Curiosities of the Sky by Garrett Putman Serviss (important books to read .TXT) 📖

else than a freak of nature. Large cities, with their radiating lines of communication, would at once betray their real character. Cultivated tracts, and the changes produced by the interference of intelligent beings, would be clearly recognizable. The electric illumination of a large town at night would probably be markedly visible. Gleams of reflected sunlight would come to us from the surfaces of the lakes and oceans, and a huge ``liner'' traversing a lunar sea could probably be followed by its trail of smoke. As to communications by ``wireless'' signals, which certain enthusiasts have thought of in connection with Mars, in the case of the moon they should be a relatively simple matter, and the feat might actually be accomplished. Think what a literature would grow up about the moon if it were a living world! Its very differences from the earth would only accentuate its interest for us. Night and day on the moon are each two weeks in length; how interesting it would be to watch the manner in which the lunarians dealt with such a situation as that. Lunar and terrestrial history would keep step with each other, and we should record them both. Truly one might well wish to have a neighbor world to study; one would feel so much the less alone in space.

It is not impossible that the moon did at one time have inhabitants of some kind. But, if so, they vanished with the disappearance of its atmosphere and seas, or with the advent of its cataclysmic age. At the best, its career as a living world must have been brief. If the water and air were gradually absorbed, as some have conjectured, by its cooling interior rocks, its surface might, nevertheless, have retained them for long ages; but if, as others think, their disappearance was due to the escape of their gaseous molecules in consequence of the inability of the relatively small lunar gravitation to retain them, then the final catastrophe must have been as swift as it was inevitable. Accepting Darwin's hypothesis, that the moon was separated from the earth by tidal action while both were yet plastic or nebulous, we may reasonably conclude that it began its career with a good supply of both water and air, but did not possess sufficient mass to hold them permanently. Yet it may have retained them long enough for life to develop in many forms upon its surface; in fact, there are so many indications that air and water have not always been lacking to the lunar world that we are driven to invent theories to explain both their former presence and their present absence.

But whatever the former condition of the moon may have been, its existing appearance gives it a resistless fascination, and it bears so clearly the story of a vast catastrophe sculptured on its rocky face that the thoughtful observer cannot look upon it without a feeling of awe. The gigantic character of the lunar features impresses the beholder not less than the universality of the play of destructive forces which they attest. Let us make a few comparisons. Take the lunar crater called ``Tycho'', which is a typical example of its kind. In the telescope Tycho appears as a perfect ring surrounding a circular depression, in the center of which rises a group of mountains. Its superficial resemblance to some terrestrial volcanic craters is very striking. Vesuvius, seen from a point vertically above, would no doubt look something like that (the resemblance would have been greater when the Monte del Cavallo formed a more complete circuit about the crater cone). But compare the dimensions. The remains of the outer crater ring of Vesuvius are perhaps half a mile in diameter, while the active crater itself is only two or three hundred feet across at the most; Tycho has a diameter of fifty-four miles! The group of relatively insignificant peaks in the center of the crater floor of Tycho is far more massive than the entire mountain that we call Vesuvius. The largest known volcanic crater on the earth, Aso San, in Japan, has a diameter of seven miles; it would take sixty craters like Aso San to equal Tycho in area! And Tycho, though one of the most perfect, is by no means the largest crater on the moon. Another, called ``Theophilus,'' has a diameter of sixty-four miles, and is eighteen thousand feet deep. There are hundreds from ten to forty miles in diameter, and thousands from one to ten miles. They are so numerous in many places that they break into one another, like the cells of a crushed honeycomb.

The lunar craters differ from those of the earth more fundamentally than in the matter of mere size; they are not situated on the tops of mountains. If they were, and if all the proportions were the same, a crater like Tycho might crown a conical peak fifty or one hundred miles high! Instead of being cavities in the summits of mountains, the lunar craters are rather gigantic sink-holes whose bottoms in many cases lie two or three miles below the general surface of the lunar world. Around their rims the rocks are piled up to a height of from a few hundred to two or three thousand feet, with a comparatively gentle inclination, but on the inner side they fall away in gigantic broken precipices which make the dizzy cliffs of the Matterhorn seem but ``lover's leaps.'' Down they drop, ridge below ridge, crag under crag, tottering wall beneath wall, until, in a crater named ``Newton,'' near the south lunar pole, they attain a depth where the rays of the sun never reach. Nothing more frightful than the spectacle which many of these terrible chasms present can be pictured by the imagination. As the lazy lunar day slowly advances, the sunshine, unmitigated by clouds or atmospheric veil of any kind, creeps across their rims and begins to descend the opposite walls. Presently it strikes the ragged crest of a ridge which had lain hidden in such darkness as we never know on the earth, and runs along it like a line of kindling fire. Rocky pinnacles and needles shoot up into the sunlight out of the black depths. Down sinks the line of light, mile after mile, and continually new precipices and cliffs are brought into view, until at last the vast floor is attained and begins to be illuminated. In the meanwhile the sun's rays, darting across the gulf, have touched the summits of the central peaks, twenty or thirty miles from the crater's inmost edge, and they immediately kindle and blaze like huge stars amid the darkness. So profound are some of these awful craters that days pass before the sun has risen high enough above them to chase the last shadows from their depths.

Although several long ranges of mountains resembling those of the earth exist on the moon, the great majority of its elevations assume the crateriform aspect. Sometimes, instead of a crater, we find an immense mountain ring whose form and aspect hardly suggest volcanic action. But everywhere the true craters are in evidence, even on the sea-beds, although they attain their greatest number and size on those parts of the moon -- covering sixty per cent of its visible surface -- which are distinctly mountainous in character and which constitute its most brilliant portions. Broadly speaking, the southwestern half of the moon is the most mountainous and broken, and the northeastern half the least so. Right down through the center, from pole to pole, runs a wonderful line of craters and crateriform valleys of a magnitude stupendous even for the moon. Another similar line follows the western edge. Three or four ``seas'' are thrust between these mountainous belts. By the effects of ``libration'' parts of the opposite hemisphere of the moon which is turned away from the earth are from time to time brought into view, and their aspect indicates that that hemisphere resembles in its surface features the one which faces the earth. There are many things about the craters which seem to give some warrant for the hypothesis which has been particularly urged by Mr G. K. Gilbert, that they were formed by the impact of meteors; but there are also many things which militate against that idea, and, upon the whole, the volcanic theory of their origin is to be preferred.

The enormous size of the lunar volcanoes is not so difficult to account for when we remember how slight is the force of lunar gravity as compared with that of the earth. With equal size and density, bodies on the moon weigh only one-sixth as much as on the earth. Impelled by the same force, a projectile that would go ten miles on the earth would go sixty miles on the moon. A lunar giant thirty-five feet tall would weigh no more than an ordinary son of Adam weighs on his greater planet. To shoot a body from the earth so that it would not drop back again, we should have to start it with a velocity of seven miles per second; a mile and a half per second would serve on the moon. It is by no means difficult to believe, then, that a lunar volcano