Part 13

“You are by no means compelled to give up your idea,” I replied. “On the contrary you are supported by the opinion of many astronomers, including Messrs. Loewy and Puiseux, whom I quoted a little while ago. They aver that the resemblances between the lunar _mares_ and the beds of our terrestrial oceans are too numerous and too decided to permit any other conclusion than that in the one case as in the other a deep covering of water has produced the characteristic features. One striking resemblance that they note is in the surface contours. The lunar sea beds are generally deepest along the shores; the same is true of the terrestrial seas. Continents on the other hand are characterized by concave surfaces. But before we study the two lunar ‘seas’ in detail let us first look at their shores and surroundings. The upper and right-hand sides of the _Mare Serenitatis_ are bordered by hundreds of miles of magnificent cliffs, which in many places are very steep and of great height. These form what we may call the sea front of the Hæmus Mountains, which join the lunar Apennines on the southern shore of the strait leading into the _Mare Imbrium_. These mountains possess one conspicuous crater, set like a gem in the chain, at about a third of its length from the western end. This crater is Menelaus, which we saw in one of the smaller photographs. It is characterized by its exceptional brilliance as well as by the fact that the longest of the bright bands that start from Tycho passes through it, and then continues on across the _Mare Serenitatis_ and the _Lacus Somniorum_, to the _Mare Frigoris_. This band, more than 2,000 miles long, has come all the way from Tycho, high in the southern hemisphere, never turning aside to avoid anything in its path. Mountains, craters, and ring plains are equally indifferent to it. It is like a Roman road, and like that, too, it suggests for its creation a power that knew no master, and admitted of neither rivalry nor opposition. The existence of this mysterious band increases the difficulty of finding a satisfactory explanation of the Tychonic rays. In the midst of the _mare_ the band or ray crosses another lone crater, 14 miles in diameter, named Bessel. The full length of the ray is not shown in this photograph, but on its way from Bessel it touches two other small craters in the ‘sea.’

“That portion of the Hæmus range in which Menelaus is set is a very attractive scene on account of the bow shape of the mountains, and the situation of the bright crater just in the center of the bow. Menelaus and the streak from Tycho can be seen at Full Moon with no greater optical aid than that of a good binocular. On the edge of the ‘sea,’ off a lofty headland of the Hæmus chain, another lone little crater is visible, Sulpicius Gallus by name. It, too, is remarkable for its brilliant reflective power. Behind the mountains, directly back of Sulpicius Gallus, and lying in an upraised part of the _Mare Vaporum_, is a larger, and even brighter, crater ring than Menelaus. It is named Manilius, and is likewise a conspicuous object for a binocular at Full Moon. Below Sulpicius Gallus the Hæmus Mountains broaden out and assume a curious somber tone, until, in the form of a rough plateau, they blend with the wide-expanded southwestern slopes of the Apennines. The latter rise gradually to the chain of huge peaks fronting the _Mare Imbrium_. They contain one notable crater ring named Marco Polo, which lies just above a great square _massif_, which breaks the narrow chain of the illuminated summits of the Apennines. The precipitous front of this range appears very brilliant in the afternoon sun, for here again we have a photograph made after the time of Full Moon. The end of the Apennines touching the strait, of which I have previously spoken, terminates with a high cape called Mount Hadley. In the strait, off this cape, is an array of small mountain peaks, which must have been islands, if the lunar ‘seas’ were once true seas.

“Across the strait, on the northern side, stand the lunar Caucasus Mountains. They run out to a point in a long, irregular, broken ridge. The distance from Mount Hadley across the strait to the projecting point of the Caucasus range is about 50 miles. The islands narrow the main opening to a width of 30 miles. In strict fact the Caucasus range is not continuous. The point fronting the strait is, in reality, the end of a large irregular ‘island,’ with intricate channels separating it from the mainland. Still farther north the photograph shows a broad valley severing the mountain range from side to side. The main mass of the Caucasus continues northward to the great ring mountains Eudoxus and Aristoteles. In the center of the range, opposite the lower corner of the _Mare Serenitatis_, is an irregular ring plain, Calippus. West of this the mountains break down in great precipices to the level of a plain that might be compared with one of the ‘parks’ of Colorado. Beyond this, in the shape of a broad mass of hills, it skirts the border of the _Mare Serenitatis_ for nearly 200 miles to a sharp promontory which shuts off the _Lacus Somniorum_ on one side from the _mare_. West of Aristoteles and Eudoxus the mountain mass extends to a curious sharp-angled plain, which it skirts on the north and south.

“The western shore of the _Mare Serenitatis_ beyond the strait opening into the _Lacus Somniorum_ is bordered by a series of alternating ring plains and connecting mountains. The first and largest of the rings is Posidonius, an immense formation 62 miles in diameter, with a central crater and curious ridges within the inclosure. Above Posidonius is Le Monnier, a ring plain whose ‘seaward’ wall has been broken down. Above that, again, is a mountain range terminating with broken crater rings. Then we arrive at the strait opening into the _Mare Tranquillitatis_, which is twice as broad as that between the Apennines and the Caucasus, and just in the middle of it stands a very perfect crater ring named Dawes. On the eastern side of this strait the Hæmus Mountains begin with a long cape called the Promontory Acherusia. Above this promontory, at the edge of the picture, appears the ring plain Plinius, with a distinct central peak. This completes the circuit of the _Mare Serenitatis_.

“We return to the Caucasus region. These mountains front the _Mare Imbrium_ along the upper part of their course with sharp slopes and cliffs. In the ‘sea,’ nearly opposite the deep, broad valley which I pointed out as dividing the range completely across, stands a triangular-shaped ring plain dark with shadow on one of its sides. This is Theætetus, interesting as the scene of an alleged display of ‘smoke,’ reported to have been witnessed by a French observer with his telescope a few years ago. Several occurrences of this kind have been reported on the moon, but more or less doubt attaches in every instance the accuracy of the observations, or at least to that of the conclusions drawn from them. Below Theætetus is an oval ring almost entirely filled up, with two craters within it. This is named Cassini. Below Cassini begins another mass of mountains, the lunar Alps. These are by no means as extensive as the Caucasus, but they contain some lofty peaks, and are traversed by one of the most remarkable valleys on the moon. It is not very distinctly shown in this picture, but you may recognize it by a dark band commencing opposite a small bay which sets back into the mountains. The valley continues through the mountains and the adjoining hilly regions nearly to the shore of the narrow _Mare Frigoris_, which runs in a sloping direction from beyond Aristoteles to the bottom edge of the picture. The Alps spread eastward, broadening out with many separate peaks, and skirting the _Mare Imbrium_, until they reach one of the most singular and interesting of lunar formations, the oval ring plain Plato. This looks like a dark lake surrounded by high cliffs. In the photograph all of the encircling wall is illuminated on the inner side except at the east end, where the shadows extend a short distance upon the floor. Plato looks as though it might once have been a ring mountain of the usual type, which has been partly filled in the interior by a local uprush of molten lava. The diameter of the ring is 60 miles, but the inclosure sinks only about half as deep beneath the crest of the wall, as is the rule with formations of similar outline. A central peak, a group of mountains, may be buried there.

“It is within this ring of Plato that some of the strongest evidences of continued change, and possibly of continued life upon the moon, have been found. Prof. William H. Pickering, after long and careful studies of this remarkable plain, says of it:

“‘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.

“As to life on the moon, I find that I cannot be satisfied with a mere grass theory. I am so well convinced that there must be something more, that I no longer relegate my lunarians to an age antedating the volcanoes. On the contrary, as soon as I get my telescope I am going to look for signs of them and their doings in the present day, and willy nilly, sir, you have got to aid me in the search.”

APPENDIX

APPENDIX

DATES, and age of the moon, when the twenty-one serial photographs were made at the Yerkes Observatory, by Mr. Wallace, with the 12-inch telescope and a special color filter constructed by him:

No. 1, February 19, 1904; Moon’s Age 3.85 Days No. 2, September 24, 1903; Moon’s Age 3.87 Days No. 3, July 29, 1903; Moon’s Age 5.54 Days No. 4, November 24, 1903; Moon’s Age 5.74 Days No. 5, July 1, 1903; Moon’s Age 6.24 Days No. 6, November 26, 1903; Moon’s Age 7.75 Days No. 7, July 2, 1903; Moon’s Age 7.24 Days No. 8, August 31, 1903; Moon’s Age 9.22 Days No. 9, August 2, 1903; Moon’s Age 8.97 Days No. 10, November 30, 1903; Moon’s Age 11.78 Days No. 11, December 1, 1903; Moon’s Age 12.98 Days No. 12, September 4, 1903; Moon’s Age 13.27 Days No. 13, September 5, 1903; Moon’s Age 14.40 Days No. 14, August 26, 1904; Moon’s Age 15.65 Days No. 15, August 28, 1904; Moon’s Age 17.41 Days No. 16, August 29, 1904; Moon’s Age 18.62 Days No. 17, October 10, 1903; Moon’s Age 20.06 Days No. 18, September 29, 1904; Moon’s Age 20.50 Days No. 19, August 16, 1903; Moon’s Age 23.81 Days No. 20, August 17, 1903; Moon’s Age 24.84 Days No. 21, August 19, 1903; Moon’s Age 26.89 Days

INDEX

INDEX

Abenezra, 205.

Abulfeda, 200.

Air on the moon, 230.

Albategnius, 78.

Aliacensis, 78, 205.

Almamon, 205.

Alps, 97. remarkable valley in, 225.

Altai Mountains, 72, 200. chain of small craters near, 200.

Animal life on the moon, 228.

Apennines, 10, 96, 104, 137, 143, 222, 232.

Apennines and Caucasus, strait between, 234.

Apianus, 205.

Archimedes, 143, 232.

Aristarchus, 117, 153. astonishing brilliance of, 112. cause of brilliance of, 155. possible composition of, 113.

Aristoteles, 76, 138.

Atlas, 70.