life, animal as well as vegetable, there may indeed be on the ruddy planet. Reasoning creatures may exist there as on the earth. But all the conditions of life in Mars, all that tends to the comfort and well being of Martian creatures, must differ so remarkably from what is known on earth, that to reasoning beings on Mars the idea of life on our earth must appear wild and fanciful in the extreme, if not altogether untenable.-Cornhill Magazine.