GREAT SCENES ON THE MOON

The Moon: A Popular Treatise by Garrett Putman Serviss is part of the HackerNoon Books Series. You can jump to any chapter in this book here . GREAT SCENES ON THE MOON GREAT SCENES ON THE MOON My friend did not leave me in doubt on the following morning as to the genuineness of her interest in her new studies. The shadows of the trees in the park were yet as long drawn out as the silhouettes of lunar peaks at sunrise, when we resumed our place under the elm, and, at her request, I opened once more my portfolio. “The series of photographs that we are now about to examine,” I began, “are on so large a scale that only a selected part of the moon is seen in each of them. But within the restricted limits of these pictures the amount of detail shown is truly astonishing, far more indeed than can be found on the most elaborate lunar charts. These photographs were made by Mr. Ritchey with the great 40-inch telescope of the Yerkes Observatory. Many more besides those that we are going to look at were taken by him, but I have selected, where choice was difficult, six which seemed to me to be of special interest. We shall begin with one which covers the larger part of the Mare Nubium, in the southeastern quarter of the moon. You certainly must remember the Mare Nubium, for it forms the head of the ‘dark woman’ whom you discovered in the moon last evening, and if you will hold this photograph at arm’s length you will see that her face is unmistakably stamped upon it.” “I am greatly flattered,” she replied, “that you should remember my discovery so well. I begin to feel hopeful that it may yet find a place in the books.” “It certainly is as deserving of such a place as many things that get into books. You ought to find a suitable name for this woman in the moon.” “If I believed myself capable of rivaling the man who christened the ‘Marsh of a Dream,’ I should surely try my hand at lunar nomenclature, but I fear that I should fall too far short of the ideal he has set up, and so I shall leave her nameless.” “Permit me then to continue to call her the ‘dark woman’ whenever a reference to her may seem useful in fixing the localities that we shall talk about in this photograph. The most striking object shown in the picture is the great ring mountain Bullialdus which forms an extraordinary ornament on the top of the ‘dark woman’s’ ear. This photograph was taken when the line 181of sunrise ran just along the border between the Mare Nubium and the Oceanus Procellarum. The Mare Humorum is yet buried in night beyond the upper right-hand edge of the picture, but some of its bordering mountains and craters have been touched by the morning sunbeams. You will observe that a little more than half of the interior of Bullialdus—which, by the way, I did not mention by name when we were studying the series of phase photographs—is yet filled with shadow, but its double-headed central peak rises clear and bright in the sunlight. The shadow of this central mountain can be seen projecting toward the east over the floor. The east wall, which is distinctly terraced, lies in full sunshine, and the light streaming over the lofty crest of the western wall touches the floor on its eastern half. The steep outer slopes that lead up to the western rampart, and the deep parallel ravines cut near the crest are clearly shown. The distance across the ring from the summit of the wall on one side to that on the other is 38 miles. The depth of the depression is 8,000 feet below the crest of the walls, but the latter rise only 4,000 feet above the level of the Mare Nubium outside, so that Bullialdus is an excellent example of the characteristic form of the lunar volcano, which I tried to illustrate for you last evening. The central mountain is 3,000 feet high. East of the south point of the 182ring a shadow shows the existence of a profound cleft in the wall, while a little west of south appears a smaller crater ring very black with shadow, except on its eastern side. If we stood on the Mare Nubium and looked toward Bullialdus and its neighbor from a distance of 25 or 30 miles they would resemble a double, flat-topped mountain, with its serrated crests connected by a high neck. The summit of one of the little peaks shown in the photograph in the plain just west of Bullialdus would form an excellent point of observation. Still farther south stands another crater ring most of whose interior is also, at present, filled with shadow. East of this, and a little farther south, is still a third ring of similar aspect, from which a curious range of hills runs southward. Returning to Bullialdus you will notice the radiating lines of hills that surround it, and particularly a more lofty and broken range which runs eastward.” Bullialdus and the Mare Nubium. “Bullialdus verily frightens me!” exclaimed my friend. “What an unearthly look it has! The longer I regard it the stronger becomes the indescribable impression that it produces. I begin to understand now what you meant when you promised to find a history in the moon. Truly there never can have been such another history. I almost feel that I do not care whether the moon ever had inhabitants or not. Its own story is 183more fascinating than that of any puny race of beings, passing their ephemeral lives upon its wonderful surface, could possibly be.” “I am glad,” I replied, “that you have begun to enter into the spirit of those who long and carefully study the earth’s satellite. You see now, that it is not necessary to the astronomer to find evidences either of former or of present life upon the moon in order to stimulate his zeal. For him, as you have yourself intimated, the relics of its past history, which this little world in the sky exhibits so abundantly, are of higher interest than any story of human empire, for they have an incomparably vaster theme. But to lighten our labor a little, let me once more refer to the ‘dark woman,’ whose features, like the outlines of a constellation, serve for points of reference. I began by remarking that Bullialdus seems to be placed just over her ear. Observe now that, taken together with its immediate surroundings, the great crater ring forms a kind of barbaric ear-ornament of most extraordinary form and richness of detail. The line of hills east of Bullialdus, of which I spoke a few minutes ago, connects the ring with a tumbled mass of mountains on the border of the Mare Humorum. These mountains run northward, or downward in the picture, for a distance of perhaps 150 miles, and then turn abruptly westward for a like distance; after which, in the 184form of a broken chain, constituting the eastern walls of a row of half-submerged ring plains, they change direction once more and run southward in the Mare Nubium. The whole system bears some resemblance to a gigantic buckle.” “What is that curious object below Bullialdus which resembles an old-fashioned gold earring?” “I was about to speak of that. It is a ring plain named Lubiniesky, about 23 miles in diameter with a wall a thousand feet in height, except in the direction of Bullialdus where it is broken down. The interior is very flat, and it forms a fine example of the half-submerged lunar volcanoes which abound in this hemisphere. It may have had a central mountain like Bullialdus, but if so it has been completely buried under the influx of molten lava or whatever it was that covered this part of the moon. The perfect form of Bullialdus in all its details when compared with the mere outline that remains of Lubiniesky indicates that the former probably burst forth after the inundation of liquid rock that drowned the latter. Thus we have in these two neighboring formations two chapters of lunar history which, like the monuments of Egypt, tell the story of widely separated epochs. The row of still more completely submerged crater rings westward from Lubiniesky and Bullialdus show by their condition that the depth of the lava flood was 185probably greater in their vicinity than it was farther eastward. “Now look southward from Bullialdus, at a distance about twice as great as that of Lubiniesky and you will see another partially submerged ring, with a more serrated crest. The name of this is Kies. It is remarkable for the lofty mountain spur which sets off from its southern wall, and also for the fact that one of the bright streaks from Tycho—one of a parallel pair that I pointed out to you last evening—traverses its flat floor and continues on, broadening as it goes, to a deep crater ring which we have already noticed, southeast of Bullialdus. “South of Kies, at the edge of the Mare Nubium, is a lofty mountain range whose summits and slopes are very bright in the sunrise. At one point a great pass breaks through these mountains, leading to a sort of bay shut in on all sides by precipices and the walls of gigantic crater rings. The large crater ring at the eastern corner of this bay is Capuanus. The smaller ring on its western side with a conspicuous crater on its eastern wall is Cichus. Notice the fine shadow that Cichus casts, whose pointed edge is evidently due to the little crater on the wall. That ‘little’ crater is six miles across! The twin rings apparently terminating the mountain mass northeast of the bay are Mercator and Capuanus. 186Between these and Kies you perceive two short ranges of small mountains and then a kind of round swelling of the surface of the plain resembling a great mound. These formations are rare on the moon. They look like bubbles raised by imprisoned gases. The United States Geological Survey has discovered something similar in form, but infinitely inferior in magnitude, in the great mud bubbles that rise to the surface of the Gulf of Mexico off the mouth of the Mississippi River. But I do not mean to aver that the two phenomena are similar in origin. “Near the southern shore of the Mare Nubium appears a long, dark line which starts at the edge of a crater ring, crosses the southern arm of the ‘sea,’ evidently penetrates the bordering mountains, and reappears traversing the dark bay near its northern edge, cleaving both walls of a small crater ring in its way. “I should weary you, perhaps, with too much detail if I undertook to identify all of the prominent objects in this photograph. Returning to the southern shore of the Mare Nubium, I shall simply call your attention to the very large ring plain with terraced walls and a peak a little east of its center. This is Pitatus. An enormous ravine breaks through its eastern side and connects it with a smaller ring from which the dark line already mentioned starts. This dark line represents 187one of the most remarkable clefts on the moon. It looks as though the crust had been split asunder there over a distance of at least 150 miles. It bears some resemblance to the great cañon near Aristarchus and Herodotus, except that the latter is very tortuous and this is nearly straight.” “Have I not heard of something similar in connection with the California earthquake in 1906?” asked my friend. “No doubt you are thinking of the great ‘fault’ which geologists have discovered off the Pacific coast of North America. There is perhaps some resemblance between these phenomena. Pitatus, I may add, is 58 miles in diameter. You will observe how its southern wall has apparently been broken down by the deluge of lava which buried so many smaller rings in the Mare Nubium. If you will now turn your attention to the left-hand side of the photograph, somewhat above the center, you will perceive a very strange object, the so-called ‘Straight Wall.’ It lies just west of a large conical crater pit which has a much smaller pit near its western edge. You might easily mistake the ‘Straight Wall’ for an accidental mark in the photograph. It is not absolutely straight, and near its southern end it makes a slight turn eastward and terminates in a curious, branched mountain, whose most conspicuous 188part is crescent-shaped. The wall is about 65 miles in length and 500 feet in height. It is as perpendicular on its east face as the Palisades on the Hudson. It is not a ridge of hills at all, but a place where the level of the ground suddenly falls away. Approaching it from the west you would probably be unaware of its existence until you stood upon its verge. The dark line that we see in the photograph is the shadow cast by the wall upon the lower plain. In the lunar afternoon the appearance is changed, and the face of the cliff is seen bright with sunlight. This curious object has attracted the attention of students of the moon for generations, and many speculations were formerly indulged in concerning its possible artificial origin. It has sometimes been called the ‘Lunar Railroad.’ Manifestly, whatever else it may be, it is not artificial. The closest analogy perhaps is with what we were speaking of a little while ago, a geological fault, that is to say, a line in the crust of the planet where the rocky strata have been broken across and one side has dropped to a lower level. “The crater pit in the Mare Nubium, east of the ‘Straight Wall,’ is named Birt, and its twin, 75 miles farther east, is Nicollet. Look now at the hooked nose of your ‘dark woman.’ The huge wart upon it is a crater plain named Lassell. Between 189the lower end of the ‘Straight Wall’ and Lassell, and over the bridge of the ‘nose,’ a wedge-shaped mountain runs out into the mare. This is called the Promontorium Ænarium, and must have formed a magnificent outlook if ever a real ocean flowed at the foot of its cliffs. The ring with a crater on its wall below Lassell is Davy. You will note some very somber regions scattered over this part of the Mare Nubium. One of them forms the ‘dark woman’s’ eye, and just over it, like an eyebrow, is a curving range of hillocks, including some little craters. On the ‘cheek’—I am still utilizing the ‘dark woman’ as a kind of signboard—at the base of the ‘chin,’ appears a partly double range of large ring plains. The greatest of these, at the bottom, is named Fra Mauro, and you will notice within it a curious speckling of small craters. Adjoining Fra Mauro on the south are two intersecting rings, Barry being the name of the western and Bonpland that of the eastern one. The partially submerged ring is nameless, as far as I know, while the upper or southern member of the group, with a broad valley shut in between broken mountain walls opening out of its northern side, is Guerike. There is only one other object, on the extreme lower right-hand corner of the picture, to which I will ask your attention. It is a singular range of mountains thrown into a great loop 190at its northern end, and known as the Riphæan Mountains.” “It seems to me,” said my friend, putting her elbow on the table, and leaning her head a little wearily on her hand, “that there is a great sameness in these lunar scenes—always crater rings with or without central mountains, always peaks and ridges and chasms and black shadows. Truly variety is lacking.” “But what could you expect?” I replied. “Is it not enough to stimulate your curiosity that you are looking intimately into the details of a foreign world? When you go to Europe you see there mountains, plains, rivers, lakes, cities, people, absolutely identical in their main features with what you see in America. But you find them endlessly interesting because of their comparatively slight differences from similar things with which you are familiar, because of the great age of many of the objects to which your attention is directed, because of the long course of history which they represent, and principally, perhaps, because you are aware of the sensation of being far from home. It ought to be the same for you here on the moon. These things that we are looking upon belong to a globe suspended in space 239,000 miles from the earth. If the features of our globe are practically the same everywhere, differing only in the arrangement of their details, 191you should not be surprised at finding that nature does not vary from her rule of uniformity on the moon. “In the next photograph of the series,” I continued, “we have a marvelous specimen of the lunar landscapes. It is perhaps the most rugged region on the moon. It includes two objects of supreme interest, Tycho, the ‘Metropolitan Crater,’ and Clavius, the most remarkable of the ring plains. You will no doubt recognize Tycho at a glance. It is near the center of the picture. Like the last photograph this one represents an early morning scene. The western wall of Tycho throws a broad, irregular crescent of shadow into the cavernous interior, but all of the eastern, northern, and southern sides of the wall are illuminated on their inner faces. The central mountain group is emphasized by its black shadow. A little close inspection reveals the existence of the complicated system of terraces by which the walls drop from greater to lesser heights until the deep sunken floor is reached. The diameter of Tycho is 54 miles, and it is at least 17,000 feet deep, measured from the summits of the peaks that tower on both the eastern and the western sides of its wall. The vast system of bright streaks radiating from Tycho is not seen here, the time when the photograph was made being too near the sunrise on this part of the moon. The dish-shaped plains crowded around Tycho form a remarkable feature of this part of the lunar surface. It would be useless to mention them all by name, and I shall ask your attention only to some of the principal ones.” “Thank you for being so considerate,” said my friend, smiling. “I am sure that I should forget the names as fast as you mentioned them.” Tycho, Clavius, and their Surroundings. “Oh, I have no fault to find with your memory,” I replied. “I doubt if many selenographers could recall them without referring to a chart. Let us begin with the greatest of all, Clavius, which, you see, is near the top of the picture. I think I told you before that Clavius is more than 140 miles across. The great plain within the walls sinks 12,000 feet below the crest of the irregular ring, but the plateau outside, on the west, is almost level with the top of the ring. It is difficult to imagine a more wonderful or imposing spectacle than that which Clavius would present to a person approaching it from the western side, and arriving at about the time when this photograph was made, on the top of the wall. Notice how in one place the summit of a ridge, standing off on the inner side of the western wall, has come into the sunlight, and think of the frightful chasm that must yawn between. Clavius is so enormous that the two crater rings, each with a central mountain standing on its wall, seem very 193small in comparison with the giant that carries them, and yet they are 25 miles in diameter! Stretched out into a straight line, the tremendous wall of Clavius would form a range of towering mountains, extending as far as from Buffalo to New York. Look at the curved row of craters, the smallest larger than any on the earth, which runs across the interior. In addition to these there are many smaller craters and mountains standing on the vast sunken plain, some of them looking like mere pinholes, and yet all of really great size.” “Truly,” interrupted my listener, “the giantism—I think that is the word you employ—the giantism of the moon appalls me! How can I ever think, again, that the so-called great spectacles of nature on the earth are really great? You have destroyed my sense of proportion. Such immense things standing on a world so small as the moon—why it seems contrary to nature’s laws.” “I have already told you that the very smallness of the moon may be the underlying cause of the greatness of her surface features. And I may now add that if your imagined inhabitants ever existed they, too, may have been affected with ‘giantism.’ A man could be 36 feet tall on the moon and well proportioned at that, without losing anything in the way of activity.” 194“Indeed! You almost make me hope that there never were such inhabitants, for what beauty could there be in a human being as tall as a tree?” “Very little to our eyes, perhaps. You recall the impressions of Gulliver in the land of the Brobdingnags. However, they are not my inhabitants but yours, and if the law of gravitation says that they must have been twelve yards tall, then twelve yards tall they were. Take comfort, nevertheless, in the reflection that, after all, we cannot positively assert that gravitation alone governs the size of living beings on any particular world. We have microscopic creatures as well as whales and elephants on the earth, and human stature itself is very variable.” “Thank you, again. You have saved my lunarians. And now please tell me what is that frightful black chasm above Clavius?” “It is a ring plain named Blancanus, 50 miles in diameter, and exceedingly deep. It is so black and terrible because complete night yet reigns within it, except on the face of its eastern wall. It is really a magnificent formation when well lighted, but like so many other great things it suffers through its nearness to the overmastering Clavius. When Goliath was in the field his fellow Philistines cut but a sorry figure. Look at the marvelous region just below Blancanus 195and imagine yourself entangled in that labyrinth! You would have but a small chance for escape, I fancy.” “I am sure I should never have the heart to even try to get out of it. One might as well give up at once.” “Yes, you are probably right. But I will direct you to something not quite so frightful, although still very formidable in appearance. Still farther below you observe a huge ring plain whose eastern wall is brightly illuminated, while nearly all the interior plain, although comparatively dark in tone, lies in the sunshine. It is Longomontanus. I pointed it out to you in one of the smaller photographs. Longomontanus is 90 miles across and 13,000 or 14,000 feet deep, measured from its loftiest bordering peaks. The very irregular formation below it is Wilhelm I. It is remarkable for the mountainous character of its interior.” “For what William was it named?” “I do not know. We are now near the southern border of the region that we inspected in the preceding photograph. In the lower part of this picture you perceive some of the projecting bays of the Mare Nubium, and you can see again the remarkable cleft of which I spoke. The large ring near the bottom of the picture is Pitatus with its smaller neighbor Hesiodus. It is from the 196eastern side of the latter that the cleft apparently starts. Pitatus, you see, has a central peak, while Hesiodus, as if for the sake of contrast, possesses only a central crater pit. The ravine connecting the two is plainly visible. Toward the east you will recognize again Cichus, with its crater on the wall and its broad shadow with a sharp point, while still farther east, on the very edge of night, yawns Capuanus. The two walled plains above Pitatus are Gauricus on the left and Wurzelbauer on the right. The hexagonal shape of the former is very striking. This is a not uncommon phenomenon where the lunar volcanoes and rings are closely crowded, and it suggests the effect of mutual compression, like the cells of a honeycomb. Away over in the northwestern corner is a vast plain marked by a conspicuous crater ring which bears the startling name of Hell. It borrows its cognomen, however, from an astronomer, and not, as you might suppose, from Dante’s ‘Inferno.’ “Before quitting this photograph permit me to recall you to the neighborhood of Tycho and Clavius. To the left of a line joining them you will perceive a flat, oval plain with a much broken mountain ring. This is Maginus. Last evening while we were looking at one of the smaller photographs I pointed it out under a more favorable illumination, telling you at the same time that it 197possessed the peculiarity of almost completely disappearing at Full Moon. Already, although day has not advanced very far upon it, you observe that it has become relatively inconspicuous. This is a lesson in the curious effects of light and shadow in alternately revealing and concealing vast objects on the moon. You will notice that in many particulars Maginus resembles a reduced copy of Clavius. But the walls of Clavius are in a comparatively perfect condition while those of Maginus have apparently crumbled and fallen, destroyed by forces of whose nature we can only form guesses. Evidently the destruction has not been wrought, like that of some of the rings in the Mare Nubium, by an inundation of liquid rock from beneath the crust. It resembles the effects of the ‘weathering’ which gradually brings down the mountains of the earth, but if such agencies ever acted upon the moon, then it must have had an atmosphere and an abundance of water. In any event, here before us is another page of lunar chronology. Maginus is evidently far older than Clavius; Clavius is older than the craters standing on its own walls.” We now took up the third of the large photographs representing a part of the southwestern quarter of the moon, more extraordinary for its mountains, plateaus, and extinct volcanoes than the famous southwestern region of the United States. 198“Here is something that you will surely recognize without any assistance,” I said. “In the lower left-hand corner of the picture is the great three-link chain of crater rings, of which Theophilus is the principal and most perfect member.” “Oh, I recall them well,” replied my friend. “And yet they do not appear to me exactly the same as when I saw them before.” The Great Southwest on the Moon. “One reason for that is because this photograph represents them on a much larger scale, and with infinitely more detail. Another reason is that now we are looking at them in the lunar afternoon instead of the lunar morning. We are going to see them represented on a still larger scale, presently, but there are many things in this picture well worthy of study. Advancing from the west, the line of night has fallen over the extreme eastern border of the Mare Nectaris, and the shadows thrown by the setting sun point westward. Observe how beautifully the brightly illuminated terraces and mighty cliffs of the western wall of Theophilus contrast with the black shadow that projects over half of the interior from the sharp verge of the eastern wall. The complicated central mountain is particularly well shown. The loftiest peak of this mountain mass, which covers 300 square miles, is 6,000 feet in height. You will see its shadow reaching the foot of the western wall. Theophilus is 64 miles in 199diameter, ten miles more than Tycho, and it is deeper than Tycho, the floor sinking 18,000 feet below the top of the highest point on the western wall. If it were the focus of a similar ray system it would deserve to be called the ‘Metropolitan Crater’ rather than Tycho. Plainly, Theophilus was formed later than its neighbor Cyrillus, because the southwestern wall of the latter has been destroyed to make room for the perfect ring of Theophilus. “The interior of Cyrillus, you will observe, is very different from that of Theophilus. The floor is more irregular and mountainous. The wall, also, is much more complex than that of Theophilus. The broken state of the wall in itself is an indication of the greater age of Cyrillus. On the south an enormous pass in the wall of Cyrillus leads out upon a mountain-edged plateau which continues to the wall of the third of the great rings, Catharina. This formation seems to be of about the same age as Cyrillus, possibly somewhat older. Its wall is more broken and worn down, and the northern third of the inclosure is occupied by the wreck of a large ring. Observe the curious row of relatively small craters, with low mountain ranges paralleling them, which begins at the southwestern corner of Cyrillus and runs, with interruptions, for 150 miles or more. South of this is a broad valley with small craters 200on its bottom, and then comes an elongated mountainous region with a conspicuous crater in its center, beyond which appears another valley, which passes round the east side of Catharina, where it is divided in the center by a short range of hills. The southeastern side of this valley is bounded by the grand cliffs of the Altai Mountains, which continue on until they encounter the eastern wall of the great ring of Piccolomini, whose interior appears entirely dark in the picture, only a few peaks on the wall indicating the outlines of the ring. The serrated shadow of these mountains, thrown westward by the setting sun, forms one of the most striking features of the photograph. The northeastern end of the chain also terminates at a smaller ring named Tacitus. You see that Riccioli was rather cosmopolitan in his tastes, since he has placed the name of a Roman historian also on the moon. Beginning at a point on the crest of the Altai range, south of Tacitus, is a very remarkable chain of small craters, which extends eastward to the southern side of a beautiful ring plain with a white spot in the center. This ring is named Abulfeda. The chain of small craters or pits to which I have referred continues, though much less conspicuous, across the valley that lies northwest of the Altais. It is a very curious phenomenon, and recalls the theory advocated by W. K. Gilbert, the American 201geologist, that the moon’s craters were formed not by volcanic eruptions but by the impact of gigantic meteorites falling upon the moon, and originating, perhaps, in the destruction of a ring which formerly surrounded the earth, somewhat as the planet Saturn is surrounded by rings of meteoric bodies, which may eventually be precipitated upon its surface. The moon is more or less pitted with craterlets in all quarters, but there are places where they particularly abound. On inspecting this photograph carefully you will perceive several rows of much larger pits, two or three of them in the upper half of the picture, and one below the center, crossing the little chain of pits that I have just mentioned. The linear arrangement of some of the ring plains is also very striking. In regard to the theory that the lunar craters were formed by the impact of falling masses I may mention that two distinguished French students of the moon, Messrs. Loewy and Puiseux, have lately expressed the opinion that all of the features of the lunar surface are most readily explicable as the result of causes similar to those which have produced the topography of the earth. If that is so there is no need for us to invoke the agency of meteorites in pitting the surface of the moon. South of the Altai Mountains you will see a singular collocation of ring plains and craters which somewhat resemble in their 202arrangement Theophilus and its neighbors. First comes a large sunken plain just above the mountains. In fact the Altai range constitutes the northwestern wall of this formation, which you may recognize by a conspicuous oval crater near its upper side. Above this broken ring appear three other smaller ones, grouped at the corners of a triangle. The one on the right, with a central pit and a small ring plain on the inside of its western wall, is called Zagut. Its close neighbor on the west with most of its interior in shadow, is Lindenau, remarkable for its depth. The most southerly and largest of the group, with four or five large crater pits forming a curved row across its interior, is named Rabbi Levi. Starting from the east side of Rabbi Levi there is a long row of similar craters rather larger than those in its interior, which runs eastward almost to the edge of the photograph. North of these, parallel with and, in some instances, touching the crater pits, is an equally remarkable row of flat, smooth, walled valleys, which seem to overlap one another on their western sides, and which increase in size the farther east they go. The largest of these, with a very irregular wall, and having a smaller ring with a central peak apparently attached to its northern side, is Gemma Frisius.” My friend had listened to me in silence for a 203long time, following my finger as it pointed out the various objects on the photograph, but now she interrupted again: “You were pleased to compliment my memory a little while ago,” she said, “but do you really think that I can ever recall all this that you have been saying, with theories about huge flying stones hitting the moon, and a string of the strangest names that I have ever heard applied to objects that are no less bizarre?” “Pardon me,” I replied, “but you will remember more than you think you will. The very oddity of these Hebraic and Arabic names will serve to fix them in your memory, so that you will at least recognize them when you see them again. Those curious objects will also come before your mind’s eye whenever you think of, or look at, the moon. Trust me when I tell you that you are forming a better acquaintance with selenography than you are aware of. As to the theory that I have mentioned, what can appeal more powerfully to the imagination than the idea of the moon being bombarded by the fragments of an immense ring falling from the sky? The fact that men of science have believed such a thing possible ought to form a strong appeal to your lively fancy. In any case, I am disposed to be merciless just now, like a man who has found a patient listener to his hobby, and I am going to trouble you with a few more odd names and singular facts.” 204“Well,” she replied, with a sigh, ending with a smile, “go on. After all I believe I am really interested.” “I am sure you are, for who could fail to be interested by things so remarkable in themselves, and so vastly beyond all human experience, as those that this photograph shows? We stopped at Gemma Frisius. Let us use that for a new starting point. A considerable distance south, say about a hundred miles, is an old friend of ours, Maurolycus. It is the large ring plain, with another half obliterated, on its southern side, in the upper part of the picture. Notice the row of wrecked rings, beginning at a great crater on its northeast wall and running westward. The broad, flat plain directly east of Maurolycus is Stöfler, whose name you will also recall. I shall not trouble you with the names of all the rings south of Stöfler and Maurolycus, but simply ask you to observe that they form a winding row which leads to a very grand ring almost entirely buried in night, the inside of its western wall alone being bright with sunshine. This wall, and some mountain peaks near it, resemble brilliant islands lying in the edge of the Cimmerian ocean whose ethereal waves wash the broken coast of the moon. Follow the ragged sunset line downward, and all along you will see these islands of light in the darkness; tips of mountains still shining 205while the sun has set upon all the valleys around, somewhat as you have seen the snowy top of Mont Blanc and the pinnacles of its attendant giants glowing after the shades of night have fallen deep upon Chamounix. “Look next, if you please, at the right-hand side of the photograph. Somewhat above the center, three conspicuous dish-shaped ring plains are seen, two near together, the third farther away toward the left and downward. The largest of these is Aliacensis, its near neighbor is Werner, and the third is Apianus. They are from 40 to 50 miles in diameter. Still lower, and nearer the middle line of the picture, is a row of four or five ring plains, varying from 30 to 40 miles in diameter. The uppermost, or most southerly of these is double, or, in fact, partly triple, for the lower member of the pair has a broken plain attached to its southeastern side. This one, with a small central peak, is named Abenezra. Its close neighbor on the southwest is Azophi. You notice the singularity of the names. The next one below, with a small crater on its east side, is Geber. Then comes Almamon, and finally, largest of all, Abulfeda, which I pointed out to you as marking the end of the curious row of little crater pits, running eastward from the Altai Mountains. There is just one other formation to which I wish to call your attention 206in this remarkable photograph, and then we shall turn to the next in the series. West of Abenezra and Azophi, about half way to the Altai Mountains, you will notice a very irregular depression with three strongly marked craters within it. This bears the name of Sacrobosco, an old-time astronomer. Its eastern wall with its shadow looks like an elongated letter W standing on end. Sacrobosco and its surroundings constitute one of the most intricate regions on the moon, high plateaus alternating with great sunken valleys, rings, craters, and crater pits. The wall of Sacrobosco is extremely irregular in height, shooting up in some places with peaks of 12,000 feet elevation, and sinking in others almost to the level of the surrounding plateaus.” We now took up the next photograph representing Theophilus and its companions on a greatly enlarged scale. My friend uttered a cry of astonishment upon seeing it. “Dear me,” she exclaimed, “the moon becomes more terrible every moment! Positively, I almost shrink from the sight.” The Giant Ring Mountains, Theophilus and its Neighbors. “Yes,” I assented, “it surely is terrible here. In a little while, however, I shall show you a lunar scene of surpassing beauty. But study this spectacle with an inquiring mind and you will find that it, too, has its attractions. You are now looking upon Theophilus, Cyrillus, Catharina, and 207the surrounding region as the astronomer sees them with the most powerful telescopes. Indeed, with the telescope he sees the details more sharply than they are visible here, for the best photographs still lack something in distinctness. The illumination when this picture was taken was practically the same as in the last that we examined, but the magnification is much greater. Look, now, at the central mountain in Theophilus. Its great buttresses cast their shadows into profound ravines and chasms, imparting to it a most singular outline. Observe the tooth-shaped shadows of its two principal peaks, thrown westward across the floor, while the broad shadow of the western wall emphasizes the immense depth of the depression. The glare of the afternoon sun on the cliffs of the inner side of the eastern wall is so brilliant that the details are obscured. But the surface of the moon outside, particularly toward the north and the west, is beautifully brought out with all its wonderful modulations and irregularities. Judging by appearances, those who hold that Theophilus and similar formations, notwithstanding their enormous magnitude, are really of volcanic origin, have the strongest reasons for their opinions. Immense flows of lava seem to have taken place on all sides of the great ring, entering the Mare Nectaris on the west. Notice the huge mountain fold 208which runs from the parallel ridges on the southwestern side of Theophilus to the crater ring Beaumont, lying west of Catharina. Observe, also, the complicated form of the wall dividing Theophilus and Cyrillus. Two deep ravines, shown by the shadows that fill them, cross one another like the arms of a flat letter X. One of these ravines turns northward along the wall and re-enters Theophilus, while the other continues for a long distance within the western side of Cyrillus. I cannot imagine a more interesting or a more stupendous excursion for a geologist, a mountaineer, or a seeker after wonderful and sublime aspects of nature, than a climb around the crest of the wall of Theophilus—if indeed such a climb can be regarded as humanly possible. “Now, again, I am reminded of what I once told you about the amazing contrasts of light and darkness, and of heat and cold, upon the moon. Suppose yourself standing on the verge of the eastern wall of Theophilus where the edge seems sharpest, and looking down into the abyss at your feet. The sun’s rays would be unbearably hot where they touched your face and hands, but if you let yourself down a little way into the blackness beneath you would not only pass instantly into night, but you would shiver and shrink with cold so frightful that no winter experience that you have ever had could give an idea of its intensity. 209From that point of observation you would look across a chasm of inky darkness, 25 miles broad, and see, towering up from the illuminated plain afar off, with their summits more than two miles below your level, the brilliant group of the central peaks, while behind them the crest of the western wall would appear like a bright line on the horizon 60 miles away. Changing your place to one of the peaks on the dividing wall you would look down into Theophilus on one side and Cyrillus on the other. Then upon lifting your eyes to the black, airless sky you would see the stars sparkling on all hands, and, hanging in the heavens like a portentous, strangely colored moon many times larger than the disk of the sun, would appear the mottled orb of the earth. The terrific nature of the scenery around you, the meeting of day and night at your feet, and the incredible blending together of their characteristic aspects in the sky above you, the startling magnitude of the suspended earth—all these things combined would make you feel as if you were not only in another world but in another universe.” “I no longer wish to visit the moon,” interrupted my friend, shaking her head. “Not if you were assured of a safe return?” “No, it would upset my mind. I am certain that I should go crazy in such a world where everything seems to be topsy-turvy.” 210“Wait until we arrive at the ‘Sea of Serenity’ once more, and perhaps you will think better of it. Notwithstanding the increased magnification, the details in Cyrillus and Catharina are hardly better seen in this photograph than in its predecessor, but the increase of size is very effective in emphasizing some of the features of the surrounding district. Cyrillus is seen to have a decided hexagonal outline, and west of its southern corner is an exceedingly curious formation, approaching closely to a square shape. The wall is illuminated within on all four sides, and out of the midst of the lozenge-shaped shadow resting over the bottom of the included valley, rises a mountain which, like the walls, is bright with sunshine. On the southwest a semicircular ridge runs out into the darkness, its top brightly illuminated. The general effect of the entire formation is fantastic. And could you imagine a wilder scene than that presented by the elongated mountain mass, which starts from the southwestern side of Cyrillus, skirts the border of Catharina, and continues on along the northwestern side of the broad valley in the upper part of the picture? See how it has, apparently, been rent apart by tremendous forces and torn by volcanic outbursts, which have left yawning craters everywhere. Even the valley itself seems to be simply a chain of wrecked crater rings of vast size, the cross 211walls having nearly disappeared. Observe, too, the immense number of crater pits of all sizes scattered everywhere, both inside the ring plains (Theophilus alone having few of them) and over the surrounding country. We shall see a still more remarkable example of this pitting of the lunar surface in the neighborhood of Copernicus, which is the chief object in the next photograph that we take up.” We came now to the large picture of Copernicus, and my friend took it in her hands to examine it. “It is a marvelous thing to look upon,” she said, “but it doesn’t frighten me as Theophilus did.” “No, Copernicus is rather sublime than terrifying in aspect. Its comparatively lone situation, with the Mare Nubium, the Oceanus Procellarum and the Mare Imbrium surrounding it on all sides with their broad, level expanses, gives it an appearance of solitary grandeur belonging to no other single formation on the moon. ‘The monarch of the lunar ring mountains,’ Mr. Elger has termed it. First let me tell you the principal facts known about Copernicus. It is 56 miles in diameter, two miles more than Tycho, and eight less than Theophilus. It is not as deep as either of those formations, the highest points on its walls being 12,000 feet. But the walls are more 212uniform in height than is usual with so extensive a ring. They are very steep on the inside, especially near the top, where their slope has been estimated by Neison at from 50° to 60°. To a person standing on their verge they would seem almost perpendicular. The central mountain consists of five principal peaks. The outer slopes of the ring are also steep, but its maximum height above the surrounding surface does not exceed 3,000 or 4,000 feet, so that Copernicus, like the other great ring mountains, is, in reality, a vast sink, encircled with a mountain ridge. You will note that Copernicus clearly exhibits the tendency to a hexagonal form which we have observed elsewhere, although it stands alone with no other great rings pressing against its walls. Curiously enough the form of Copernicus is very closely repeated in the small crater ring Gay Lussac, situated in the mountains on the lower (north) side. This picture, I should remark, unlike the last two preceding it, was taken near lunar sunrise, and accordingly the light comes from the west. This is the best illumination for studying Copernicus and its vicinity. Of all the great ring plains Copernicus perhaps gives the most striking testimony in favor of the view of those who hold that the lunar volcanoes were once the actual centers of volcanic action, resembling the volcanoes of the earth in the ejection 213of vapors, ashes, stones, and streams of lava. The slopes around Copernicus for many miles look as though they had been covered with lava and pitted with minor craters such as appear on the shoulders and in the vicinity of many of our volcanoes, while the appearance of the great ring does not contradict the theory of Nasmyth and Carpenter, which I have previously mentioned, that it was built up by ejections from a central crater now more or less completely filled. As I have already told you the lunar volcanoes differ essentially from those of the earth in that their central depressions lie deep beneath the level of the surrounding surface of the moon. This is strikingly true of Copernicus, and it is a result that might have been foreseen from the enormous size of the craters. A mountain of sufficient magnitude to carry the vast cup of Copernicus on its head, as Vesuvius, Etna, Cotopaxi, and Popocatepetl carry their craters, could not stand even on the moon. Observe the generally radial arrangement of the lines about Copernicus, recalling the similar arrangement of lava flows about terrestrial volcanoes. Some of these lines, as you will see, consist of long rows of pits. Similar phenomena may be seen along the lava streams that we are familiar with on our planet, where small craters break forth one after another. A striking example of this arrangement is visible in the 214photograph on the northeastern slope leading up toward the Copernicus ring. But you will also see many very remarkable rows of pits in the vicinity of Copernicus which are not radial in arrangement with respect to the ring. The most conspicuous of these is on the northwestern side, about half way between Copernicus and the ring of Eratosthenes, which standing at the upper end of the chain of the Apennines appears at the left-hand edge of the picture. There are hundreds, probably thousands, of these pits on all sides of Copernicus. “One of the explanations that has been suggested for them is that they were produced by the fall of enormous volcanic bombs thrown from Copernicus when it was in eruption. I wish merely to mention this idea without comment. It however calls up another interesting theory, which has not met with much acceptance, to the effect that such lunar volcanoes as Copernicus may have been powerful enough to eject masses of lava and rocks with a velocity sufficient to enable them to escape from the attraction of the moon, whereupon they became meteorites traveling in independent orbits around the sun. Some of these, the theory suggests, may be among those that have fallen upon the earth. A velocity of a mile and a half per second would be sufficient to overcome the gravitation of the moon. That is only 215three or four times the initial velocity which some modern guns are capable of imparting to their projectiles.” “I am sorry,” explained my friend, “that you seem to attach little importance to so interesting a theory. It stirs my imagination to think of the moon sending bits of herself back to her mother planet. For my part, the theory does not seem to be any harder to believe than that of your Professor Darwin that the whole moon was thrown off from the earth. Besides, it intensifies my appreciation of the grandeur of Copernicus when I am told that that great volcano could once bombard the earth across—what is it, 240,000 miles?—of space.” “As you always choose the most picturesque theories to rest your belief upon, I shall not complain if you accept the lunar volcano theory of meteorites,” I replied. “But, for the present, we have done with it, and I am now going to ask you to inspect the photograph for other interesting objects. East and north of the great ring you will see an extensive mass of mountains. Those on the north, with immense buttresses projecting into the Mare Imbrium, are the lunar Carpathians. I have already directed your attention to a comparatively small crater ring which resembles a reduced copy of Copernicus, situated in these mountains at the head of a bay which penetrates 216southward between high ridges, for about 30 miles. This crater is named Gay Lussac. It has a small deep neighbor on the southwest. West of Gay Lussac the Carpathians gradually dwindle away until they sink to the level of the plain. Toward the east they project in several bold headlands, terminating with towering peaks into the ‘sea.’ Lying off the point of the headland on the western side of the bay that leads to Gay Lussac you will perceive two charming little craters, almost perfect twins. Much farther toward the north and west is a larger crater, more than half of whose interior is black with shadow. This is Pytheas. Its lonely situation is very striking, but upon close inspection you will notice that a low range of hills appears to connect it with the twin craters that I have just pointed out. This range of hills, lying on the ‘sea’ bottom, is curiously forked, the other branch leading to a pair of small peaks in the ‘sea,’ which possess no craters. The little crater east of Pytheas is also a beautiful object in the picture. “Near the eastern end of the Carpathians the mountains make their greatest advance into the Mare Imbrium, leaving a large square-cornered bay on the west. From this point they turn southward, forming a complicated mass of peaks and ridges interspersed with craters and pits. 217These mountains east of Copernicus are among the most singular upon the moon, for they inclose a group of irregular-shaped plains, the walls of which consist of immense, more or less separate, masses. Look at the one nearest to Copernicus, which has somewhat the form of a starfish, and observe how curiously its southern border reflects, on a smaller scale, the forms characteristic of the headlands and bays along the shore of the Mare Imbrium below. “Above Copernicus you see a large crater ring more than half in shadow, with a plain of an irregular hexagonal shape, northwest of it. The large ring is named Reinhold. A broken mass of mountains extends from its southern side far into the Mare Nubium. In the upper right-hand corner of the picture is another large ring called Landsberg. In the upper left-hand corner you see a roughly hexagonal ring plain, level on the interior, named Gambart. Mountains break the level of the mare both south and north of Gambart. Those on the north are remarkable for the darkness of the surface, especially in the northwestern part. “Almost directly west of Copernicus lies an exceedingly singular object. It is a part of the underworld of the moon, the buried moon, which was covered up ages ago by that immense outgush of lava of which I have so often spoken. Once 218evidently it was a ring larger than Eratosthenes. Now, only its outlines can be traced, the whole immense depression of the interior and the surrounding walls to their very top having been covered up. It is pitted and surrounded with little craters of a later date. I have already told you that Eratosthenes, the ring at the left-hand edge of the photograph, marks the termination of the great range of the lunar Apennines. But these mountains seem to be continued beyond Eratosthenes in two short branches, one turning eastward toward the Carpathians, and the other reaching to the highest part of the buried wall of the submerged ring that we have been talking about and which bears the name of Stadius. You will be interested in knowing that southwest of Stadius, but off the edge of the picture, there is a place in which low hills and ridges abound, where the German astronomer Schröter imagined that he had discovered a lunar city! His mistake was, perhaps, natural, considering the slight power of his telescope and the strangely regular arrangement of the lines of hills which he mistook for streets.” “I regret that he was deceived.” Two Great Lunar “Seas” The Mare Serenitatis and a Part of the Mare Imbrium. “So do I. We shall now leave Copernicus and its marvelous surroundings, and turn to the last photograph in our series, representing the Mare Serenitatis in its full extent, and a large 219part of the Mare Imbrium. Is it not a beautiful picture?” “It is, indeed, but so strange!” “There is, I believe, nothing in the lunar world that would not seem strange to our eyes. To understand just what this picture means you should imagine yourself floating in an airship at an immense height above the surface of the moon. The Mare Serenitatis you will recognize as the great oval plain occupying the upper left-hand part of the photograph. It is entirely encircled by mountains except in three places—at its eastern end, where a broad strait opens between the Apennines on the south and the Caucasus on the north, leading into the Mare Imbrium; on the northwest, where another strait opens into the Lacus Somniorum, the ‘Lake of the Sleepers,’ or ‘The Dreamers,’ and on the southwest, where a third strait with a conspicuous crater in its center leads into the Mare Tranquillitatis. The Mare Serenitatis is 430 miles long and nearly as broad, and covers an area of about 125,000 square miles. A great many details are visible on its floor. Even if it were covered with water we might see these, for, as you have probably heard, the bottom of deep lakes is visible when one looks down upon them from a great height. The surface of water, however, at certain angles of view and of illumination, would produce flashes and glares of 220light which are never seen on this vast lunar plain.” “Oh, but it must once have been a sea,” said my friend, poring over the photograph. “I cannot give up that idea. It gives the interest of life to the moon, if not now at least in the past.” “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 221southern 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 222situation 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, 223off 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 224to 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 225ring 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 226by 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 227illumination 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?” 228“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 229quantities 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 230planet’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 231to 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 232Cape 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 233indications 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 234surprising 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 235you 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 236‘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.” About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Garrett Putman Serviss (2021). The Moon: A Popular Treatise. Urbana, Illinois: Project Gutenberg. Retrieved October 2022 https://www.gutenberg.org/cache/epub/66510/pg66510-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org , located at https://www.gutenberg.org/policy/license.html .