Chapter VI: Introduction (4)

“With your great telescope you could probably render possible many discoveries at present beyond our reach. But the mightiest telescope that you could make would enable no one to _see_ inhabitants on the moon, even if they existed.”

“Not if it magnified the moon a million times?”

“No, for optical imperfections and the disturbances to clear vision produced by our atmosphere would absolutely prohibit the use of any such magnification. And even supposing that one could use a magnifying power of 1,000,000 diameters in viewing the moon, how near do you think that would place us to the lunar surface? It would still appear to be more than a quarter of a mile away.”

“That is not much. I am sure I can see people at that distance.”

“Oh, yes, but the distinctness of view would be nothing like so great as if you were looking at the same objects on the earth. Still, if we could obviate the atmospheric and other difficulties, a magnifying power of one million would certainly enable us to discover the works of the moon’s inhabitants—their houses, their fields, their plantations, their great establishments of art and industry. But I assure you that a telescope of such power is a mere dream. It could never be constructed without some fundamentally new and unheard-of discovery in optics. We shall do better to turn once more to our photographs which, at least, have no deceptions. Dropping No. 12, we shall take up No. 13, which brings us practically to the Full Moon phase. The moon’s age at the time this photograph was made was nearly fourteen and one-half days. You see that its whole eastward face is now lying in the sunlight. The march of day across its surface has been completed, and on the western edge of the moon the sun is about to set, while on the eastern edge it is just rising. Among the new things that have come into view is a conspicuous dark oval, shaped like Plato, but very much larger, near the eastern edge. This is a walled plain named Grimaldi, and it enjoys the distinction of being the darkest on the moon. Near it on the northeast and consequently closer to the limb is another walled plain, which I promised some time ago to point out to you because it bears the name of the astronomer Riccioli, the great bestower of names on the moon, and upon whose lack of imagination you have so severely commented. But, as you have already learned, the time of Full Moon is not the best for studying the mountains and rings, because then the light strikes too nearly vertical upon them and they cast no shadows. But it is the best time for seeing the broad general features of the lunar surface. Turn the picture upside down again, thus bringing the disk into its natural position as seen with the naked eye, and this photograph shows the moon very much as it appears with a small pocket telescope, or with a powerful binocular. The new prism binoculars that have come into use within the past few years are excellent for general views of the moon. Their defining powers are superb, and one who has never seen the moon with such a glass is always greatly surprised and delighted with the view which it affords. You see now that Tycho forms a blazing brooch, resting on the Maiden’s neck, while its rays extend across her profile, and the long one lying over the _Mare Serenitatis_ bears some resemblance to a pin displayed in her hair, with the crater ring, Menelaus, glittering at its lower end. The other bright point, to the left of Menelaus (we will henceforth keep the picture reversed), is a ring mountain named Manilius. After the detailed study which we have given to the various ‘seas’ and formations you should be able to recognize them with the picture in this position, and I wish that you should do so because, as I have just remarked, this is the position of the Full Moon as it is always seen with the naked eye or with a simple binocular, for the latter does not reverse it, as does a telescope. The western edge is now at the right hand, and the north at the top. All the _mares_ are clearly visible. On the right the _Mare Crisium_, the _Mare Fœcunditatis_, the _Mare Nectaris_ and the _Mare Tranquillitatis_; in the center, above, the _Mare Serenitatis_; on the left the _Mare Imbrium_, the _Mare Vaporum_, the _Mare Nubium_, the _Mare Humorum_, and the _Oceanus Procellarum_. The two bright spots on the right, lower than the _Mare Fœcunditatis_, are Petavius and a neighboring ring. Vendelinus forms a less brilliant spot at the western edge of an extension of the _Mare Fœcunditatis_, and Langrenus is distinctly seen on the western shore of the main body of that _mare_. Proclus and the remarkable diamond of the ‘Marsh of a Dream’ are very plain just under the large oval of the _Mare Crisium_. The mountains and cliffs encircling the _Mare Imbrium_ on the west, north, and east you will recognize at a glance. The dark Plato is conspicuous in the lighter mountainous area north of this ‘sea,’ and the semicircle of the ‘Bay of Rainbows’ is sharply defined. Farther north is the long, dark _Mare Frigoris_, whose eastern end merges into the broad _Oceanus Procellarum_. Aristarchus appears as a very bright point in this ‘ocean,’ and far to the right of Aristarchus, toward the center of the disk, Copernicus, with its splatter of irregular rays, is conspicuous. Following the eastern limb round toward the south we see again the dark oval of Grimaldi, beyond which the bright mountainous region broadens as we approach the South Pole.

NO. 13. SEPTEMBER 5, 1903; MOON’S AGE 14.40 DAYS.
]

“There is just one other thing on which I should like to dwell a little while we have the Full Moon before us. I have already referred to it once or twice—I mean the system of bright rays or bands radiating from Tycho. These rays, as I have told you, are among the greatest mysteries of the moon. Their appearance is so singular and, if I may so describe it, unnatural, that when the first photographs of the Full Moon were published, some persons actually thought that they were being imposed upon. They imagined that the photographer had indulged in a practical joke, by photographing a peeled orange and dubbing it ‘the moon.’ The mysterious rays do not start from the central mountain of Tycho, nor even from the ring itself, but from a considerable distance outside the ring. Nevertheless, Tycho is manifestly the center from which they arise. It looks as though some irresistible force had been focused at that point—a force that split the moon along a hundred radiating lines. This is, in substance, the theory of the English selenographer Nasmyth. He supposed that, the lunar globe being burst by internal stress, molten lava welled up and filled the cracks. After solidifying this lava possessed a lighter color and greater reflecting power than its surroundings and thus gave rise to the appearance of long bands.”

“Really, your moon history seems to me to be made up of extremely tragical chapters. But I am content as long as you put all these terrific events sufficiently far in the past to leave time for the moon to have enjoyed a different kind of history since they occurred.”

“But,” I said, “even if I grant what you wish, you must admit that the greatest tragedy of all succeeded.”

“What do you mean?”

“I mean simply that your imagined lunar age of gold, when the moon was full of animated existences and beautiful scenes, has also become a thing of the past; and what geological cataclysm can be compared in tragic intensity with the disappearance of a world of life?”

“But that disappearance was gradual, was it not?”

“Very likely it was, if it depended upon the slow withdrawal of the atmosphere and water.”

“Good! Then again I am fairly well content, for all things must have an end. The most beautiful life finally merges into old age and death. I think I have read that some of your _savants_ predict that the earth will not always be a living world. All that I ask is that you leave room somewhere in your lunar history for an age of life on the moon.”

“Very well then. As I have told you several times, Science does not positively forbid you to picture such an age if you will. She only says that she cannot find the evidences of its existence. Still, as we are going to see later, there are those who think that they can perceive indications of some simple forms of life on the moon even now. I will grant you that in the past these may have been more numerous and more highly organized.”

By this time the afternoon had waned and the trees were lengthening their shadows upon the lawns of the park.

“Perhaps,” I said, “we had better postpone an examination of the remaining photographs of the series exhibiting the moon’s various phases until after dinner. They will show very well in the light of the electric chandelier. I have but a few words to add concerning the rays of Tycho. The opinion of Nasmyth concerning their mode of origin has not been universally accepted. Prof. William H. Pickering, for instance, has suggested that the rays are formed by some whitish deposit from the emanations blown out of comparatively minute craters lying in rows. He supposes large quantities of gas and steam given forth from craters surrounding the rim of Tycho, and, in consequence of these gases and vapors being absorbed and condensed in more distant regions, a wind constantly blowing away from Tycho and distributing the white deposit in windrows. A similar explanation has been applied to the shorter and more irregular systems of rays surrounding Copernicus, and a few other ring mountains.”

“I prefer the Nasmyth hypothesis,” said my friend, as we rose and took the path to the house. “It is, to be sure, more gigantically tragic, but then it is simpler and more easily comprehended.”

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III

FULL MOON TO OLD MOON

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III

FULL MOON TO OLD MOON

AFTER dinner, in the brilliantly lighted drawing-room, we once more spread out the photographs on a table.

“This time,” I said, taking up No. 14, “we are going to watch the advance of night over the moon. Before, it was the march of sunrise that we followed. Both begin at the same place, the western edge or limb of the moon. Comparing this photograph, which was taken when the moon was about fifteen and two-third days old, with No. 13, taken when the moon’s age was more than a day less, you perceive, at a glance, wherein the chief difference lies. In No. 13 sunrise is just reaching the eastern limb; in No. 14 sunset has begun at the western limb. Having watched day sweep across the lunar world, we shall now see night following on its track. West of the _Mare Crisium_ and the _Mare Fœcunditatis_, which I expect you to recognize on sight by this time, darkness has already fallen, and the edge of the moon in that direction is invisible. The long, cold night of a fortnight’s duration has begun its reign there. The setting sun illuminates the western wall of the ring mountain Langrenus, which you will remember was one of the first notable formations of the kind that we saw emerging in the lunar morning. But then it was its eastern wall that was most conspicuous in the increasing sunlight. For the selenographer the difference of aspect presented by the various objects of the lunar world when seen first under morning and then under evening illumination is extremely interesting and important. Many details not readily seen, or not visible at all, in the one case become conspicuous in the other. But it is only close along the line where night is advancing that notable changes are to be seen. Over the general surface of the moon there is not yet any perceptible change, because the sunshine still falls nearly vertical upon it. Tycho’s rays are as conspicuous as ever. Aristarchus, away over on the eastern side, is, if possible, brighter than before, and the three small dark ovals, Endymion a little west of the north (or lower) point, Plato at the edge of the _Mare Imbrium_, and Grimaldi near the bright eastern limb, are all conspicuous.”

NO. 14. AUGUST 26, 1904; MOON’S AGE 15.65 DAYS.
]

“But look!” exclaimed my friend, putting her finger upon the photograph. “Here is something that you have not mentioned at all. I believe that I have made a discovery, although you probably will not accept it as a scientific one. I see here a dark woman in the moon.”

“I confess,” I replied, “that I am not acquainted with her, and do not even see her. Please point her out to me.”

“She appears in profile, like the brilliant Moon Maiden, but is not so much of a beauty. In fact I begin to suspect that she is the ‘Old Woman in the Moon,’ that I have often heard of.”

“Positively I do not see her.”

“Then I will try to recall some of the names that you have been telling me in order to indicate where you should. She faces west and occupies most of the eastern half of the disk. Her head is under Tycho, toward the northeast, I suppose you would say. The bright double ray that you pointed out in one of the preceding pictures lies across the top of her head and over her ear. Her face seems to be formed by a part of the _Mare Nubium_—you observe how well I have learned your selenographical terms—and her hooked nose is composed of a kind of bay, projecting into the bright part below Tycho. Her front hair is banged, and the _Mare Humorum_ constitutes her chignon. She has a short neck, and a humped back, consisting of the _Oceanus Procellarum_. Copernicus resembles a starry badge that she wears on her breast, and Aristarchus glitters on the inner side of the elbow of her long arm. The _Mare Imbrium_ seems to be a sort of round, bulky object that she carries on her knee, and she appears to be gazing with intentness in the direction of the _Mare Tranquillitatis_.”

“Ah, yes,” I said, laughing, “I see her plainly enough now. I really cannot say that your discovery is likely to be recorded in astronomical annals, but nevertheless I congratulate you upon having made it, if only for the reason that henceforth you can never forget the names and locations of the lunar ‘seas’ and other objects that you have been compelled to remember in pointing out your ‘dark woman.’ In truth, her features are almost as well marked as those of the Moon Maiden, but you will hardly be able to find her again, except in a photograph, or with the aid of a telescope, because you must recollect that this picture shows the moon reversed top for bottom as compared with her appearance to the naked eye, or with an opera glass. But please look again at the objects along the western edge, for we are about to turn our attention to photograph No. 15 in which this will be no longer visible. You must say ‘good-by,’ or rather ‘good night,’ to the _Mare Crisium_ and the _Mare Fœcunditatis_; for you will see them no more, until another lunar day has dawned.”

We next picked up photograph No. 15.

NO. 15. AUGUST 28, 1904; MOON’S AGE 17.41 DAYS.
]

“Here the age of the moon has increased to nearly seventeen and a half days. The sunset line has advanced to the borders of the _Mare Nectaris_ and the _Mare Tranquillitatis_. Toward the south a vast region which was very brilliant in the morning and midday light with the reflections from mountain slopes and the rays of Tycho, has passed under the curtain of night. The great crater rings on the eastern border of the _Mare Nectaris_, and thence upward to the South Pole, are beginning to reappear, but with the shadows of their walls thrown in a direction opposite to that which they assumed before. By a little close inspection you will recognize Theophilus and its neighbors which were so conspicuous for many days while the sunrise was advancing, but which have been almost concealed in the universal glare of the perpendicular sunshine since the Full Moon phase was approached. On the _Mare Tranquillitatis_ and the _Mare Serenitatis_ it is late afternoon, and your favorite ‘Marsh of a Dream’ has become a true dreamland.”

“This oncoming of night,” said my friend, “seems to me more imposing, and more suggestive of mystery than was the advance of day.”

“Surely it is. Do we not experience similar sensations when night silently creeps over the earth? But it imparts a feeling of loneliness and desolation when we watch it swallowing up the barren mountains and plains of the lunar world that we do not experience in terrestrial life. There are no cheerful interiors on the moon to which one can retreat when darkness hides the landscapes. There is another thing about the lunar night to which I have made but scant reference thus far. I mean it’s more than Arctic chill. Imagine yourself standing there in the midst of the broad plain of the _Mare Tranquillitatis_. Toward the east you would see the sun close to the horizon, yet blazing bright and hot, without clouds or mists to temper its rays. The rocks or soil beneath your feet would perhaps be cold to the touch, because the surface of the moon radiates away the heat very quickly, but your face and hands would be almost scorched by the intense solar beams. Looking toward the west you would see the shining tips of mountains suddenly extinguished, one after another, and when the sharply defined edge of the advancing night passed over you it would be as if you had plunged into a cold bath. In a little while, if you remained motionless, you would be frozen. No clothing would suffice to keep you warm. Nothing that polar explorers have ever experienced can be likened to the cold of the lunar night. Only the apparatus of the laboratories for producing temperatures, capable, when combined with pressure, of liquifying and solidifying the air itself, can bring about upon the earth a lowering of temperature comparable with that which occurs during the lunar night.”

“But I do not exactly see why night should be so much colder on the moon than on the earth. She is not farther from the sun.”

“No, her average distance from the sun is the same as that of the earth. The reason why her nights are so cold is to be found in the absence of an atmosphere like ours. The air is the earth’s blanket, which serves a double purpose, tempering the heat by day with its vapors and winds, and keeping the earth warm at night by preventing the rapid radiation into space of the heat accumulated during the daylight hours. If there is any atmosphere at all upon the moon—and I shall tell you by and by what has been learned on that subject—it is so rare as compared with ours that it can exercise very little effect upon the temperature of the lunar surface.

“Now, look at the great range of the lunar Apennines. You will see that the eastern faces of these mountains are in the sunlight, and they cast no shadows, as they did in the lunar morning, over the _Mare Imbrium_. The same is true of the lunar Caucasus, and the lunar Alps. All of these mountains are very steep on the side facing the plains, and that is the side presented sunward in the lunar afternoon. By turning to photograph No. 16, we shall see this phenomenon more clearly displayed. This photograph, measured by the age of the moon when it was taken, is more than a day older than the other, but once again the effect of libration has, in part, counteracted for us the advance of the line of sunset. Still it has distinctly advanced. You will observe that it has now passed completely across the _Mare Nectaris_, and more than half across the _Mare Tranquillitatis_, while only the mountain tops along the western edge of the _Mare Serenitatis_ remain to indicate its outlines in that direction. Theophilus, Cyrillus, and Catharina, on the eastern border of the _Mare Nectaris_, have again become very conspicuous, but this time in evening instead of morning light. See how sharply the western wall of Theophilus stands out against the darkness of night behind it, and how its central peak glows in the setting sun while all the vast hollow beneath it is black. The floors of Cyrillus and Catharina, being less profoundly sunken, are still illuminated. Below the _Mare Serenitatis_, the twin rings, Aristoteles and Eudoxus, are very conspicuous, and they show the same change of illumination as Theophilus, their western sides being strongly illuminated on their inner faces, while the eastern walls cast shadows into the interior. The mountainous character of the surface in the neighborhood of the North Pole of the moon seems to be more clearly brought out in evening than in morning light. In this picture the North Polar Region seems to be almost as much broken up with gigantic rings as is that surrounding the South Pole. In both cases, you observe, many of the rings are poised just on the edge of the lunar disk, and their libration alternately swings them in or out of view.”

NO. 16. AUGUST 29, 1904; MOON’S AGE 18.62 DAYS.
]

“Then the other side of the moon may not be very different from the side that is turned toward us.”

“In its general features I doubt if it is at all different. There was once a theory, which had considerable vogue, that the side of the moon turned away from the earth presented a great contrast with its earthward side. A German mathematician, Hansen, drew conclusions, which are no longer accepted, as to the form of the moon. He thought that the moon was elongated in the direction of the earth, somewhat like an egg, her center of figure being about thirty miles nearer to us than her center of gravity. This, if true, would make the part of the lunar surface that we see lie at a great elevation as compared with the other part, and the center of gravity being toward the other side would cause the atmosphere and water to gravitate in that direction.”

“What a pity that so interesting a theory should have been abandoned!”

“If interest were the only test of the value of a scientific theory knowledge would not advance very fast. Notice how this very photograph before us vindicates the true scientific attitude toward nature. It records all the facts within its range, and leaves the theories to us. The features of your ‘dark woman’ are, in their way, as clearly marked in the photograph as is the range of the lunar Apennines. It is for us to recognize the essential difference between the interpretations which we choose to put upon these two phenomena. Giving play to fancy, we see the figure of an old woman in the one case, and employing our reason we find a chain of unmistakable mountains in the other.”

“But surely you do not mean to aver that science has no other business than that of recording facts.”

“By no means. It is also the business of science to find hypotheses and to build up theories that will explain its facts and connect them together systematically, according to some underlying law. But as I have just intimated it is the mark of true science that it never retains a theory merely because it is interesting. The truth is the only touchstone. Still, even the most conscientious scientific investigator may be misled by his imagination. His greatest virtue is that he never lets his fancies deceive him after he has recognized their false character. Point out your ‘dark woman’ to the child, or the savage, and it will be in vain afterward to explain that her profile is made up of plains and mountains. The child and the savage are not scientific but imaginative, and only after a long education will they abandon the apparent for the real.

“I will ask you now to take up photograph No. 17. The age of the moon here is twenty days. Comparing it with the last photograph we see that Theophilus has disappeared, although Cyrillus and Catharina, being a little farther east, are yet visible. Half of the _Mare Serenitatis_ is buried in night, and only a little of the eastern edge of the _Mare Tranquillitatis_ remains visible. Aristoteles and Eudoxus are now very close to the terminator, and the shadows of their eastern walls are spreading farther over their floors. Aristarchus is very brilliant, as it is still early afternoon on that part of the moon, and the sunshine is intense. Observe that Kepler, the crater ring directly east of Copernicus, has become more conspicuous than we have seen it in any preceding photograph. This is especially true of the system of bright rays surrounding it, and it is due to the change of illumination. In the southern part of the moon, west of Tycho, you will now recognize many gigantic formations which we first saw when the sun was rising over them. Some of them are even more prominent in the sunset light. Among these is our old acquaintance Maurolycus, whose western wall is so brilliant that it resembles a tiny crescent moon. The double row of broad, dish-shaped walled plains along the central meridian has also become visible once more. In fact the amount of delicate detail and the sharpness of the definition in these photographs are very remarkable. Observe the curious mottling of the ‘seas.’ It is in some of the differences of tint, which correspond in telescopic views of the moon more or less closely with the varying shades in the photographs, that some selenographers have thought they could detect evidences of the presence of vegetation on the moon. We shall talk about that more in detail another time. It is sufficient just now to notice that the beds of the _mares_ are by no means uniform either in tint or in level. All of them are more or less ‘rolling,’ like many of our prairies, and often winding chains of hills and huge cracklike ravines are visible in them. In this photograph the amount of detail shown in the _Mare Imbrium_ is particularly striking. Notice how some of the crinkled rays from Copernicus extend almost to the center of the ‘sea,’ and how in front of the precipitous base of the Apennine range the lighter-colored ground, with three prominent ring plains in it, presents the appearance of shallows. Lying off the shore south of Plato and the Alps a number of isolated mountain peaks are seen, mere white specks on the gray background. The undulating character of the ‘bottom’ of the ‘Bay of Rainbows’ is also distinctly indicated. By the way, I should perhaps mention the names of the three rings lying off the front of the Apennines, for although they are among the most interesting on the moon they have hitherto escaped our special attention. The largest of the three is Archimedes, the second in size is Aristillus, and the smallest is Autolycus. You will hear of them again when we come to the large photograph of the _Mare Imbrium_ and the _Mare Serenitatis_.

NO. 17. OCTOBER 10, 1903; MOON’S AGE 20.06 DAYS.
]

“Let me now prepare you for an almost dramatic change in the appearance of some of the most conspicuous lunar features which will take place when we pass from this photograph to No. 18. Direct your attention particularly to the chain of the Apennines. In No. 17 it lies very brilliant in the sunlight, with its western slopes distinctly visible, rising gradually from the shores of the _Mare Serenitatis_ and the _Mare Vaporum_, while the ‘sea’ along its eastern front is bright with day. In No. 18 the Apennines have become simply a chain of illuminated mountain tips with comparative darkness all around them. Their western slopes are practically invisible, the _Mare Imbrium_ on the east has turned dark, as if twilight had fallen over it—although as I have told you there is no twilight on the moon—and at its northern end the great range, with only its summits illuminated, projects like a row of electric lights far into the black night that has covered the plains beneath.

“Yet, although the _Mare Imbrium_ has turned so dark as to be barely visible over its western half, the sun has by no means set upon it, and the darkness is perhaps greater than it should, theoretically, be under the circumstances. This phenomenon of the rapid darkening of the great lunar levels as the sun declines is one of the arguments that have been found to favor the hypothesis of the existence of vegetation. If, for the sake of discussion, we admit the possibility of vegetation growing on the lunar plains, it will be interesting once more to compare photographs Nos. 17 and 18.”

“Don’t say that it is merely for the sake of a discussion,” interrupted my friend. “I shall be far more deeply interested if you will simply say that it may be true.”

NO. 18. SEPTEMBER 29, 1904; MOON’S AGE 20.50 DAYS.
]

“Very well, let us put it that way, then. As I was remarking, if we again compare the two photographs, keeping the vegetation hypothesis in view, we may ascribe at least a part of the rapid darkening of the plain of the _Mare Imbrium_ to a change in the color of the—what shall I say, grass?—covering it.”

“Good! good!” exclaimed my friend, clapping her hands. “Just listen to him! After gravely rebuking me so many times for my unscientific faith in the lunar inhabitants of a long past age, now you are talking of ‘grass’ on the moon.”

“You are hardly fair,” I protested. “It is you who have just led me to make an admission which many astronomers would laugh at, and you ought to support me with all the brilliance of your imagination when I try to picture a state of things so consistent with your predilections about the moon.”

“Oh, I do support you with all my heart!” she replied. “Pray go on, and tell me about the lunar grass.”

“Not just at present,” I said. “We are going to take that subject up again, and I may then succeed in convincing you that there is far more evidence for believing that vegetation exists on the moon in the present day than for believing that intellectual beings inhabited it at some unknown former period. I should warn you, too, that I have been using the contrasts of light and darkness between these two successive photographs simply as an illustration of what occurs in visual telescopic views; but that, for some reason, the lunar plains nearly always appear darker in photographs when contrasted with the mountainous regions than they do when viewed with the eye. Owing, also, to a variety of influences two successive photographs of the moon may differ in tone when the eye would detect no corresponding difference. All this, however, does not invalidate what I have said about the lunar ‘seas,’ or plains, darkening near sunset more rapidly than we should expect them to do, as a simple result of the low angle at which the sunlight strikes them.

“You will notice that the waning of day between photographs Nos. 17 and 18 has produced a remarkable change in the appearance of Tycho. Since the Full Moon phase Tycho has resembled a button rather than a volcanic crater, but now it has once more assumed the form of a very beautiful ring with its central peak clearly shown, its western wall, bright and its eastern wall casting a broad, black shadow. Most of the rays have now disappeared, only two or three, running over the eastern hemisphere, remaining visible. The immense walled plains near Tycho have again become prominent, Maginus toward the southwest, Clavius toward the south, and Longomontanus toward the southeast being the most conspicuous. Clavius is always a wonderful object for the telescope, but it is rather more interesting in the lunar morning than in the evening. Away over near the eastern limb, where the sun is still high, Grimaldi shows its dark oval, with a couple of mountain peaks on its western rampart shining brilliantly. The small, dark spot below it, toward the east, is in the walled plain, Riccioli. The bright spot with starlike rays, a long way south of Grimaldi, and east of the _Mare Humorum_, is Byrgius, a walled plain near which exists a small system of bright streaks resembling those surrounding Copernicus and Kepler, but much less extensive.”

“Do you recall my expression of impatience this morning when you were giving me the names of a long string of crater rings?” said my friend, smiling. “Well, I am now going to make a confession. Perhaps it is slightly of a penitential nature. I find now that these names, although they certainly are far from picturesque in most cases, begin to interest me, because, I suppose, I understand better the character and meaning of the things that they represent. The ceaseless Latin terminations no longer annoy me, for I do not think of them, but of the things themselves.”

“It is always so,” I replied, “whenever one takes up a new study. I know that you have dipped a little into botany, and I am sure that the Latin names which abound in that science must have repelled you at first. But after a time, when you had begun to recognize the beautiful flowers and the remarkable plants for which they stood, you found that even these names assumed a new character and became interesting and memorable. You will find it the same if you continue to study the moon. The most stupid designations will derive interest from their applications.”

“Yes, that is no doubt true. Still, I wish that Riccioli had possessed a little more imagination.”

“Be thankful, then, that he did not name the lunar ‘seas’ and ‘bays.’ You must now bid good night to your ‘dark woman.’ You observe that the _Mare Nubium_ is beginning to fall under the shadow, and that her features are growing indistinct. If you will turn the photograph upside down you will find that the Moon Maiden has retired. She belongs exclusively to the western hemisphere, and it is only the eastern hemisphere of the moon that now remains visible to us, for we are close to the phase of Last Quarter. This is an aspect of the moon with which you may not be very familiar. To see the moon at Last Quarter, and particularly after she has passed that phase, we must rise near midnight and devote the early morning hours to observation. During these later phases, however, one may see the moon in the heavens during the daytime all through the forenoon and a part of the afternoon. She is a very beautiful object then, although few persons, I fear, ever take the trouble to look at her. The lighter parts of her surface assume a silvery tint in the daylight, and the dark plains seem suffused with a delicate blue from the surrounding sky. Exquisite views of the moon may then be obtained with a telescope. The glare of reflected light from the mountains and crater rings, which dazzles the eye at night, is so reduced that the telescopic image becomes beautiful, soft, and pleasing. The same principle has been very successfully applied in recent years to the study of the planet Venus. Her atmosphere is so abundant, in contrast to what we find on the moon, that she is as blinding in a telescope as a ball of snow glittering in full sunshine; but when seen in the daytime, her features, indistinct at the best, may be more clearly discerned.”

“Oh, you interest me deeply! If Venus is supplied with such an abundance of air, I suppose she is inhabited?”

“It is not exactly orthodox among those calling themselves astronomers to talk of inhabitants on the planets, but I do not mind telling you privately that I think that Venus is most likely a world filled with all kinds of animate existences. Our present business, however, is with the moon, and I must recall your attention to the photographs. We shall next take up No. 19. Here the crescent shape becomes again evident, but reversed in position as compared with the crescent of the new and waxing moon. Only two of the ‘seas’ now remain completely in view—the _Mare Humorum_ and the _Oceanus Procellarum_.”

“That term I think you have translated as the ‘Ocean of Tempests.’ Pray, do you know any reason why it should have been thus named?”

NO. 19. AUGUST 16, 1903; MOON’S AGE 23.81 DAYS.
]

“There is not the slightest reason that I know of. You must ascribe it to the vivid imagination of that old astronomer whom you so greatly admire. I regret, sometimes, that he cannot be here to explain to you the thoughts that occupied his mind. They must surely have been very captivating, even though not very scientific. Remark that there are many of the features of the eastern part of the moon which we can now discern more clearly than in any of the preceding pictures. Beginning at the top we see the vast inclosure of Longomontanus with the top of its encircling walls illuminated, while the interior is all in deep shadow. Its western rampart projects into the night and seems detached from the main body of the moon. Along the terminator below Longomontanus, what appears to be another immense walled plain presents a similar aspect. This, however, consists of several smaller formations grouped near together, only their loftiest points being illuminated. The steep borders of the _Mare Humorum_ are finely shown. Notice how the floor of that little ‘sea,’ which is about the size of England, as Mr. Elger has remarked, is mottled with whitish spots, and how distinct the ring of Gassendi appears at the northern end of the _mare_. You can even see the comparatively small crater that crowns the northern wall of the ring. Southeast of the _Mare Humorum_ are visible the great flat plains of Schiller and Schickard. Notice also how all the surface of the moon in that direction is freckled with crater pits, which resemble the impressions made by raindrops in soft sand. But the smallest of these pits is larger than the greatest volcanic crater on the earth.

“The _Oceanus Procellarum_ is beautifully illuminated in this picture. In several places, particularly north of the _Mare Humorum_, parts of _submerged_ rings are visible. These are great curiosities, and we shall see more of them elsewhere. Some selenographers believe that they are the remains of an earlier world in the moon, which was buried by a tremendous upheaval and outrush of molten material from the interior. You will remember, perhaps, that I spoke of a catastrophe of that kind when pointing out the half-buried ring of Fracastorius at the southern end of the _Mare Nectaris_.”

“Did that catastrophe occur after the formation of the huge lunar volcanoes?”

“It is difficult to say just when it occurred, but the appearances generally favor the view that it was subsequent to the great volcanic age. It is the opinion of Mr. Elger, whom I have once or twice mentioned as an English observer who has devoted special attention to the study of the moon’s surface, that the _mares_, as we now see them, do not represent the original beds of the lunar oceans. These beds, which, according to this view, were at first deeper, have been covered up, at least over a great part of their areas, by the outrush of molten lava. If they were ever filled with water it was very likely prior to that occurrence. But you must remember that all this is speculation, very interesting, it is true, but based upon insufficient data to enable us to be sure of our conclusions. I shall show you later that some recent students of lunar phenomena have formed the opinion that there is a strong argument to be drawn from geological analogies in favor of the view that the lunar _mares_, practically in the state in which we see them, have been true sea beds.

“Let us continue our inspection of photograph No. 19, which is one of the most interesting of the series. Look at the crater ring Kepler, in the midst of the _Oceanus Procellarum_. We have not before seen it in the aspect which it now presents. Hitherto it has appeared only as a bright point surrounded by a light patch covered with radiating streaks. But now, with the late afternoon sunlight striking across it, its walls are illuminated in such a manner that its very perfect ring shows very clearly, about half of the interior lying in shadow, which serves to give it a striking relief. If we suppose a time when the _Oceanus Procellarum_ was a real ocean, and when Kepler was an active volcano rising above its waters, its situation, far from all shores, would have been not unlike that of the great volcano of Kilauea in the Hawaiian Islands. In that case we might assume that the streaks around it represent ancient lava flows, which spread far about over the bed of the ocean. The same explanation would apply to the streaks and rays around Copernicus, and half a dozen other similar ring mountains.

“You will also observe that the afternoon slant of the solar rays has considerably changed the appearance of Aristarchus. Now for the first time the crateriform shape of that most remarkable mountain has become evident on account of the shadow in the interior. This shadow has almost reached the central peak which is the brightest part of the entire formation. You may be interested in the fact that the brilliance of the central peak of Aristarchus is so great that it stands in an order by itself, in what may be called the photometry of the moon’s surface. Ten orders of relative brightness have been adopted to represent the various reflective powers of different parts and spots of the moon. I copy them from Mr. Elger’s list. They are as follows:

“0° = Black (example, the shadows of mountains).

“1° = Gray black (example, darkest places in the walled plains of Grimaldi and Riccioli).

“2° = Dark gray (example, the floor of Endymion).

“3° = Medium gray (example, interior of Theophilus).

“4° = Yellowish gray (example, interior of Manilius).

“5° = Pure light gray (example, surface around Kepler).

“6° = Light whitish gray (example, walls of Macrobius).

“7° = Grayish white (example, Kepler).

“8° = Pure white (example, walls of Copernicus).

“9° = Glittering white (example, Proclus).

“10° = Dazzling white (sole example, the central peak of Aristarchus).”

“Really, I am greatly surprised by what you tell me,” said my friend. “I would never have imagined that there were so many different neutral tints on the moon.”

“You would be still more surprised,” I replied, “if I could present to you a similar table of the different tints of color that have been discovered there. But I am not aware that any scale of lunar colors has been prepared. There are, however, various shades of brown, yellow, and green. Most of them are found in the _mares_ and walled inclosures. Some of them appear to be variable, and some are only to be detected under particular illuminations.”

“Are not such colors an indication of something living there?”

“It may be so—an indication, for instance, of the existence of ‘lunar grass,’ the mention of which so amused you a little while ago.”

“Oh, it was not the ‘grass’ that amused me, but your unexpected way of introducing it. I _want_ to be convinced that there is grass there, and a great many other things besides grass. But I am not yet satisfied concerning that unique peak in Aristarchus. ‘Dazzling white’ you say is its description in the scale of tints. That excites my curiosity immensely. I think you have told me already that it cannot be snow, but you have spoken of the possibility of crystals and of metal. Do you know, I like the idea of ascribing the phenomenon to metal. It recalls something that I read in childhood about the first discoverer of a silver mine in Mexico. As I remember the story, an Aztec hunter, chasing his game across a mountain, seized upon a bush to aid him, and the roots giving way disclosed a glittering mass of silver. Why not let me imagine that the peak of Aristarchus is composed of pure silver?”

“There is no harm in imagining that if you wish to do so. But then your imagination, or rather your knowledge, should go a little farther and recall the fact that silver does not remain dazzling bright when exposed.”

“Ah, but you say there is no air, no water, no rains, no moisture on the moon. Under such circumstances might not a metal remain bright?”

“It is possible, but I hardly think that it would. It is likely that other corroding influences exist. A better explanation, I think, is afforded by supposing that the reflecting surface is simply composed of a rocky mineral, resembling in its power of reflection a mass of quartz crystals or imbedded planes of mica. There is no absolute impossibility involved in thinking that it may be simply white rock.”

“Why not say marble—a gigantic Carrara mountain on the moon?”

“I fear that that would involve a geological history for the lunar world for which we have not sufficient warrant in observed facts. I prefer to assume a volcanic origin for the phenomenon. Since you are so interested in the mystery of Aristarchus I may add that a part of the floor and the inner side of the ring are also extremely bright, but not quite so bright as the central peak. That alone stands at the top of the scale. Putting the peak at 10°, Mr. Elger finds that the other brilliant parts of Aristarchus possess only 9½° of brightness. Yet the whole interior is so glistening that when the sunlight falls vertically it almost resembles the inside of a crystal cup, and details are hidden in the glare.

“Now please look at the ‘Bay of Rainbows’ in the photograph before us. Cape Laplace at its western end lies close to the terminator and appears as a minute speck of light. The great bow-shaped shore is clearly defined, the level surface within being very dark and the highlands around it comparatively bright. The crater mountain Bianchini you will recognize near the center of the bow. Several other similar crateriform mountains are visible toward the north and east. In this light the surface of the moon eastward from the North Pole appears as rough and broken with craters and crater plains as we saw in the earlier pictures that it is toward the west.

“Before directing our attention to photograph No. 20, let us return for a moment to Aristarchus. When speaking of that formation a few minutes ago I interrupted myself in order to give you the scale of tints on the moon, which demonstrated the unique brilliance of the peak inclosed by the ring. I intended to point out to you then the fact that in photograph No. 19 we see, for the first time, not only the ring of Aristarchus but its curious neighbor Herodotus. A light streak, which we observed in an earlier picture, seems to connect the two. It is better, however, to notice this now because in turning from No. 19 to No. 20 you will perceive once more a change in the appearance of Aristarchus and its neighborhood. In No. 20 Aristarchus is distinctly more conspicuous. The night has advanced during almost exactly twenty-four hours, having in the meantime swept across the entire length of the ‘Bay of Rainbows,’ which we now no longer see. If we had been using a telescope during that interval we should have beheld a very interesting spectacle, for sunset on the ‘Bay of Rainbows’ is quite as remarkable, although in a very different way, as sunset on the Bay of Naples. The astronomer, seated amid the lonely gloom of his observatory dome, and watching the change of light and illumination on the surface of the moon, has many an hour of solitary enjoyment of aspects of nature that are quite impossible on the earth, and that frequently lure him into poetic meditations which find no place in his notebook.”

“I am very glad to hear you say that. It enhances my opinion of the astronomers, and convinces me that after all they are not so severely scientific as they describe themselves.”

NO. 20. AUGUST 17, 1903; MOON’S AGE 24.84 DAYS.
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“If they were,” I replied, “or if all of them were, it would be a bad augury for the future of their science. Do not think that in occasionally seeking to restrain your imagination I wish to express condemnation of what, after all, is the noblest of human faculties. But again we are forgetting our principal business, which is with the facts. Aristarchus, as I have said, has undergone another distinct change of appearance from that which it showed before. The central peak is now covered by the shadow of the eastern wall, but still the reflection from the western wall alone is sufficient to make it the brightest spot on the moon. Herodotus, on the other hand, has become indistinct and the Harbinger Mountains are practically invisible, but we can detect the existence of the enormous chasm or cañon, which I told you once issues from the interior of Herodotus and goes winding nearly a hundred miles over the floor of the _Oceanus Procellarum_.

“Notice, also, how clearly visible three or four relatively small craters east of the ‘Bay of Rainbows’ have become, and how conspicuous are several large walled plains on the northern ‘horn.’ The dark level south of these formations and between them and the small craters has also a name which I have not before mentioned. It is the _Sinus Roris_, ‘Gulf of Dew.’ It connects the _Mare Frigoris_ with the _Oceanus Procellarum_. It is another legacy from your friend the imaginative astronomer.”

“Then once more he receives my thanks for having done his best to make the moon an ideal world. It is always painful to have one’s ideals destroyed.”

“I hope that I have not been destroying any of yours.”

“No, but at least you have caused a change in my impressions about the character of the moon. Henceforth there will be an element of terror as well as of unexpected grandeur mingled with my thoughts of the ‘Queen of Night.’”

“That element will not be diminished by what I am about to point out. Look far over near the eastern border of the _Oceanus Procellarum_, directly east of Aristarchus. There you will distinguish the outlines of two or three vast submerged ring plains, which we may regard as relics of that earlier lunar world, which preceded the outgush of lava that Mr. Elger thinks covered the sea bottoms. Observe also the singular light streak that runs from Kepler, now barely visible at the edge of night, to a dark little crater, beyond which lies a bright point off the coast of the ‘ocean.’ South of this there are other submerged ring plains, one of which, named Letronne, has a high western wall, which forms in the picture a sort of promontory projecting from the southern border of the _Oceanus Procellarum_, almost directly north of Gassendi. The latter is very clearly shown at the lower end of the _Mare Humorum_, the western side of which is in shadow, while its whole surface has turned very dark. On the southern horn of the crescent the ring plains, Schickard and Schiller, are still prominent, and the northern and eastern edges of the _Mare Humorum_ appear more ragged with mountains and crater rings than before.”

“And have all these mountains and craters names?”

“Not all of them, but many more, perhaps, than you suppose. On the whole visible surface of the moon about 500 objects, not including the ‘seas,’ have received names. It may surprise you to learn that the position of the most important of these objects has been ascertained with an accuracy which is still lacking in our determination of positions on the earth. In other words our charts of the moon are more exact than those of our own planet.”

“That does indeed surprise me. I should have thought that, living on the earth, we could make very correct maps of it, while, as for the moon, two or three hundred thousand miles away, it seems to me not so easy to do that.”