Part 22

“‘Plato is, I believe, more active [in a volcanic sense] than any area of similar size upon the earth. There seems to be no evidence of lava, but the white streaks indicate apparently something analogous to snow or clouds. There must be a certain escape of gases, presumably steam and carbonic acid, the former of which probably aids in the production of the white markings.’

“The white marks to which Professor Pickering refers are but faintly indicated in the photograph before us, but with the telescope, when the illumination is favorable, they are plainly seen. There are a number of very small crater pits scattered over the floor of Plato, and around these changes of color occur which have been ascribed to the emission of some substance from the pits and to the presence of vegetation, nourished by the gases and vapors, and springing into renewed life every time the sun rises upon the plain. Broad areas of the inclosure gradually change color as the sun rises, and again as the sun sets, and these phenomena have also been ascribed to the presence of vegetation. You may, if you wish, regard Plato as a kind of mountain-ringed prairie, covered with something analogous to prairie grass and shrubs, which depends for its existence, partly, upon the supply of gases spreading over the surface from the crater pits.”

“So this, then, is your ‘lunar grass’?”

“Yes, but not all of it. Mark, I do not aver that it actually exists; I only say that it has been suspected to exist. On some of the mares similar appearances are seen, as I have already told you, on a much more extensive scale, and I may again quote Professor Pickering, who says that some of his observations ‘point very strongly to the existence of vegetation upon the surface of the moon in large quantities at the present time.’”

“Does this vegetation resemble that of the earth?”

“I cannot tell you.”

“But where vegetation exists animal life is possible, is it not?”

“Yes, it is possible.”

“What forms would it have?”

“I cannot tell you. But I certainly should not expect to find manlike creatures there.”

“Oh, men are not necessary everywhere,” said my friend, laughing. “I am content if you admit that there may be living creatures of some kind. Henceforth I shall never forget Plato and the other places on the moon where such significant changes are seen.”

“I shall presently point out to you one of the most notable of those other places,” I replied. “Let me now fulfill my promise to tell you more about the lunar atmosphere. I have told you already that there are strong reasons for supposing that the moon once had a far more dense atmosphere than she possesses at present, and I have mentioned some of the ways in which this atmosphere is supposed to have disappeared. I think that it is worth our while to refer to them again. In the first place the moon’s atmosphere may have been withdrawn into vast internal cavities formed by the gigantic volcanic eruptions. Secondly, it may have been absorbed both mechanically and chemically by the core of the moon as it cooled off. We know that cooling rocks absorb immense quantities of the gases constituting the air we breathe. In fact we may look forward to a time, fortunately for us extremely remote, when the interior rocks of the earth will, in this manner, absorb perhaps all of its atmosphere.”

“But if the air of the moon has gone into great cavities in the interior, why might not the living beings of the moon have followed it there?”

“According to some of the theorists,” I answered, “that may really be what has occurred, and thus the moon has become a ‘cavern world’ on a gigantic scale. But science does not regard seriously these speculations about ‘cave life’ in the moon. A third hypothesis is that which I have mentioned concerning the escape of the atmospheric gases from the moon on account of its attraction being insufficient permanently to retain them. This process would be gradual, because the molecules of a gas fly in all directions, only a small proportion having their trajectories directly away from the center of the globe on which they are held. But a singular consequence of this theory is that interplanetary space must contain an enormous number of such wandering molecules, and every attracting body must draw more or less of them to its surface, thus forming an atmosphere for itself. As Professor Young has remarked, if as many of these molecules enter a planet’s atmosphere in a day as escape from it there can be no decrease of the total amount of air. If more escape than enter, the atmosphere will diminish. If more enter than escape, the atmosphere will grow. Finally if none escape the atmosphere may increase indefinitely. This, as far as the effect of gravitation is concerned, should be the case on the sun, for the solar attraction is more than sufficient to retain any gas known to us. In consequence, the sun’s atmosphere may be increasing in extent and density. Even the earth’s atmosphere may be slowly increasing from this cause, and herein may lie the explanation of the enormous atmosphere surrounding the great planet Jupiter.

“In view of what I have said it is evident that the moon cannot be entirely airless. Recent observations have confirmed this conclusion, and some observers have thought that they could detect the presence of something resembling clouds occasionally creeping like low fogs over certain places on the moon. All this, you will observe, has an important bearing upon the question of life on the moon at the present day. Certain forms of plant life and low animal organizations might exist in such an atmosphere as the moon still possesses.”

“But,” interjected my friend, “is not this that you have been telling me in contradiction to what you said about the cause of the sharp division between day and night on the moon, and about the visibility of the stars there in the daytime?”

“Not at all,” I replied, “for the effects of which I spoke are relative. In any case the atmosphere of the moon must be too rare to diffuse any perceptible amount of light into the shadows, or to illuminate the sky sufficiently to render the stars invisible. The same reasoning applies to what I have told you about the contrasts of cold and heat on the moon.

“But we have not yet finished with our photograph. We were looking at the plain of Plato, you will recollect. Notice, now, the Mare Imbrium off the coast that adjoins Plato on the south. You see there several bright spots resembling islands. Islands they must have been if the mare once had water covering it. One of these, standing by itself, an irregular, bright clump with a distinct shadow on the western side, bears the name of Pico, taken from the sharp peak in the Azores Islands. The broken mass southeast of Pico, and nearer the coast, constitutes the Teneriffe Mountains. You will notice that terrestrial geography has been drawn upon in this case also to supply a name. Still farther east is a long ‘island’ named the Straight Range. Beyond that, at the edge of the picture, appears Cape Laplace, at the western end of the ‘Bay of Rainbows.’

“We now turn to the southwestern border of the Mare Imbrium, in the upper part of the photograph. This, as I have already pointed out, is skirted by the steep cliffs of the Apennines for a distance of more than 400 miles. Opposite the crater ring Marco Polo, in the Apennines, you will notice how the floor of the ‘sea’ is upheaved, containing a great number of irregularities, and some small peaks. This would have been a dangerous part of the ‘Sea of Rains’ for the lunar navigators. At the northwestern corner of this region lies a large ring plain, with indefinite light stripes crossing its floor, which is named Archimedes. It is about 50 miles in diameter. Northwest of it are two smaller ring mountains, Aristillus (the larger) and Autolycus. If we could suppose these immense volcanoes to have been in eruption when these seas were navigable, imagine the magnificent spectacle that they would have presented to anyone approaching in a ship from the direction of the strait between the Apennines and the Caucasus.

“Let us now pass this strait and enter the Mare Serenitatis. You will admire the beautiful modulation of the bottom, as shown in the photograph. Lighter and darker regions are curiously interspersed, and in some places there are faint indications of that wonderful lunar world of remote antiquity which lies buried in the grave of a planet. Directly opposite the opening of the strait, a small, round, light spot is seen in the midst of the sea. This is Linné, very famous for its strange and suggestive history. Here, if anywhere on the moon, changes visible to human eyes have taken place, and, in the opinion of Professor Pickering, are still taking place every fortnight. In the center of the light spot is a minute crater, and from this crater there seems to issue some kind of vapor which spreads over the surrounding surface, alternately expanding and shrinking in extent. A remarkable change in the form and appearance of Linné was recorded by the astronomer Schmidt, at Athens, in 1866. What had occurred has been explained by some as the falling in of a crater floor some six miles in diameter. But the observations of Professor Pickering are more interesting and suggestive. According to him the bright patch about the crater pit extends during the lunar night and diminishes by day, indicating that something issues from the pit and is deposited over the surrounding plain in the form of hoar frost, which melts away in the sunshine. He has even recorded an apparent expansion of the white area during a lunar eclipse when the cold shadow of the earth tends to condense the vapors. If this is true it seems rather surprising that many more similar phenomena are not visible elsewhere.

“Among the most remarkable and beautiful features of this photograph are the winding ridges like half-submerged mountain ranges that appear on the sea bottom in various places. Notice particularly the long twisted chain that lies across the western part. Between this and a shorter range, close to the west shore, runs a broad, dark valley, with the crater Dawes lying in the middle of it at the upper end. Some of these winding ridges suggest by their shape and modulation the action of water. Finally, let us return to the strait through which we recently passed. Notice that the Apennines and the Caucasus look as though they had once formed a continuous line of mountains, which has been broken through in its center, leaving huge buttresses on each side, like the Pillars of Hercules at the Strait of Gibraltar?”

“That place has an irresistible attraction for me,” said my companion. “I cannot withhold my imagination from picturing the scene there when the waters rolled deep over those great bottoms, and when white-sailed ships were passing and repassing between the towering capes, carrying the commerce of opulent cities situated along those marvelously picturesque shores.”

“Perhaps,” I suggested, “the lunarians, whom you have reconstructed in your fancy, reached, before the catastrophe came that ended their existence, a higher state of civilization than ours, and learned to substitute electrically driven vessels for white-winged ships.”

“That would be like the introduction of vulgar steamboats on the canals of Venice,” she replied.

“Well,” I said, “this ends our survey and one month of photographic journeying on the moon, and I am glad that you have finished it with so pleasing a vision.”

* * * * *

Upon parting from my friend I left the photographs in her possession. A few weeks later I received a letter from her in which she said:

“I have been studying and restudying those wonderful pictures of the moon. I have ordered a telescope to be set up in my park near the elm, and when it is ready I wish you to come and instruct me how to view the moon for myself. I believe that I am becoming a learned and enthusiastic selenographer, and those strange names—Gemma Frisius, Bullialdus, Abulfeda, Abenezra, Rabbi Levi, Maurolycus, Fra Mauro, Sacrobosco, Zagut, Cichus, Sulpicius Gallus—have established their fascination over my mind. Theophilus no longer terrifies me with its formidable aspect, and I spend hours poring over the Mare Serenitatis. But my fancy remains faithful to the ‘Marsh of a Dream,’ which still represents for me the culmination of lunar ideality.