“Here, then,” Mr. Lowell remarks, “we have an end and reason for the existence of canals, and the most natural conceivable—namely, that the canals are constructed for the express purpose of fertilizing the oases. When we consider the amazing system of the canal lines, we are carried to this conclusion as forthright as is the water itself; what we see being not the canal itself, indeed, but the vegetation along its banks.”
The proportion of water to land is much smaller on Mars than on the earth. Only two-sevenths of the disk are covered by the dusky areas, and of late the aqueous nature of some, if not all, of these has been seriously called in question. Professor Pickering was convinced by his observations, in 1892 and 1894, “that the permanent water area upon Mars, if it exist at all, is extremely limited in its dimensions.” He estimated it at about half the size of the Mediterranean. Professor Schaeberle is similarly incredulous. If the dark markings are seas, he asks, how explain the irregular gradations of shade in them? How, above all, explain their apparent intersection by well-marked canals? Professor Barnard, observing with the Lick thirty-six inch in 1894, discerned on the Martian surface an astonishing wealth of detail, “so intricate, small, and abundant, that it baffled all attempts to properly delineate it.” It was embarrassing to find these minute features belonging more characteristically to the “seas” than to the “continents.” Under the best conditions, the dark regions lost all trace of uniformity. Their appearance resembled that of a mountainous country, broken by cañon, rift, and ridge, seen from a great elevation. These effects were especially marked in the “ocean” area of the Hour-Glass Sea.
Evidently the relations of solid and liquid in that remote orb are abnormal; they can not be completely explained by terrestrial analogies. Yet a series of well-attested phenomena are intelligible only on the supposition that Mars is, in some real sense, a terraqueous globe. Where snows melt there must be water; and the origin of the Rhone from a great glacier is scarcely more evident to our senses than the dissolution of Martian ice-caps into pools and streams.
The testimony of the spectroscope is to the same effect. Dr. Huggins found, in 1867, the spectrum of Mars impressed with the distinct traces of aqueous absorption, and the fact, although called in question by Professor Campbell of Lick, in 1894, has been reaffirmed both at Tulse Hill and at Potsdam. That clouds form and mists rise in the thin Martian air, admits of doubt. During the latter half of October, 1894, an area much larger than Europe remained densely obscured. Whether or no actual rain was at that time falling over the Maraldi Sea and the adjacent continent it would be useless to conjecture. We only know that with the low barometric pressure at the surface of Mars, the boiling point of water must be proportionately depressed (Flammarion puts it at 115° Fahrenheit), which implies that it evaporates rapidly, and can be transported easily.
If the Martian atmosphere be of the same proportionate mass as that of our earth, it can possess no more than one-seventh its superficial density. That is to say, it is more than twice as tenuous as the air at the summits of the Himalayas. The corresponding height of a terrestrial barometer would be four and a half inches. Owing, however, to the reduced strength of gravity on Mars, this slender envelope is exceedingly extensive. In the pure sky scarcely veiled by it, the sun, diminished to less than half his size at our horizons, probably exhibits his coronal streamers and prominences as a regular part of his noontide glory; atmospheric circulation proceeds so tranquilly as not to trouble the repose of a land “in which it seemeth always afternoon”; no cyclones traverse its surface, only mild trade-winds flow toward the equator, to supply for the volumes of air gently lifted by the power of the sun, to carry reinforcements of water-vapor north and south. Aerial movements are, in fact, by a very strong presumption, of the terrestrial type, but executed with greatly abated vigor.
Brilliant projections above the terminator of Mars were first distinctly perceived at the Lick Observatory in 1890. They have been reobserved at Nice, Arequipa, and Flagstaff (Mr. Lowell’s observatory), coming into view, as a rule, when circumstances concur to favor their visibility. They strictly resemble lunar peaks and craters, catching the first rays of the sun, while the ground about them is still immersed in darkness; and Professor Campbell connects them with “mountain chains lying across the terminator of the planet,” and in some cases possibly snow-covered. He calculates their height at about ten thousand feet. Their presence was unlooked for, since a flat expanse is a condition sine quâ non for the minute intersection of land by water, which seems to prevail on Mars.
Although the sun is less than half as powerful on Mars as it is here, the Martian climate, to outward appearance, compares favorably with our own. Polar glaciation is less extensive and more evanescent, and little snow falls outside the arctic and antarctic regions. Yet the theoretical mean temperature is minus 4° C., or 61° of Fahrenheit below freezing. This means a tremendous ice-grip. The coldest spot on the earth’s surface is considerably warmer than this cruel average. Fortunately, it exists only on paper. Some compensatory store of warmth must then be possessed by Mars, and it can scarcely be provided by its attenuated air. Possibly, internal heat may still be effective, and we see exemplified in Mars the geological period when vines and magnolias flourished in Greenland, and date-palms ripened their fruit on the coast of Hampshire.
The climate of Mars, according to Schiaparelli, “must resemble that of a clear day upon a high mountain. By day a very strong solar radiation hardly at all mitigated by mist or vapor; by night a copious radiation from the soil toward celestial space, and hence a very marked refrigeration; consequently, a climate of extremes, and great changes of temperature from day to night, and from one season to another. And as on the earth, at altitudes of from 17,000 to 20,000 feet, the vapor of the atmosphere is condensed only into the solid form, producing those whitish masses of suspended crystals which we call cirrus-clouds, so in the atmosphere of Mars it would be rarely possible to find collections of cloud capable of producing rain of any consequence. The variation of temperature from one season to another would be notably increased by their long duration, and thus we can understand the great freezing and melting of the snow, renewed in turn at the poles at each complete revolution of the planet round the sun.”
The German astronomer Mädler searched in 1830 for a Martian satellite, and although his telescope was of less than four inches aperture, he satisfied himself that none with a diameter of as much as twenty-three miles could be in existence. As it happened, he was right. The pair of moons detected by Professor Asaph Hall with the Washington twenty-six refractor, August 11 and 17, 1877, are unquestionably below that limit of size. Neither of them can well be more than ten miles across. Their names, “Deimos” and “Phobos,” are taken from the Iliad, where Fear and Panic are introduced as attendants upon the God of War. Deimos revolves in 30 hours and 18 minutes at a distance of 14,600 miles from the centre of Mars. And since the planet rotates in 24 hours, 37 minutes, the diurnal motion of the sphere from east to west is so nearly neutralized by the orbital circulation of the satellite from west to east that nearly 132 hours elapse between its rising and its setting. During the interval, it changes four times from new to full, and vice versâ.