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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..b2a3af4 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #66510 (https://www.gutenberg.org/ebooks/66510) diff --git a/old/66510-0.txt b/old/66510-0.txt deleted file mode 100644 index 41f3fa1..0000000 --- a/old/66510-0.txt +++ /dev/null @@ -1,6563 +0,0 @@ -The Project Gutenberg eBook of The Moon: A Popular Treatise, by Garrett P. -Serviss - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world 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. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: The Moon: A Popular Treatise - -Author: Garrett P. Serviss - -Release Date: October 10, 2021 [eBook #66510] - -Language: English - -Character set encoding: UTF-8 - -Produced by: Tim Lindell, Barry Abrahamsen, and the Online Distributed - Proofreading Team at https://www.pgdp.net (This file was - produced from images generously made available by The Internet - Archive/Canadian Libraries) - -*** START OF THE PROJECT GUTENBERG EBOOK THE MOON: A POPULAR TREATISE *** - - - - - THE MOON - - - - ------------------------------------------------------------------------- - -[Illustration: - - COPERNICUS AND THE CARPATHIAN MOUNTAINS. -] - ------------------------------------------------------------------------- - - - - - - +THE MOON+ - - - +A POPULAR TREATISE+ - - - - _By_ - - GARRETT P. SERVISS - - - - - -[Illustration] - - - - - - +D. APPLETON AND COMPANY - NEW YORK+ - 1907 - - ------------------------------------------------------------------------- - - - - - COPYRIGHT, 1907, BY - D. APPLETON AND COMPANY - - - - - _Published October, 1907_ - - - - ------------------------------------------------------------------------- - - - - - PREFACE - - -THE reader familiar with astronomical literature will doubtless remark a -certain resemblance between the plan on which this book is written and -that of Fontenelle’s “Conversations on the Plurality of Worlds,” a -French classic of the eighteenth century. The author freely acknowledges -that it was the recollection of the pleasure which the reading of -Fontenelle’s book gave him, years ago, that led to the adoption of a -somewhat similar plan for this description of the moon. But, except that -in both cases the conversational method is employed, no great likeness -will be found between what is here presented and the work of the witty -Frenchman. - -Having been invited by the Messrs. Appleton & Co. to prepare a small -volume, to be based on a series of lunar photographs representing the -moon as it appears on successive evenings during an entire lunation, the -author felt that the work should be made as entertaining as possible. He -has, therefore, avoided technicalities, while endeavoring to present all -the most essential facts known about our satellite. What he has written -is intended for the general reader, who desires to learn the results of -the great advances in astronomy without being too much troubled with the -scientific methods by whose aid those results have been reached. - -This is the first time, as far as the author is aware, that a series of -lunar photographs, showing our satellite in its varying aspects from New -to Old Moon, has been presented in a book, accompanied with a -description of the mountains, plains, volcanoes, and other formations -shown in each successive photograph. The reader is enabled to place -himself, as it were, in an observatory of the first rank, provided with -the most powerful apparatus of the astronomer, and, during an entire -month, view the moon in her changing phases. - -The photographs here reproduced were made at the Yerkes Observatory, and -the most grateful acknowledgments are tendered to Prof. Edwin B. Frost, -its director, for generously consenting to their use for this purpose. -He could only have been induced to do so by his desire to see the fruits -of the admirable work accomplished by his associates enjoyed by an -ever-widening circle. - -The series of photographs representing the moon on successive evenings -were taken with the 12-inch telescope of the Yerkes Observatory by Mr. -James Wallace, who employed a color filter that he constructed specially -for this telescope, which possesses a visual and not a photographic -objective. The larger scale photographs, representing certain selected -regions on the moon, were taken by Mr. Ritchey, now of the Carnegie -Solar Observatory at Mount Wilson, California, with the great 40-inch -telescope of the Yerkes Observatory. It is unnecessary to speak of the -extraordinary quality of these photographs, which have been admired by -astronomers in all lands. - -It should, perhaps, be added that while the director of the Yerkes -Observatory has shown confidence in the author by intrusting to him the -use of these photographs, yet, neither Professor Frost, nor Messrs. -Wallace and Ritchey are in any way responsible for the statements made -in this book. The author has taken pains to be accurate, but if any -errors of fact or opinion have crept in, he alone must be blamed for -them. - - GARRETT P. SERVISS. - -CHÂTEAU D’ARCEAU, - - CÔTE D’OR, FRANCE, June, 1907. - - ------------------------------------------------------------------------- - - - - - CONTENTS - - - PAGE - INTRODUCTION 3 - - I. —NEW MOON TO FIRST QUARTER 47 - - II. —FIRST QUARTER TO FULL MOON 83 - - III. —FULL MOON TO OLD MOON 131 - - IV. —GREAT SCENES ON THE MOON 181 - - APPENDIX 239 - - INDEX 243 - - ------------------------------------------------------------------------- - - - - - LIST OF ILLUSTRATIONS - - - FULL-PAGE ILLUSTRATIONS - - Copernicus and the Carpathian Mountains _Frontispiece_ - - - PHOTOGRAPHS OF THE MOON SHOWING PHASES OF CHANGE - - PAGE - No. 1, February 19, 1904; Moon’s Age 3.85 Days 50 - No. 2, September 24, 1903; Moon’s Age 3.87 Days 56 - No. 3, July 29, 1903; Moon’s Age 5.54 Days 66 - No. 4, November 24, 1903; Moon’s Age 5.74 Days 72 - No. 5, July 1, 1903; Moon’s Age 6.24 Days 74 - No. 6, November 26, 1903; Moon’s Age 7.75 Days 78 - No. 7, July 2, 1903; Moon’s Age 7.24 Days 90 - No. 8, August 31, 1903; Moon’s Age 9.22 Days 94 - No. 9, August 2, 1903; Moon’s Age 8.97 Days 102 - No. 10, November 30, 1903; Moon’s Age 11.78 Days 106 - No. 11, December 1, 1903; Moon’s Age 12.98 Days 112 - No. 12, September 4, 1903; Moon’s Age 13.27 Days 118 - No. 13, September 5, 1903; Moon’s Age 14.40 Days 122 - No. 14, August 26, 1904; Moon’s Age 15.65 Days 132 - No. 15, August 28, 1904; Moon’s Age 17.41 Days 134 - No. 16, August 29, 1904; Moon’s Age 18.62 Days 138 - No. 17, October 10, 1903; Moon’s Age 20.06 Days 142 - No. 18, September 29, 1904; Moon’s Age 20.50 Days 144 - No. 19, August 16, 1903; Moon’s Age 23.81 Days 150 - No. 20, August 17, 1903; Moon’s Age 24.84 Days 158 - No. 21, August 19, 1903; Moon’s Age 26.89 Days 168 - - - PHOTOGRAPHS OF THE MOON SHOWING SIGNIFICANT FEATURES - - PAGE - - Bullialdus and the _Mare Nubium_ 182 - - Tycho, Clavius, and their Surroundings 192 - - The Great Southwest on the Moon 198 - - The Giant Ring Mountain Theophilus and its 206 - Neighbors. - - Two Great Lunar “Seas”—the _Mare Serenitatis_ and 218 - a Part of the _Mare Imbrium_ - - - DIAGRAMS IN TEXT - - PAGE - - Phases and Rotation of the Moon 14 - - The Moon’s Path with Respect to the Sun and the 17 - Earth - - The Moon and the Tides 23 - - Effect of Moon, Varying Velocity in Orbit 58 - Producing Libration in Longitude - - Lunar Volcano, in Section 85 - - Terrestrial Volcano, in Section 85 - - Diagram Showing Why the Winter Moon Runs High 170 - - Diagram Showing Why Moon Rises Later Every Night 173 - - Diagram Illustrating the Harvest Moon 174 - - ------------------------------------------------------------------------- - - - - - INTRODUCTION - - - - ------------------------------------------------------------------------- - - - - - INTRODUCTION - - -ONE serene evening, when the full moon, rising slowly above the tree -tops, began to spread over the landscape that peculiar radiance which, -by half revealing and half concealing, by softening all outlines, and by -imparting a certain mystery to the most familiar objects, fascinates at -once the eye and the imagination, I was walking with a friend, a lady of -charming intelligence, in a private park adjoining an old mansion in one -of the most beautiful districts of central New York. For a long time we -both remained silent, admiring the scene before us, so different in -every aspect from its appearance in the glare of daylight—each occupied -with the thoughts that such a spectacle suggests. Suddenly my friend -turned to me and said: - -“Tell me—for, like so many thousand others, I am virtually ignorant of -these mysteries of the sky—tell me, what is that moon? What do -astronomers really know about it?” - -“But,” I replied, “you certainly exaggerate your ignorance. You must -have read what so many books have told about the moon.” - -“Not a word,” was the reply, “or at least, what I have read has made -little impression upon my mind. I read few books of science; generally -they repel me. But face to face with that marvelous moon, I find it -irresistible, and my desire for knowledge concerning it becomes intense. -I remember something about eclipses, and something about tides, with -which, I believe, the moon is concerned. I recall the statement that the -moon has no atmosphere, but does possess great mountains and volcanoes. -Yet these things are so jumbled in my memory with technical statements -which failed to interest me, that really my ignorance remains profound. -But I have heard that many surprising discoveries have been made lately -concerning the moon, and that astronomers have succeeded in taking -wonderful photographs of scenes in the lunar world. I have, indeed, seen -copies of some of these photographs, but beyond awaking curiosity by -their _bizarre_ effects of light and shadow, they impressed me little, -for lack, I suppose, of information as to their meaning. I beg you, -then, to tell me what is really known about the world of the moon. There -it is; I see it; I experience the delightful impressions which its light -produces—but, after all, what is it, and what should we behold if we -could go there? I once read Jules Verne’s romance of a trip to the moon, -but unfortunately his adventurers never really got there, and I finished -the story with a keen sense of disappointment because, in the end, he -told so very little about the moon itself. As for the professional books -of the astronomers they are useless to me. Then, please tell me that -which, at this moment, with that wonderful orb actually in sight, I so -much desire to know.” - -It was not possible to resist an appeal so earnestly urged, but I felt -compelled to say: “Since you remember so little about the fundamental -facts which generations of astronomers have accumulated concerning our -nearest neighbor in the sky, I must, for the sake of completeness, and -in order to put you _au courant_ with the more captivating things that -will come later, begin at the beginning, and the true beginning is not -among the mountains of the moon, but here on the earth. We must start -from our own globe—as the moon herself did.” - -“What do you mean by that?” my friend asked with a tone of surprise. - -“Have you not read, somewhere, in the last ten years, that the moon was -actually born from the earth?” - -“Yes, now that you mention it, I dimly recall something of the kind, but -I took it for an extravagant speculation of some _savant_ who possessed -more imagination than solid knowledge.” - -“The _savant_ who originally demonstrated the earthly origin of the -moon,” I replied, “is not one to be easily led into extravagance by his -imagination. It is Prof. George Darwin, the son of the famous author of -the ‘Origin of Species.’ I shall not mention his mathematics, which are -troublesome, but allow me to tell you, in a word, that his -investigations have satisfied astronomers that the earth and the moon -once composed a single body. How many million years ago that was we can -only guess. The causes of the separation which eventually occurred were -the plastic condition of the original body while it was yet hot and -molten, its swift axial rotation producing an immense centrifugal force -at its equator, and the attraction of the sun raising huge tides which -affected its entire mass instead of affecting only the waters of the -ocean as the tides do at present. At last there came a time when an -enormous portion of the swiftly rotating globe was torn loose. That -portion included about one-eightieth of the entire mass of the earth. -Some astronomers and geologists think that the ‘wound’ left in the side -of the earth by this stupendous excision is yet traceable in the basin -of the Pacific Ocean. - -“The separation being once effected, the material that had escaped -gradually assumed a globular form under the influence of the gravitation -of its own particles; and, at the same time, by virtue of a curious -reaction of the tidal attractions of the two bodies upon each other, the -new-born globe was slowly forced away from its mother earth, becoming, -in fact, its satellite. Thus, by a process which certainly does seem -extravagantly imaginative, but which, nevertheless, is approved by -strict mathematical deductions from known physical facts, the moon is -believed to have had her birth.” - -“Surely,” said my companion, “my imagination would never have dared to -form such a picture, even if it had been capable of so extraordinary a -flight.” - -“No,” I replied, “nor the imagination of the most learned astronomer. -You perceive that in things celestial as in things terrestrial fact is -far more strange than fiction. We shall have occasion to refer to some -of the consequences of the earthly origin of the moon later on, but just -now in order that the knowledge you seek may not be too fragmentary, I -must tell you some other, more commonly known, facts about our -satellite.” - -“Judging by myself I doubt if there are many such facts _commonly_ -known.” - -“Perhaps you are right, but do not judge too severely the authors of -astronomical books. Such books are written primarily for those who wish -to study, not for those who desire to be intellectually entertained. But -let me get through with my preliminaries, and then, under the guidance -of science and photography, we shall try to visit the moon. One of the -first questions that naturally arise concerning the objects that we see -in the heavens relates to their distance from us. The average, or mean, -distance of the moon from the earth is 238,840 miles. For the sake of a -round number we usually call it 240,000 miles. But the orbit, or path, -of the moon in her monthly journey around the earth, is so far from -being a true circle that the distance is variable to the extent of -31,000 miles. Even the form of the moon’s path in space is not constant. -Owing to the varying effects of the attraction of the earth and the sun, -her elliptical orbit becomes now a little more and now a little less -eccentric, the consequence being that the moon’s distance from the earth -is continually changing. When she is at her greatest possible distance -she is 253,000 miles away, but this distance at certain times, may be -reduced to only 221,600 miles. As a result of these changes of distance -the moon sometimes appears noticeably larger to our eyes than at other -times. - -“This leads us next to inquire, ‘What is the actual size of the moon?’ -When we know the distance of any body from the eye it is not difficult -to determine its size. The diameter of the moon is 2,163 miles. The face -of the full moon contains 7,300,000 square miles. It is a little larger -than the continent of South America. For a reason that we will speak of -presently, the moon always keeps the same side toward us no matter in -what part of its orbit it may be. Consequently we always see the same -features of her surface and, except through inference, we do not know -what exists on the other side of the lunar globe. Of the 7,300,000 -square miles of surface which the moon presents to us, about 2,900,000 -are occupied by those dark gray patches which you see so plainly -spotting her face, and which were once supposed to be seas. The -remaining 4,400,000 square miles consist of a very rough, broken -country, ridged with gigantic mountains and containing hundreds of -enormous craters, and mountain-ringed valleys, which are so vast that -one hesitates to call them, what many of them seem evidently to be, -extinct volcanoes. A single explosion of a volcano of the dimensions of -some of these lunar monsters would shake the whole earth to its center!” - -“Please stop a moment,” my friend laughingly interrupted. “So many -merciless facts, chasing one at the heels of another, are as bad as the -books on your science that I have tried to read. Give my imagination -time to overtake you.” - -“Very well,” I said, “then relieve your attention a little while by -regarding the face of the moon. Do you perceive the portrait of the Moon -Maiden there?” - -“I believe I do, although I never noticed it before. It is in profile, -is it not?” - -“Yes, and it occupies all the central portion of the western half of the -disk. Take the opera glass and you will see it more clearly.” - -“Really, I find her quite charming,” said my companion, after gazing for -a minute through the glass. “But what a coquette! Look at the -magnificent jewel she wears at her throat, and the _parure_ of pearls -that binds her hair!” - -“Yes,” I replied, “and no terrestrial coquette ever wore gems so -unpurchasable as those with which the Moon Maiden has decked herself. -That flaming jewel on her breast is a _volcano_, with a crater more than -fifty miles across! Tycho, astronomers call it. Observe with the glass -how broad rays shoot out from it in all directions. They are among the -greatest mysteries of lunar scenery. And the string of brilliants in her -hair consists of a _chain of mountains_ greater than the Alps—the lunar -Apennines. They extend more than 450 miles, and have peaks 20,000 feet -high, which gleam like polished facets.” - -“Truly,” said my companion, smiling, “these gigantesque facts of yours -rather tend to dissipate the romantic impression that I had conceived of -the Moon Maiden.” - -“No doubt,” I replied. “It is only distance that lends her enchantment. -But we must not disregard the facts. Her hair, you perceive, is formed -by some of the vast gray plains of which I spoke a few minutes ago. She -is like a face in the clouds—approach her, or change the point of view -and she disappears or dissolves into something else. - -“Now, to return to my preliminaries, upon which I must insist. Knowing -the distance and the size of the moon, the next question relates to her -motions. You are aware that she travels around the earth about once -every month. There are two ways in which we measure the length of time -that the moon takes for each revolution. First, regarding the face of -the sky as a great dial, with the stars for marks upon it, we notice the -time that elapses between two successive conjunctions of the moon with -the same star. In the interval she has gone completely around the earth -and come back to the starting point. This is called the moon’s sidereal -revolution, and it occupies, on the average, twenty-seven days, seven -hours, forty-three minutes, twelve seconds. Every twenty-four hours the -moon advances among the stars, from west to east, about 13° 11´. - -“But there is another, more usual way of measuring the orbital period of -the moon. This way is connected with her phases, or changes of shape, -from the sickle of the New Moon to the round disk of the Full Moon, and -back again to the reversed sickle of the waning moon. It is the time -that elapses from one New Moon to the next, or from one Full Moon to the -next which now concerns us, and it amounts, on the average, to -twenty-nine days, twelve hours, forty-four minutes. This is called the -moon’s synodic revolution, and it is equivalent to the ordinary lunar -month. It is variable to the amount of about thirteen hours. The reason -why the synodic revolution is more than two days longer than the -sidereal revolution is because the continual advance of the earth in its -orbit around the sun causes the latter to move eastward among the stars, -and before the moon’s monthly phases, which depend upon her position -with regard to the sun, can recommence, she must overtake the sun.” - -“What a hopeless task to try to remember all that!” - -“At any rate, if you cannot remember these things my conscience will be -clear, for I am simply doing my duty in telling you of them. If you -forget, go to the books on astronomy and refresh your memory. But do not -persuade yourself that the preliminaries are now finished. You are going -to think that my story of the moon resembles Walter Scott’s novels in -the length of its introduction; but if, in the end, I can interest you -half as much as he finally interests his readers I shall thank the stars -for my good fortune. - -“The next thing that I must try to explain,” I continued, “is the cause -of the moon’s phases, or her continual changes of form. You know that -the New Moon is shaped like a thin crescent, and always appears in the -west immediately after sundown, with the convex side facing the setting -sun. The moon at First Quarter is a half circle and is visible in the -southern part of the sky just after sunset. The Full Moon, which we have -at present, is a complete round disk, and is always seen directly -opposite to the place of the sun, so that she rises when the sun sets. -The moon at last quarter is again a half circle, and appears on the -meridian in the south at sunrise. The waning moon is like the new moon, -crescent-shaped, but the convexity of the bow faces the rising sun, and -she is visible only in the morning sky just as dawn begins. To explain -the reasons for these changes of shape, which the moon regularly -undergoes every month, I must ask you to go indoors and examine a little -diagram which I have made.” - -“Oh!” said my companion, “it is too bad to abandon this charming -spectacle, illuminated by rays so fascinating, for the sake of looking -at mathematical lines drawn on paper! But I suppose that this is one of -the sacrifices demanded by your inexorable science, and must be made.” - -“Yes,” I said, “but if science sometimes demands sacrifices, at least -she always rewards them most generously.” - -When we had returned to the house I placed upon the drawing-room table -this diagram. - -[Illustration: - - Phases and Rotation of the Moon. -] - -As I spread it out, my companion, after a regretful glance through the -open door at the silvery lawn, on which the moon, having cleared the -obstructing branches of the bordering trees, was now pouring down the -full splendor of her rays, put her elbows on the table to follow my -explanation. - -“The globe, half bright and half black, in the center,” I said, -“represents the earth. The large circle surrounding the earth we will -call the moon’s orbit, which she traverses once every month. The smaller -globe, also half white and half black, shown in four successive -positions in the orbit, is the moon. Suppose the sun to be away off here -on the left. It illuminates the earth and the moon only on the side -turned toward it. The opposite side of both is buried in night. Now, let -us begin with the moon at the point A. She is then between the earth and -the sun, the bright side being necessarily toward the sun and the dark -side toward the earth. In that position we do not see the moon at all -from the earth, unless she happens to come so exactly in a line with the -sun as to cover the latter, in which event we have an eclipse of the -sun. Now, suppose the moon to move in her orbit toward B. In a little -more than seven days she will arrive at B. In the meantime, while moving -away from the position of the sun, she begins to present a part of her -illuminated hemisphere toward the earth. This part appears in the form -of a sickle, or crescent, which grows gradually broader, until, at B, it -has grown to a half circle. In other words, when the moon is in the -position B we on the earth see one half of her illuminated surface. This -phase is called First Quarter. The narrow crescent, which appears as -soon as the moon begins to move from A toward B, is the New Moon. As the -moon continues on from B toward C, more and more of her illuminated half -is visible from the earth, and when she arrives at C, just opposite to -the position of the sun, she becomes a Full Moon. We then see, as occurs -to-night, the whole of that face of the moon which is presented sunward. -The upper half of the diagram shows how the moon moves from the position -of Full Moon back again to New Moon, or conjunction with the sun. During -this latter part of her course the moon rises later and later every -night, until, when she assumes the form of a waning crescent, she is -visible only in the morning sky just before sunrise.[1] - -“Now, there is another interesting thing shown by this diagram,” I -continued—but my companion, who had followed my explanations thus far -with flattering attention, here suddenly ran to the door exclaiming: - -“For mercy’s sake, what is happening to the moon?” - -Footnote 1: - -[Illustration: - - The Moon’s Path with Respect to the Sun and the Earth. -] - - It may be well to add to what is said in the text about the orbit of - the moon, that, while the moon does perform a revolution around the - earth once a month, yet her orbit is drawn out, by the common motion - of both earth and moon around the sun, into a long curve, whose radius - is continually changing, but which is always concave toward the sun. - This is illustrated in the accompanying diagram. Suppose we start with - the earth at A. The moon is then between the sun and the earth, or in - the phase of New Moon. The earth’s orbit at this point is more curved - than the moon’s, and the earth is moving relatively faster than the - moon. At B (First Quarter) the earth is directly ahead of the moon. - But now the moon’s orbit becomes more curved than the earth’s and it - begins to overtake the earth. At C (Full Moon) the moon has come up - even with the earth, but on the opposite side from the sun. From that - point to D (Last Quarter) the moon gains upon the earth until she is - directly ahead of it. Then, from D to E (New Moon, once more) the - earth gains until the two bodies are in the same relative positions - which they occupied at A. Throughout the entire lunation, however, - notwithstanding the changes which the shape of the moon’s orbit - undergoes, the latter is constantly concave toward the sun. This shows - that the sun’s attraction is really the governing force, and that the - attraction of the earth simply serves to vary the form of the moon’s - path, and cause it to move in a virtual ellipse with the earth for its - focus. - -I glanced over her shoulder, and saw a smudgy scallop in the moon’s -edge. - -“Really,” I said, “I am ashamed of myself. There is an eclipse of the -moon to-night, and I had positively forgotten it! What you see is the -shadow of the earth, which has the form of a long cone stretching away -more than eight hundred thousand miles into space, and whenever our -satellite at the time of Full Moon gets nearly in a direct line with the -earth and the sun, it passes through that shadow and undergoes an -eclipse. That is what is happening at the present moment.” - -“And the shadow has a round form because the earth is round, I suppose.” - -“Certainly; the shadow of a globe must have a circular outline. But the -shadow of the earth, although it finally diminishes to a point, is, at -the moon’s distance, still about 5,700 miles in diameter, or more than -two and a half times the diameter of the moon. In consequence of the -motion of the earth in its orbit around the sun, its shadow constantly -moves eastward, like a great pencil of darkness sweeping straight across -the heavens, but invisible to us except when the moon, traveling -eastward faster than the shadow, overtakes and passes through it. This -does not by any means happen at every full moon, because, for a reason -which I shall explain presently, the moon usually passes either above or -below the shadow of the earth, and thus escapes an eclipse. When an -eclipse does occur it lasts a long time because the shadow is moving in -the same direction as the moon. The moon must pass entirely through it -before the eclipse ends. On this occasion the moon will be in the shadow -more than three hours, and during an hour and a half she will be totally -immersed. We shall have plenty of time, then, to observe the phenomenon, -and after you have satisfied your curiosity a little by watching the -slow advance of the shadow movement across the moon, we can return to -our diagram and finish its explanation before the eclipse becomes -total.” - -Accordingly, after having watched the progress of the eclipse for half -an hour, during which time the shadow began perceptibly to diminish the -moonlight in the park, we returned to the lamplight and the diagram on -the table. - -“I was saying,” I resumed, “that another interesting thing in addition -to the cause of the moon’s changing phases is represented here. You -observe that a little cross stands on each of the four circles -representing the moon, and that, in every case, the cross is in the -center of that side of the moon which faces the earth. In fact the -position of the cross upon the moon is fixed and invariable, and it -always points toward the earth because the moon makes exactly one -rotation on her axis in the course of one revolution around her orbit, -or, as it is often called, one lunation. We know that this is so because -we always see the same features of the lunar surface, no matter where -the moon may be situated. This is true although, in consequence of the -phases, we cannot see the whole face of the moon except when she is -full. But whether it is the New Moon, or First Quarter, or Full Moon, or -Last Quarter, or Old Moon, that we look at, the mountains and plains -visible are identically the same. If the moon did not turn once on her -axis in going once around the earth we would see all of her sides in -succession, although only at Full Moon could we see an entire hemisphere -illuminated by the sun. At Old and New Moon the side presented to the -earth would be just the opposite to that presented at Full Moon. At Last -Quarter the side facing the earth would be the opposite to that facing -the earth at First Quarter.” - -“But, tell me,” said my friend, “how did the moon ever come to so -humiliating a pass that she must be forever turning on her heel to face -the earth?” - -“That,” I replied, “is a result of the same forces which originally -separated her from the earth and gradually pushed her off to her present -distance. In a word it is due to ‘tidal friction.’ Before the moon had -solidified, the attraction of the earth raised huge tides in her molten -mass. These tides acted on the rotating moon like brakes on a wheel, and -at length they slowed down her rotation until its period became -identical with that of her revolution around the earth. For the -mathematical calculations on which all this is based you must go to -Professor Darwin’s book on ‘The Tides,’ or some similar technical -treatise; but I imagine you will never do that.” - -“Not just at present, I assure you. I do not know what unexpected -ambition for the acquirement of scientific knowledge may arise after I -have seen those wonders that you have promised to show me in the moon, -but, for the moment, I am content to accept your statement of the simple -fact.” - -“Good!” I replied. “And now, perhaps, you will have the patience to -listen to an explanation of a very important relation which exists -between the moon and the earth. We are led to it by what I have just -said concerning tides. You know, of course that the tides in the oceans -are due principally to the attraction of the moon. The sun also raises -tides in the seas, but the moon, being so much nearer than the sun, is -the chief agent in producing them. Sometimes the moon and the sun act -together; at other times they pull in different directions. At Full Moon -and at New Moon they pull together, because then they are either on -opposite sides of the earth, or both on the same side. At such times we -have the highest tides in all our seaports. That occurs about once every -fortnight. But when the moon is at either First or Last Quarter, as you -will perceive by looking at the diagram, her position, as seen from the -earth, is at a right angle with a line drawn to the sun. Then the sun -raises tides in one direction and the moon in another direction. The -result is that at such periods the tides are lowest. An exact knowledge -of these things is very important for mariners because there are harbors -whose channels can be navigated by large ships only when the tides are -high. Tables predicting the times and heights of the tides have been -prepared for all the principal seaports of the world. In truth, the moon -renders important services to the inhabitants of the earth, not merely -in supplying them with a certain amount of light in the absence of the -sun, but also in enabling them to navigate waters which are too shallow -for ships except when deepened by the tide. The tides also, in many -cases, serve to scour out channels and keep them open.” - -“Really, I am quite interested, and the more so because I find the moon, -like a dutiful daughter, trying to be of some use to her mother. But -have I not heard that the tides occur on both sides of the earth at -once, and not simply on the side where the moon happens to be at the -time? Please tell me how that can be so?” - -“A complete reply to your question would carry us into the realm of -mathematical physics, but perhaps I can throw a little light upon the -matter with the aid of this second diagram. - -[Illustration: - - The Moon and the Tides. -] - -“The eclipse is not yet total,” I continued, glancing out of the door, -“and we can finish our explanation before it becomes so. Have the -kindness, then, to look at the diagram. Suppose E to be the center of -the earth, and M the center of the moon. The protuberant portions of the -earth C A D and D B C represent the waters of the ocean pulled away from -the surface of the earth, if I may so describe it, by the moon’s -attraction. You are probably aware that the attraction of gravitation -varies with the distance of the attracting body. The distance from the -center of the earth to the center of the moon is about 239,000 miles. -But the earth being nearly 8,000 miles in diameter, the surface of the -ocean at A is about 4,000 miles nearer to the moon than is the center of -the earth E. It follows that the force of the moon’s attraction is -greater at A than at E. If the water of the ocean were a fixed, solid -part of the earth there would be no perceptible effect resulting from -this difference in the amount of the moon’s attraction. But since the -water is free to move, to a certain extent, it yields to the attraction, -and is drawn up a little toward the moon. At the same time it is, in -effect, drawn away from C and D. The consequence is the production of a -tide on the side facing the moon. - -“Now, for the other tide, produced at the same time on that side of the -earth which is turned away from the moon. The point B is about 4,000 -miles farther from the moon than E; consequently the moon’s attractive -force is less at B than at E. From this it results that the body of the -earth is more forcibly attracted by the moon than is the water at B. The -earth therefore tends to move away from the water at that point, and -another tidal protuberance is produced, with its highest part at B. I -should add that while the water of the ocean is, to a certain degree, -free to respond to these differences of attraction, the earth itself, -being solid, can only move as a single body, and, mathematically, we may -regard it as if its entire mass were concentrated at the center E. -Please remember, however, that this explanation is only elementary, only -intended as a graphic representation of the tides, and not as a -mathematical demonstration of the way they are produced. Such a -demonstration would only be suited to one of the technical books that -you have not found as interesting as—some other branches of literature. - -“There is just one other thing to which I must ask your attention, and -then we shall return to the moon herself and the phenomena of the -eclipse now in progress. You will notice in the diagram, that two arrows -show the direction in which the earth is continually rotating on its -axis, and that a dotted curve, terminating with an arrow point, -indicates the course of the moon in her orbit surrounding the earth. The -rotation of the earth is so much more rapid than the motion of the moon -that the points A and B are carried out of the line drawn from the -center of the moon to the center of the earth, in the direction of the -arrows. From this it follows that the tides are never directly under the -moon, or exactly opposite to her, but sweep in great waves round the -globe. The tides produced by the attraction of the sun are only about -two fifths as high as those caused by the moon. As I have already -explained they are sometimes superposed upon the lunar tides—at New and -at Full Moon—and sometimes they are situated at right angles to the -lunar tides—at First and Last Quarters.” - -“But the eclipse!” interrupted my friend, whose attention had evidently -begun to wander. “I think the totality of which you spoke must be at -hand, for notice how dark the park has become, and the fireflies are so -brilliant under the trees.” - -The total phase of the eclipse was, indeed, beginning, and we stepped -out on the lawn before the door to watch it. The moon had now passed -entirely within the earth’s shadow, but although her light was almost -completely obscured as far as its power to illuminate the landscape was -concerned, still the face of the moon was dimly visible, as if concealed -behind a thick veil. Certain parts of it had a coppery color, producing -a very weird effect. - -“Dear me!” exclaimed my companion, “I did not think it would look like -that! I naïvely supposed that one could not see the eclipsed moon at -all, but that she either disappeared or was turned into a kind of black -circle in the heavens. And what a strange color she has! Positively it -fills me with awe.” - -“It is very rare,” I said, “for the moon to become invisible during an -eclipse. That can only occur when the earth is enveloped in clouds.” - -“Indeed, and what have the clouds to do with it? If the solid body of -the earth cannot cast a shadow dense enough to hide the moon, I should -not expect things so evanescent as clouds to be more effective.” - -“It is all owing to the earth’s atmosphere,” I replied. “If our globe -were not surrounded with a shell of air the moon would always be totally -invisible when eclipsed. But the atmosphere acts like a lens of glass -inclosing the earth; that is to say, it refracts, or bends the rays of -sunlight around the edge of the earth on all sides, and throws a portion -of them even into the middle of the shadow, at the moon’s distance. It -is these refracted rays which cause the singular illumination that you -perceive on the moon. But when, as occurs only occasionally, all that -part of the atmosphere which surrounds the earth along the edge visible -from the moon is filled with clouds, the air can no longer transmit the -refracted rays, and then, no light being sent into the shadow, a ‘dark -eclipse,’ as astronomers call it, results. An eclipse of the sun is a -very different thing. That is caused not by a shadow but by the opaque -globe of the moon passing between the earth and the solar orb. When this -occurs the sun is completely hidden behind the moon, and only its -corona, which projects beyond the moon on all sides, is visible.” - -“Indeed! I supposed that all eclipses were very much the same thing.” - -“By no means. An eclipse of the sun is an event of extreme importance to -astronomers, while an eclipse of the moon possesses comparatively little -scientific interest.” - -“I do not see why that should be so.” - -“It is so, for the reason that when the sun is eclipsed, as I have just -told you, the solar corona, which cannot be seen at any other time owing -to the overpowering brilliance of the solar orb, becomes plainly -visible, and by studying the form and other particulars of the corona -astronomers are able to draw most important conclusions concerning the -constitution of the sun, the mechanism of its radiation, and its effects -upon the earth. During an eclipse of the moon, on the other hand, -practically nothing new is revealed, and, accordingly, astronomers pay -comparatively little attention to such phenomena. Lunar eclipses, -however, possess a certain importance, because by predicting the times -of their occurrence and then comparing the predictions with the events, -something is learned about the motions of the moon. I should add that -recently eclipses of the moon have been carefully watched by a few -astronomers, notably by Prof. William H. Pickering, because of peculiar -effects which seem to be produced at certain points on the moon by the -chill which the shadow casts upon her surface. There are also -interesting observations to be made concerning the reflection of heat -from the moon during an eclipse. But, upon the whole, a lunar eclipse is -mainly interesting as a curious spectacle, and as a test of the -correctness of astronomical calculations of the motions of the heavenly -bodies. - -“I may add, however, that eclipses of the moon have been of some use to -historians in fixing the dates of important occurrences thousands of -years ago. This is possible because astronomers can by calculation -ascertain the times of eclipses in the past as well as in the future. -Perhaps the most interesting of all instances of this kind is that which -relates to the date of the beginning of the Christian era. This has been -fixed by means of an eclipse of the moon mentioned by the ancients as -having happened the night before the death of Herod, king of the Jews.” - -“It seems to me,” said my friend, “that the faint light on the moon’s -face is continually changing. It does not appear constantly to have the -same tint. While we have been standing here, I have noticed that some -parts have grown darker and others lighter, and that the red color on -the right has become a little more intense.” - -“Yes, and that, too, is no doubt caused by the earth’s atmosphere. While -the eclipse lasts, the earth is rapidly rotating, and consequently new -parts of the atmosphere are continually brought to the edge where their -refractive effects come into play. If the atmosphere at the edge of the -earth is a little more or a little less dense its refraction varies -proportionally. Then, changes in the relative clearness or cloudiness of -the air are taking place all the time, and these are reflected in the -illumination on the moon.” - -“It seems to me, then, that the earth would present a very remarkable -spectacle if we were now on the moon looking at it.” - -“Surely it would. Seen from the moon the earth appears several times -larger than the sun. For the people of the moon, if we imagine them to -exist, an eclipse of the sun is now in progress. For them the earth now -occupies the same relative position which the moon occupies for us just -before it appears in the west as New Moon. They cannot see it except in -silhouette as it passes over the sun. More than an hour ago, if they -were watching (and if they exist, and are intelligent beings we may be -sure that they were on the alert), they suddenly perceived a black -round-edged notch in the side of the sun. Instead of being more or less -cloudlike and indefinite in outline, like the shadow of the earth on the -moon, this notch appeared to them perfectly black and smooth. At a -glance, they saw that the body producing it was much larger than the -sun. As the sun’s disk was gradually hidden behind the earth the shadow -of the latter fell over them, until the sun was wholly concealed. -Then—and this is true at the present moment—they perceived that the huge -disk of the earth was ringed with light, probably of a reddish tinge. -This light, as I have already indicated, is that which the atmosphere -refracts around the edge of the earth.” - -“It must be truly a magnificent sight,” said my companion. - -“Yes, and it is doubtless rendered far more magnificent by the other -phenomena which our people at the moon have before their eyes. In -consequence of the virtual absence of air there, an observer on the moon -would see all the stars, even in full daylight, blazing in a jet black -sky. The brilliance of the stars and of the Milky Way would hardly be -increased by the hiding of the sun, but probably the long silvery -streamers of the solar corona would glow perceptibly brighter when seen -projecting out on each side of the enormous disk of the earth.” - -“But is it true that the moon has no air?” - -“Very, very little, and what little she has is probably different in -composition from our atmosphere. Some observations seem to indicate that -there is a very rare atmosphere on the moon, but to us it would seem a -perfect vacuum. We could not breathe there at all.” - -“How then do those intelligent inhabitants, whom you have pictured for -me watching the earth at this moment, manage to survive?” - -“Ah, I did not say that there actually are inhabitants in the moon. I -only imagined them to exist for the sake of showing how this eclipse -would appear seen from the moon. Still, we cannot be absolutely sure -that there are no inhabitants on the moon. Even without air like ours it -is conceivable that beings of some kind, and intelligent beings, too, -_might_ exist there. However, astronomers have never yet been able to -discover evidence of their presence. Lately, indications have been found -of the probable existence of vegetation on the moon, but I shall speak -of that later, when with the aid of the series of lunar pictures made at -the Yerkes observatory we try to make a ‘photographic journey’ in the -moon.” - -“But tell me, has the moon always been so airless?” - -“That is another unsettled question. Some astronomers have thought that -formerly, ages ago, the moon possessed a much more dense atmosphere than -she has at present. Having separated from the earth, in the way I have -described, it is natural to suppose that at first she may have had an -atmosphere very like ours. The explanation of its disappearance which -was once generally accepted was that it had been absorbed into the lunar -rocks, as the globe of the moon cooled off. But recent progress in our -knowledge of the nature of the gases composing the atmosphere has led to -a different explanation. This assumes that nearly all of the moon’s -atmosphere has _flown away from her_ because the lunar globe does not -possess sufficient gravitating force or attraction to retain it. If the -mass of the earth were no greater than that of the moon, our atmosphere -also would probably have escaped by flying off into space.” - -“But how, and why, do these gases fly away?” - -“They do it by virtue of what physicists call their molecular velocity. -A gas, of whatever kind, is a mass of molecules which are in continual -vibration, moving in all directions among one another with very great -velocities. These velocities have been measured, and it has been found -that the molecules of nitrogen, one of the components of the air, move -at the rate of two miles in a second. The velocity of the molecules of -oxygen is a little less; that of the molecules of hydrogen is very -great, nearly seven and a half miles in a second! Now, it is also known -that the attraction of the earth is sufficient to retain permanently -upon its surface all moving particles or molecules which have a velocity -less than seven miles in a second, while the attraction of the moon only -suffices to retain those whose velocities fall under a mile and a half -in a second. So you perceive that all of the gases I have named would -soon escape from the moon, even if they were present upon it at the -beginning of its history. - -“I must also remind you that there is no water upon the moon, at least -not in the form of rivers, oceans, lakes, ponds, or even of clouds. But -Professor Pickering has recently noted certain appearances which may be -due to the formation of a kind of hoar frost. If there were once oceans -upon the moon, as the great plains, called _maria_, or seas, in the -lunar charts, seem to indicate, they, too, have escaped by evaporation. -The velocity of the molecules of water vapor is two and a half miles per -second, a mile greater than the ‘critical velocity’ which the attraction -of the moon would be able to control.” - -“But,” interrupted my companion, “I am puzzled to understand how you -know so much about the power of the moon to hold things.” - -“It is really quite simple,” I replied. “The attraction of gravitation, -which is a property belonging to all known bodies, is measured by the -mass, or amount of matter, in a body. It also varies with the distance -between the attracting and attracted bodies. We know, by means which I -shall not attempt to describe here, the mass both of the earth and of -the moon. We also know the size of both of these bodies. They attract -objects as if their entire masses were concentrated at their centers. A -body of a certain kind and size at the surface of the earth weighs just -one pound. If the earth were reduced to half its actual diameter, while -retaining the same mass or amount of matter, more closely packed -together, the body which now weighs one pound would then weigh four -pounds, because it would be twice as near to the center of the earth as -before, and the attraction of gravitation varies according to the square -of the distance from the center. As the distance diminishes the force -increases. The square of two is four, therefore the body would be -attracted with four times the force which it experiences at present. -Now, the moon is not only much smaller than the earth, but its average -density, or the closeness with which the molecules of its rocks are -packed together, is less. It results from these facts that the ratio of -the entire mass of the moon is to that of the earth as one to -eighty-one. Hence the inherent power of the moon to attract bodies is -less than one-eightieth as great as the earth’s. If the diameter of the -moon were the same as that of the earth, a body weighing one pound on -the earth would weigh only one eighty-oneth part of a pound on the moon. -But the diameter of the moon is less than one quarter as great as that -of the earth. It follows that bodies on the moon are almost four times -(more accurately about 3.66 times) nearer to the center of attraction. -This fact must be taken into account in calculating the force of gravity -on the moon’s surface. As far as the mass of the moon is concerned, -bodies on her surface experience less than one-eightieth of the -attractive force which the earth exercises upon bodies on its surface, -but this is so far counterbalanced by their greater nearness to the -center, that the actual attraction upon them is about one sixth of that -which they would experience on the earth.” - -“Thank you,” said my companion dryly, “your explanation appears to me to -be very scientific.” - -“Not by any means as scientific as it might be, or as it ought to be,” I -replied, laughing. “But, really, if you wish to understand these things -you should not be too much afraid of the bugbear ‘science.’ Science -makes the world go nowadays, and everybody ought to know a little about -it, just as everybody with any pretensions to education a hundred years -ago had to learn more or less Greek and Latin. But let me continue a -little farther. Since the force of attraction on the moon is only one -sixth as great as it is on the earth, the weight of all bodies is in the -same proportion. Pardon me if I guess at your weight; it is, perhaps, -120 pounds. Very well, translated to the moon you would weigh only 20 -pounds.” - -“Dear me, then skipping the rope may be the favorite pastime of -middle-aged ladies on the moon.” - -“And throwing somersaults that of gray-haired lunar gentlemen. Let me -tell you of one very interesting consequence of the small force of the -moon’s gravity, which affects not merely the weight of bodies but the -flight of projectiles, and, indeed, all motions of every kind. You will -see, when we come to the photographs, that some of the lunar volcanoes -are of a magnitude almost incredible. This is doubtless due to the fact -that the ejections from volcanic craters there were able, with no -greater expenditure of explosive force, to attain an elevation six times -that which they would attain if thrown from a volcano on the earth. -During the eruption of Vesuvius in April, 1906, the column of smoke, -steam, and cinders from its crater reached, according to the measures of -Professor Matteucci, a maximum height of about eight miles. On the moon -the same force would have blown these things almost fifty miles high! It -is not difficult, in view of such facts, to see how the giant volcanic -craters and mountain rings of the moon were formed.” - -In the meantime the eclipse continued, and, having tired of watching it, -we returned to the drawing-room. - -“When shall we see these famous photographs and begin our imaginary -journey in the moon?” my companion asked. - -“To-morrow,” I replied. “But I shall have to demand one more brief -exercise of your patience this evening, while I finish with this subject -of eclipses.” - -“Then we are not through yet?” - -“Not quite, for I have not yet told you why the moon is not eclipsed -every time she approaches the earth’s shadow, and why she does not -eclipse the sun once every month at the time of New Moon.” - -“Well, tell me then, and I promise to be as interested as possible; only -please don’t talk any more mathematics than is absolutely necessary.” - -“Very well, I’ll spare your attention as much as possible. To begin with -the eclipses of the moon: The reason why they are not of regular monthly -occurrence is simply because the orbit of the moon is a little inclined, -about 5¼°, to the orbit of the earth. Even then there would be an -eclipse once every month if the orbit of the moon were fixed in space, -and if the point where that orbit crosses the plane of the earth’s orbit -were always directly opposite to the sun. But instead of being fixed in -position the orbit of the moon has a curious motion of revolution of its -own. This causes the two opposite points, where it crosses the plane of -the earth’s orbit, and which are called the moon’s ‘nodes,’ to move -continually onward in a direction opposite to that in which the moon -revolves, but much more slowly. A period of about nineteen years is -required for the moon’s nodes to complete a revolution. The consequence -is that the nodes are not always in line with the earth and the sun, and -except when they _are_ nearly in line no eclipse can occur. To enter -into a complete explanation of this would require more ‘mathematics’ -than you would like, but what I have said may at least serve to give you -an idea of the reason why eclipses are comparatively of rare -occurrence.” - -“I think I understand the reason sufficiently. But what a complicated -affair you astronomers make of what, it seems to me, should really be a -very simple thing.” - -“It is like a sewing machine,” I replied, “which seems very simple when -you see it running smoothly, and do not trouble yourself about all the -various parts of its mechanism. But if you undertake to explain to -yourself, or to make clear to another person, exactly how the machine -works, you find that your attention is rather severely taxed, and that -the apparent simplicity is based upon no little complexity of -construction and interaction of parts. You will have understood from -what I have said, that the reason why the moon does not eclipse the sun -once every month is based upon the same fact, namely, the inclination of -the moon’s orbit to the plane of the orbit of the earth; and that when -she does eclipse the sun her nodes must be somewhere near a line drawn -from the earth to the sun. There is one broad difference between an -eclipse of the moon and an eclipse of the sun which I have not yet -mentioned. This arises from the fact that the moon being so much smaller -than the earth, her shadow, when she hides the sun, does not cover the -entire earth, as the earth’s shadow covers the whole moon, but comes -almost to a point before reaching the earth. The average length of the -moon’s shadow is only 232,150 miles, 6,690 miles less than the average -distance between the moon and the earth. But since, in consequence of -the eccentricity of her orbit, the moon’s distance is continually -varying, the length of her shadow also varies to the extent of about -4,000 miles each way. Thus it may be as short as 228,300 miles, or as -long as 236,050 miles. When the greatest length of the moon’s shadow -coincides with her least distance from the earth (221,600 miles), her -shadow extends more than 18,000 miles beyond the earth. Under such -circumstances its diameter at the surface of the earth is about 167 -miles. That is the greatest diameter that the shadow of the moon can -have at its intersection with the earth. Ordinarily, when it reaches the -earth at all, its diameter is less than 100 miles, and often very much -less. If the earth and the moon were motionless during an eclipse, her -shadow would form a round, dark spot on the earth, and all observers -within the circumference of that spot would behold the sun totally -eclipsed. But, in consequence both of the motion of the moon in her -orbit, and the rotation of the earth on its axis, the shadow spot moves -swiftly in an easterly direction over the earth’s surface, forming what -is called the path of the eclipse. The astronomer calculates beforehand -across what parts of the earth the path will lie, and selects his points -of observation accordingly. - -“When the length of the shadow is too small to reach the earth, the moon -appears projected against the sun as a round black disk, hiding the -center of the solar orb, but leaving a brilliant ring all around. Such -phenomena are called annular eclipses. There are about three annular -eclipses for every two total ones. When the moon, as often occurs, does -not traverse the center of the sun’s disk, as seen from any part of the -earth, a partial eclipse is the result. This means that only a portion -of the sun is hidden by the moon. Even a total eclipse appears as a -partial one to observers who are not placed within the limits of the -shadow path.” - -“But it seems to me,” said my friend, “you have hedged round your -eclipses with so many difficulties, what with the tip of the moon’s -orbit, and what with the shortness of her shadow, that they must be very -few in number. Yet I often hear of an eclipse, although I have never -seen one before to-night.” - -“They are not so rare as you might suppose,” I replied. “It is not -necessary, in order that an eclipse, either partial, or total, or -annular, may occur, that the moon’s nodes be in a _direct_ line with the -centers of the sun and the earth. The moon may be a few degrees out of -line, and yet either pass into the earth’s shadow or be seen crossing -the sun from one point or another on the earth. There are about 70 -eclipses in every eighteen years, 41 of the sun and 29 of the moon, but -the number varies a little. Generally there can be no more than two -eclipses of the moon in any one year, but it is possible for three to -occur. The greatest number of solar eclipses in a year is five, but this -is very rare, the usual number being two. In fact, there must be at -least two solar eclipses in a year, but there are many years which have -no eclipses of the moon at all. And now, I think I have said all that is -necessary about eclipses, and we arrive very opportunely at the end of -the discourse, for behold the moon is passing out of the shadow, and her -light begins once more to glow in the park.” - -This was indeed the case. Going to the door, we saw the earth’s shadow -slowly withdrawing from the face of the moon, while the landscape was -brightening under her returning rays. For a few minutes we watched, in -silence, the brilliant spectacle. Then my companion turned to me. - -“Would you know my whole thought?” she asked. “I fear that I cannot -recall many of the scientific facts you have just been telling me, but -for them I can go back, at need, to the books. Yet one thing I feel that -I have certainly gained. It is a sense of friendly, companionable -interest in the moon. Henceforth she will be more to me than she ever -was before. I shall always be conscious, when looking at her face, that -she is the offspring of the earth, and that there exists between these -two bodies an intimacy that I had never imagined possible. For me your -tides and your eclipses seem an inarticulate language, a caressing -exchange of communications between these two celestial beings of one -blood. To my mind they are, in a certain sense, personalities, and, as a -creature of the earth, I feel now my relationship to the moon.” - -“Very good,” I replied. “All science and all forms of knowledge are -rooted in the imagination. To-morrow we shall begin with the -photographs, and many most interesting things that I have not yet -mentioned will then naturally present themselves before us.” - -“Good night then,” said my companion, “and to-morrow I shall count upon -the delights of a photographic journey in the moon.” - ------------------------------------------------------------------------- - - - - - I - - NEW MOON TO FIRST QUARTER - - - - ------------------------------------------------------------------------- - - - - - I - - NEW MOON TO FIRST QUARTER - - -AT breakfast the next morning I asked my friend if she still had -sufficient curiosity concerning the moon to induce her to undertake the -contemplated journey amid lunar scenes. - -“Yes, surely,” she replied. “My dreams last night were filled with -wonderful spectacles; great cones of shadow flitted continually through -the heavens, eclipsing, in turn, moon, sun, and stars; and I stared, as -it seemed, for hours at strange faces veiled behind a maze of -mathematical diagrams covering the moon. I am not sure that your -discourses have made me scientifically much wiser, but I feel that my -imagination is sufficiently aroused to enable me to enjoy the -photographic excursion that you have proposed, and I am quite ready to -start at once.” - -“Excellent!” I said, producing my portfolio. “Here then are the -photographs which I trust will enable us, in imagination, to spend an -interesting month upon the moon. These photographs were made at the -Yerkes observatory and they represent the moon, as you will perceive, in -all of her principal phases, beginning with the narrow crescent of the -New Moon, and ending with the similar, but reversed, sickle of the Old -Moon.” - -“Let us take them out into the park under the trees,” my friend -suggested. - -The shafts of morning sunshine, falling through the branches and -illuminating the broad lawns and brilliant flower-beds, offered the -greatest possible contrast with the strange scenes of the preceding -night. We chose the shadow of a huge elm, and had a table placed there -for our accommodation. On this I spread the photographs, and my -companion began to examine them with many expressions of interest. - -“It is not often,” I said, “that science finds so flattering an -audience.” - -“And I hope, surely, never so small a one,” she responded, laughing. -“But you must admit that science very seldom presents herself in so -attractive a form as that of these pictures.” - -“They are indeed of the highest excellence,” I replied. “It is the very -moon herself that you see there.” - -“But are you certain that they have not been embellished? Has not the -hand of an artist retouched and improved them—particularly these large -ones that seem to contain a thousand curious things which I can hardly -believe really exist on the moon?” - -“No,” I said, “there is nothing fictitious or imaginary in what you see. -The only art displayed here is that of the astronomer-photographer, -whose greatest ambition is to make his pictures absolutely true to -nature. A defect in one of his plates, producing the appearance of a -speck of light or shadow which does not actually exist, causes him as -much distress of mind as you would experience upon hearing a false note -from your piano. Indeed, the astronomer is so desirous of having nothing -but the truth represented in his pictures that he often prefers, for his -own study, the original negatives alone, because every time that they -are reversed to make a ‘positive’ copy something is sure to be lost, and -some slight defect is certain to be introduced. Let us begin, if you -please, with the series of smaller pictures showing the various phases, -and the gradual advance of daylight across the moon’s surface. Take -first the photograph which I have labeled No. 1. It shows the New Moon -when it is between three and four days old. You must often have seen it -in that form in the western sky soon after sunset. Photographs of the -New Moon have been made when the crescent is still narrower than that -here shown, but there is no such photograph in this series, and it would -possess little interest for you because almost no details of mountains, -craters, and plains would be visible. It is hardly possible to make a -good photograph of the moon when it is only one or two days from the sun -in its monthly journey, on account both of the glare of the solar light -in our atmosphere and of the nearness of the moon to the horizon, where -the air lacks transparency and steadiness. In the photograph before us -you will observe a great number of strange forms and shadings. I shall -tell you what these are presently, but first let me call your attention -to the fact that the picture does not exhibit a phenomenon which you -would behold if you were actually looking at the moon in the phase here -represented. You see here the New Moon very clearly, but not the Old -Moon in her arms.” - -“Indeed! It is a pity that the photograph does not show so interesting a -sight.” - -“Yes, it is a pity. The cause lies in the defect of light from what I -have called the ‘Old Moon.’ The part that we see in the photograph is -illuminated with sunshine, while the remainder of the moon reflects only -the earthshine, which is too faint to be photographed (at least with the -amount of exposure required to make a good picture of the brightly -lighted crescent); although, as I have said, you would see it clearly if -you were looking at the New Moon herself.” - -[Illustration: - - NO. 1. FEBRUARY 19, 1904; MOON’S AGE 3.85 DAYS. -] - -“But,” interrupted my companion, “do you mean to tell me that the earth -illuminates the moon?” - -“Surely it does. Why not?” I replied, smiling. “You must remember that -the earth is simply a huge moon to our imagined inhabitants of the lunar -world. Our globe sends to the moon about fourteen times as much -reflected sunlight as the moon sends to the earth. The consequence is -than an earthlit night on the moon is far more brilliant than a moonlit -night on the earth.” - -“Then why do we not always see the moon shining with light from the -earth?” - -“It is a question of contrast. You cannot see a faint light in the -immediate presence of an overpoweringly brighter light. The part of the -moon that the sun illuminates is in the full glare of day, and this is -so much more brilliant than the reflected earthlight that that portion -of the moon which enjoys only the latter is not visible to us, except -for a few days after New Moon, when the amount of light from the -crescent is not yet great enough to dazzle our eyes and hide the rest -from sight. I should advise you when the next New Moon occurs—you can -find the date in any almanac—to look at it in the western sky. You will -see in addition to the bright crescent the full round orb of the moon, -shining faintly, with a dull, rather copperish, tint, and you will find -it interesting, then, to remember that that light is reflected from our -earth. - -“And now,” I continued, “let us examine our photograph more closely. -There is one remark that I had expected which you have not made; it -concerns the position of the crescent. You observe that it is bowed -toward the left. If you saw it with the naked eye in the sky it would be -bowed toward the right, or toward the place of sunset. The reason is -that the photograph presents the moon as seen with a telescope, which -reverses objects, turning them top for bottom. In this picture, and in -all the others that we shall examine, the southern part of the moon is -at the top and the northern part at the bottom, the western part at the -left and the eastern part at the right. The first thing that you -probably notice in the photograph is a conspicuous oval plain, somewhat -below the center of the crescent.” - -“Yes, and I see clearly why you call it a plain, for it is perfectly -flat and smooth.” - -“Not quite so flat and smooth as you suppose. This object is one of the -most celebrated on the moon. It is the so-called _Mare Crisium_, or Sea -of Crises, as we may translate the name given to it by the astronomers -of a couple of centuries ago, many of whom knew more Latin than science. -Owing to its apparent smoothness of surface, as well as to its form and -general aspect, they took it for a great lake or sea.” - -“To tell you the truth,” said my friend, “if I were an astronomer and -had discovered this curious place on the moon, I should certainly -believe just what your Latin-loving predecessors believed, but I doubt -if I should have been capable of inventing so singular a name for it.” - -“In the singularity of the names they chose for objects on the moon,” I -replied, “their invention is unrivaled. We shall see some remarkable -examples. Of course they are not at all to be blamed for thinking that -this oval spot, and other similar ones of much greater magnitude, were -seas and oceans. They simply judged by appearance and by analogy. -Finding mountains on the moon, they saw no improbability in supposing -that there were bodies of water also. They had not the means of knowing, -as we know to-day, that there is no water on the moon. Yet, perhaps, -they were not so far wrong after all. The _Mare Crisium_ certainly has -the look of an empty sea bed, and I should not be willing to assert that -ages ago it was not filled with water.” - -“Like the Great Salt Lake, dried up,” suggested my companion. - -“Not exactly, for the Great Salt Lake dried up would probably present a -surface as white as snow, whereas the _Mare Crisium_ is very dark. It -must be admitted, however, that gradually the white deposit would grow -darker, and there may be much significance in the fact, which some -observers have noticed, that, at times, parts of the dark plains on the -moon seem to glitter with minute points of light. Your imagination is at -liberty to see deposits of salt there.” - -“In that case,” said my companion, laughing, “I should prefer to regard -the _Mare Crisium_ as resembling that wonderful valley discovered by -Sindbad the Sailor, whose floor was sprinkled with diamonds.” - -“Well,” I replied, “science certainly cannot deny the possibility of -diamonds on the moon, for she is _par excellence_ the world of -volcanoes, and one of the most striking discoveries of recent years is -that of the intimate association existing between ancient volcanic vents -and deposits of diamonds. The diamonds of South Africa are found in lava -rocks that cooled off ages ago.” - -“Then I hope that no future Columbus will find a way to the moon, for we -should have too many diamonds, and they would lose all their charm.” - -“That is true, but suppose that not only diamonds but even more -beautiful gems should be discovered in the lunar world? You surely would -not object to a transethereal traffic bringing them to our doors. -However, there is not the slightest prospect that we shall ever be able -to go from the earth to the moon. Let us resume our examination of the -photograph, and concentrate our attention on the known facts.” - -I then proceeded to tell my friend, whose interest I was delighted to -find had not yet begun to flag even in the face of comparatively -matter-of-fact statements, that the _Mare Crisium_ is a profound -depression, about 350 miles in length by 280 in breadth. Exactly how far -it lies below the general level of the lunar surface we do not know; -but, at any rate, if it was ever filled with water it formed a deep, -navigable sea. Its encircling mountains, which appear generally bright -in the photograph, especially along the eastern border, where the -sunlight strikes directly against their slopes, are in many places steep -and abrupt. At one place, on the southwestern side, there is a -mountainous promontory 11,000 feet in height. There are a number of -small craters on the floor of the _Mare Crisium_, but the scale of this -photograph is not large enough to show them clearly. - -“You will notice,” I continued, “that there is a kind of bay on the -eastern side, which runs back into the mountains, and is bordered with -high, steep cliffs. Near this point, on that part of the moon over which -the sun has not yet risen, there is a very remarkable mountain which we -shall see in a later photograph. But let us finish with this one. Look -at the comparatively small oval adjoining the _Mare Crisium_ below -(toward the north). It is one of the great crater rings of the moon, and -is named Cleomedes. It is much larger than it looks, being nearly 80 -miles in its greatest diameter, and there is a peak on its surrounding -wall 10,000 feet in height. Still farther toward the north you will -observe two or three other smaller craters or rings, which are very -interesting when studied with the telescope. - -“Now, please turn your attention to the photograph bearing the number 2. -You see again the _Mare Crisium_, and nearly in the center of the -crescent, and just on the border line between day and night, a perfect -oval ring with a central peak. It is called Langrenus. It is even larger -than Cleomedes, being about 90 miles across. It has the form of an oval, -as we see it, but that is an effect of perspective, since it is so far -round the side of the lunar globe. In reality it is a nearly circular -circumvallation, or rather an almost perfect hexagon, composed of -gigantic mountains including a valley, in the center of which rises a -cluster of peaks 3,000 feet in height.” - -“This second photograph,” interrupted my friend, “was taken later than -the first, I suppose, since it shows more of the moon’s surface.” - -[Illustration: - - NO. 2. SEPTEMBER 24, 1903; MOON’S AGE 3.87 DAYS. -] - -“I should have told you that,” I replied. “Yes, it does represent the -moon at a time when more of its surface, visible to us, is illuminated -by the sun. In fact, we may regard it as a picture of the moon made -about a day later than the other. But I must now tell you that these -photographs were not all taken in regular succession, a day apart, or -even two days apart. That was impracticable for reasons that I need not -explain. Some of them were made at one season of the year and some at -another. Yet taken together they form a sufficiently continuous series -to enable us, with their aid, to follow the changing aspects of the moon -during more than three weeks, or all that part of a lunation in which -the moon is a conspicuous object in the sky.”[2] - -Footnote 2: - - In addition to what is said in the text concerning the photographs the - reader should be informed that, in consequence of her “librations,” - the moon does not, all the time, present _exactly_ the same surface - toward the earth. If she did we should never see more than one half of - her surface. In fact, however, at one time or another, we see, in all - (but never at the same time), about fifty-nine per cent of her - surface, leaving forty-one per cent which is forever invisible because - never turned in our direction. The librations, or “balancings,” of the - moon, which bring now one and now another portion of the usually - invisible hemisphere into view, are of three kinds: First, the - libration in latitude, arising from the combined effects of the - inclination of the moon’s orbit to the plane of the earth’s orbit, and - the inclination of her axis of rotation to the plane of her own orbit. - When added together these two inclinations make the axis of the moon - lean one way or the other with respect to the earth about 6½°. But, - since the inclination of the moon’s orbit to that of the earth is - continually varying to a small extent, the amount of this libration is - also variable. Its effect is to cause now the North and now the South - Pole of the moon to incline slightly toward the observer on the earth, - so that he can see alternately a little way round the northern and the - southern edges of the moon’s disk. - - Second, the libration in longitude, which arises from the eccentricity - of the moon’s orbit, causing her to move a little faster when she is - nearer the earth, or in perigee, and a little slower when she is - farther from the earth, or in apogee. In consequence of this, she gets - alternately about 6° ahead of, or behind, the position which she would - have if her orbit were a perfect circle and her motion perfectly - uniform. But, inasmuch as her rotation on her axis is never either - faster or slower, she shows a little of her usually invisible - hemisphere on the western side when she is between perigee and apogee, - and a little on the eastern side when she is between apogee and - perigee. The accompanying diagram is designed to aid the reader in - understanding these effects. - -[Illustration: - - Effect of Moon, Varying Velocity in Orbit Producing Libration in - Longitude. -] - - Third, the diurnal libration, which arises from the fact that the - diameter of the earth bears a considerable proportion to the distance - of the moon. If the observer were at the center of the earth there - would be no effect of this kind, but being situated about 4,000 miles - from the center, there is a parallactic effect in consequence of which - we see a little around the western side of the moon when she is rising - and a little around the eastern side when she is setting. The maximum - diurnal libration is a little more than one degree. The maximum - libration in latitude is 6° 44´, and that in longitude 7° 45´. An - illustration of the results of libration will be found by comparing - photographs Nos. 1 and 2. They were both taken at nearly the same “age - of the moon,” about three days, twenty hours, but under different - librations, so that in No. 2 more of the western edge of the moon is - visible, and the crescent appears broader. Even more remarkable - examples of the results of libration are seen in Nos. 6 and 7, and 8 - and 9. In No. 6, the moon is actually “older” by about half a day than - in No. 7, yet, owing to libration, the “terminator,” or line between - day and night on the moon, is considerably farther toward the east in - the latter than in the former. A similar effect is seen in comparing - Nos. 8 and 9. The exact dates and ages of the moon corresponding to - these photographs are given in the Appendix. - -“If you will follow the curve of the terminator toward the south (upward -in the photograph), you will perceive that there is a long line of -ovals, more or less resembling Langrenus. The first of these, darker in -appearance than Langrenus, is named Vendelinus.” - -“What extraordinary names!” exclaimed my companion, “and how -unpicturesque!” - -“Yes, it is true that the invention of the old astronomers who supplied -these names seems to have failed a little at times. They did exceedingly -well in naming the ‘seas’ and similar objects, but for the mountains, -craters, and ring plains they could think of no better plan than that of -attaching to them their own names, and the names of other _savants_, or -supposed _savants_ of their time, or of preceding centuries. And in -Latinizing these names they gave them a kind of uniformity, which is -hardly pleasing to our taste to-day. But let me continue. Vendelinus is -an extremely beautiful sight when the sunlight strikes its broken walls -in such a manner as to bring into prominence, by contrast with the deep -shadows, the rugged peaks, precipices, and ridges of which its very -irregular ring is composed. You should see it with a powerful telescope, -especially under the rays of the setting sun. Then the bottom of the -valley within has been described by Mr. Eiger, an English student of -lunar phenomena, as appearing punctured like a sieve with holes.” - -“And what are they?” - -“Volcanic craters, probably, long since extinct.” - -“So many volcanoes in one place?” - -“Oh, yes. You have been at Naples and have seen Vesuvius. But probably -you have not visited the Phlægrean Fields which lie northwest of Naples. -If you had had a passion for geology when you were in Italy you would -have explored that region, and there you would have found something not -altogether unlike the valley of Vendelinus in the moon. There is a great -number of extinct volcanic craters near Naples, and they show how -similar in many ways the moon is, or has been, to the earth.” - -“But, dear me,” my friend exclaimed, “are we going to see nothing but -burned-out craters and wild, ragged mountains on the moon? I am sure -that I should never have thought of visiting Naples for the sake of -looking at its Phlægrean Fields.” - -“Still,” I replied, “you must certainly know that Pompeii and -Herculaneum and the memories of their tragic fate are the most vivid -attraction of Naples to-day, although the Pompeiians have all been dead -for almost 2,000 years. So in looking at these spectacles in the moon we -cannot but be interested by the reflection that they are reminders and -relics of a wonderful history, whatever its precise character may have -been. The moon seems to me to stand for the most affecting of all -tragedies—the passing of a world. When I survey its extraordinary -landscapes, it is like looking upon a long-abandoned stage, whose actors -are in their graves, whose scenery is moldering under a gaping roof, -whose machinery is broken, whose very traditions are forgotten, but -which yet retains a semblance of its former brilliance. I do not have to -imagine inhabitants in the moon at the present day in order to find it -interesting. The possibility that it may once have had inhabitants is -enough, remembering its nearness to the earth and the manner of its -origin, to make it the most fascinating thing that the heavens contain.” - -“Indeed, I had never thought of the moon quite in that way,” was the -reply. “If you can read a history for me in these craters and ring -plains I believe I shall find them more interesting than I expected.” - -“I cannot promise you a history as full of romantic details as that of -Herodotus,” I said, “but it may contain nearly as many actual facts. -However, we shall see about that as we go along. Let us now return to -the inspection of the photograph. Be kind enough to look a little above -Vendelinus. You observe there another still larger ring plain, or walled -valley, with a conspicuous mountain in the center. This is Petavius. It -belongs to the chain of similar formations which includes Langrenus and -Vendelinus, but it is more wonderful than either of them. It is nearly a -hundred miles long from north to south. For some reason, as with -Vendelinus, its ruggedness and complexity of structure are more -conspicuous in the lunar afternoon than in the lunar morning. It is a -question of the direction in which the light falls across it. A curious -thing about Petavius is the convexity of its vast floor. The center is -about 800 feet higher than the edges along the feet of the surrounding -mountains.” - -“How do you know that?” - -“The shadows tell the story. The height of objects on the moon is -measured by observing the length of their shadows under a known -inclination of the sun’s rays. When I stand this book upright on the -table, allowing the sunlight to strike it on one side, it casts a shadow -on the table. If I did not know the height of the book, and could not -measure it directly, I could find it out by measuring the length of its -shadow, other simple trigonometrical data, easily ascertained, being -known. There is an enormous cleft not clearly visible in the photograph, -extending from the central mountains of Petavius to the southwestern -wall of the valley. Still farther south, above Petavius, you will notice -another conspicuous oval plain and several smaller ones near it. The -largest of these is named Furnerius. They all lay in the morning -sunshine, not far from the terminator, when this photograph was taken.” - -“Tell me, please, about the ‘terminator’ of which you have spoken -several times. As I understand you it is the line between day and night -on the moon.” - -“Yes, and a very wonderful line it is, too. There is nothing just like -it on the earth. Owing to the effects of our atmosphere in dispersing -the light, day and night do not stand face to face with one another on -the earth in the same way that they do on the moon. Here we have -twilight in the evening and dawn in the morning, and night neither comes -nor goes for us with the startling suddenness that characterizes it on -the moon. For an hour or two after sunset and before sunrise, we receive -rays of reflected and refracted light from the atmosphere above us, -which spread a soft, pleasing illumination over the landscape, and -render all objects more or less distinctly visible. But if you were on -the moon in certain situations, the passage from day to night or from -night to-day would be as rapid as the falling or rising of a curtain. -Imagine yourself standing on the western wall of Vendelinus or Petavius -at the time when this photograph was taken. You would be in a blaze of -pitiless, untempered sunshine, but glancing down the precipice at your -feet you would seem to be looking into a gulf of blackness. But for the -light reflected back from the eastern cliff, and that coming from the -earth, there would be scarcely a ray of illumination on the rocks below -you. You would look down into inky darkness, and would scarcely dare to -make a step from fear of falling over the edge of a bottomless pit. At -the same time, as I told you last night, you would see the stars all -about you in the sky, even close to the sun. - -“This is the reason,” I continued, “why the march of day across the -moon, always keeping sharp on the heels of night, is a spectacle so -imposing and unparalleled. It is this wonderful march that we are going -to follow with the aid of the photographs. I shall now ask you to give -your attention to photograph No. 3. It was made more than a day and a -half later than the others, measured by the age of the moon, which, in -this case, was about five days and a half. You notice how in the -interval the sunlight has swept eastward over the moon’s surface. The -_Mare Crisium_ is recognizable in the lowest or most northerly, of three -large, dark plains. The small white oval a considerable distance above -it is our old acquaintance Langrenus, whose floor and walls are now very -brilliant in the full sunshine, which falls upon them at a high angle. -Vendelinus and Petavius are less conspicuous. The broad, dark plain -which has come into view eastward from Langrenus is the _Mare -Fœcunditatis_, which we may translate ‘Sea of Fecundity’! You certainly -cannot aver that on this occasion the invention of the old astronomers -failed in the matter of romantic suggestiveness. The name calls up -pictures of a great body of tranquil water, fanned by gentle, -stimulating breezes, filled with fish of every variety, dotted with -vine- and flower-garlanded islets, and bordered by well-watered shores, -rich with vegetation, and supporting a numerous and happy population. -Some such idea of the _Mare Fœcunditatis_ may have been in the minds of -its sponsors a couple of centuries ago. But telescopes have become too -powerful in our day to permit us to be any longer deceived as to the -actual nature of this singular lunar region. Like the _Mare Crisium_, it -may have been the bed of a sea many years ago, but at the present time -it contains no water, and its shores present an endless succession of -fire-scarred cliffs, peaks, and volcanoes. The only ‘islands’ in it are -extinct craters.” - -“But,” said my companion, smiling, “where then is its history?” - -“Ah!” I replied, “is not this old sea itself history enough? When it has -receded sufficiently into the past, all history loses its details, and -presents only its setting and its grand primary elements. Suppose that, -some ages in the future, you should be an inhabitant of a distant -planet, surveying with a telescope the dried-up basin of the Atlantic -Ocean. Provided only that you were convinced, in your own mind, that it -had once been an ocean, with fertile, inhabited shores, and with ships -sailing upon it, you would be singularly lacking in imagination if you -could not reconstruct its history for yourself. The details could safely -be left to your invention and you could change them from time to time to -suit your varying moods. Terrestrial historians have sometimes done -that.” - -[Illustration: - - NO. 3. JULY 29, 1903; MOON’S AGE 5.54 DAYS. -] - -“But do _you_ believe that the _Mare Fœcunditatis_ was ever such a sea, -and the scene of such events?” - -“That is certainly a very pointed question. Questions of that kind are -always in order when one is treating of ascertained verifiable facts, -but just now, you know, we have wandered a little aside from the -straight path of scientific exactitude. Still, I will be frank with you -and say that I really possess no settled opinion concerning the former -condition of the moon, except so far as what we may call its -‘geological’ history is revealed by its present state. I am sure that -the moon was once the seat of tremendous volcanic action, and I think it -not improbable that its great depressed plains were once occupied by -water, but as to inhabitants, I know no more about them than you do. -Still, I am disposed to think that, as we go on, _you_, at least, will -reach the conclusion that all life has not yet disappeared from the -moon. We are going to learn some very suggestive and significant things -before we are through. - -“Farther toward the south and closer toward the terminator you will see -in the photograph a third dark plain with five sides, the northern one -convex and ill-defined. At its upper corner is an incomplete ring plain. -This region bears a still more curious name than the _Mare -Fœcunditatis_. It is the _Mare Nectaris_ or ‘Sea of Nectar.’” - -“Apparently your astronomers of old took the moon for an abode of the -gods.” - -“Yes, or for their wine cellar. But we shall get a better look at the -surroundings of this Sea of Nectar in a later photograph, and then I -shall have more to tell you about it. In the meantime let us return to -the _Mare Crisium_. To the east (right-hand side) of the _Mare Crisium_ -you will observe a diamond-shaped district, not very dark, with a bright -point at the corner which faces the _Mare_. You could never guess its -name. It is called the _Palus Somnii_, which may be translated ‘Marsh of -a Dream.’ It is a very singular place, and, seen with the telescope, -possesses a color which is unique upon the moon, a kind of light brown, -quite unlike the hue of any of the other plains or mountain regions. It -is covered all over with short, low ridges, as if its surface had been -broken up in a most irregular manner with a giant plow. What the person -who named it saw there to lead him to connect it in his mind with dreams -I have never been able to imagine. The bright point on its western edge -is a remarkable crater mountain, named Proclus. What that mountain is -made of nobody knows, but it gleams with extraordinary brilliance when -the sun strikes it.” - -“Why may it not be snow-covered?” - -“That is a suggestion which has often been made, but one great objection -to it is that we have reason for believing that snow, at least in such a -situation, cannot exist on the moon. Another objection is that only a -few of the lunar mountains are comparable in brightness with Proclus, -and they are not the loftiest ones. Upon the whole it is much more -probable that the reflecting power of Proclus is due to the composition -of its rocks, perhaps to broad crystalline surfaces exposed in the -sunshine.” - -“It is a surprise to me, then, that that ‘earthly godfather’ of lunar -wonders, who had a sufficiently vivid fancy to invent the ‘Marsh of a -Dream’ close by, did not name this mountain for some jewel, real or -imaginary.” - -“It would have been more poetic, indeed, but as I have already told you, -the mountains and volcanoes of the moon nearly all bear very prosaic -designations, while a wealth of fancy has been lavished in naming the -‘seas’ and plains. The astronomer Riccioli is responsible for most of -the commonplace nomenclature that we find in lunar charts. If you will -now glance at the northern (lower) ‘horn’ of the moon in the photograph -you will notice, near the terminator, about two thirds of the way from -the _Mare Crisium_ to the end of the horn, a pair of ring plains, or -crater rings, apparently almost touching one another. They are Atlas and -Hercules, the latter being the smaller one on the right. A darker oval -below them near the bright edge of the moon is Endymion.” - -“That, at least,” exclaimed my companion, delighted, “is a romantic and -appropriate name! I am enchanted to think that Endymion has not been -separated by your cold-hearted science from her who loved him so well.” - -“But if you should look at Endymion with a telescope you would wonder -what the moon could find in him to admire. He has been turned into a -huge, broken-walled ring plain. You will observe that the other, the -southern or upper horn of the moon in the photograph, appears -extraordinarily roughened. It is completely pitted with craters and -rings. There are so many of them, and they are so entangled, that I -shall not undertake to indicate them by their individual names, -especially as there is none among them of the very first importance. If, -however, you will bring your attention back to the _Mare Nectaris_ I -shall be able to point out to you a very extraordinary object, which -lies just on the border between day and night here, but will be seen in -the next photograph that we examine, in full morning light. The object -that I mean is a ring on the right-hand edge of the _Mare Nectaris_. Its -eastern wall and the top of its central peak are brightly illuminated by -the rays of the rising sun; while beyond it, to the eastward, -everything, with the exception of the tips of one or two high peaks, is -steeped in night. This is one of the mightiest volcanic formations that -the moon contains. Its name is Theophilus. To see it and certain -gigantic neighbors that it has, fully displayed, we shall turn, after -this glance at its first appearance, to photograph No. 4. - -“In this photograph the sunrise line on the moon has advanced so much -farther eastward that the _Mare Nectaris_ lies well within the -illuminated part of the disk, and Theophilus has become the most -conspicuous object of the kind in view. You now observe that it does not -stand alone, but is linked, so to speak, with another similar ring on -its southeastern side, while still farther southward is a third less -regular ring which seems to belong to the same group.” - -“Oh, yes,” cried my companion, “they certainly do seem to be connected. -They look like three links of an enormous broken chain dropped upon the -moon.” - -“The ring nearest to Theophilus,” I continued, “and whose northwestern -side has been destroyed to give room for the full circle of the wall of -Theophilus, is named Cyrillus. The other more distant one is Catharina. -If you wish to become a little learned in the geography of the moon it -is necessary that you should remember these names. As to the objects -that the names designate, they are far too wonderful ever to be -forgotten, and it is impossible to confuse them with any other features -of the lunar world. There is a great deal of ‘history’ connected with -these three enormous volcanic formations, but I am going to reserve that -for a while, because by and by we shall examine a larger photograph of -these same objects in which you will see their marvelous details -displayed. Now let me direct your attention to the first chain of -mountains that we have found upon the moon. Above Catharina you will -notice a thin, crinkled line of light passing through a comparatively -level district and ending at another ring. It is a range of peaks and -cliffs named the Altai Mountains. They are of no great height, and -cannot be compared in magnificence with the lunar Alps and the lunar -Apennines which we shall see in the photographs taken a few days later, -but they are nevertheless very interesting. The ring mountain at which -the Altai range terminates is named Piccolomini. It is another marvelous -object for telescopic study. The incomplete ring, with a dark interior, -which forms the southern corner of the _Mare Nectaris_, resembling a -semicircular bay, is Fracastorius. It is a very curious object because -close inspection reveals that the missing part of its ring has been -submerged, but is still faintly visible through the surface of the -_Mare_.” - -[Illustration: - - NO. 4. NOVEMBER 24, 1903; MOON’S AGE 5.74 DAYS. -] - -“I suppose it cannot be water that has covered it, since you have so -often assured me that there is no water on the moon.” - -“No, it is not water, but rock or sand or solidified lava, or some kind -of solid matter. It looks as though the whole bed of the _Mare Nectaris_ -had welled up in one mighty convulsive outpouring of liquid lava, which -broke down the wall of Fracastorius, inundated the interior, and then -hardened like a floor of cement. The probability that a catastrophe of -the kind I have described has occurred here is heightened by the fact -that the bed of the _Mare Nectaris_ is concave, sunken in the center, as -if it had broken and settled down ‘like ice upon a pond.’ Scattered more -or less all over its surface and particularly near its shores, there are -indications of this breaking down, and of something that has been -covered up.” - -“To me it seems very mysterious,” said my friend, “and very terrible -also.” - -“It is more or less mysterious to the astronomer likewise. Still, -geology shows that there have been somewhat similar occurrences on the -earth. If you will now direct your eyes to the lower (northern) part of -the photograph you will notice some additional things that have come -into view with the advance of the sunlight. You observe that a vast -somber region occupies the inner portion of the crescent below the -center. This consists of two immense plains, one of which sends a large -‘bay’ as far south as the ring of Theophilus, where it is connected by a -narrow ‘strait’ with the _Mare Nectaris_. - -“Turning to photograph No. 5 we see the two plains to which I have -referred more fully displayed. The sun has now risen over their entire -surface. The upper one is the _Mare Tranquillitatis_, ‘Sea of -Tranquillity’; and the lower one the _Mare Serenitatis_, ‘Sea of -Serenity.’” - -“I have always thought that astronomers must be happy persons,” said my -companion, with a smile, “and these names are convincing.” - -[Illustration: - - NO. 5. JULY 1, 1903; MOON’S AGE 6.24 DAYS. -] - -“Yes, perhaps, but then in bestowing the names they may have been -transferring to the moon ideals of tranquillity and serenity which they -did not find realized upon the earth. I am not going to talk about these -two ‘seas’ at present because they are better represented upon one of -the large photographs which we shall examine later. I prefer to direct -your attention just now to some other things. In the first place look -once more at Theophilus and its companion rings, and observe how they -maintain their preëminence. The entire surface of the moon to the -eastward and southward is broken and heaped up with mountains, craters, -and rings, but nowhere do we see anything comparable with Theophilus -except, perhaps, far toward the south, where near the inner border -appear two still larger, but less regular, rings lying in line at a -right angle to the terminator. The one on the left is Maurolycus, and -the other, still half obscured by night, is Stöfler.” - -“The names of old astronomers, I suppose.” - -“Yes, astronomers sufficiently famous in their day, but who would be -virtually forgotten at the present time if their friend Riccioli had not -thus immortalized them. You see it is a great piece of good fortune to -have your name in the moon. It is a kind of revenge for the neglect of -future generations at home.” - -“And it seems to me an equal good fortune to have had an admirer willing -to set your name up in the moon.” - -“Surely. But Riccioli’s own name is there also. Afterwards I shall show -you his lunar monument, a truly magnificent one. Permit me now to tell -you that Maurolycus is much greater in extent than any of the rings that -we have yet seen. Not by any means so perfect in form as Theophilus, it -covers a vast extent of surface, as much as 150 miles across, with an -amazing mass of broken rings, walls, ramparts, ridges and chasms. Some -of its peaks are 14,000 or 15,000 feet in height. It has a very lofty -central mountain, visible in the photograph, and whose peak comes into -view when the sun is rising long before the surroundings have been -illuminated, so that it resembles a star glowing amid the blackest -night. The neighbor of Maurolycus, Stöfler, is equally extensive and -almost equally wild and magnificent when the sunlight is leaping across -it from pinnacle to pinnacle and ridge to ridge. In this photograph, -however, it is too near the terminator to be well seen. We shall -presently pass to photograph No. 6, where Stöfler appears in full light, -but before doing so let us glance at the northern part of the moon as -here pictured. Close to the terminator, below the grand oval form of the -_Mare Serenitatis_, you will perceive two rings, one above the other. -They seem to be the complement of the other pair, Atlas and Hercules, -which we looked at when the sun had recently risen upon them in another -photograph, and which now appear far off toward the west. You observe -that Atlas and Hercules lie upon an east and west line, and the others -upon a north and south line. The northernmost one is named Aristoteles, -and the other Eudoxus. They are situated near the edge of a plain called -the _Mare Frigoris_, ‘Sea of Cold,’ thus named, I suppose, because it -lies so far north. Aristoteles is about 60 miles in diameter, and its -immense wall is very high and splendidly terraced. Eudoxus, equally -deep, is only 40 miles in diameter. - -“Turning to photograph No. 6, taken when the moon was more than a day -older than it was when No. 5 was made, we have a striking example of the -effect of libration in presenting the moon at perceptibly different -angles to our line of sight at corresponding phases. We have now arrived -at First Quarter, and behold all the western half of the moon -illuminated by the sun. You will perceive that we now have in view, -simultaneously, six of the great plains called ‘seas,’ namely, the _Mare -Crisium_, the _Mare Fœcunditatis_, the _Mare Nectaris_, the _Mare -Tranquillitatis_, the _Mare Serenitatis_, and the _Mare Frigoris_, while -others are beginning to emerge out of night on the east. Maurolycus and -Stöfler, the pair of giant rings in the south, are better seen than -before because daylight has advanced farther across them. In fact -Stöfler now appears more imposing than its great neighbor, and a smaller -ring breaking the continuity of its wall on the western side is visible. -Above these, in the direction of the south pole of the moon, and around -the pole itself, the surface is marvelously rough and broken. It looks -as if it would be impossible to find a level acre of ground in all that -region. The rings and craters are veritably innumerable. It is the -existence of these irregularities which causes the terminator to appear -so crooked and broken. At some places you perceive small bright points -within the edge of the night half of the moon. These, of course, are the -summits of peaks, which have just been touched by the sunlight while the -surface all around them is still covered with darkness. - -“Below Stöfler, all along the terminator, as far as the middle of the -moon, an irregular row of rings appears. Three of these bear some -resemblance to the great group of which Theophilus is the chief member. -They are, counting from south toward north, Aliacensis, Werner, and -Blanchinus. Below them two other much larger ones are conspicuous, -Albategnius, the more southerly, and Hipparchus. These two are full of -moon history. Albategnius, the smaller, is very deep and comparatively -perfect in condition, while Hipparchus, more than 90 miles across, has -been vividly described as a ‘wreck and ruin,’ its walls, once possibly -of great height, being now low and broken, and traversed with gaps and -valleys, while a great cleft exists crossing a part of the broad, -irregular floor. It is probable that Hipparchus is an older formation -than Albategnius.” - -[Illustration: - - NO. 6. NOVEMBER 26, 1903; MOON’S AGE 7.75 DAYS. -] - -“Pardon me,” interrupted my companion, “but I must cry for mercy. -Really, these strange names escape from my mind as fast as you mention -them. Is there not something a little more romantic in the -moon—something to relieve the strain of all this nomenclature of words -terminating in ‘us,’ and this frightful lunar geology?” - -“Yes,” I said, “I believe that on the other half of the moon, which has -not yet seen the sun rise, we shall find something better to your taste. -But do not be too impatient. Reflect that these names represent very -wonderful things visible to us in another world than ours, things the -knowledge of which has cost the lifelong labors of many gifted men, and -that will be remembered, studied, talked, and written about centuries -after we are dead. Fortunately for your powers of attention the eastern -half of the moon, upon which day will be seen gradually dawning in the -next set of photographs, has a general character quite different from -that of the western half. It contains the greatest ranges of lunar -mountains, yet upon the whole it is more level, being covered to a great -extent with broad plains, in the midst and along the borders of which -stand the most remarkable and interesting of all the lunar formations. -In and around some of them we shall search for the evidences which some -astronomers think that they have found of life upon the moon.” - -“Oh, that indeed will be interesting!” exclaimed my friend with reviving -animation. - -“But,” I added, “do not place your expectations too high. Keep your -imagination under control, try always to be just a little ‘scientific’ -in your way of looking at things, and then I believe you will not be -disappointed.” - -“Oh, please do not think that I have been disappointed,” she said -deprecatingly. “But positively you must admit that ‘Albategnius,’ -‘Aliacensis,’ ‘Blanchinus,’ and ‘Maurolycus,’ are not precisely -captivating. Remember that I have read little except poetry and romance, -and those histories that are full of stories.” - -“You will find a deep vein of poetry and romance in the moon,” I -replied, “before we have finished, and after you have reflected upon -what we have seen and what we have been saying.” - -Leaving the remaining photographs to be examined after lunch, we now -entered the house. - ------------------------------------------------------------------------- - - - - - II - - FIRST QUARTER TO FULL MOON - - - - ------------------------------------------------------------------------- - - - - - II - - FIRST QUARTER TO FULL MOON - - -NOTWITHSTANDING the signs of impatience which my friend had manifested -when we were passing, in our review of the photographs, from one lunar -ring mountain to another, all more or less similar in appearance and -characteristics, I was gratified to see that her mind was still -attracted to the subject of the moon, and during the lunch she, of her -own accord, began to talk of it. - -“You have said so much about volcanic occurrences on the moon,” she -remarked, “that I wonder why you do not call those immense mountains -‘volcanoes.’ I observe that you always speak of them as ‘rings,’ or -‘mountain rings,’ or ‘ring plains’; while to me, although to be sure I -am no geologist and have perhaps no right to an opinion, they seem -plainly to be just huge volcanoes and nothing else.” - -“Your observation is quite correct,” I replied, “as far as superficial -appearance goes, and I may add that these great rings are often called -volcanoes. If we apply the proper adjective and name them ‘lunar -volcanoes,’ perhaps there can be no objection to the term. But they are -certainly widely different from our terrestrial volcanoes. The -difference is not in size alone, although in that regard it is enormous. -There is a far more significant difference, which you could hardly be -expected to notice in a simple inspection of the photographs, although -it is evident when once pointed out. I refer to the fact that what seem -to be the craters of lunar volcanoes are not situated on the tops of -mountains. They are immense plains, more or less irregular in surface, -and often having a peak or a group of peaks in the center, while around -these plains always extends a mountain ring, steep on the inner side, -and having a gradual slope without. But most significant fact of all, -the plains, or floors inside the ring, are almost invariably situated -thousands of feet below the general level of the moon. If the -terrestrial volcanoes were formed on the plan of the lunar ones, when we -visit Vesuvius, instead of climbing up a mountain rising out of the -midst of a plain and capped with a cone, having a funnel-shaped crater -in the center, we should find before us a relatively low, circular -elevation, on surmounting which there would appear on the inside of the -circle a great basinlike hollow, far below the level of the surrounding -country. In the center of this, distant from the lofty encircling walls, -would be seen a conical hill with smoke and vapor issuing from a vent at -its summit. The top of this crater hill would be lower than the rim of -the basin-shaped hollow, so that the whole volcano with its immediate -surroundings would be inclosed and shut off from the environing upper -world by the sides of the basin. While you finish your coffee I will -make a sketch which may render this difference between lunar and -terrestrial volcanoes evident at a glance.” - -[Illustration: - - Lunar Volcano, in Section. -] - -[Illustration: - - Terrestrial Volcano, in Section. -] - -Accordingly, after a few minutes, I presented to her these two diagrams, -remarking that it should be borne in mind that the two sketches were not -made on the same relative scale. “I was compelled,” I said, “to change -the true proportions in the section of the lunar volcano, for if I had -drawn them as they are in fact, the width of the basin would have been -enormous in proportion to its depth. You will recall that I told you -that such rings as Albategnius and Maurolycus are a hundred miles and -even more in diameter, while their depth does not exceed two or three -miles. It results from this necessary falsification of proportions in -the sketch that the terrestrial volcano, although so widely different in -form, appears comparable in magnitude with the lunar one. But the fact -is that you could take a dozen of the largest volcanic mountains on the -earth and throw them into one of the great lunar rings without filling -it.” - -“I am the more astonished by what you say,” remarked my friend, “because -you have already told me that the moon is so much smaller than the -earth. How does it happen, then, that her volcanoes are so much larger? -I should think that in a little world all things would be small in -proportion.” - -“It is quite natural to think so,” I replied, “until you reflect upon -the consequences of the smaller force of gravitation on a small world. I -told you last evening that gravitation on the moon, is only one sixth as -powerful as it is on the earth, and you will recall that one consequence -which I pointed out was that you would weigh only twenty pounds if you -were on the moon. Since the same reasoning applies to all objects in the -lunar world, it is clear that a similar force exerted there would be -able to produce enormously greater effects, as for instance in the -formation of vast hollows or depressions, by violent explosions, the -products of which would be thrown to immense distances. Some -selenographers, which is a term applied to those who study the features -of the lunar world, have suggested that in this cause alone is to be -found the explanation of the giant lunar ring mountains. At some remote -period of the past, according to them, the volcanic forces of the moon -reached a maximum of activity and energy. The lava, cinders, ashes, and -other products of ejection, were hurled to a height of scores of miles, -and when this fell back at a great distance from the centers of eruption -these were piled up in huge rings, fifty, eighty, or a hundred miles in -diameter, while the surface of the moon within the rings sank in -consequence of the withdrawal of the material thus ejected. To account -for the existence of the central mountains so often found in the middle -of the rings, it has been suggested that at a much later period, when -the volcanic energy had become comparatively insignificant, as a result -of the cooling of the interior of the moon, less violent explosions, not -greater than many that have occurred on the earth, took place, and by -these the central peaks were formed.” - -“You are going to think me too romantic, or too imaginative, again,” -said my friend, with a smile, “but I cannot prevent myself from -wondering what the inhabitants of the moon did and thought while all -those marvelous things were happening.” - -“I have not said that there were inhabitants of the moon.” - -“No, but you have confessed that there might have been inhabitants, some -time, and I should like to know whether they were there when those -terrible volcanoes were formed.” - -“If they were,” I replied, “they could not have survived such a -universal upheaval as the surface of the moon has undergone. You have -seen in the photographs that the great rings and smaller craters are -scattered thickly over the moon. It is true that comparatively few are -found in the level expanses called ‘seas,’ but if those regions were -covered with water they could only have been inhabited by beings -provided with gills and fins.” - -“How long ago did these explosions occur?” - -“I cannot tell you, except that it must have been many ages in the past; -so long ago, indeed, that the whole course of human history seems but a -day in comparison.” - -“Then,” said my friend with animation, “there has been time enough -_since_ that dreadful period for inhabitants to develop upon the moon, -has there not?” - -“Yes, time enough, perhaps, provided that sufficient water and air and -other vital requisites remained after the exhaustion of the volcanic -energies.” - -“Oh, let us say that they did remain. I am eager to believe that the -moon has not always been so desolate as she appears at present.” - -“Very well, you are at liberty to believe that if you like. No -astronomer is likely positively to contradict you, although he may smile -a little incredulously. Besides, as I have already told you, there are -certain rather inconclusive indications of some kind of life, and of -some kind of activity, still on the moon.” - -“Please show them to me, then, or tell me about them. Perhaps I shall -find them less inconclusive than you do.” - -“Everything in its turn,” I replied. “We shall come to the indications -that I have spoken of after we resume the inspection of the -photographs.” - -“Then I am ready to resume at once.” - -Accordingly we returned to the table and the photographs under the -pleasant shade of the elm. Taking up the photograph numbered 7, I -remarked that it exhibited the moon as it appears a little after First -Quarter; that is to say, a trifle more than half the face turned toward -the earth is in the sunlight. I called attention once more to the six -“seas,” which we had already remarked, and to the continued -conspicuousness of Theophilus and its companions, a little above the -middle of the visible hemisphere. - -“You observe now,” I continued, “how the rotundity of the lunar globe -begins to manifest itself as the sunlight sweeps farther eastward. The -crescent shape is gone and the line between day and night begins to be -bowed outward, convexly. The _Mare Crisium_ is particularly well -defined, and also the diamond-shaped region called the _Palus Somnii_. -With the sun so nearly vertical above it, the remarkable peak of -Proclus, between the _Palus Somnii_ and the _Mare Crisium_, has become -very brilliant. In a telescope you would see it glowing almost like a -star. You observe also that several long, straight, bright rays proceed -from it in several directions.” - -“All the more reason, it seems to me,” said my friend, “why your -unimaginative astronomer, Riccioli, should have named it for some -brilliant gem instead of attaching to so dazzling an object the prosaic -designation of ‘Proclus.’” - -“After all,” I replied, “what’s in a name?” Now that you are familiar -with the appearance of Proclus, its name will henceforth call up to your -mind an image as brilliant as if it had been named ‘Mount Diamond’ or -‘Mount Amethyst.’” - -[Illustration: - - NO. 7. JULY 2, 1903; MOON’S AGE 7.24 DAYS. -] - -“Pardon me,” said my friend, “but it was not of names like those that I -was thinking. Observe how he who named the neighboring _Palus Somnii_, -‘Marsh of a Dream,’ exhibited an exquisite delicacy of fancy. It -suggests something indefinitely strange, romantic, imaginative. That -unknown astronomer, unknown at least to me, put a little of himself, a -little of his inmost mind, into the name, and I thank him for it. I -shall never forget the ‘Marsh of a Dream’ in the moon. It will haunt my -own dreams. I shall be all my life seeking and never finding its -meaning.” - -“Since you are in so poetic a mood,” I responded, “I rejoice that -besides its bald facts, its fireless volcanoes, and its dried-up plains, -the moon possesses many things that can stir the imagination of the most -sentimental observer. But, in order that we may not wander too far from -the paths of science, let me recall your attention to the photograph. We -have been going over ground already trodden by returning to the -neighborhood of the _Mare Crisium_. I shall now lead you back to the -terminator, where we shall find a little that is new. Still nearly -hidden in night we perceive many great rings on which the sun is -beginning to rise, and four of the most important ranges of mountains -are coming into view. One of these, on the southern border of the _Mare -Serenitatis_, is visible throughout its entire extent. It forms a -portion of the coquettish ornaments with which the Moon Maiden has -decorated her hair, as we shall see clearly in the next photograph. This -range is named the Hæmus mountains. Near its center, quite at the edge -of the ‘sea,’ is a bright crater ring, one of the most conspicuous on -the moon. It is called Menelaus.” - -“Menelaus?” exclaimed my friend. “Ah, then Riccioli did not confine his -favoritism to the astronomers and philosophers in putting their names in -the moon. Menelaus, if I remember my classical reading correctly, was -the husband of Helen of Troy.” - -“Yes, the brother of Agamemnon himself. You must admit that Riccioli -occasionally felt his imagination a little awakened. He was not -altogether destitute of the spirit of poetry.” - -“But did he also put Helen in the moon?” - -“I am sorry to say that he did not. It would have been a very suitable -abode for her. However, if you like, you may recognize Helen in the Moon -Maiden herself.” - -“Thank you, that will be, indeed, an unexpected pleasure.” - -“Meanwhile allow me to point out to you that there is a curious light -streak, very faintly shown in the photograph, which crosses the _Mare -Serenitatis_ from Menelaus to the opposite shore, and reappears more -distinctly, on the lighter-colored plain toward the north. This streak -comes all the way from a great ring mountain named Tycho in the southern -part of the moon. It is more than 2,000 miles long, and is one of the -greatest mysteries of the lunar world. Tycho, which lies just on the -sunrise line, is not well seen in this photograph. It has a great number -of these strange streaks or rays proceeding from it in all directions. -We shall study them in one of the photographs which are to come. One -word in regard to the plain north of the _Mare Serenitatis_ of which I -have just spoken. It, too, has a name that is calculated to appeal to -your lively imagination. It is called the _Lacus Somniorum_, which if my -knowledge of Latin is correct, means ‘Lake of the Sleepers.’” - -“Then your old friend Riccioli certainly did not bestow the -appellation.” - -“No, it was one of his more fanciful, or, if you prefer, more poetical -predecessors, perhaps the same who imagined the ‘Marsh of a Dream.’” - -“Oh, that gives me another reason to think of him with admiration and -gratitude. He, at least, had a soul that rose above mere prosaic facts.” - -“Perhaps. But do not think too lightly of the facts of the moon. After -all the human mind must base itself upon the solid ground of fact. -Without that we should become mere dreamers, and be suited only to -inhabit your favorite ‘Marsh.’” - -“The other mountain ranges of which I have spoken,” I continued, “are -faintly distinguishable eastward from the _Mare Serenitatis_. They are -the Apennines, the Caucasus, and the Alps. But perhaps we had better -turn at once to photograph No. 8 where they are much more clearly seen, -because the sunrise there has advanced a couple of hundred miles farther -east.” - -“But, dear me, how slowly the sun rises on the moon! Was this photograph -taken a day later than the other?” - -[Illustration: - - NO. 8. AUGUST 31, 1903; MOON’S AGE 9.22 DAYS. -] - -“Almost exactly two days later. When it was made the moon was nearly -nine and a quarter days old, and its age at the time No. 7 was made was -only seven and a quarter days. But, owing to the effects of libration, -an explanation of which I have put into a note for your private reading -when you feel like it, [see p. 57, footnote], the difference of phase -amounts to less than two days. You are right, however, in remarking that -sunrise is a very slow process on the moon. It requires about two weeks -to pass from the western side of the moon to the eastern side, and both -day and night at any point on the moon last about a fortnight. This -results from the fact that, as I have told you, the moon does not turn -rapidly on its axis like our own globe, but keeps always the same side -directed toward the earth. Accordingly, a lunar day and night are -together about a month long.” - -“And was it so when, as I must persist in believing, there were -inhabitants on the moon?” - -“Probably, although it may have been shorter then. The consequences of -these excessively long days and nights would be very serious to beings -fashioned upon the terrestrial plan. In the practical absence of an -atmosphere the heat of the sun’s rays, pouring down without interruption -and without the intervention of any clouds or vapors for fourteen days -at a time, must be simply overpowering. And then, during the equally -long night that ensues, the radiation into open space must quickly leave -the surface of the moon exposed to the most frightful degree of cold, -comparable with the absolute zero of empty space!” - -“But think, what a merciless environment you are picturing for my -inhabitants of the moon. Please do not forget that I insist that their -comfort shall be considered.” - -“Oh, as for that, you know you were content a little while ago to -relegate your inhabitants to a remote period in the past, after the -volcanic fury of the lunar world had ceased, and before its present -airless and waterless condition had supervened. Possibly at that time -things were not so uncomfortable for them. They may have had clouds to -temper the sunshine, rains to cool the days and dews the nights, and -shady parks like yours for philosophic and scientific contemplation.” - -“Do not forget the poets.” - -“Certainly not. But is not the moon herself the very spirit of poetry? -What in nature is more poetical in its suggestions than the moon wading -through fleecy clouds on a serene summer’s night? But pardon me, we are -forgetting my mountains, upon which I insist as strongly as you do upon -your inhabitants. The mountains have this advantage that they are very -real, and no exercise of the imagination is required to bring them -clearly before us. In photograph No. 8 they are all visible. The -Apennines, the greatest of them, start from the eastern end of the _Mare -Serenitatis_, and run in a slightly curved line southeastward, a -distance of about 450 miles. They form the singular ornament which the -Moon Maiden (or shall we now call her Helen of Troy?) wears upon her -forehead. Turn the photograph upside down so that the moon is presented -as the naked eye sees it in the sky, and you will find that, although he -aimed only to be scientifically exact and to exclude everything but the -real facts, Mr. Wallace has produced an excellent picture of this -wonderful face in the moon.” - -“But what is that face?” - -“It is humanity projected upon the moon. It is a lesson on the powers of -the imagination. We perceive a certain collocation of mountains, peaks, -and plains on the disk of the moon, and our fancy sees in them a human -likeness. We should congratulate ourselves that we are able to do this. -It is a kind of proof of superiority. Many brute animals do not -recognize even their own likenesses in a mirror, much less in a picture. -But the Moon Maiden is perhaps as real as your inhabitants.” - -“I am not prepared to confess that yet.” - -“Very well, let us go on. The lunar Caucasus is the broader, but -shorter, range of mountains at the northeastern corner of the _Mare -Serenitatis_, and the Alps extend eastward from the Caucasus to a -conspicuous dark oval close to the terminator, which is one of the most -remarkable formations on the moon, and which, when we come to study it -in one of the larger photographs, will probably interest you deeply -because it is one of the places where recent studies have discovered -indications of what may possibly be some form of lunar life. I wish now -to direct your attention to the central and upper parts of the -photograph. Running downward from the south, a little west of the -terminator, you will perceive a double row of immense rings and ring -plains. They are not only remarkable individually, but quite as -remarkable for their juxtaposition in two long ranges. Among them, in -the westernmost row, are three or four whose names you may -remember—Maurolycus, Stöfler, Aliacensis and Werner. Still larger ones -are included in the eastern row, the largest of all being at the bottom. -It is rather a hexagon than a circle. It is 115 miles in diameter, and -the flat plain inside the bordering mountains contains about 9,000 -square miles. By close inspection you will perceive a small crater -mountain near the northwestern side. This immense walled plain is named -Ptolemæus after a great astronomer of antiquity, the author of the -Ptolemæic system, which treated the earth as the center of the universe. - -“Still more interesting are the things visible farther south. You cannot -fail to remark a very beautiful ring, a perfect circle, brightly -illuminated on the eastern side, and having a bright point symmetrically -placed in the exact center. It is named Tycho, after another great -astronomer, and is generally regarded as the most perfect crater ring on -the moon. It is 54 miles in diameter, and its walls are about 17,000 -feet high on the inner side, more than a thousand feet higher than Mt. -Blanc, the giant of the terrestrial Alps. Its central mountain is 5,000 -feet high. The most remarkable thing about Tycho is the vast system of -‘rays’ or bands which seem to shoot out from it in all directions, -traversing the surface of the moon, north, south, east, and west for -hundreds of miles, and never turning aside on account of any obstacle. -They lie straight across mountains, valleys, and plains. We have already -seen one of them, the largest of all perhaps, crossing the _Mare -Serenitatis_ and the _Lacus Somniorum_, in the northern hemisphere of -the moon. Nobody knows exactly what these rays mean or what they consist -of. We shall from this time on see them in all the photographs that we -examine, and later I shall have more to say about them, and the -speculations to which they have given rise. - -“About half way between Tycho and the south pole of the moon, you will -see an enormous irregular plain, with lofty broken walls, interrupted by -a number of crater rings. Several similar rings also appear in the -interior of the plain. If Tycho is the most perfect in form of the lunar -crater rings, this great inclosure, which is named Clavius, is the -finest example of the walled valleys. It is more than 140 miles across, -and covers an area of not less than 16,000 square miles. Two of the -rings within it, which seem so small in comparison, are 25 miles across. -A smaller walled plain, yet one of really immense size, is seen half way -between Tycho and Clavius, and farther from the terminator than either -of them. This is Maginus, and it possesses the peculiarity that at full -moon it practically disappears!” - -“But how can that be possible? I see nothing behind which it can be -hidden.” - -“It is the sunlight that hides it. You must have noticed already that -the rings and mountains are best seen when at no great distance from the -terminator, because there the sunlight strikes across them at a low -angle, and their shadows are thrown sharply upon the adjoining slopes -and levels. Look at the western part of the moon in the photograph -before us. Many of the huge rings and walled plains that were so -striking in appearance when the sun was rising upon them are now barely -visible. Langrenus and Petavius, for instance, have become no more than -whitish blotches, and even Theophilus is no longer conspicuous. The -reason is because when the sunlight falls vertically upon any part of -the moon there are no shadows there, and without shadows there can be no -appearance of relief. Then the mightiest mountains are almost lost from -sight in the universal glare. The same thing would be apparent if you -were suspended above the earth at a great height in a balloon and -looking down upon the tops of the snowclad Rockies. Without shadows -serving to reveal their true character and to throw their outlines in -silhouette upon the adjacent plains, they would resemble only white -spots and lines on the generally darker expanse of the continent. But -Maginus is an extreme case. Owing to the relatively small elevation of -its walls, and their broken-up state, and owing also, probably, to a -similarity of color between the mountain ring and the inclosed plain, -when the light is vertical upon them, as at the time of Full Moon, they -blend together and become barely distinguishable from one another, and -from the surrounding surface of the moon. - -“Take now photograph No. 9. The age of the moon here is actually less -than it was in the photograph that we last examined, yet, in consequence -of libration, which has caused the moon, in effect, to roll a little to -one side, the sunlight is farther advanced toward the east, and we see -many features of the lunar world that before had not yet emerged from -night. Clavius you will notice is much more fully illuminated. See how -distinctly the shadow of its vast western wall is cast upon the floor of -the valley within, while the opposite eastern wall with its immense -cliffs and precipices glows in full sunshine, its shadow, thrown toward -the east, blending with the darkness of night still covering that side -of the moon. Southeast of Tycho, which is beautifully shown here, two -other great walled plains have come into view. The uppermost of these is -Longomontanus and the other Wilhelm I. For a considerable distance below -these (toward the north) the surface continues broken with rings and -craters, but at length these give place to a dark, level expanse. This -is a part of the _Mare Nubium_, or ‘Sea of Clouds.’” - -“Not quite so romantic a name as some of the others,” remarked my -friend, “but still I think I can be sure that Riccioli had nothing to do -with the selection. There is certainly something poetic in the idea of a -sea of clouds.” - -“It is a very beautiful region when examined with a telescope,” I -continued, “and its mountainous shores contain many interesting -formations. Farther north, you will observe, near the terminator, and -apparently lying in the midst of the _Mare Nubium_, a large ring, as -perfect in form as Tycho itself. This is a very famous object, and it -bears the name of the great astronomer Copernicus, who overthrew the -Ptolemæic system and established in its place the true idea of the solar -system, namely, that the sun is its center, while the earth and the -other planets revolve as satellites around him.” - -“Surely,” said my friend, “Copernicus deserved to have his name placed -in the moon, and very conspicuously, too.” - -[Illustration: - - NO. 9. AUGUST 2, 1903; MOON’S AGE 8.97 DAYS. -] - -“It could not have been made more conspicuous,” I replied, “for the -situation of the great ring mountain called Copernicus, in the midst of -an immense level expanse, makes it one of the most marked features of -the lunar world. Copernicus is the subject of one of the larger -photographs that we are going to examine later, and I reserve a -description of its peculiarities. North of Copernicus you will observe -apparently a continuation of the _Mare Nubium_. But it is really another -‘sea’ that we are looking upon there, the _Mare Imbrium_, ‘Sea of -Rains.’ The baylike projection that runs out into the bright highlands -west of Copernicus bears the name of the _Sinus Medii_, ‘Central Gulf,’ -and the one just below it is the _Sinus Æstuum_, ‘Gulf of Heats,’ which -is certainly suggestive of dog days on the moon. Observe that the _Sinus -Æstuum_ merges on the west with a dark, oval area, which is called the -_Mare Vaporum_, ‘Sea of Mists.’ It is one of the darkest districts on -the moon. If you will now turn the photograph upside down you will find -that the _Sinus Medii_ constitutes the dark eye of the Moon Maiden, -while the _Sinus Æstuum_ and the _Mare Vaporum_ form that portion of her -hair which droops upon her forehead.” - -“Why not frankly call it frizzed?” - -“Because I feared that you would not consider that a sufficiently poetic -term.” - -“But I find poetry enough in the names ‘Gulf of Heats’ and ‘Sea of -Mists.’ My admiration for the man who could think of such appellations -continually increases.” - -“Then please reverse the photograph, for we must not lose ourselves in -dreams. You will notice that the range of the lunar Apennines runs -between the _Mare Vaporum_ and the _Sinus Æstuum_ on one side, and the -_Mare Imbrium_ on the other. The entire chain of the Apennines is -beautifully shown here. They are exceedingly steep on the side facing -the _Mare Imbrium_, and gigantic peaks standing upon their long wall -cast immense shadows over the ‘sea.’ Their southwestern slopes are -comparatively gentle, rising gradually from the level of the _Mare -Vaporum_. At their upper or southern end, in the direction of -Copernicus, they suddenly terminate with a beautiful ring, which is -called Eratosthenes. This is a fine example of the disk or cup shape of -the lunar volcano. The bottom of Eratosthenes lies 8,000 feet below the -level of the surrounding _Mare_, while peaks on its wall are as much as -15,000 or 16,000 feet in height. Between the lower end of the Apennines -and the upper end of the Caucasus Mountains a strait opens a broad, -level way between the _Mare Imbrium_ and the _Mare Serenitatis_. On one -of the large photographs these two ‘seas’ and the strait connecting them -are represented in all their picturesque details, as you will see when -we come to study them. I promise you at that time a free rein to your -imagination and plenty of room for its flights. On the northern border -of the _Mare Imbrium_ and close to the terminator we see once more the -remarkable oval valley to which I referred when pointing out the lunar -Alps, and which bears the name of Plato. I call your attention to it and -also, again, to Copernicus, in order that you may compare their -appearance here with that which they present in the next photograph, -taken when the moon’s age was eleven and three-quarter days.” - -[Illustration: - - NO. 10. NOVEMBER 30, 1903; MOON’S AGE 11.78 DAYS. -] - -We hereupon turned to photograph No. 10. - -“Now,” I continued, “observe the difference that some two days’ advance -of the sunlight has produced. Plato is far within the illuminated part -of the disk, and it looks darker than before. Copernicus, on the other -hand, which appeared as a sharp ring with one border dark when it was -near the sunrise line, has now become a round, white spot, somewhat -darker in the center, with a great grayish splatter surrounding it upon -the surface of the _Mare_. In the meantime, over nearly the whole extent -of the _Mare Imbrium_ the sun has risen and two other _mares_ have made -their appearance, one of which, extending across half the width of the -eastern hemisphere, might be called the Pacific Ocean of the moon, if it -had any water. It is named the _Oceanus Procellarum_, the ‘Ocean of -Tempests,’ while at its southern extremity a very dark nearly circular -expanse, inclosed with mountains, bears the name of the _Mare Humorum_, -‘Sea of Humors.’” - -“Evidently the astronomer who bestowed that name was not in a joking -mood else he would surely have called it the ‘Sea of Humor.’” - -“No, apparently he was in deep earnest. But what kind of humors he was -thinking of I cannot tell. Perhaps the name occurred to him because the -_Mare Humorum_ is the darkest of all the great levels on the moon. It is -very conspicuous to the naked eye at Full Moon. You will perceive that -Tycho has now become the most prominent of all the rings on the moon. It -will maintain this distinction and continue to gain in conspicuousness -up to the time of Full Moon. Seen as we now see it, Tycho manifestly -merits the appellation sometimes bestowed upon it of the ‘metropolitan -crater of the moon.’ Notice how bright the mysterious bands radiating -from it have become. The higher the sun rises upon them the more -brilliantly they glow, almost as if they were streaks of new-fallen -snow. They spread over the whole of the southwestern quarter of the -moon, hiding rings and mountains with their brightness. One very notable -ray runs down into the _Mare Nubium_, and a fainter one parallel with it -produces the semblance of a long, walled way. - -“The South Pole of the moon lies in the midst of a marvelously upheaved -and tumbled region, where one huge ring is seen breaking into another on -every hand. One of these rings, named Newton—it lies just on the upper -edge of the disk, south of Clavius—surrounds the deepest known -depression on the moon. Its bottom sinks to a depth of 24,000 feet below -the highest point on the wall. This gigantic hole is so profound that, -situated where it is, close to the pole, where the sun can never rise -very high, its depths remain forever buried in night. It is the very -ideal of a dungeon, for if you were imprisoned at the bottom you would -never see either the sun or the earth.” - -“You make me shudder! Truly, after all, the moon appears to be a world -filled with dreadful things. Who would ever imagine it, seeing how -serene and beautiful she is in a calm night?” - -“Yet is there not a kind of beauty even in those things, like the abyss -of Newton, which appall you only when you know the real facts about -them? There is a certain grace in their shapes and outlines, and a great -attraction for the eye in their contrasts of light and shadow. It is the -same sort of attraction which we find in such terrestrial scenes as the -Yosemite Valley viewed from Inspiration Point, or the awful depths and -chasms of the Grand Cañon of the Colorado. The presence of man and his -works is not always essential in order to fix our attention upon the -wonders of nature. Their very grandeur exalts us until we forget our -little race and its ephemeral achievements.” - -“Still, I hope that you will show me something on the moon less -awe-inspiring and suited to awaken more quiet thoughts, and especially -to reassure me concerning my lunarians, as I suppose you would call -them.” - -“You shall not be kept long in expectation. Turn your eyes once more to -the _Mare Imbrium_. You will observe that its northern shore consists of -a series of curves, each terminating with a promontory projecting into -the sea. When looking at it I am often reminded of an entrancing view -which I once enjoyed from the summit of Mt. Etna over the island of -Sicily. From that great elevation nearly the whole eastern and -southeastern coast of the island was visible as upon a map. The indented -shore stretched away in long, graceful curves, where the blue -Mediterranean contrasted sharply with the yellow sands, and the eye, -wandering from Catania to Syracuse, was enchanted with the beauty of -those geometric lines. But the winding coast of the _Mare Imbrium_ is -far longer than the shores of Sicily, and the mountains and cliffs -bordering it are more wonderful than any corresponding scenes on the -earth. I wish, particularly, to have you look at the easternmost of the -indentations on the northern side of the _mare_. It bears a designation -that must surely please your imagination. It is the _Sinus Iridum_, -‘Gulf or Bay of Rainbows.’” - -“I recognize the work of my old friend the unknown astronomer. Verily he -had a poetic soul! And he has written his poem on the chart of the moon, -for those to read who can.” - -“It is a charming landscape that the telescope reveals there,” I said, -“even though no rainbows are visible.” - -“But you will not deny that they may once have spanned that bay and its -shores with their exquisite arches?” - -“No, I shall not deny so pleasing a possibility. I will only say that it -lies beyond the ken, and even outside the field, of science.” - -“Then I regard it as fortunate that _he_ was not too exclusive in his -devotion to science, for then he could never have seen the rainbows with -the eye of fancy, and your charts would not have been adorned with so -delightful a name.” - -“Let me tell you about this bay or gulf,” I said, tapping the photograph -to recall her from her reverie. “You observe that it terminates at each -end with a promontory. That at the western end is named Laplace, and the -other Heraclides. The latter is the more picturesque. If ever you have -an opportunity to see the moon with a good telescope do not fail to look -at the promontory of Heraclides, for if you are fortunate in the choice -of the time of observation when the setting sun is throwing its shadow -over the adjoining ‘bay,’ you will find that the serrated outlines of -the promontory represent, in a very striking manner, the profile of a -woman, more sharply defined than the face of our familiar Moon Maiden, -but a mere miniature in relative size. The shores of the _Sinus Iridum_ -are bordered with high cliffs, behind which rise the peaks of a mighty -mountain mass. Just back of the center of the great bowed shore of the -‘bay’ appears, in the photograph, a small, bright crater ring. This -bears the name of Bianchini. It is a lunar volcano, 18 miles in -diameter, rising out of the midst of many ranges of nearly parallel -hills and mountains, the general direction of which corresponds with -that of the shore of the ‘bay.’ If there is any place on the moon where -one is tempted to think that the scenes of a living world might once -have been witnessed it is the _Sinus Iridum_ and its neighborhood. Its -latitude is between 40° and 50° north, corresponding with the most -thickly populated zone of our own globe. The surface of the ‘bay’—once -its bottom, if we admit that it was ever filled with water—is gently -undulating, with winding ridges that suggest the action of tides and -currents in sweeping to and fro deposits of sand and gravel, and piling -them in long rows of bars and shallows. One can hardly help picturing in -the mind’s eye waves breaking on the curving beach and dashing against -the projecting rocks of the promontories; a white city seated just at -the center of the shore of the ‘bay,’ near Bianchini, like Naples at the -feet of Vesuvius; a rich vegetation covering the slopes of the mountain -valleys, and romantic sails dotting the ‘bay’ and the neighboring -‘sea.’” - -“I am very glad to observe,” interrupted my friend, “that you are not -hopelessly prejudiced against my opinion that the moon has not always -been ‘dead,’ as you call it.” - -“I am so far from it,” I replied, “that I am half disposed to admit that -she is not altogether dead even yet. But it is my duty to keep you as -close as possible to the known facts. We shall see the _Mare Imbrium_ -and the neighborhood of the ‘Bay of Rainbows’ again. Meanwhile, suppose -we turn to the next photograph of the series, No. 11. The age of the -moon here is about thirteen days. She is fast approaching the phase of -Full Moon. The first thing to which I would direct your attention now is -the exceedingly brilliant point of light which has come into view near -the terminator, a little north of east where the _Mare Imbrium_ merges -into the _Oceanus Procellarum_. In several ways this is the most -noteworthy object on the moon. It led the famous English astronomer, Sir -William Herschel, to believe that he had seen an active volcano on our -satellite. He naïvely wrote in his notebook on a certain occasion: ‘The -volcano glows more brightly to-night!’ Yet it is no more active than the -other craters and crater rings in the lunar world. It is only -extraordinarily, almost incredibly brilliant—by far the most dazzling -point on the moon. It is a ring mountain, and is named Aristarchus. It -has a near neighbor, barely visible in this photograph, close by toward -the east named Herodotus. Herodotus is by no means remarkable for -brilliancy. The central peak and a part of the floor and the east wall -of Aristarchus consist of some material—nobody can tell what it is—which -gleams in the sunlight, I had almost said like diamonds, although that -would be an exaggeration. There are three or four other crater rings on -the moon, including Proclus, which are also very brilliant, but not one -of them can be regarded as a rival of Aristarchus. Its power of -reflection is so great that it is even visible with a telescope in the -lunar night, when the only light of any consequence that reaches it is -that sent from the earth. It was, indeed, this fact which misled -Herschel. He saw Aristarchus shining on the night side of the moon, and -naturally thought that only the fires of an active volcano could have -rendered it thus visible.” - -[Illustration: - - NO. 11. DECEMBER 1, 1903; MOON’S AGE 12.98 DAYS. -] - -“And are you sure that he was mistaken?” - -“Positively. There is no fire in Aristarchus, and has been none for -ages.” - -“But why do not astronomers undertake to find out what it is that makes -Aristarchus so brilliant, then?” - -“They have almost no data to go upon. You should be informed that even -the greatest telescopes, with their highest powers, are unable to bring -the moon within less than an apparent distance of say forty miles. At -such a distance it is manifestly impossible to tell of what a lunar -formation consists. We cannot analyze the moon with the spectroscope as -we can the sun and the stars, because she does not shine with her own -inherent light. We can only infer that a large part of the substance of -Aristarchus consists of something which reflects a very great proportion -of the light that falls upon it. If a mountain on the earth were -composed of a vast mass of crystals, or of bare polished metal, we might -expect it to present, when seen from the moon, some such appearance as -we notice when we look at Aristarchus. - -“In this photograph the _Sinus Iridum_, having the sun higher above it, -is more brilliantly illuminated than in No. 10. Particularly you will -notice the brightness of the line of cliffs along its eastern curve, -terminating at the promontory of Heraclides.” - -“That is the promontory which presents the profile of a woman’s face, if -I recall correctly what you told me.” - -“Yes. Please observe also that the oval of Plato is as dark as ever, -while Copernicus has, if possible, increased in brightness, and the -great splatter of broken rays around it seems to have extended farther -over the surrounding maria. Almost directly east of Copernicus, in the -_Oceanus Procellarum_, appears a much smaller crater ring, Kepler, which -resembles a miniature of Copernicus because it, too, is encircled with a -kind of corona of short, bright rays. Copernicus, Kepler, and -Aristarchus mark the corners of a large triangle. Speaking of rays -recalls us to Tycho. You will see that, as I told you, this wonderful -formation grows in relative prominence when the period of Full Moon -approaches. Its ringed wall and central mountain are obscured by their -own brilliance, while the gigantic system of bright bands, or rays, -which have their center of origin at Tycho, is gradually becoming the -master feature of the bright part of the moon. - -“I have told you that the _Mare Humorum_, which is very sharply defined -in the picture before us, is the darkest of all the level areas that go -under the name of ‘seas.’ It is not, however, the darkest _spot_ on the -moon. There are several places where the surface appears, at times, much -duskier than in any part of the _Mare Humorum_. Three or four of these -are clearly discernible in this photograph. They lie westward from -Copernicus in the _Sinus Medii_, the _Sinus Æstuum_, and the _Mare -Vaporum_. Their dusky hue strikes the eye at once. They give the -impression of sink holes. No special name is attached to them, but they -must have been evident to the first observers, with the smallest -telescopes, and it is rather surprising they should have escaped special -designation on the lunar charts. A fact which will especially interest -you is that some observers look upon these and other dusky areas on the -moon as being, possibly, indications of the existence of some kind of -vegetation there.” - -“But if there is vegetation there may be other kinds of life also, may -there not?” - -“Ah, I have not said positively that there _is_ vegetation, but _if_ -there is then your conclusion as to other life may be correct. Glance -next at the upper part of the disk along the terminator. Two or three -broad oval rings have come into view there. The largest of these with -its long eastern wall lying exactly on the line between day and night is -an extremely interesting formation, bearing the name of Schickard. The -plain within the ring is almost large enough to have been called a ‘sea’ -or at least a ‘lake.’ It is about 134 miles in diameter, and is in -reality much more nearly circular than it appears to be. Like all -similar formations situated near the ‘limb’ of the moon, by which we -mean the edge as viewed from the earth, it is greatly foreshortened by -perspective. The scale of the photograph is, unfortunately, not large -enough to reveal an unique thing in the immediate neighborhood of -Schickard, toward the southeast. I refer to what, as far as its -telescopic appearance goes, might be described as an enormous bubble—a -bubble 54 miles in diameter. Unlike the other formations the surface of -this singular ring is elevated above the general level of the moon. When -we come to examine it in detail it hardly answers, perhaps, to my -designation of a bubble, since the edges are a little higher than the -center, giving it the form of a shallow dish. If we could visit it we -should find on approaching that we were climbing the slopes of what -would seem to be a chain of low mountains, and on reaching the summit we -should see before us an elevated circular plain, sinking gradually -toward the middle. Filled with water it would form a shallow lake lying -on the top of a broad, flat mountain. There is nothing else quite like -it on the moon and certainly nothing on the earth.” - -“It must have been a great curiosity in the days when the moon was -inhabited, and I suppose that scientific ‘lunarians’ organized -expeditions to explore it.” - -“Perhaps, if you choose to regard it in that way. Now look again at the -_Mare Humorum_. You perceive that its eastern side is lined with -mountains and crater rings, while near the center of the northern border -there is a conspicuous ring with a bright line running from the southern -edge to the center. This is one of the most beautiful of lunar -formations, and is named Gassendi. It is a favorite object for those who -study the moon with telescopes on account of the great variety and -singularity of the details visible within the ring. When you become a -selenographer and possess your own telescope you will find few things -more interesting to study than Gassendi. - -“Next let us take up photograph No. 12. Here the moon is once more a -little ‘older’ than before, and the sunrise line has again advanced a -little eastward. This advance does not appear so rapid when the -terminator is near the moon’s limb, because, on account of the rounding -away of the lunar globe, the illuminated surface is foreshortened from -our point of view on the earth. In this photograph you perceive that the -wonderful shining mountain Aristarchus has become even brighter than it -was before, or at least it is more conspicuous on account of the -appearance of what seems to be a short ray shooting out from it in a -southeasterly direction. There is also a light spot just below it which -is caused by a little mountain group called the Harbinger Mountains. The -bright ray connects Aristarchus with its neighbor Herodotus, of which I -spoke a little while ago. There is a very remarkable feature of the moon -here, not shown in the photograph, but to which I must briefly refer. It -is an enormous cleft, or crack, or, if you please, cañon, which starts -from Herodotus, whose northern wall seems to have been broken through to -give passage to it, and goes winding across the surface of the _Oceanus -Procellarum_ with several sharp turns and angles for a total distance of -nearly a hundred miles. What produced this remarkable chasm on the moon -it is difficult to say. Some have suggested that it may once have been -the bed of a river, but there are many serious objections to that view. -Nevertheless, there seems to be little doubt that if we were to visit -the moon we should find, in many ways, a striking resemblance between -this prodigious cañon and that of the Colorado River.” - -“And are not all these things so ancient, as far as you can tell, that, -like the terrible volcanic rings, they might have been formed before the -appearance of inhabitants upon the moon?” - -[Illustration: - - NO. 12. SEPTEMBER 4, 1903; MOON’S AGE 13.27 DAYS. -] - -“They certainly seem to be very ancient, and I cannot deny the -_possibility_ of what you say.” - -“Very well, then, I, for my part, am convinced that curious eyes, filled -with the light of intelligence, have peered down from the verge of that -chasm into its fearful depths. If you will not permit me this flight of -imagination I shall refuse to take any further interest in the moon.” - -“Oh, I should not think of refusing. Imagine what you will, and draw -your own inferences, only remembering that they are not supported by -_ascertained_ facts, and probably never will be. Yet for all that they -may have an element of truth.” - -“Pardon me for saying that your astronomical science, as far as it -concerns the moon at least, does not seem to me quite satisfying. You -are not bold enough in drawing conclusions.” - -“On the contrary many astronomers think that some of their brethren are -altogether too bold in that respect. However, it must be freely -confessed that astronomical science, except perhaps in its mathematics, -is not satisfying even to those who have created it. Nobody would -rejoice more sincerely than the astronomer at the discovery of evidence -of the former, or even the present, habitability of the moon. It is -surely a great disappointment that we have not been able to settle so -apparently simple a question in regard to our nearest neighbor in the -sky.” - -“Then if I were a multimillionaire I should certainly devote several of -my millions to the construction of a telescope great and powerful enough -to reveal so interesting a secret.” - -“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. - -[Illustration: - - 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.” - - ------------------------------------------------------------------------- - - - - - III - - FULL MOON TO OLD MOON - - - - ------------------------------------------------------------------------- - - - - - 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.” - -[Illustration: - - 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. - -[Illustration: - - 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.” - -[Illustration: - - 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_. - -[Illustration: - - 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.” - -[Illustration: - - 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?” - -[Illustration: - - 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.” - -[Illustration: - - NO. 20. AUGUST 17, 1903; MOON’S AGE 24.84 DAYS. -] - -“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.” - -“It is mainly because we are on the earth that we find such great -difficulty in making accurate maps of it. We cannot look at the earth as -a whole, but we have to crawl over its surface, making measurements as -we go, and afterwards translating those measurements into lines and -angles on paper. Thus we are still uncertain about the precise distance -between many important points on our globe, while for points on the moon -no corresponding uncertainty exists. The moon hangs before us in the -sky, with no clouds except those in our own atmosphere to obscure it, -and it is only necessary carefully to observe the position of particular -points, and with the proper instruments to measure their distance and -directions from one another. But even this is not a thing that can be -accomplished without much pains and much knowledge. The astronomer, no -matter what field he chooses, is necessarily a hard worker, and his -motto, above everything else, is accuracy. No one is more tempted than -he by the sublimity and the extraordinary character of the objects of -his study, to give rein to the imagination, and yet imagination is the -thing of all others from whose vagaries he must most carefully guard -himself. So you must not blame him too severely if he has not dotted the -shores of the moon with cities, and populated its plains with -industrious farmers.” - -“If you will permit me to wander a little aside from our photographic -studies for a few minutes,” said my friend, “I should like to ask you -about two or three things concerning the moon which have long puzzled -me. From my earliest days, living the greater part of the time in the -country, I have heard that the moon exercises a decided influence over -the weather, and over the growth of vegetation. I have neighbors who -would never think of planting certain things except ‘in the New of the -moon’! Some will not cut timber except ‘in the Old of the Moon,’ as they -say that the sap is drawn up by the moon’s influence when she is -growing. Is there really any truth in all this?” - -“Not the least. At any rate there is no scientific evidence whatever for -such statements, and no probability that they are based on facts. They -are the result of faulty observation, misled by coincidences. It is -_imaginable_ that the light of the moon might have some influence upon -vegetable growth if it were an original kind of light coming from the -moon herself. But moonlight is only reflected sunlight, and when we -examine it with the spectroscope we do not find that the rays of light -in visiting the moon and returning thence to the earth have had either -anything added to or anything taken away from them, except intensity. -The total amount of light reflected from the moon upon the earth is -estimated to be about 1/618000 of the total amount that comes to us from -the sun. Curiously enough the moon appears to reflect proportionally -more heat than light, the amount of lunar heat received by the earth -being reckoned at 1/185000 of the amount coming from the sun. The -popular idea that the moon affects the movement of sap in plants is -equally illusory.” - -“But about the weather? I know people who believe that a change of the -moon from one phase to another brings about a change of weather. Is that -true?” - -“Certainly it is not true. The moon is changing its apparent form all -the time. There is no sudden alteration at any phase. The popular -belief, however, has always been so firmly fixed that many -investigations have been made to ascertain whether there is, in reality, -any foundation for it. These investigations have shown that no -measurable effect of the kind exists.” - -“And the Full Moon does not drive away clouds, as some assert?” - -“Surely she does not. I will now tell you something that the persons who -plant and sow and cut timber according to the phases of the moon, and -who believe that she exercises a kind of magic control over the clouds, -probably have never heard of, although if they knew it they might use it -as an argument in favor of lunar influences. It is this: The alternate -approach and retreat of the moon with respect to the earth, as she -travels round her elliptical orbit, produce measurable, although slight, -disturbances of the magnetism of our planet. The distance of the moon -varies to the extent of about 30,000 miles. Now, if it could be shown -that these magnetic disturbances were reflected in the character of the -weather, then the supposed influence of the moon would be established. -But that has not been shown, and if it were shown it would still be -found that the phases of the moon had no relation to the fact, for the -moon may be at its greatest or its least distance from the earth, or at -any intermediate distance during any possible phase.” - -“You will, perhaps, think me very persistent in asking foolish -questions, but there is one other on my mind that I should like to put, -now that we have gone so far. It is this: I have read, since the great -earthquakes at San Francisco and Valparaiso, and the great eruption of -Vesuvius in the same year, 1906, that the moon has an influence over -such things. Is this another unfounded popular superstition?” - -“It is not a notion of _popular_ origin at all,” I replied. “It -originated rather from scientific considerations, and there may possibly -be a germ of truth in it, although it yet remains to be demonstrated, -and the evidence concerning it is confusingly contradictory. You will -recall, I trust, what has been said about the sun and the moon producing -tides in the oceans. We have also seen that before our globe had assumed -its present condition, while it was yet more or less plastic throughout -its whole mass, and before the birth of the moon, great tides were -produced in the body of the earth. The _tendency_ to the production of -such bodily tides still exists, and now that the moon has become a -near-by attendant of the earth, she acts more effectively in this regard -than does the sun. If the earth were still plastic the moon would -produce bodily tides in it. In other words the earth would be deformed -by the attraction of the moon. The question has arisen whether or not -the tendency to the production of such tides, now that the earth has -become rigid, may not disturb its crust sufficiently to induce -earthquakes and volcanic eruptions. Some students of the subject have -thought that they could detect evidence that this is the case. It has -frequently happened that such phenomena have occurred on a large scale, -at or very close to, the periods of New and of Full Moon. Those are the -times, as we saw when we were talking of the oceanic tides, when the sun -and the moon pull together. If all great eruptions and earthquakes -occurred at these conjunctions there would be little doubt of the -correctness of the theory. But, unfortunately for the clearness of our -conceptions, this is by no means the case. There have been many -earthquakes and volcanic outbursts when the sun and the moon were not -thus combining their tidal attractions. Thus the evidence is found to be -contradictory or inconsistent, and the question remains unsettled. It -is, however, a very interesting one, and the time will come, it is to be -hoped, when it will be answered decisively one way or the other.” - -After this digression we returned to the study of the photographs. - -“Photograph No. 20, which we have just been examining,” I said, -“represents the moon at the age of about twenty-four days and twenty -hours. The next, and the last of the series showing the moon in -progressive phases, is No. 21. Here the age of the moon is about -twenty-six days and twenty hours. It is the fast waning sickle of the -Old Moon which we behold. You perceive that it is relatively -uninteresting when compared with No. 20, because very little except the -eastern limb is illuminated. Nearly all the great circular and oval -formations and craters, and all the ‘seas,’ have passed into the lunar -night. Only the eastern verge of the _Oceanus Procellarum_ remains in -sight, dulling the brilliance of the inner curve of the sickle. The dark -walled plain above the center is Riccioli, and just below it appears -Hevel, a smaller, but yet large formation, with a low central mountain. -It is hardly worth our while to attempt to identify the other features -shown in the photograph. They include none that we have previously -studied. Yet this picture has an interest all its own because it is an -excellent representation of the moon at a time when she is so near to -the sun. Do not forget that, as I warned you when we began with the -crescent of the New Moon, in these photographs the moon appears reversed -top for bottom. Seen in the sky in the early morning this sickle would -have its rounded edge toward the left hand and directed more or less -downward, according to the position of the sun. A great deal of -confusion exists in the minds of well-educated people concerning the -position of the sickle of the New and the Old Moon. You have, of course, -heard of the classic instances in which artists have drawn the New Moon -with the concave side toward the sun! It is only necessary to remember -that a line drawn straight from the center of the convex side of the -sickle, whether it be the New Moon or the Old Moon, always extends -directly toward the place occupied by the sun.” - -[Illustration: - - NO. 21. AUGUST 19, 1903; MOON’S AGE 26.89 DAYS. -] - -“There is,” said my friend, “an interesting old superstition -which I have often heard—I suppose it must of course be a -superstition—concerning ‘wet moons’ and ‘dry moons.’ As I recall it they -say that when the sickle of the New Moon appears nearly upright in the -sky that is a sign of dry weather, because the moon is then like an -overturned cup, but when the sickle has its ends turned upward that is a -sign of wet weather, because then the cup can hold water. I suppose that -these various positions of the moon actually occur, but I do not know -how they are brought about.” - -“The supposed influence of the position of the New Moon on the weather,” -I replied, “is too gross a superstition to be worthy of any notice, but -the different attitudes of the sickle are interesting. They arise from -the changes in the position of the moon as seen from the earth with -respect to the direction of the sun, and these changes depend in turn on -the inclination of the moon’s path in the sky to the plane of the -earth’s equator as well as to the plane of the ecliptic or the earth’s -orbit. The ecliptic has an inclination of about 23½° to the plane of the -equator, and the moon’s orbit is inclined a little over 5° to the -ecliptic. The moon may, in consequence, appear more than 28° above or -below the equator. But since, as I told you in the beginning, the orbit -of the moon itself turns slowly about in space, the distance of the moon -above or below the equator is not constant. It may be only a little more -than 18°. In consequence of these changes of relative position the -situation of the horns of the crescent moon varies. But you need never -be in doubt as to what position they will occupy at any time if you will -simply remember that a straight line drawn from the point of one horn to -that of the other must always form a right angle with the direction of -the sun. - -[Illustration: - - Diagram Showing Why the Winter Moon Runs High. -] - -“There is another very interesting fact about the position of the moon -in the sky which we should not neglect to notice. Did you ever observe -the superior brilliancy of the light of the Full Moon in winter? It is -one of the compensations that nature offers us. Since the Full Moon is -necessarily situated opposite to the point occupied by the sun, and -since the sun is far south of the equator in midwinter, it follows that -at the same season the Full Moon appears high above the equator in the -northern hemisphere. You will, perhaps, permit me to show you a diagram -intended to explain this phenomenon. - -You observe that the sun being south of the equator, in the direction -indicated by the dotted line, the Full Moon is correspondingly situated -north of the equator, and must necessarily appear high in the sky at -midnight, when the sun is at its lowest declination. This is the reason -why the winter Full Moons are so brilliant, making the snow-clad hills -gleam with a splendor that sometimes dazzles the eyes of the beholders. -In the Arctic regions the long winter night, when the sun does not rise -for months, is periodically brightened by the presence of the Full Moon. -Just the opposite condition of affairs exists in summer. Then the sun -being north of the equator the Full Moon is south of it, and ‘runs low,’ -appearing in high latitudes to skim along the southern horizon.” - -“Thank you, and now I will ask you one more question,” said my friend. -“I have often heard of the ‘Harvest Moon’ and the ‘Hunter’s Moon.’ Will -you not kindly explain what is meant by these terms and when the -‘Harvest Moon’ can be seen? There is a poetic suggestiveness in the name -that appeals to me.” - -“I will try with pleasure,” I said, “but I fear that I shall have to -trouble you with another diagram, or perhaps with two.” - -“Oh, I shall not mind that at all. I have grown used to diagrams as well -as to the nomenclature of the moon.” - -“Well, if my diagrams conduct your thoughts to things as interesting as -many that lie concealed behind the prosaic names on the moon I shall be -content. To begin, then, I must remind you that in her monthly journey -around the earth the moon moves from west toward east in her orbit, and -thus she gets a little over 12° farther east every twenty-four hours, as -reckoned from the position of the sun. The earth turning on its axis in -the same direction causes the moon to appear to rise in the east and set -in the west once every twenty-four hours. But in consequence of the -constant eastward motion of the moon she rises at a later hour every -night. Here is a graphic representation of what I mean: - -“The earth is turning on its axis in the direction represented by the -arrows, and simultaneously the moon is moving in its orbit in the same -direction, as is shown by the large arrow. Suppose that some night the -moon is seen rising at a particular hour from the point A on the earth. -Then, the following night, when the observer has again arrived at A, -with the rotation of the earth, the moon will have advanced from M^1 to -M^2, and will not be seen rising until the point occupied by the -observer has arrived at B. This retardation of the hour of moonrise is -variable on account of changes in the position of the moon, arising from -the inclination of her orbit to the plane of the equator, and from the -inequalities of her motion, to which I have before referred. On the -average it amounts to fifty-one minutes daily. It varies also with the -distance of the observer from the equator, the variation being greater -in high latitudes. In the latitude of New York the retardation of -moonrise may be as great as an hour and a quarter, or as little as -twenty-three minutes. - -[Illustration: - - Diagram Showing Why Moon Rises Later Every Night. -] - -“Now it is upon this variation that the phenomenon of the ‘Harvest’ and -the ‘Hunter’s Moon’ depends. If I had a celestial globe here I could -show you that at the time of the Autumn Equinox, September 22d, when the -sun crosses the equator moving southward, the apparent path of the moon -in the sky intersects the eastern horizon at a comparatively small -inclination. In other words the moon at that time instead of rising -steeply from the horizon rises on a long slope almost parallel with the -horizon. The consequence is that for several evenings in succession the -Full Moon near the time of the Autumn Equinox may be seen rising just -after sunset at almost the same hour. Look at this second diagram and -you will see why this is so. - -[Illustration: - - Diagram Illustrating the Harvest Moon. -] - -“The little circles M show the moon at several successive positions in -her orbit, just twenty-four hours apart. You perceive that in -consequence of the slight inclination to the eastern horizon the sinking -of the latter caused by the earth’s rotation will bring the moon into -view night after night at almost the same hour. In fact, in high -northern latitudes like those of Norway and Sweden the moon’s path at -this time of the year may actually coincide with the horizon, so that -for several evenings she will rise at exactly the same hour. The name -‘Harvest Moon’ explains itself, since it always occurs at the time of -the autumn harvests and the vintage, and seems to supplement the fading -daylight for the benefit of late laborers in the fields. The ‘Harvest -Moon’ does not occur every year at precisely the same date. It is very -rare that Full Moon happens to fall just on September 22d. It usually -either precedes or follows that date. The ‘Harvest Moon’ is the Full -Moon which occurs nearest to the Autumn Equinox, either before or after. -The ‘Hunter’s Moon’ is the first Full Moon which follows the ‘Harvest -Moon.’ Like the former it rises for several successive evenings near the -same hour, but this phenomenon is less marked in the case of the -‘Hunter’s Moon,’ because it is farther from the Equinox.” - -“Thank you, again,” said my friend. “I shall never henceforth look at -the moon without thinking of circles, straight lines, and arrows as well -as of ‘ring mountains’ and ‘seas.’” - -“Then you are making good progress toward science,” I replied. “One last -look, now, at the photograph of the Old Moon’s sickle, and then we had -better postpone our examination of the large photographs, showing -certain particularly interesting districts on the moon, until to-morrow -morning. There is here another interesting point for artists to note. -The convex side of the sickle of the Old Moon, or the New Moon, is -always an arc of a circle, but the concave side is never circular -although it is often thus represented. The concave side, neglecting its -irregularities arising from the differences of level and of brilliancy -of the lunar surface, is elliptical in outline, that is to say, it is a -semicircle viewed obliquely.” - -“Whatever its geometry may be,” replied my friend, “it is certainly very -beautiful. Good night, and I shall demand to see those large photographs -before the sun is very high to-morrow.” - - ------------------------------------------------------------------------- - - - - - IV - - GREAT SCENES ON THE MOON - - - - ------------------------------------------------------------------------- - - - - - IV - - 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 of 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 ring 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.” - -[Illustration: - - 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 -more 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 form 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 probably 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. Between 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 one 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 part 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 the 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 at 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, you 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.” - -[Illustration: - - 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 small 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.” - -“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 and 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 eastern 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 possessed 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. - -“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.” - -[Illustration: - - 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 diameter, 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 on 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 geologist, 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 arrangement 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 long 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.” - -“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 while 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 in 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.” - -[Illustration: - - 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 the 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 -which 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. From 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.” - -“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 walls 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 uniform 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 of 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 photograph 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 three 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 southward 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. These 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 evidently 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.” - -[Illustration: - - 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 part 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 light -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 southern shore of the -strait leading into the _Mare Imbrium_. These mountains possess one -conspicuous crater, set like a gem in the chain, at about a third of its -length from the western end. This crater is Menelaus, which we saw in -one of the smaller photographs. It is characterized by its exceptional -brilliance as well as by the fact that the longest of the bright bands -that start from Tycho passes through it, and then continues on across -the _Mare Serenitatis_ and the _Lacus Somniorum_, to the _Mare -Frigoris_. This band, more than 2,000 miles long, has come all the way -from Tycho, high in the southern hemisphere, never turning aside to -avoid anything in its path. Mountains, craters, and ring plains are -equally indifferent to it. It is like a Roman road, and like that, too, -it suggests for its creation a power that knew no master, and admitted -of neither rivalry nor opposition. The existence of this mysterious band -increases the difficulty of finding a satisfactory explanation of the -Tychonic rays. In the midst of the _mare_ the band or ray crosses -another lone crater, 14 miles in diameter, named Bessel. The full length -of the ray is not shown in this photograph, but on its way from Bessel -it touches two other small craters in the ‘sea.’ - -“That portion of the Hæmus range in which Menelaus is set is a very -attractive scene on account of the bow shape of the mountains, and the -situation of the bright crater just in the center of the bow. Menelaus -and the streak from Tycho can be seen at Full Moon with no greater -optical aid than that of a good binocular. On the edge of the ‘sea,’ off -a lofty headland of the Hæmus chain, another lone little crater is -visible, Sulpicius Gallus by name. It, too, is remarkable for its -brilliant reflective power. Behind the mountains, directly back of -Sulpicius Gallus, and lying in an upraised part of the _Mare Vaporum_, -is a larger, and even brighter, crater ring than Menelaus. It is named -Manilius, and is likewise a conspicuous object for a binocular at Full -Moon. Below Sulpicius Gallus the Hæmus Mountains broaden out and assume -a curious somber tone, until, in the form of a rough plateau, they blend -with the wide-expanded southwestern slopes of the Apennines. The latter -rise gradually to the chain of huge peaks fronting the _Mare Imbrium_. -They contain one notable crater ring named Marco Polo, which lies just -above a great square _massif_, which breaks the narrow chain of the -illuminated summits of the Apennines. The precipitous front of this -range appears very brilliant in the afternoon sun, for here again we -have a photograph made after the time of Full Moon. The end of the -Apennines touching the strait, of which I have previously spoken, -terminates with a high cape called Mount Hadley. In the strait, off this -cape, is an array of small mountain peaks, which must have been islands, -if the lunar ‘seas’ were once true seas. - -“Across the strait, on the northern side, stand the lunar Caucasus -Mountains. They run out to a point in a long, irregular, broken ridge. -The distance from Mount Hadley across the strait to the projecting point -of the Caucasus range is about 50 miles. The islands narrow the main -opening to a width of 30 miles. In strict fact the Caucasus range is not -continuous. The point fronting the strait is, in reality, the end of a -large irregular ‘island,’ with intricate channels separating it from the -mainland. Still farther north the photograph shows a broad valley -severing the mountain range from side to side. The main mass of the -Caucasus continues northward to the great ring mountains Eudoxus and -Aristoteles. In the center of the range, opposite the lower corner of -the _Mare Serenitatis_, is an irregular ring plain, Calippus. West of -this the mountains break down in great precipices to the level of a -plain that might be compared with one of the ‘parks’ of Colorado. Beyond -this, in the shape of a broad mass of hills, it skirts the border of the -_Mare Serenitatis_ for nearly 200 miles to a sharp promontory which -shuts off the _Lacus Somniorum_ on one side from the _mare_. West of -Aristoteles and Eudoxus the mountain mass extends to a curious -sharp-angled plain, which it skirts on the north and south. - -“The western shore of the _Mare Serenitatis_ beyond the strait opening -into the _Lacus Somniorum_ is bordered by a series of alternating ring -plains and connecting mountains. The first and largest of the rings is -Posidonius, an immense formation 62 miles in diameter, with a central -crater and curious ridges within the inclosure. Above Posidonius is Le -Monnier, a ring plain whose ‘seaward’ wall has been broken down. Above -that, again, is a mountain range terminating with broken crater rings. -Then we arrive at the strait opening into the _Mare Tranquillitatis_, -which is twice as broad as that between the Apennines and the Caucasus, -and just in the middle of it stands a very perfect crater ring named -Dawes. On the eastern side of this strait the Hæmus Mountains begin with -a long cape called the Promontory Acherusia. Above this promontory, at -the edge of the picture, appears the ring plain Plinius, with a distinct -central peak. This completes the circuit of the _Mare Serenitatis_. - -“We return to the Caucasus region. These mountains front the _Mare -Imbrium_ along the upper part of their course with sharp slopes and -cliffs. In the ‘sea,’ nearly opposite the deep, broad valley which I -pointed out as dividing the range completely across, stands a -triangular-shaped ring plain dark with shadow on one of its sides. This -is Theætetus, interesting as the scene of an alleged display of ‘smoke,’ -reported to have been witnessed by a French observer with his telescope -a few years ago. Several occurrences of this kind have been reported on -the moon, but more or less doubt attaches in every instance the accuracy -of the observations, or at least to that of the conclusions drawn from -them. Below Theætetus is an oval ring almost entirely filled up, with -two craters within it. This is named Cassini. Below Cassini begins -another mass of mountains, the lunar Alps. These are by no means as -extensive as the Caucasus, but they contain some lofty peaks, and are -traversed by one of the most remarkable valleys on the moon. It is not -very distinctly shown in this picture, but you may recognize it by a -dark band commencing opposite a small bay which sets back into the -mountains. The valley continues through the mountains and the adjoining -hilly regions nearly to the shore of the narrow _Mare Frigoris_, which -runs in a sloping direction from beyond Aristoteles to the bottom edge -of the picture. The Alps spread eastward, broadening out with many -separate peaks, and skirting the _Mare Imbrium_, until they reach one of -the most singular and interesting of lunar formations, the oval ring -plain Plato. This looks like a dark lake surrounded by high cliffs. In -the photograph all of the encircling wall is illuminated on the inner -side except at the east end, where the shadows extend a short distance -upon the floor. Plato looks as though it might once have been a ring -mountain of the usual type, which has been partly filled in the interior -by a local uprush of molten lava. The diameter of the ring is 60 miles, -but the inclosure sinks only about half as deep beneath the crest of the -wall, as is the rule with formations of similar outline. A central peak, -a group of mountains, may be buried there. - -“It is within this ring of Plato that some of the strongest evidences of -continued change, and possibly of continued life upon the moon, have -been found. Prof. William H. Pickering, after long and careful studies -of this remarkable plain, says of it: - -“‘Plato is, I believe, more active [in a volcanic sense] than any area -of similar size upon the earth. There seems to be no evidence of lava, -but the white streaks indicate apparently something analogous to snow or -clouds. There must be a certain escape of gases, presumably steam and -carbonic acid, the former of which probably aids in the production of -the white markings.’ - -“The white marks to which Professor Pickering refers are but faintly -indicated in the photograph before us, but with the telescope, when the -illumination is favorable, they are plainly seen. There are a number of -very small crater pits scattered over the floor of Plato, and around -these changes of color occur which have been ascribed to the emission of -some substance from the pits and to the presence of vegetation, -nourished by the gases and vapors, and springing into renewed life every -time the sun rises upon the plain. Broad areas of the inclosure -gradually change color as the sun rises, and again as the sun sets, and -these phenomena have also been ascribed to the presence of vegetation. -You may, if you wish, regard Plato as a kind of mountain-ringed prairie, -covered with something analogous to prairie grass and shrubs, which -depends for its existence, partly, upon the supply of gases spreading -over the surface from the crater pits.” - -“So this, then, is your ‘lunar grass’?” - -“Yes, but not all of it. Mark, I do not aver that it actually exists; I -only say that it has been suspected to exist. On some of the _mares_ -similar appearances are seen, as I have already told you, on a much more -extensive scale, and I may again quote Professor Pickering, who says -that some of his observations ‘point very strongly to the existence of -vegetation upon the surface of the moon in large quantities at the -present time.’” - -“Does this vegetation resemble that of the earth?” - -“I cannot tell you.” - -“But where vegetation exists animal life is possible, is it not?” - -“Yes, it is _possible_.” - -“What forms would it have?” - -“I cannot tell you. But I certainly should not expect to find manlike -creatures there.” - -“Oh, men are not _necessary_ everywhere,” said my friend, laughing. “I -am content if you admit that there may be living creatures of some kind. -Henceforth I shall never forget Plato and the other places on the moon -where such significant changes are seen.” - -“I shall presently point out to you one of the most notable of those -other places,” I replied. “Let me now fulfill my promise to tell you -more about the lunar atmosphere. I have told you already that there are -strong reasons for supposing that the moon once had a far more dense -atmosphere than she possesses at present, and I have mentioned some of -the ways in which this atmosphere is supposed to have disappeared. I -think that it is worth our while to refer to them again. In the first -place the moon’s atmosphere may have been withdrawn into vast internal -cavities formed by the gigantic volcanic eruptions. Secondly, it may -have been absorbed both mechanically and chemically by the core of the -moon as it cooled off. We know that cooling rocks absorb immense -quantities of the gases constituting the air we breathe. In fact we may -look forward to a time, fortunately for us extremely remote, when the -interior rocks of the earth will, in this manner, absorb perhaps all of -its atmosphere.” - -“But if the air of the moon has gone into great cavities in the -interior, why might not the living beings of the moon have followed it -there?” - -“According to some of the theorists,” I answered, “that may really be -what has occurred, and thus the moon has become a ‘cavern world’ on a -gigantic scale. But science does not regard seriously these speculations -about ‘cave life’ in the moon. A third hypothesis is that which I have -mentioned concerning the escape of the atmospheric gases from the moon -on account of its attraction being insufficient permanently to retain -them. This process would be gradual, because the molecules of a gas fly -in _all_ directions, only a small proportion having their trajectories -directly away from the center of the globe on which they are held. But a -singular consequence of this theory is that interplanetary space must -contain an enormous number of such wandering molecules, and every -attracting body must draw more or less of them to its surface, thus -forming an atmosphere for itself. As Professor Young has remarked, if as -many of these molecules enter a planet’s atmosphere in a day as escape -from it there can be no decrease of the total amount of air. If more -escape than enter, the atmosphere will diminish. If more enter than -escape, the atmosphere will grow. Finally if none escape the atmosphere -may increase indefinitely. This, as far as the effect of gravitation is -concerned, should be the case on the sun, for the solar attraction is -more than sufficient to retain any gas known to us. In consequence, the -sun’s atmosphere may be increasing in extent and density. Even the -earth’s atmosphere may be slowly increasing from this cause, and herein -may lie the explanation of the enormous atmosphere surrounding the great -planet Jupiter. - -“In view of what I have said it is evident that the moon cannot be -entirely airless. Recent observations have confirmed this conclusion, -and some observers have thought that they could detect the presence of -something resembling clouds occasionally creeping like low fogs over -certain places on the moon. All this, you will observe, has an important -bearing upon the question of life on the moon at the present day. -Certain forms of plant life and low animal organizations might exist in -such an atmosphere as the moon still possesses.” - -“But,” interjected my friend, “is not this that you have been telling me -in contradiction to what you said about the cause of the sharp division -between day and night on the moon, and about the visibility of the stars -there in the daytime?” - -“Not at all,” I replied, “for the effects of which I spoke are relative. -In any case the atmosphere of the moon must be too rare to diffuse any -perceptible amount of light into the shadows, or to illuminate the sky -sufficiently to render the stars invisible. The same reasoning applies -to what I have told you about the contrasts of cold and heat on the -moon. - -“But we have not yet finished with our photograph. We were looking at -the plain of Plato, you will recollect. Notice, now, the _Mare Imbrium_ -off the coast that adjoins Plato on the south. You see there several -bright spots resembling islands. Islands they must have been if the -_mare_ once had water covering it. One of these, standing by itself, an -irregular, bright clump with a distinct shadow on the western side, -bears the name of Pico, taken from the sharp peak in the Azores Islands. -The broken mass southeast of Pico, and nearer the coast, constitutes the -Teneriffe Mountains. You will notice that terrestrial geography has been -drawn upon in this case also to supply a name. Still farther east is a -long ‘island’ named the Straight Range. Beyond that, at the edge of the -picture, appears Cape Laplace, at the western end of the ‘Bay of -Rainbows.’ - -“We now turn to the southwestern border of the _Mare Imbrium_, in the -upper part of the photograph. This, as I have already pointed out, is -skirted by the steep cliffs of the Apennines for a distance of more than -400 miles. Opposite the crater ring Marco Polo, in the Apennines, you -will notice how the floor of the ‘sea’ is upheaved, containing a great -number of irregularities, and some small peaks. This would have been a -dangerous part of the ‘Sea of Rains’ for the lunar navigators. At the -northwestern corner of this region lies a large ring plain, with -indefinite light stripes crossing its floor, which is named Archimedes. -It is about 50 miles in diameter. Northwest of it are two smaller ring -mountains, Aristillus (the larger) and Autolycus. If we could suppose -these immense volcanoes to have been in eruption when these seas were -navigable, imagine the magnificent spectacle that they would have -presented to anyone approaching in a ship from the direction of the -strait between the Apennines and the Caucasus. - -“Let us now pass this strait and enter the _Mare Serenitatis_. You will -admire the beautiful modulation of the bottom, as shown in the -photograph. Lighter and darker regions are curiously interspersed, and -in some places there are faint indications of that wonderful lunar world -of remote antiquity which lies buried in the grave of a planet. Directly -opposite the opening of the strait, a small, round, light spot is seen -in the midst of the sea. This is Linné, very famous for its strange and -suggestive history. Here, if anywhere on the moon, changes visible to -human eyes have taken place, and, in the opinion of Professor Pickering, -are still taking place every fortnight. In the center of the light spot -is a minute crater, and from this crater there seems to issue some kind -of vapor which spreads over the surrounding surface, alternately -expanding and shrinking in extent. A remarkable change in the form and -appearance of Linné was recorded by the astronomer Schmidt, at Athens, -in 1866. What had occurred has been explained by some as the falling in -of a crater floor some six miles in diameter. But the observations of -Professor Pickering are more interesting and suggestive. According to -him the bright patch about the crater pit extends during the lunar night -and diminishes by day, indicating that something issues from the pit and -is deposited over the surrounding plain in the form of hoar frost, which -melts away in the sunshine. He has even recorded an apparent expansion -of the white area during a lunar eclipse when the cold shadow of the -earth tends to condense the vapors. If this is true it seems rather -surprising that many more similar phenomena are not visible elsewhere. - -“Among the most remarkable and beautiful features of this photograph are -the winding ridges like half-submerged mountain ranges that appear on -the sea bottom in various places. Notice particularly the long twisted -chain that lies across the western part. Between this and a shorter -range, close to the west shore, runs a broad, dark valley, with the -crater Dawes lying in the middle of it at the upper end. Some of these -winding ridges suggest by their shape and modulation the action of -water. Finally, let us return to the strait through which we recently -passed. Notice that the Apennines and the Caucasus look as though they -had once formed a continuous line of mountains, which has been broken -through in its center, leaving huge buttresses on each side, like the -Pillars of Hercules at the Strait of Gibraltar?” - -“That place has an irresistible attraction for me,” said my companion. -“I cannot withhold my imagination from picturing the scene there when -the waters rolled deep over those great bottoms, and when white-sailed -ships were passing and repassing between the towering capes, carrying -the commerce of opulent cities situated along those marvelously -picturesque shores.” - -“Perhaps,” I suggested, “the lunarians, whom you have reconstructed in -your fancy, reached, before the catastrophe came that ended their -existence, a higher state of civilization than ours, and learned to -substitute electrically driven vessels for white-winged ships.” - -“That would be like the introduction of vulgar steamboats on the canals -of Venice,” she replied. - -“Well,” I said, “this ends our survey and one month of photographic -journeying on the moon, and I am glad that you have finished it with so -pleasing a vision.” - - * * * * * - -Upon parting from my friend I left the photographs in her possession. A -few weeks later I received a letter from her in which she said: - -“I have been studying and restudying those wonderful pictures of the -moon. I have ordered a telescope to be set up in my park near the elm, -and when it is ready I wish you to come and instruct me how to view the -moon for myself. I believe that I am becoming a learned and enthusiastic -selenographer, and those strange names—Gemma Frisius, Bullialdus, -Abulfeda, Abenezra, Rabbi Levi, Maurolycus, Fra Mauro, Sacrobosco, -Zagut, Cichus, Sulpicius Gallus—have established their fascination over -my mind. Theophilus no longer terrifies me with its formidable aspect, -and I spend hours poring over the _Mare Serenitatis_. But my fancy -remains faithful to the ‘Marsh of a Dream,’ which still represents for -me the culmination of lunar ideality. - -“As to life on the moon, I find that I cannot be satisfied with a mere -grass theory. I am so well convinced that there must be something more, -that I no longer relegate my lunarians to an age antedating the -volcanoes. On the contrary, as soon as I get my telescope I am going to -look for signs of them and their doings in the present day, and willy -nilly, sir, you have got to aid me in the search.” - - ------------------------------------------------------------------------- - - - - - APPENDIX - - - - ------------------------------------------------------------------------- - - - - - APPENDIX - - -DATES, and age of the moon, when the twenty-one serial photographs were -made at the Yerkes Observatory, by Mr. Wallace, with the 12-inch -telescope and a special color filter constructed by him: - - No. 1, February 19, 1904; Moon’s Age 3.85 Days - No. 2, September 24, 1903; Moon’s Age 3.87 Days - No. 3, July 29, 1903; Moon’s Age 5.54 Days - No. 4, November 24, 1903; Moon’s Age 5.74 Days - No. 5, July 1, 1903; Moon’s Age 6.24 Days - No. 6, November 26, 1903; Moon’s Age 7.75 Days - No. 7, July 2, 1903; Moon’s Age 7.24 Days - No. 8, August 31, 1903; Moon’s Age 9.22 Days - No. 9, August 2, 1903; Moon’s Age 8.97 Days - No. 10, November 30, 1903; Moon’s Age 11.78 Days - No. 11, December 1, 1903; Moon’s Age 12.98 Days - No. 12, September 4, 1903; Moon’s Age 13.27 Days - No. 13, September 5, 1903; Moon’s Age 14.40 Days - No. 14, August 26, 1904; Moon’s Age 15.65 Days - No. 15, August 28, 1904; Moon’s Age 17.41 Days - No. 16, August 29, 1904; Moon’s Age 18.62 Days - No. 17, October 10, 1903; Moon’s Age 20.06 Days - No. 18, September 29, 1904; Moon’s Age 20.50 Days - No. 19, August 16, 1903; Moon’s Age 23.81 Days - No. 20, August 17, 1903; Moon’s Age 24.84 Days - No. 21, August 19, 1903; Moon’s Age 26.89 Days - - ------------------------------------------------------------------------- - - - - - INDEX - - - - ------------------------------------------------------------------------- - - - - - INDEX - - - Abenezra, 205. - - Abulfeda, 200. - - Air on the moon, 230. - - Albategnius, 78. - - Aliacensis, 78, 205. - - Almamon, 205. - - Alps, 97. - remarkable valley in, 225. - - Altai Mountains, 72, 200. - chain of small craters near, 200. - - Animal life on the moon, 228. - - Apennines, 10, 96, 104, 137, 143, 222, 232. - - Apennines and Caucasus, strait between, 234. - - Apianus, 205. - - Archimedes, 143, 232. - - Aristarchus, 117, 153. - astonishing brilliance of, 112. - cause of brilliance of, 155. - possible composition of, 113. - - Aristoteles, 76, 138. - - Atlas, 70. - - Atmosphere, lunar, 31. - disappearance of, 228. - what has become of it, 32. - - Atmospheres, how they may grow or decrease, 230. - - Azophi, 205. - - - Barry, 189. - - “Bay of Rainbows,” 109, 111, 142, 157, 158. - - Bessel, 221. - - Bianchini, 110. - - Birt, 188. - - Blancanus, 78, 194. - - Bonpland, 189. - - Bubbles on the moon, 186. - - Bullialdus, 180-182, 183. - mountains near, 183. - - Byrgius, 147. - - - Calippus, 223. - - Campanus, 185. - - Capuanus, 185, 196. - - Carpathian Mountains, 215. - - Cassini, 225. - - Catharina, 72, 138, 199, 206. - remarkable valleys near, 199-200. - - Caucasus Mountains, 97, 223. - - Caucasus and Apennines, strait between, 234. - - “Cavern life” on moon, 229. - - Cichus, 185, 196. - - Clavius, 99, 101, 146, 192. - length of great wall of, 193. - - Cleft near shore of _Mare Nubium_, 186. - - Clefts on moon, resemblance of, to geological “faults,” 187. - - Cleomedes, 56. - - Color on moon, 155. - - Colorado Cañon, possible likeness of, to cleft on moon, 118. - - Copernicus, 102, 211. - an argument for the volcanic theory, 212. - buried ring near, 217-218. - crater pits near, 213. - hexagonal form of, 212. - - Craters, lunar, formation of, ascribed to falling masses, 201. - theory of, advanced by W. K. Gilbert, 200. - - Cyrillus, 72, 138, 199, 206, 210. - - - “Dark woman” in moon, 133. - - Darwin, Prof. George, 6. - - Dawes, 224. - - Day and night on moon, 63. - - Day on moon, length of, 95. - - - Earth, light of, on moon, 50. - shadow of, effects of, as shown by Prof. William H. Pickering, 28. - shadow of, its size and length, 18. - - Eclipse, lunar, 17-18. - earth’s atmosphere and, 27. - moon visible during, 26. - - Eclipses, lunar, colors visible during, 29. - fix historic dates, 29. - number of, in year, 42. - when annular, 41. - - Eclipses, why they do not occur every month, 38. - solar, different from lunar, 27. - number of, in year, 42. - why of greater scientific value than lunar, 28. - - Endymion, 70, 132. - - Eratosthenes, 104. - - Eudoxus, 76, 138. - - - Fracastorius, 73. - - Fra Mauro, 189. - - Full Moon in winter, why it runs high, 170. - - Furnerius, 63. - - - Gases, escape of, from moon, 229. - from planets, 33. - molecular velocity of, 33, 229. - - Gassendi, 117. - - Gauricus, 196. - - Gay Lussac, 216. - - Gemma Frisius, 202. - - “Geology” of moon, 67. - - “Giantism” on the moon, 193. - - Gilbert, W. K., theory of lunar craters advanced by, 200. - - Gravitation on moon, 34-36. - - Grimaldi, 121, 132. - - - Hæmus Mountains, 92, 220. - - Hansen, theory of, in regard to the other side of moon, 139. - - Harbinger Mountains, 118. - - “Harvest Moon,” 171. - - Heat of moon compared with that of sun, 164. - - Helen of Troy, 92. - - Hell, 196. - - Hercules, 70. - - Herodotus, 112, 158. - cleft near, 118. - - Herschel, Sir William, his supposed discovery of active lunar volcano, - 112. - - Hipparchus, 78. - - Hoar frost on moon, 34. - - “Hunter’s Moon,” 171. - - - Inhabitants of moon, 31-32, 88, 95. - would not be visible with most powerful telescope, 120. - why they might be giants, 193. - - - Kepler, 114, 141, 152. - - Kies, 185. - - - _Lacus Somniorum_, 93, 219. - - Landsberg, 217. - - Langrenus, 56, 123, 132. - - Lava floods on moon, 73, 152. - - Libration, effects of, on visibility of parts of moon, 57-58, _Note_. - - Life on the moon, 230. - - Light of moon compared with that of sun, 163. - - Lindenau, 202. - - Linné, changes in, 233. - observations of, by Professor Pickering, 233. - observations of, by Schmidt, 233. - - Loewy and Puiseux, opinion of, on lunar “seas,” 220. - - Longomontanus, 101, 146, 150, 195. - - Lubiniesky, 184. - - Lunar charts, their relative accuracy, 161. - - Lunar history, 62. - - Lunar month, 12. - - Lunar nomenclature, 59, 147. - number of objects bearing names, 161. - singularity of, 203. - - Lunar plains, darkening of, near sunset, 144. - - Lunar sickle, rule to determine position of, 168. - - Lunar vegetation, 32. - - - Maginus, 100, 146, 196. - - Manilius, 122, 222. - - Marco Polo, 222. - - _Mare Crisium_, 52, 55. - - _Mare Fœcunditatis_, 65. - - _Mare Frigoris_, 76. - - _Mare Humorum_, 106, 117, 150. - - _Mare Imbrium_, 103, 142, 144, 224. - irregularities in the floor of, 232. - islands in, 231. - - _Mare Nectaris_, 68, 135. - - _Mare Nubium_, 102, 148, 180. - - _Mare Serenitatis_, 74, 135, 219, 232. - bordering cliffs of, 220. - ridges in the floor of, 234. - - _Mare Tranquillitatis_, 74, 135. - - _Mare Vaporum_, 103. - - “Marsh of a Dream,” 68, 91. - - Mass of moon, 35. - - Maurolycus, 75, 142, 204. - - Menelaus, 92, 221. - - Mercator, 185. - - Month, lunar, 12. - - Moon, birth of, and Pacific Ocean, 6. - distance of, from earth, 8. - greatest distance of, from earth, 8. - influence of, on growth of vegetation, 163. - least distance of, from earth, 8. - life on, 230. - other side of, 139. - seen by daylight, 149. - separation of, from the earth, 6. - turning of same face of, toward earth, 19. - - Moon and earthquakes, 165. - - Moon and the weather, 164. - - Moon and volcanoes, 165. - - “Moon Maiden,” 10, 96, 103, 122. - - Mount Hadley, 222. - - - New Moon, photograph of, 49. - - New Moon and the weather, 169. - - Newton, deepest crater on moon, 107. - - Nicollet, 188. - - Night, advance of, over moon, 131. - length of, on moon, 95. - lunar, coldness of, 136. - - Nodes of moon and their revolution, 38-39. - - - _Oceanus Procellarum_, 105, 150. - submerged rays in, 151. - - Orbit of moon, 8. - - Origin of moon, 6. - - - Pacific Ocean and birth of moon, 6. - - _Palus Somnii_, 68. - - Path of moon about sun, 16-17, _Note_. - - Petavius, 62, 123. - - Phases of moon explained, 13-16. - - Phlægrean Fields, 60. - - Photographs, lunar, 47-49. - in series, 57. - peculiar tone of, 145. - why they are reversed, 52. - - Photometry, lunar, 153-154. - - Piccolomini, 72, 200. - - Pickering, Prof. William H., observations of Linné by, 233. - on effects of earth’s shadow on moon, 28. - opinion of, regarding changes in Plato, 226. - theory of Tycho’s rays by, 126. - - Pico, 231. - - Pitatus, 186, 195. - - Plato, 105, 114, 132, 225. - changes observed in, opinion of Prof. William H. Pickering regarding, - 226. - vegetation in, 227. - - Plinius, 224. - - Poetry of the moon, 96. - - Posidonius, 224. - - Prism binoculars for viewing moon, 122. - - Proclus, 68. - remarkable brilliance of, 90. - - Projectile force on moon, 37. - - Promontorium Ænarium, 189. - - Promontory Acherusia, 224. - - Promontory Heraclides, 109. - - Promontory Laplace, 109. - - Ptolemæus, 98. - - Pytheas, 216. - - - Rabbi Levi, 202. - - Reinhold, 217. - - Riccioli, nomenclature of, for lunar objects, 69. - - Rings, ranges of, on moon, 97-98. - - Riphæan Mountains, 190. - - Rotation of moon “braked” by tides, 20. - - Rotation of moon, illustrated, 19-20. - - - Sacrobosco, 206. - - Schickard, 115. - - Schmidt, observation of Linné by, 233. - - Schröter, “lunar city” discovered by, 218. - - “Seas,” lunar, character of beds of, 142. - - Shadow of moon during eclipse, 40. - length of, 40. - - Shadows on moon, topography revealed by, 100-101. - used to measure heights on moon, 63. - - Sidereal revolution of moon, 11. - - _Sinus Æstuum_, 103. - - _Sinus Iridum_, 109. - - _Sinus Medii_, 103. - - _Sinus Roris_, 159. - - Size of moon, 8. - - Sky as seen from moon, 29. - - Snow, can it exist on the moon? 69. - - Snow, non-existence of, on moon, 69. - - South polar region of moon, 77. - - South pole of moon, 106. - - Stadius, 218. - - Stöfler, 75. - row of rings near, 204. - - “Straight wall,” 187. - - Strait between Apennines and Caucasus, 234. - - Sulpicius Gallus, 222. - - Sunrise, slow progress of, on moon, 94. - - Sunshine, effects of, when vertical on moon, 100. - - Surface of moon, nature of, 9. - size of, 9. - - Synodic revolution of, 11-12. - - - Tacitus, 200. - - Telescopic power, limits of, 120. - - Teneriffe Mountains, 231. - - “Terminator,” meaning of, 63. - - Theætetus, 225. - - Theophilus, 71, 138, 198, 206. - crater pits near, 211. - grandeur of appearance of, when highly magnified, 207. - great mountain fold near, 207-208. - what would be seen from wall of, near sunset, 208. - - Tidal attraction, forcing moon away in reaction of, 6. - - “Tidal friction,” 20. - - Tides, causing of, by moon and sun, 21. - effect of earth’s rotation on, 25. - service rendered by, 22. - simultaneous occurrence of, on opposite sides of earth, 23. - when highest, 21. - when lowest, 22. - - Twilight, why none on moon, 64. - - Tycho, 10, 98, 106, 146, 191. - longest ray of, 93, 221. - ray system of, 124. - rays of, 99. - theory of Nasmyth, 124-125. - theory of Pickering, 126. - - - Vegetation on moon, 32, 115, 142, 144, 227. - - Vendelinus, 59, 123. - - Venus seen by daylight, 149. - - Verne, Jules, “Trip to the Moon,” 4. - - Volcanic craters on moon, 60. - - Volcanoes, lunar, 54. - contrasted with those of earth, 84. - effects of gravitation on size of, 86. - - - Water on the moon, 53. - - “Weathering” on the moon, 197. - - Weight on the moon, 36. - - Werner, 78, 205. - - Wilhelm I., 102, 195. - - - Zagut, 202. - - ------------------------------------------------------------------------- - - - =BOOKS BY GARRETT P. 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margin-right: 5.56%; font-size: 85%; text-indent: 1em; - margin-top: 0.5em; margin-bottom: 0.5em; } - .c028 { margin-top: 1em; text-indent: 1em; margin-bottom: 0.5em; } - body {width:80%; margin:auto; } - .tnbox {background-color:#E3E4FA;border:1px solid silver;padding: 0.5em; - margin:2em 10% 0 10%; } - .fn {font-size: 0.85em; line-height: 125%; } - h1 {font-size: 2em; text-align: center; } - h2 {font-size: 1.50em; } - body {line-height: 150% } - .lh1 {line-height: 100% } - </style> - </head> - <body> - -<div style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of The Moon: A Popular Treatise, by Garrett P. Serviss</div> - -<div style='display:block; margin:1em 0'> -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world 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 <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you -are not located in the United States, you will have to check the laws of the -country where you are located before using this eBook. -</div> - -<p style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: The Moon: A Popular Treatise</p> - -<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: Garrett P. Serviss</div> - -<div style='display:block; margin:1em 0'>Release Date: October 10, 2021 [eBook #66510]</div> - -<div style='display:block; margin:1em 0'>Language: English</div> - -<div style='display:block; margin:1em 0'>Character set encoding: UTF-8</div> - -<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: Tim Lindell, Barry Abrahamsen, and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/Canadian Libraries)</div> - -<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK THE MOON: A POPULAR TREATISE ***</div> - -<div class='figcenter id001'> -<img src='images/cover.jpg' alt='' class='ig001' /> -</div> -<div class='pbb'> - <hr class='pb c000' /> -</div> -<div> - <h1 class='c001'>THE MOON</h1> -</div> -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div id='frontis' class='figcenter id002'> -<img src='images/frontis.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>Copernicus and the Carpathian Mountains.</span></p> -</div> -</div> -<div class='pbb'> - <hr class='pb c000' /> -</div> -<p class='c003'> </p> - -<div class='nf-center-c0'> - <div class='nf-center'> - <div><em class='gesperrt'><span class='c004'>THE MOON</span></em></div> - <div class='c005'><em class='gesperrt'><span class='c006'>A POPULAR TREATISE</span></em></div> - <div class='c007'><span class='c008'><i>By</i></span></div> - <div class='c000'><span class='c008'>GARRETT P. SERVISS</span></div> - </div> -</div> - -<p class='c003'> </p> -<div class='figcenter id003'> -<img src='images/publogo.jpg' alt='' class='ig001' /> -</div> -<p class='c009'> </p> - -<div class='nf-center-c0'> -<div class='nf-center c007'> - <div><span class='c006'><em class='gesperrt'>D. APPLETON AND COMPANY</em></span></div> - <div><span class='c006'><em class='gesperrt'>NEW YORK</em></span></div> - <div><span class='c006'>1907</span></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c005' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c002'> - <div><span class='sc'>Copyright, 1907, by</span></div> - <div>D. APPLETON AND COMPANY</div> - <div class='c002'><i>Published October, 1907</i></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_v'>v</span> - <h2 class='c010'>PREFACE</h2> -</div> -<p class='c011'><span class='sc'>The</span> reader familiar with astronomical literature -will doubtless remark a certain resemblance -between the plan on which this book is written -and that of Fontenelle’s “Conversations on the -Plurality of Worlds,” a French classic of the -eighteenth century. The author freely acknowledges -that it was the recollection of the pleasure -which the reading of Fontenelle’s book gave him, -years ago, that led to the adoption of a somewhat -similar plan for this description of the moon. -But, except that in both cases the conversational -method is employed, no great likeness will be -found between what is here presented and the -work of the witty Frenchman.</p> - -<p class='c009'>Having been invited by the Messrs. Appleton & -Co. to prepare a small volume, to be based on a -series of lunar photographs representing the -moon as it appears on successive evenings during -<span class='pageno' id='Page_vi'>vi</span>an entire lunation, the author felt that the work -should be made as entertaining as possible. He -has, therefore, avoided technicalities, while endeavoring -to present all the most essential facts -known about our satellite. What he has written -is intended for the general reader, who desires -to learn the results of the great advances in astronomy -without being too much troubled with -the scientific methods by whose aid those results -have been reached.</p> - -<p class='c009'>This is the first time, as far as the author is -aware, that a series of lunar photographs, showing -our satellite in its varying aspects from New -to Old Moon, has been presented in a book, accompanied -with a description of the mountains, -plains, volcanoes, and other formations shown -in each successive photograph. The reader is -enabled to place himself, as it were, in an observatory -of the first rank, provided with the most -powerful apparatus of the astronomer, and, during -an entire month, view the moon in her changing -phases.</p> - -<p class='c009'>The photographs here reproduced were made -at the Yerkes Observatory, and the most grateful -acknowledgments are tendered to Prof. Edwin -<span class='pageno' id='Page_vii'>vii</span>B. Frost, its director, for generously consenting -to their use for this purpose. He could only -have been induced to do so by his desire to see -the fruits of the admirable work accomplished -by his associates enjoyed by an ever-widening -circle.</p> - -<p class='c009'>The series of photographs representing the -moon on successive evenings were taken with -the 12-inch telescope of the Yerkes Observatory -by Mr. James Wallace, who employed a color -filter that he constructed specially for this telescope, -which possesses a visual and not a photographic -objective. The larger scale photographs, -representing certain selected regions on the moon, -were taken by Mr. Ritchey, now of the Carnegie -Solar Observatory at Mount Wilson, California, -with the great 40-inch telescope of the Yerkes -Observatory. It is unnecessary to speak of -the extraordinary quality of these photographs, -which have been admired by astronomers in -all lands.</p> - -<p class='c009'>It should, perhaps, be added that while the -director of the Yerkes Observatory has shown -confidence in the author by intrusting to him the -use of these photographs, yet, neither Professor -<span class='pageno' id='Page_viii'>viii</span>Frost, nor Messrs. Wallace and Ritchey are in -any way responsible for the statements made in -this book. The author has taken pains to be accurate, -but if any errors of fact or opinion have -crept in, he alone must be blamed for them.</p> -<div class='c012'><span class='sc'>Garrett P. Serviss.</span></div> -<p class='c013'><span class='sc'>Château d’Arceau,</span></p> -<p class='c014'><span class='sc'>Côte d’Or, France</span>, June, 1907.</p> -<div class='pbb'> - <hr class='pb c005' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_ix'>ix</span> - <h2 class='c010'>CONTENTS</h2> -</div> -<div class='lh1'> - -<table class='table0' summary=''> -<colgroup> -<col width='13%' /> -<col width='71%' /> -<col width='15%' /> -</colgroup> - <tr> - <td class='c015'> </td> - <td class='c016'> </td> - <td class='c017'><span class='small'>PAGE</span></td> - </tr> - <tr> - <td class='c015'> </td> - <td class='c016'><span class='sc'>Introduction</span></td> - <td class='c017'><a href='#intro'>3</a></td> - </tr> - <tr><td> </td></tr> - <tr> - <td class='c015'>I.</td> - <td class='c016'>—<span class='sc'>New Moon to First Quarter</span></td> - <td class='c017'><a href='#ch01'>47</a></td> - </tr> - <tr><td> </td></tr> - <tr> - <td class='c015'>II.</td> - <td class='c016'>—<span class='sc'>First Quarter to Full Moon</span></td> - <td class='c017'><a href='#ch02'>83</a></td> - </tr> - <tr><td> </td></tr> - <tr> - <td class='c015'>III.</td> - <td class='c016'>—<span class='sc'>Full Moon to Old Moon</span></td> - <td class='c017'><a href='#ch03'>131</a></td> - </tr> - <tr><td> </td></tr> - <tr> - <td class='c015'>IV.</td> - <td class='c016'>—<span class='sc'>Great Scenes on the Moon</span></td> - <td class='c017'><a href='#ch04'>181</a></td> - </tr> - <tr><td> </td></tr> - <tr> - <td class='c015'> </td> - <td class='c016'><span class='sc'>Appendix</span></td> - <td class='c017'><a href='#apndx'>239</a></td> - </tr> - <tr><td> </td></tr> - <tr> - <td class='c015'> </td> - <td class='c016'><span class='sc'>Index</span></td> - <td class='c017'><a href='#idx'>243</a></td> - </tr> -</table> - -</div> -<div class='pbb'> - <hr class='pb c005' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_xi'>xi</span> - <h2 class='c010'>LIST OF ILLUSTRATIONS</h2> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c005'> - <div><span class='large'>FULL-PAGE ILLUSTRATIONS</span></div> - <div class='c000'>Copernicus and the Carpathian Mountains <a href='#frontis'><i>Frontispiece</i></a></div> - <div class='c005'>PHOTOGRAPHS OF THE MOON SHOWING PHASES OF CHANGE</div> - </div> -</div> - -<table class='table1' summary=''> -<colgroup> -<col width='12%' /> -<col width='35%' /> -<col width='40%' /> -<col width='11%' /> -</colgroup> - <tr> - <td class='c016'> </td> - <td class='c016'> </td> - <td class='c016'> </td> - <td class='c017'><span class='xsmall'>PAGE</span></td> - </tr> - <tr> - <td class='c016'>No. 1,</td> - <td class='c016'>February 19, 1904;</td> - <td class='c016'>Moon’s Age 3.85 Days</td> - <td class='c017'><a href='#i050'>50</a></td> - </tr> - <tr> - <td class='c016'>No. 2,</td> - <td class='c016'>September 24, 1903;</td> - <td class='c016'>Moon’s Age 3.87 Days</td> - <td class='c017'><a href='#i056'>56</a></td> - </tr> - <tr> - <td class='c016'>No. 3,</td> - <td class='c016'>July 29, 1903;</td> - <td class='c016'>Moon’s Age 5.54 Days</td> - <td class='c017'><a href='#i066'>66</a></td> - </tr> - <tr> - <td class='c016'>No. 4,</td> - <td class='c016'>November 24, 1903;</td> - <td class='c016'>Moon’s Age 5.74 Days</td> - <td class='c017'><a href='#i072'>72</a></td> - </tr> - <tr> - <td class='c016'>No. 5,</td> - <td class='c016'>July 1, 1903;</td> - <td class='c016'>Moon’s Age 6.24 Days</td> - <td class='c017'><a href='#i074'>74</a></td> - </tr> - <tr> - <td class='c016'>No. 6,</td> - <td class='c016'>November 26, 1903;</td> - <td class='c016'>Moon’s Age 7.75 Days</td> - <td class='c017'><a href='#i078'>78</a></td> - </tr> - <tr> - <td class='c016'>No. 7,</td> - <td class='c016'>July 2, 1903;</td> - <td class='c016'>Moon’s Age 7.24 Days</td> - <td class='c017'><a href='#i090'>90</a></td> - </tr> - <tr> - <td class='c016'>No. 8,</td> - <td class='c016'>August 31, 1903;</td> - <td class='c016'>Moon’s Age 9.22 Days</td> - <td class='c017'><a href='#i094'>94</a></td> - </tr> - <tr> - <td class='c016'>No. 9,</td> - <td class='c016'>August 2, 1903;</td> - <td class='c016'>Moon’s Age 8.97 Days</td> - <td class='c017'><a href='#i102'>102</a></td> - </tr> - <tr> - <td class='c016'>No. 10,</td> - <td class='c016'>November 30, 1903;</td> - <td class='c016'>Moon’s Age 11.78 Days</td> - <td class='c017'><a href='#i106'>106</a></td> - </tr> - <tr> - <td class='c016'>No. 11,</td> - <td class='c016'>December 1, 1903;</td> - <td class='c016'>Moon’s Age 12.98 Days</td> - <td class='c017'><a href='#i112'>112</a></td> - </tr> - <tr> - <td class='c016'>No. 12,</td> - <td class='c016'>September 4, 1903;</td> - <td class='c016'>Moon’s Age 13.27 Days</td> - <td class='c017'><a href='#i118'>118</a></td> - </tr> - <tr> - <td class='c016'>No. 13,</td> - <td class='c016'>September 5, 1903;</td> - <td class='c016'>Moon’s Age 14.40 Days</td> - <td class='c017'><a href='#i122'>122</a></td> - </tr> - <tr> - <td class='c016'>No. 14,</td> - <td class='c016'>August 26, 1904;</td> - <td class='c016'>Moon’s Age 15.65 Days</td> - <td class='c017'><a href='#i132'>132</a></td> - </tr> - <tr> - <td class='c016'>No. 15,</td> - <td class='c016'>August 28, 1904;</td> - <td class='c016'>Moon’s Age 17.41 Days</td> - <td class='c017'><a href='#i134'>134</a></td> - </tr> - <tr> - <td class='c016'>No. 16,</td> - <td class='c016'>August 29, 1904;</td> - <td class='c016'>Moon’s Age 18.62 Days</td> - <td class='c017'><a href='#i138'>138</a></td> - </tr> - <tr> - <td class='c016'>No. 17,</td> - <td class='c016'>October 10, 1903;</td> - <td class='c016'>Moon’s Age 20.06 Days</td> - <td class='c017'><a href='#i142'>142</a></td> - </tr> - <tr> - <td class='c016'>No. 18,</td> - <td class='c016'>September 29, 1904;</td> - <td class='c016'>Moon’s Age 20.50 Days</td> - <td class='c017'><a href='#i144'>144</a></td> - </tr> - <tr> - <td class='c016'>No. 19,</td> - <td class='c016'>August 16, 1903;</td> - <td class='c016'>Moon’s Age 23.81 Days</td> - <td class='c017'><a href='#i150'>150</a></td> - </tr> - <tr> - <td class='c016'>No. 20,</td> - <td class='c016'>August 17, 1903;</td> - <td class='c016'>Moon’s Age 24.84 Days</td> - <td class='c017'><a href='#i158'>158</a></td> - </tr> - <tr> - <td class='c016'>No. 21,</td> - <td class='c016'>August 19, 1903;</td> - <td class='c016'>Moon’s Age 26.89 Days</td> - <td class='c017'><a href='#i168'>168</a></td> - </tr> -</table> - -<div class='nf-center-c0'> -<div class='nf-center c005'> - <div><span class='large'>PHOTOGRAPHS OF THE MOON SHOWING SIGNIFICANT FEATURES</span></div> - </div> -</div> - -<table class='table2' summary=''> -<colgroup> -<col width='89%' /> -<col width='10%' /> -</colgroup> - <tr> - <td class='c018'> </td> - <td class='c017'><span class='xsmall'>PAGE</span></td> - </tr> - <tr> - <td class='c018'>Bullialdus and the <i>Mare Nubium</i></td> - <td class='c017'><a href='#i182'>182</a></td> - </tr> - <tr> - <td class='c018'>Tycho, Clavius, and their Surroundings</td> - <td class='c017'><a href='#i192'>192</a></td> - </tr> - <tr> - <td class='c018'><span class='pageno' id='Page_xii'>xii</span>The Great Southwest on the Moon</td> - <td class='c017'><a href='#i198'>198</a></td> - </tr> - <tr> - <td class='c018'>The Giant Ring Mountain Theophilus and its Neighbors.</td> - <td class='c017'><a href='#i206'>206</a></td> - </tr> - <tr> - <td class='c018'>Two Great Lunar “Seas”—the <i>Mare Serenitatis</i> and a Part of the <i>Mare Imbrium</i></td> - <td class='c017'><a href='#i218'>218</a></td> - </tr> -</table> - -<div class='nf-center-c0'> -<div class='nf-center c005'> - <div><span class='large'>DIAGRAMS IN TEXT</span></div> - </div> -</div> - -<table class='table2' summary=''> -<colgroup> -<col width='89%' /> -<col width='10%' /> -</colgroup> - <tr> - <td class='c018'> </td> - <td class='c017'><span class='xsmall'>PAGE</span></td> - </tr> - <tr> - <td class='c018'>Phases and Rotation of the Moon</td> - <td class='c017'><a href='#i014'>14</a></td> - </tr> - <tr> - <td class='c018'>The Moon’s Path with Respect to the Sun and the Earth</td> - <td class='c017'><a href='#i017'>17</a></td> - </tr> - <tr> - <td class='c018'>The Moon and the Tides</td> - <td class='c017'><a href='#i023'>23</a></td> - </tr> - <tr> - <td class='c018'>Effect of Moon, Varying Velocity in Orbit Producing Libration in Longitude</td> - <td class='c017'><a href='#i058'>58</a></td> - </tr> - <tr> - <td class='c018'>Lunar Volcano, in Section</td> - <td class='c017'><a href='#i085a'>85</a></td> - </tr> - <tr> - <td class='c018'>Terrestrial Volcano, in Section</td> - <td class='c017'><a href='#i085b'>85</a></td> - </tr> - <tr> - <td class='c018'>Diagram Showing Why the Winter Moon Runs High</td> - <td class='c017'><a href='#i170'>170</a></td> - </tr> - <tr> - <td class='c018'>Diagram Showing Why Moon Rises Later Every Night</td> - <td class='c017'><a href='#i173'>173</a></td> - </tr> - <tr> - <td class='c018'>Diagram Illustrating the Harvest Moon</td> - <td class='c017'><a href='#i174'>174</a></td> - </tr> -</table> -<div class='pbb'> - <hr class='pb c005' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c002'> - <div><span class='c019'>INTRODUCTION</span></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_3'>3</span> - <h2 id='intro' class='c010'>INTRODUCTION</h2> -</div> -<p class='drop-capa0_25_0_7 c020'>ONE serene evening, when the full moon, -rising slowly above the tree tops, began -to spread over the landscape that peculiar -radiance which, by half revealing and half -concealing, by softening all outlines, and by imparting -a certain mystery to the most familiar -objects, fascinates at once the eye and the imagination, -I was walking with a friend, a lady of -charming intelligence, in a private park adjoining -an old mansion in one of the most beautiful districts -of central New York. For a long time we -both remained silent, admiring the scene before -us, so different in every aspect from its appearance -in the glare of daylight—each occupied with -the thoughts that such a spectacle suggests. -Suddenly my friend turned to me and said:</p> - -<p class='c009'>“Tell me—for, like so many thousand others, -I am virtually ignorant of these mysteries of the -sky—tell me, what is that moon? What do astronomers -really know about it?”</p> - -<p class='c009'>“But,” I replied, “you certainly exaggerate -your ignorance. You must have read what so -many books have told about the moon.”</p> - -<p class='c009'><span class='pageno' id='Page_4'>4</span>“Not a word,” was the reply, “or at least, -what I have read has made little impression upon -my mind. I read few books of science; generally -they repel me. But face to face with that marvelous -moon, I find it irresistible, and my desire for -knowledge concerning it becomes intense. I remember -something about eclipses, and something -about tides, with which, I believe, the moon is concerned. -I recall the statement that the moon has -no atmosphere, but does possess great mountains -and volcanoes. Yet these things are so jumbled in -my memory with technical statements which failed -to interest me, that really my ignorance remains -profound. But I have heard that many surprising -discoveries have been made lately concerning the -moon, and that astronomers have succeeded in -taking wonderful photographs of scenes in the -lunar world. I have, indeed, seen copies of some -of these photographs, but beyond awaking curiosity -by their <i>bizarre</i> effects of light and shadow, -they impressed me little, for lack, I suppose, of -information as to their meaning. I beg you, then, -to tell me what is really known about the world of -the moon. There it is; I see it; I experience the -delightful impressions which its light produces—but, -after all, what is it, and what should we behold -if we could go there? I once read Jules -Verne’s romance of a trip to the moon, but unfortunately -his adventurers never really got there, -<span class='pageno' id='Page_5'>5</span>and I finished the story with a keen sense of disappointment -because, in the end, he told so very -little about the moon itself. As for the professional -books of the astronomers they are useless -to me. Then, please tell me that which, at this moment, -with that wonderful orb actually in sight, -I so much desire to know.”</p> - -<p class='c009'>It was not possible to resist an appeal so earnestly -urged, but I felt compelled to say: “Since -you remember so little about the fundamental -facts which generations of astronomers have accumulated -concerning our nearest neighbor in the -sky, I must, for the sake of completeness, and in -order to put you <i>au courant</i> with the more captivating -things that will come later, begin at the -beginning, and the true beginning is not among -the mountains of the moon, but here on the earth. -We must start from our own globe—as the moon -herself did.”</p> - -<p class='c009'>“What do you mean by that?” my friend -asked with a tone of surprise.</p> - -<p class='c009'>“Have you not read, somewhere, in the last -ten years, that the moon was actually born from -the earth?”</p> - -<p class='c009'>“Yes, now that you mention it, I dimly recall -something of the kind, but I took it for an extravagant -speculation of some <i>savant</i> who possessed -more imagination than solid knowledge.”</p> - -<p class='c009'>“The <i>savant</i> who originally demonstrated the -<span class='pageno' id='Page_6'>6</span>earthly origin of the moon,” I replied, “is not -one to be easily led into extravagance by his imagination. -It is Prof. George Darwin, the son -of the famous author of the ‘Origin of Species.’ -I shall not mention his mathematics, which are -troublesome, but allow me to tell you, in a word, -that his investigations have satisfied astronomers -that the earth and the moon once composed a -single body. How many million years ago that -was we can only guess. The causes of the separation -which eventually occurred were the plastic -condition of the original body while it was yet hot -and molten, its swift axial rotation producing an -immense centrifugal force at its equator, and the -attraction of the sun raising huge tides which -affected its entire mass instead of affecting only -the waters of the ocean as the tides do at present. -At last there came a time when an enormous portion -of the swiftly rotating globe was torn loose. -That portion included about one-eightieth of the -entire mass of the earth. Some astronomers -and geologists think that the ‘wound’ left in the -side of the earth by this stupendous excision is -yet traceable in the basin of the Pacific Ocean.</p> - -<p class='c009'>“The separation being once effected, the material -that had escaped gradually assumed a globular -form under the influence of the gravitation -of its own particles; and, at the same time, by -virtue of a curious reaction of the tidal attractions -<span class='pageno' id='Page_7'>7</span>of the two bodies upon each other, the new-born -globe was slowly forced away from its -mother earth, becoming, in fact, its satellite. -Thus, by a process which certainly does seem extravagantly -imaginative, but which, nevertheless, -is approved by strict mathematical deductions -from known physical facts, the moon is believed -to have had her birth.”</p> - -<p class='c009'>“Surely,” said my companion, “my imagination -would never have dared to form such a picture, -even if it had been capable of so extraordinary -a flight.”</p> - -<p class='c009'>“No,” I replied, “nor the imagination of the -most learned astronomer. You perceive that in -things celestial as in things terrestrial fact is far -more strange than fiction. We shall have occasion -to refer to some of the consequences of the -earthly origin of the moon later on, but just now -in order that the knowledge you seek may not -be too fragmentary, I must tell you some other, -more commonly known, facts about our satellite.”</p> - -<p class='c009'>“Judging by myself I doubt if there are many -such facts <i>commonly</i> known.”</p> - -<p class='c009'>“Perhaps you are right, but do not judge too -severely the authors of astronomical books. Such -books are written primarily for those who wish -to study, not for those who desire to be intellectually -entertained. But let me get through with -my preliminaries, and then, under the guidance -<span class='pageno' id='Page_8'>8</span>of science and photography, we shall try to visit -the moon. One of the first questions that naturally -arise concerning the objects that we see -in the heavens relates to their distance from us. -The average, or mean, distance of the moon from -the earth is 238,840 miles. For the sake of a -round number we usually call it 240,000 miles. -But the orbit, or path, of the moon in her monthly -journey around the earth, is so far from being -a true circle that the distance is variable to the -extent of 31,000 miles. Even the form of the -moon’s path in space is not constant. Owing -to the varying effects of the attraction of the -earth and the sun, her elliptical orbit becomes -now a little more and now a little less eccentric, -the consequence being that the moon’s distance -from the earth is continually changing. When -she is at her greatest possible distance she is -253,000 miles away, but this distance at certain -times, may be reduced to only 221,600 miles. As -a result of these changes of distance the moon -sometimes appears noticeably larger to our eyes -than at other times.</p> - -<p class='c009'>“This leads us next to inquire, ‘What is the -actual size of the moon?’ When we know the distance -of any body from the eye it is not difficult -to determine its size. The diameter of the moon -is 2,163 miles. The face of the full moon contains -7,300,000 square miles. It is a little larger -<span class='pageno' id='Page_9'>9</span>than the continent of South America. For a reason -that we will speak of presently, the moon always -keeps the same side toward us no matter -in what part of its orbit it may be. Consequently -we always see the same features of her surface -and, except through inference, we do not know -what exists on the other side of the lunar globe. -Of the 7,300,000 square miles of surface which -the moon presents to us, about 2,900,000 are occupied -by those dark gray patches which you see -so plainly spotting her face, and which were once -supposed to be seas. The remaining 4,400,000 -square miles consist of a very rough, broken -country, ridged with gigantic mountains and containing -hundreds of enormous craters, and mountain-ringed -valleys, which are so vast that one -hesitates to call them, what many of them seem -evidently to be, extinct volcanoes. A single explosion -of a volcano of the dimensions of some -of these lunar monsters would shake the whole -earth to its center!”</p> - -<p class='c009'>“Please stop a moment,” my friend laughingly -interrupted. “So many merciless facts, chasing -one at the heels of another, are as bad as -the books on your science that I have tried to -read. Give my imagination time to overtake -you.”</p> - -<p class='c009'>“Very well,” I said, “then relieve your attention -a little while by regarding the face of the -<span class='pageno' id='Page_10'>10</span>moon. Do you perceive the portrait of the Moon -Maiden there?”</p> - -<p class='c009'>“I believe I do, although I never noticed it -before. It is in profile, is it not?”</p> - -<p class='c009'>“Yes, and it occupies all the central portion -of the western half of the disk. Take the opera -glass and you will see it more clearly.”</p> - -<p class='c009'>“Really, I find her quite charming,” said my -companion, after gazing for a minute through the -glass. “But what a coquette! Look at the magnificent -jewel she wears at her throat, and the -<i>parure</i> of pearls that binds her hair!”</p> - -<p class='c009'>“Yes,” I replied, “and no terrestrial coquette -ever wore gems so unpurchasable as those with -which the Moon Maiden has decked herself. That -flaming jewel on her breast is a <i>volcano</i>, with a crater -more than fifty miles across! Tycho, astronomers -call it. Observe with the glass how broad -rays shoot out from it in all directions. They -are among the greatest mysteries of lunar -scenery. And the string of brilliants in her hair -consists of a <i>chain of mountains</i> greater than the -Alps—the lunar Apennines. They extend more -than 450 miles, and have peaks 20,000 feet high, -which gleam like polished facets.”</p> - -<p class='c009'>“Truly,” said my companion, smiling, “these -gigantesque facts of yours rather tend to dissipate -the romantic impression that I had conceived -of the Moon Maiden.”</p> - -<p class='c009'><span class='pageno' id='Page_11'>11</span>“No doubt,” I replied. “It is only distance -that lends her enchantment. But we must not -disregard the facts. Her hair, you perceive, is -formed by some of the vast gray plains of which -I spoke a few minutes ago. She is like a face -in the clouds—approach her, or change the point -of view and she disappears or dissolves into something -else.</p> - -<p class='c009'>“Now, to return to my preliminaries, upon -which I must insist. Knowing the distance and -the size of the moon, the next question relates -to her motions. You are aware that she travels -around the earth about once every month. There -are two ways in which we measure the length -of time that the moon takes for each revolution. -First, regarding the face of the sky as a great -dial, with the stars for marks upon it, we notice -the time that elapses between two successive conjunctions -of the moon with the same star. In the -interval she has gone completely around the earth -and come back to the starting point. This is -called the moon’s sidereal revolution, and it occupies, -on the average, twenty-seven days, seven -hours, forty-three minutes, twelve seconds. -Every twenty-four hours the moon advances -among the stars, from west to east, about 13° 11´.</p> - -<p class='c009'>“But there is another, more usual way of -measuring the orbital period of the moon. This -way is connected with her phases, or changes -<span class='pageno' id='Page_12'>12</span>of shape, from the sickle of the New Moon to the -round disk of the Full Moon, and back again to -the reversed sickle of the waning moon. It is -the time that elapses from one New Moon to the -next, or from one Full Moon to the next which -now concerns us, and it amounts, on the average, -to twenty-nine days, twelve hours, forty-four -minutes. This is called the moon’s synodic revolution, -and it is equivalent to the ordinary lunar -month. It is variable to the amount of about -thirteen hours. The reason why the synodic revolution -is more than two days longer than the -sidereal revolution is because the continual advance -of the earth in its orbit around the sun -causes the latter to move eastward among the -stars, and before the moon’s monthly phases, -which depend upon her position with regard to -the sun, can recommence, she must overtake the -sun.”</p> - -<p class='c009'>“What a hopeless task to try to remember -all that!”</p> - -<p class='c009'>“At any rate, if you cannot remember these -things my conscience will be clear, for I am -simply doing my duty in telling you of them. -If you forget, go to the books on astronomy and -refresh your memory. But do not persuade -yourself that the preliminaries are now finished. -You are going to think that my story of the moon -resembles Walter Scott’s novels in the length of -<span class='pageno' id='Page_13'>13</span>its introduction; but if, in the end, I can interest -you half as much as he finally interests his readers -I shall thank the stars for my good fortune.</p> - -<p class='c009'>“The next thing that I must try to explain,” -I continued, “is the cause of the moon’s phases, -or her continual changes of form. You know -that the New Moon is shaped like a thin crescent, -and always appears in the west immediately after -sundown, with the convex side facing the setting -sun. The moon at First Quarter is a half -circle and is visible in the southern part of the -sky just after sunset. The Full Moon, which we -have at present, is a complete round disk, and -is always seen directly opposite to the place of -the sun, so that she rises when the sun sets. The -moon at last quarter is again a half circle, and -appears on the meridian in the south at sunrise. -The waning moon is like the new moon, crescent-shaped, -but the convexity of the bow faces the -rising sun, and she is visible only in the morning -sky just as dawn begins. To explain the reasons -for these changes of shape, which the moon regularly -undergoes every month, I must ask you to -go indoors and examine a little diagram which -I have made.”</p> - -<p class='c009'>“Oh!” said my companion, “it is too bad to -abandon this charming spectacle, illuminated by -rays so fascinating, for the sake of looking at -mathematical lines drawn on paper! But I suppose -<span class='pageno' id='Page_14'>14</span>that this is one of the sacrifices demanded -by your inexorable science, and must be made.”</p> - -<p class='c009'>“Yes,” I said, “but if science sometimes demands -sacrifices, at least she always rewards -them most generously.”</p> - -<p class='c009'>When we had returned to the house I placed -upon the drawing-room table this diagram.</p> - -<div id='i014' class='figcenter id002'> -<img src='images/i014.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>Phases and Rotation of the Moon.</p> -</div> -</div> - -<p class='c009'>As I spread it out, my companion, after a regretful -glance through the open door at the silvery -lawn, on which the moon, having cleared the -obstructing branches of the bordering trees, was -now pouring down the full splendor of her rays, -<span class='pageno' id='Page_15'>15</span>put her elbows on the table to follow my -explanation.</p> - -<p class='c009'>“The globe, half bright and half black, in the -center,” I said, “represents the earth. The large -circle surrounding the earth we will call the -moon’s orbit, which she traverses once every -month. The smaller globe, also half white and -half black, shown in four successive positions in -the orbit, is the moon. Suppose the sun to be -away off here on the left. It illuminates the -earth and the moon only on the side turned -toward it. The opposite side of both is buried -in night. Now, let us begin with the moon at the -point A. She is then between the earth and the -sun, the bright side being necessarily toward the -sun and the dark side toward the earth. In that -position we do not see the moon at all from the -earth, unless she happens to come so exactly in -a line with the sun as to cover the latter, in which -event we have an eclipse of the sun. Now, suppose -the moon to move in her orbit toward B. -In a little more than seven days she will arrive -at B. In the meantime, while moving away from -the position of the sun, she begins to present a -part of her illuminated hemisphere toward the -earth. This part appears in the form of a sickle, -or crescent, which grows gradually broader, until, -at B, it has grown to a half circle. In other -words, when the moon is in the position B we on -<span class='pageno' id='Page_16'>16</span>the earth see one half of her illuminated surface. -This phase is called First Quarter. The -narrow crescent, which appears as soon as the -moon begins to move from A toward B, is the -New Moon. As the moon continues on from B -toward C, more and more of her illuminated -half is visible from the earth, and when she arrives -at C, just opposite to the position of the sun, -she becomes a Full Moon. We then see, as occurs -to-night, the whole of that face of the moon -which is presented sunward. The upper half -of the diagram shows how the moon moves from -the position of Full Moon back again to New -Moon, or conjunction with the sun. During this -latter part of her course the moon rises later and -later every night, until, when she assumes the -form of a waning crescent, she is visible only in -the morning sky just before sunrise.<a id='r1' /><a href='#f1' class='c021'><sup>[1]</sup></a></p> - -<p class='c009'>“Now, there is another interesting thing -shown by this diagram,” I continued—but my -companion, who had followed my explanations -thus far with flattering attention, here suddenly -ran to the door exclaiming:</p> - -<p class='c009'>“For mercy’s sake, what is happening to the -moon?”</p> - -<div class='fn'> - -<div class='footnote' id='f1'> -<p class='c022'><span class='label'><a href='#r1'>1</a>. </span></p> -<div id='i017' class='figcenter id002'> -<img src='images/i017.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>The Moon’s Path with Respect to the Sun and the Earth.</p> -</div> -</div> -<p class='c009'>It may be well to add to what is said in the text about the orbit -of the moon, that, while the moon does perform a revolution around -the earth once a month, yet her orbit is drawn out, by the common -motion of both earth and moon around the sun, into a long curve, -whose radius is continually changing, but which is always concave -toward the sun. This is illustrated in the accompanying diagram. -Suppose we start with the earth at A. The moon is then between -the sun and the earth, or in the phase of New Moon. The -earth’s orbit at this point is more curved than the moon’s, and the -earth is moving relatively faster than the moon. At B (First Quarter) -the earth is directly ahead of the moon. But now the moon’s -orbit becomes more curved than the earth’s and it begins to overtake -the earth. At C (Full Moon) the moon has come up even with -the earth, but on the opposite side from the sun. From that point -to D (Last Quarter) the moon gains upon the earth until she is -directly ahead of it. Then, from D to E (New Moon, once more) -the earth gains until the two bodies are in the same relative positions -which they occupied at A. Throughout the entire lunation, however, -notwithstanding the changes which the shape of the moon’s -orbit undergoes, the latter is constantly concave toward the sun. -This shows that the sun’s attraction is really the governing force, -and that the attraction of the earth simply serves to vary the form -of the moon’s path, and cause it to move in a virtual ellipse with the -earth for its focus.</p> -</div> - -</div> - -<p class='c009'><span class='pageno' id='Page_17'>17</span>I glanced over her shoulder, and saw a smudgy -scallop in the moon’s edge.</p> - -<p class='c009'>“Really,” I said, “I am ashamed of myself. -There is an eclipse of the moon to-night, and I -had positively forgotten it! What you see is the -shadow of the earth, which has the form of a long -<span class='pageno' id='Page_18'>18</span>cone stretching away more than eight hundred -thousand miles into space, and whenever our -satellite at the time of Full Moon gets nearly -in a direct line with the earth and the sun, it -passes through that shadow and undergoes an -eclipse. That is what is happening at the present -moment.”</p> - -<p class='c009'>“And the shadow has a round form because -the earth is round, I suppose.”</p> - -<p class='c009'>“Certainly; the shadow of a globe must have -a circular outline. But the shadow of the earth, -although it finally diminishes to a point, is, at the -moon’s distance, still about 5,700 miles in diameter, -or more than two and a half times the -diameter of the moon. In consequence of the motion -of the earth in its orbit around the sun, its -shadow constantly moves eastward, like a great -pencil of darkness sweeping straight across the -heavens, but invisible to us except when the moon, -traveling eastward faster than the shadow, overtakes -and passes through it. This does not by -any means happen at every full moon, because, -for a reason which I shall explain presently, the -moon usually passes either above or below the -shadow of the earth, and thus escapes an eclipse. -When an eclipse does occur it lasts a long time -because the shadow is moving in the same direction -as the moon. The moon must pass entirely -through it before the eclipse ends. On this occasion -<span class='pageno' id='Page_19'>19</span>the moon will be in the shadow more than -three hours, and during an hour and a half she -will be totally immersed. We shall have plenty -of time, then, to observe the phenomenon, and after -you have satisfied your curiosity a little by -watching the slow advance of the shadow movement -across the moon, we can return to our diagram -and finish its explanation before the eclipse -becomes total.”</p> - -<p class='c009'>Accordingly, after having watched the progress -of the eclipse for half an hour, during which -time the shadow began perceptibly to diminish -the moonlight in the park, we returned to the -lamplight and the diagram on the table.</p> - -<p class='c009'>“I was saying,” I resumed, “that another -interesting thing in addition to the cause of the -moon’s changing phases is represented here. -You observe that a little cross stands on each of -the four circles representing the moon, and that, -in every case, the cross is in the center of that -side of the moon which faces the earth. In fact -the position of the cross upon the moon is fixed -and invariable, and it always points toward the -earth because the moon makes exactly one rotation -on her axis in the course of one revolution -around her orbit, or, as it is often called, one -lunation. We know that this is so because we -always see the same features of the lunar surface, -no matter where the moon may be situated. This -<span class='pageno' id='Page_20'>20</span>is true although, in consequence of the phases, we -cannot see the whole face of the moon except -when she is full. But whether it is the New -Moon, or First Quarter, or Full Moon, or Last -Quarter, or Old Moon, that we look at, the mountains -and plains visible are identically the same. -If the moon did not turn once on her axis in going -once around the earth we would see all of her -sides in succession, although only at Full Moon -could we see an entire hemisphere illuminated -by the sun. At Old and New Moon the side -presented to the earth would be just the opposite -to that presented at Full Moon. At Last -Quarter the side facing the earth would be -the opposite to that facing the earth at First -Quarter.”</p> - -<p class='c009'>“But, tell me,” said my friend, “how did the -moon ever come to so humiliating a pass that she -must be forever turning on her heel to face the -earth?”</p> - -<p class='c009'>“That,” I replied, “is a result of the same -forces which originally separated her from the -earth and gradually pushed her off to her present -distance. In a word it is due to ‘tidal friction.’ -Before the moon had solidified, the attraction of -the earth raised huge tides in her molten mass. -These tides acted on the rotating moon like brakes -on a wheel, and at length they slowed down her -rotation until its period became identical with -<span class='pageno' id='Page_21'>21</span>that of her revolution around the earth. For the -mathematical calculations on which all this is -based you must go to Professor Darwin’s book -on ‘The Tides,’ or some similar technical treatise; -but I imagine you will never do that.”</p> - -<p class='c009'>“Not just at present, I assure you. I do not -know what unexpected ambition for the acquirement -of scientific knowledge may arise after I -have seen those wonders that you have promised -to show me in the moon, but, for the moment, I -am content to accept your statement of the simple -fact.”</p> - -<p class='c009'>“Good!” I replied. “And now, perhaps, you -will have the patience to listen to an explanation -of a very important relation which exists between -the moon and the earth. We are led to it by what -I have just said concerning tides. You know, of -course that the tides in the oceans are due principally -to the attraction of the moon. The sun -also raises tides in the seas, but the moon, being -so much nearer than the sun, is the chief agent -in producing them. Sometimes the moon and the -sun act together; at other times they pull in different -directions. At Full Moon and at New -Moon they pull together, because then they are -either on opposite sides of the earth, or both on -the same side. At such times we have the highest -tides in all our seaports. That occurs about -once every fortnight. But when the moon is at -<span class='pageno' id='Page_22'>22</span>either First or Last Quarter, as you will perceive -by looking at the diagram, her position, as seen -from the earth, is at a right angle with a line -drawn to the sun. Then the sun raises tides in -one direction and the moon in another direction. -The result is that at such periods the tides are -lowest. An exact knowledge of these things is -very important for mariners because there are -harbors whose channels can be navigated by large -ships only when the tides are high. Tables predicting -the times and heights of the tides have -been prepared for all the principal seaports of -the world. In truth, the moon renders important -services to the inhabitants of the earth, -not merely in supplying them with a certain -amount of light in the absence of the sun, -but also in enabling them to navigate waters -which are too shallow for ships except when -deepened by the tide. The tides also, in many -cases, serve to scour out channels and keep them -open.”</p> - -<p class='c009'>“Really, I am quite interested, and the more -so because I find the moon, like a dutiful daughter, -trying to be of some use to her mother. But -have I not heard that the tides occur on both sides -of the earth at once, and not simply on the side -where the moon happens to be at the time? -Please tell me how that can be so?”</p> - -<p class='c009'>“A complete reply to your question would -<span class='pageno' id='Page_23'>23</span>carry us into the realm of mathematical physics, -but perhaps I can throw a little light upon the -matter with the aid of this second diagram.</p> - -<div id='i023' class='figright id004'> -<img src='images/i023.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>The Moon and the Tides.</p> -</div> -</div> - -<p class='c009'>“The eclipse is not yet -total,” I continued, glancing -out of the door, “and we can -finish our explanation before -it becomes so. Have the -kindness, then, to look at -the diagram. Suppose E to -be the center of the earth, -and M the center of the -moon. The protuberant portions -of the earth C A D and -D B C represent the waters -of the ocean pulled away -from the surface of the -earth, if I may so describe -it, by the moon’s attraction. -You are probably aware that the attraction -of gravitation varies with the distance of the -attracting body. The distance from the center -of the earth to the center of the moon is about -239,000 miles. But the earth being nearly 8,000 -miles in diameter, the surface of the ocean at A is -about 4,000 miles nearer to the moon than is the -center of the earth E. It follows that the force -of the moon’s attraction is greater at A than at E. -If the water of the ocean were a fixed, solid part -<span class='pageno' id='Page_24'>24</span>of the earth there would be no perceptible effect -resulting from this difference in the amount of -the moon’s attraction. But since the water is free -to move, to a certain extent, it yields to the attraction, -and is drawn up a little toward the moon. -At the same time it is, in effect, drawn away from -C and D. The consequence is the production of a -tide on the side facing the moon.</p> - -<p class='c009'>“Now, for the other tide, produced at the -same time on that side of the earth which is -turned away from the moon. The point B is -about 4,000 miles farther from the moon than E; -consequently the moon’s attractive force is less at -B than at E. From this it results that the body -of the earth is more forcibly attracted by the -moon than is the water at B. The earth therefore -tends to move away from the water at that -point, and another tidal protuberance is produced, -with its highest part at B. I should add that -while the water of the ocean is, to a certain degree, -free to respond to these differences of attraction, -the earth itself, being solid, can only -move as a single body, and, mathematically, we -may regard it as if its entire mass were concentrated -at the center E. Please remember, however, -that this explanation is only elementary, -only intended as a graphic representation of the -tides, and not as a mathematical demonstration -of the way they are produced. Such a demonstration -<span class='pageno' id='Page_25'>25</span>would only be suited to one of the technical -books that you have not found as interesting -as—some other branches of literature.</p> - -<p class='c009'>“There is just one other thing to which I -must ask your attention, and then we shall return -to the moon herself and the phenomena of the -eclipse now in progress. You will notice in the -diagram, that two arrows show the direction in -which the earth is continually rotating on its axis, -and that a dotted curve, terminating with an arrow -point, indicates the course of the moon in her -orbit surrounding the earth. The rotation of the -earth is so much more rapid than the motion of -the moon that the points A and B are carried out -of the line drawn from the center of the moon to -the center of the earth, in the direction of the arrows. -From this it follows that the tides are -never directly under the moon, or exactly opposite -to her, but sweep in great waves round the -globe. The tides produced by the attraction of -the sun are only about two fifths as high as those -caused by the moon. As I have already explained -they are sometimes superposed upon the -lunar tides—at New and at Full Moon—and sometimes -they are situated at right angles to the -lunar tides—at First and Last Quarters.”</p> - -<p class='c009'>“But the eclipse!” interrupted my friend, -whose attention had evidently begun to wander. -“I think the totality of which you spoke must be -<span class='pageno' id='Page_26'>26</span>at hand, for notice how dark the park has become, -and the fireflies are so brilliant under the -trees.”</p> - -<p class='c009'>The total phase of the eclipse was, indeed, beginning, -and we stepped out on the lawn before -the door to watch it. The moon had now passed -entirely within the earth’s shadow, but although -her light was almost completely obscured as far -as its power to illuminate the landscape was concerned, -still the face of the moon was dimly visible, -as if concealed behind a thick veil. Certain -parts of it had a coppery color, producing a very -weird effect.</p> - -<p class='c009'>“Dear me!” exclaimed my companion, “I did -not think it would look like that! I naïvely supposed -that one could not see the eclipsed moon -at all, but that she either disappeared or was -turned into a kind of black circle in the heavens. -And what a strange color she has! Positively it -fills me with awe.”</p> - -<p class='c009'>“It is very rare,” I said, “for the moon to become -invisible during an eclipse. That can only -occur when the earth is enveloped in clouds.”</p> - -<p class='c009'>“Indeed, and what have the clouds to do with -it? If the solid body of the earth cannot cast a -shadow dense enough to hide the moon, I should -not expect things so evanescent as clouds to be -more effective.”</p> - -<p class='c009'>“It is all owing to the earth’s atmosphere,” I -<span class='pageno' id='Page_27'>27</span>replied. “If our globe were not surrounded with -a shell of air the moon would always be totally -invisible when eclipsed. But the atmosphere -acts like a lens of glass inclosing the earth; that -is to say, it refracts, or bends the rays of sunlight -around the edge of the earth on all sides, -and throws a portion of them even into the middle -of the shadow, at the moon’s distance. It is these -refracted rays which cause the singular illumination -that you perceive on the moon. But when, -as occurs only occasionally, all that part of the -atmosphere which surrounds the earth along the -edge visible from the moon is filled with clouds, -the air can no longer transmit the refracted rays, -and then, no light being sent into the shadow, a -‘dark eclipse,’ as astronomers call it, results. An -eclipse of the sun is a very different thing. That -is caused not by a shadow but by the opaque globe -of the moon passing between the earth and the -solar orb. When this occurs the sun is completely -hidden behind the moon, and only its -corona, which projects beyond the moon on all -sides, is visible.”</p> - -<p class='c009'>“Indeed! I supposed that all eclipses were -very much the same thing.”</p> - -<p class='c009'>“By no means. An eclipse of the sun is an -event of extreme importance to astronomers, -while an eclipse of the moon possesses comparatively -little scientific interest.”</p> - -<p class='c009'><span class='pageno' id='Page_28'>28</span>“I do not see why that should be so.”</p> - -<p class='c009'>“It is so, for the reason that when the sun -is eclipsed, as I have just told you, the solar corona, -which cannot be seen at any other time owing -to the overpowering brilliance of the solar -orb, becomes plainly visible, and by studying the -form and other particulars of the corona astronomers -are able to draw most important conclusions -concerning the constitution of the sun, the mechanism -of its radiation, and its effects upon the -earth. During an eclipse of the moon, on the -other hand, practically nothing new is revealed, -and, accordingly, astronomers pay comparatively -little attention to such phenomena. Lunar -eclipses, however, possess a certain importance, -because by predicting the times of their occurrence -and then comparing the predictions with -the events, something is learned about the motions -of the moon. I should add that recently -eclipses of the moon have been carefully watched -by a few astronomers, notably by Prof. William -H. Pickering, because of peculiar effects which -seem to be produced at certain points on the -moon by the chill which the shadow casts upon -her surface. There are also interesting observations -to be made concerning the reflection of heat -from the moon during an eclipse. But, upon the -whole, a lunar eclipse is mainly interesting as a -curious spectacle, and as a test of the correctness -<span class='pageno' id='Page_29'>29</span>of astronomical calculations of the motions of -the heavenly bodies.</p> - -<p class='c009'>“I may add, however, that eclipses of the moon -have been of some use to historians in fixing the -dates of important occurrences thousands of -years ago. This is possible because astronomers -can by calculation ascertain the times of eclipses -in the past as well as in the future. Perhaps the -most interesting of all instances of this kind is -that which relates to the date of the beginning -of the Christian era. This has been fixed by -means of an eclipse of the moon mentioned by the -ancients as having happened the night before the -death of Herod, king of the Jews.”</p> - -<p class='c009'>“It seems to me,” said my friend, “that the -faint light on the moon’s face is continually changing. -It does not appear constantly to have the -same tint. While we have been standing here, I -have noticed that some parts have grown darker -and others lighter, and that the red color on the -right has become a little more intense.”</p> - -<p class='c009'>“Yes, and that, too, is no doubt caused by the -earth’s atmosphere. While the eclipse lasts, the -earth is rapidly rotating, and consequently new -parts of the atmosphere are continually brought -to the edge where their refractive effects come -into play. If the atmosphere at the edge of the -earth is a little more or a little less dense its refraction -varies proportionally. Then, changes -<span class='pageno' id='Page_30'>30</span>in the relative clearness or cloudiness of the air -are taking place all the time, and these are reflected -in the illumination on the moon.”</p> - -<p class='c009'>“It seems to me, then, that the earth would -present a very remarkable spectacle if we were -now on the moon looking at it.”</p> - -<p class='c009'>“Surely it would. Seen from the moon the -earth appears several times larger than the sun. -For the people of the moon, if we imagine them -to exist, an eclipse of the sun is now in progress. -For them the earth now occupies the same relative -position which the moon occupies for us just before -it appears in the west as New Moon. They -cannot see it except in silhouette as it passes over -the sun. More than an hour ago, if they were -watching (and if they exist, and are intelligent -beings we may be sure that they were on the -alert), they suddenly perceived a black round-edged -notch in the side of the sun. Instead of -being more or less cloudlike and indefinite in outline, -like the shadow of the earth on the moon, this -notch appeared to them perfectly black and -smooth. At a glance, they saw that the body -producing it was much larger than the sun. As -the sun’s disk was gradually hidden behind the -earth the shadow of the latter fell over them, until -the sun was wholly concealed. Then—and this -is true at the present moment—they perceived -that the huge disk of the earth was ringed with -<span class='pageno' id='Page_31'>31</span>light, probably of a reddish tinge. This light, -as I have already indicated, is that which the atmosphere -refracts around the edge of the earth.”</p> - -<p class='c009'>“It must be truly a magnificent sight,” said -my companion.</p> - -<p class='c009'>“Yes, and it is doubtless rendered far more -magnificent by the other phenomena which our -people at the moon have before their eyes. In -consequence of the virtual absence of air there, -an observer on the moon would see all the stars, -even in full daylight, blazing in a jet black sky. -The brilliance of the stars and of the Milky Way -would hardly be increased by the hiding of the -sun, but probably the long silvery streamers of -the solar corona would glow perceptibly brighter -when seen projecting out on each side of the enormous -disk of the earth.”</p> - -<p class='c009'>“But is it true that the moon has no air?”</p> - -<p class='c009'>“Very, very little, and what little she has is -probably different in composition from our atmosphere. -Some observations seem to indicate -that there is a very rare atmosphere on the moon, -but to us it would seem a perfect vacuum. We -could not breathe there at all.”</p> - -<p class='c009'>“How then do those intelligent inhabitants, -whom you have pictured for me watching the -earth at this moment, manage to survive?”</p> - -<p class='c009'>“Ah, I did not say that there actually are -inhabitants in the moon. I only imagined them -<span class='pageno' id='Page_32'>32</span>to exist for the sake of showing how this eclipse -would appear seen from the moon. Still, we cannot -be absolutely sure that there are no inhabitants -on the moon. Even without air like ours -it is conceivable that beings of some kind, and intelligent -beings, too, <i>might</i> exist there. However, -astronomers have never yet been able to discover -evidence of their presence. Lately, indications -have been found of the probable existence of vegetation -on the moon, but I shall speak of that later, -when with the aid of the series of lunar pictures -made at the Yerkes observatory we try to make -a ‘photographic journey’ in the moon.”</p> - -<p class='c009'>“But tell me, has the moon always been so -airless?”</p> - -<p class='c009'>“That is another unsettled question. Some -astronomers have thought that formerly, ages -ago, the moon possessed a much more dense atmosphere -than she has at present. Having separated -from the earth, in the way I have described, -it is natural to suppose that at first she may have -had an atmosphere very like ours. The explanation -of its disappearance which was once generally -accepted was that it had been absorbed into -the lunar rocks, as the globe of the moon cooled -off. But recent progress in our knowledge of the -nature of the gases composing the atmosphere -has led to a different explanation. This assumes -that nearly all of the moon’s atmosphere has -<span class='pageno' id='Page_33'>33</span><i>flown away from her</i> because the lunar globe does -not possess sufficient gravitating force or attraction -to retain it. If the mass of the earth were -no greater than that of the moon, our atmosphere -also would probably have escaped by flying off -into space.”</p> - -<p class='c009'>“But how, and why, do these gases fly away?”</p> - -<p class='c009'>“They do it by virtue of what physicists call -their molecular velocity. A gas, of whatever -kind, is a mass of molecules which are in continual -vibration, moving in all directions among -one another with very great velocities. These -velocities have been measured, and it has been -found that the molecules of nitrogen, one of the -components of the air, move at the rate of two -miles in a second. The velocity of the molecules -of oxygen is a little less; that of the molecules of -hydrogen is very great, nearly seven and a half -miles in a second! Now, it is also known that -the attraction of the earth is sufficient to retain -permanently upon its surface all moving particles -or molecules which have a velocity less than -seven miles in a second, while the attraction of the -moon only suffices to retain those whose velocities -fall under a mile and a half in a second. So you -perceive that all of the gases I have named would -soon escape from the moon, even if they were -present upon it at the beginning of its history.</p> - -<p class='c009'>“I must also remind you that there is no -<span class='pageno' id='Page_34'>34</span>water upon the moon, at least not in the form of -rivers, oceans, lakes, ponds, or even of clouds. -But Professor Pickering has recently noted certain -appearances which may be due to the formation -of a kind of hoar frost. If there were once -oceans upon the moon, as the great plains, called -<i>maria</i>, or seas, in the lunar charts, seem to indicate, -they, too, have escaped by evaporation. The -velocity of the molecules of water vapor is two -and a half miles per second, a mile greater than -the ‘critical velocity’ which the attraction of the -moon would be able to control.”</p> - -<p class='c009'>“But,” interrupted my companion, “I am -puzzled to understand how you know so much -about the power of the moon to hold things.”</p> - -<p class='c009'>“It is really quite simple,” I replied. “The -attraction of gravitation, which is a property belonging -to all known bodies, is measured by the -mass, or amount of matter, in a body. It also -varies with the distance between the attracting -and attracted bodies. We know, by means which -I shall not attempt to describe here, the mass both -of the earth and of the moon. We also know the -size of both of these bodies. They attract objects -as if their entire masses were concentrated at -their centers. A body of a certain kind and size -at the surface of the earth weighs just one pound. -If the earth were reduced to half its actual diameter, -while retaining the same mass or amount -<span class='pageno' id='Page_35'>35</span>of matter, more closely packed together, the body -which now weighs one pound would then weigh -four pounds, because it would be twice as near to -the center of the earth as before, and the attraction -of gravitation varies according to the square of -the distance from the center. As the distance -diminishes the force increases. The square of -two is four, therefore the body would be attracted -with four times the force which it experiences at -present. Now, the moon is not only much smaller -than the earth, but its average density, or the -closeness with which the molecules of its rocks -are packed together, is less. It results from -these facts that the ratio of the entire mass of the -moon is to that of the earth as one to eighty-one. -Hence the inherent power of the moon to attract -bodies is less than one-eightieth as great as the -earth’s. If the diameter of the moon were the -same as that of the earth, a body weighing one -pound on the earth would weigh only one eighty-oneth -part of a pound on the moon. But the diameter -of the moon is less than one quarter as -great as that of the earth. It follows that bodies -on the moon are almost four times (more accurately -about 3.66 times) nearer to the center of -attraction. This fact must be taken into account -in calculating the force of gravity on the moon’s -surface. As far as the mass of the moon is concerned, -bodies on her surface experience less than -<span class='pageno' id='Page_36'>36</span>one-eightieth of the attractive force which the -earth exercises upon bodies on its surface, but -this is so far counterbalanced by their greater -nearness to the center, that the actual attraction -upon them is about one sixth of that which they -would experience on the earth.”</p> - -<p class='c009'>“Thank you,” said my companion dryly, “your -explanation appears to me to be very scientific.”</p> - -<p class='c009'>“Not by any means as scientific as it might -be, or as it ought to be,” I replied, laughing. -“But, really, if you wish to understand these -things you should not be too much afraid of the -bugbear ‘science.’ Science makes the world go -nowadays, and everybody ought to know a little -about it, just as everybody with any pretensions -to education a hundred years ago had to learn -more or less Greek and Latin. But let me continue -a little farther. Since the force of attraction -on the moon is only one sixth as great as it -is on the earth, the weight of all bodies is in the -same proportion. Pardon me if I guess at your -weight; it is, perhaps, 120 pounds. Very well, -translated to the moon you would weigh only 20 -pounds.”</p> - -<p class='c009'>“Dear me, then skipping the rope may be the -favorite pastime of middle-aged ladies on the -moon.”</p> - -<p class='c009'>“And throwing somersaults that of gray-haired -<span class='pageno' id='Page_37'>37</span>lunar gentlemen. Let me tell you of one -very interesting consequence of the small force of -the moon’s gravity, which affects not merely the -weight of bodies but the flight of projectiles, and, -indeed, all motions of every kind. You will see, -when we come to the photographs, that some of -the lunar volcanoes are of a magnitude almost -incredible. This is doubtless due to the fact that -the ejections from volcanic craters there were -able, with no greater expenditure of explosive -force, to attain an elevation six times that which -they would attain if thrown from a volcano on the -earth. During the eruption of Vesuvius in April, -1906, the column of smoke, steam, and cinders -from its crater reached, according to the measures -of Professor Matteucci, a maximum height of -about eight miles. On the moon the same force -would have blown these things almost fifty miles -high! It is not difficult, in view of such facts, to -see how the giant volcanic craters and mountain -rings of the moon were formed.”</p> - -<p class='c009'>In the meantime the eclipse continued, and, -having tired of watching it, we returned to the -drawing-room.</p> - -<p class='c009'>“When shall we see these famous photographs -and begin our imaginary journey in the -moon?” my companion asked.</p> - -<p class='c009'>“To-morrow,” I replied. “But I shall have -to demand one more brief exercise of your patience -<span class='pageno' id='Page_38'>38</span>this evening, while I finish with this subject -of eclipses.”</p> - -<p class='c009'>“Then we are not through yet?”</p> - -<p class='c009'>“Not quite, for I have not yet told you why -the moon is not eclipsed every time she approaches -the earth’s shadow, and why she does -not eclipse the sun once every month at the time -of New Moon.”</p> - -<p class='c009'>“Well, tell me then, and I promise to be as interested -as possible; only please don’t talk any -more mathematics than is absolutely necessary.”</p> - -<p class='c009'>“Very well, I’ll spare your attention as much -as possible. To begin with the eclipses of the -moon: The reason why they are not of regular -monthly occurrence is simply because the orbit -of the moon is a little inclined, about 5¼°, to the -orbit of the earth. Even then there would be an -eclipse once every month if the orbit of the moon -were fixed in space, and if the point where that -orbit crosses the plane of the earth’s orbit were -always directly opposite to the sun. But instead -of being fixed in position the orbit of the moon -has a curious motion of revolution of its own. -This causes the two opposite points, where it -crosses the plane of the earth’s orbit, and which -are called the moon’s ‘nodes,’ to move continually -onward in a direction opposite to that in which -the moon revolves, but much more slowly. -A period of about nineteen years is required for -<span class='pageno' id='Page_39'>39</span>the moon’s nodes to complete a revolution. -The consequence is that the nodes are not always -in line with the earth and the sun, and except -when they <i>are</i> nearly in line no eclipse can occur. -To enter into a complete explanation of this -would require more ‘mathematics’ than you would -like, but what I have said may at least serve -to give you an idea of the reason why eclipses -are comparatively of rare occurrence.”</p> - -<p class='c009'>“I think I understand the reason sufficiently. -But what a complicated affair you astronomers -make of what, it seems to me, should really be a -very simple thing.”</p> - -<p class='c009'>“It is like a sewing machine,” I replied, -“which seems very simple when you see it running -smoothly, and do not trouble yourself about -all the various parts of its mechanism. But if -you undertake to explain to yourself, or to make -clear to another person, exactly how the machine -works, you find that your attention is rather severely -taxed, and that the apparent simplicity is -based upon no little complexity of construction -and interaction of parts. You will have understood -from what I have said, that the reason why -the moon does not eclipse the sun once every -month is based upon the same fact, namely, the -inclination of the moon’s orbit to the plane of the -orbit of the earth; and that when she does eclipse -the sun her nodes must be somewhere near a line -<span class='pageno' id='Page_40'>40</span>drawn from the earth to the sun. There is one -broad difference between an eclipse of the moon -and an eclipse of the sun which I have not yet -mentioned. This arises from the fact that the -moon being so much smaller than the earth, her -shadow, when she hides the sun, does not cover -the entire earth, as the earth’s shadow covers the -whole moon, but comes almost to a point before -reaching the earth. The average length of the -moon’s shadow is only 232,150 miles, 6,690 miles -less than the average distance between the moon -and the earth. But since, in consequence of the -eccentricity of her orbit, the moon’s distance is -continually varying, the length of her shadow -also varies to the extent of about 4,000 miles each -way. Thus it may be as short as 228,300 miles, -or as long as 236,050 miles. When the greatest -length of the moon’s shadow coincides with her -least distance from the earth (221,600 miles), her -shadow extends more than 18,000 miles beyond -the earth. Under such circumstances its diameter -at the surface of the earth is about 167 miles. -That is the greatest diameter that the shadow -of the moon can have at its intersection with the -earth. Ordinarily, when it reaches the earth at -all, its diameter is less than 100 miles, and often -very much less. If the earth and the moon were -motionless during an eclipse, her shadow would -form a round, dark spot on the earth, and all observers -<span class='pageno' id='Page_41'>41</span>within the circumference of that spot -would behold the sun totally eclipsed. But, in -consequence both of the motion of the moon in -her orbit, and the rotation of the earth on its -axis, the shadow spot moves swiftly in an easterly -direction over the earth’s surface, forming what -is called the path of the eclipse. The astronomer -calculates beforehand across what parts of the -earth the path will lie, and selects his points of -observation accordingly.</p> - -<p class='c009'>“When the length of the shadow is too small -to reach the earth, the moon appears projected -against the sun as a round black disk, hiding the -center of the solar orb, but leaving a brilliant ring -all around. Such phenomena are called annular -eclipses. There are about three annular eclipses -for every two total ones. When the moon, as -often occurs, does not traverse the center of the -sun’s disk, as seen from any part of the earth, -a partial eclipse is the result. This means that -only a portion of the sun is hidden by the moon. -Even a total eclipse appears as a partial one to -observers who are not placed within the limits -of the shadow path.”</p> - -<p class='c009'>“But it seems to me,” said my friend, “you -have hedged round your eclipses with so many -difficulties, what with the tip of the moon’s orbit, -and what with the shortness of her shadow, -that they must be very few in number. Yet I -<span class='pageno' id='Page_42'>42</span>often hear of an eclipse, although I have never -seen one before to-night.”</p> - -<p class='c009'>“They are not so rare as you might suppose,” -I replied. “It is not necessary, in order that -an eclipse, either partial, or total, or annular, may -occur, that the moon’s nodes be in a <i>direct</i> line -with the centers of the sun and the earth. The -moon may be a few degrees out of line, and yet -either pass into the earth’s shadow or be seen -crossing the sun from one point or another on -the earth. There are about 70 eclipses in every -eighteen years, 41 of the sun and 29 of the moon, -but the number varies a little. Generally there -can be no more than two eclipses of the moon in -any one year, but it is possible for three to occur. -The greatest number of solar eclipses in a year -is five, but this is very rare, the usual number -being two. In fact, there must be at least two -solar eclipses in a year, but there are many years -which have no eclipses of the moon at all. And -now, I think I have said all that is necessary about -eclipses, and we arrive very opportunely at the -end of the discourse, for behold the moon is passing -out of the shadow, and her light begins once -more to glow in the park.”</p> - -<p class='c009'>This was indeed the case. Going to the door, -we saw the earth’s shadow slowly withdrawing -from the face of the moon, while the landscape -was brightening under her returning rays. For -<span class='pageno' id='Page_43'>43</span>a few minutes we watched, in silence, the brilliant -spectacle. Then my companion turned to me.</p> - -<p class='c009'>“Would you know my whole thought?” she -asked. “I fear that I cannot recall many of the -scientific facts you have just been telling me, but -for them I can go back, at need, to the books. -Yet one thing I feel that I have certainly gained. -It is a sense of friendly, companionable interest -in the moon. Henceforth she will be more to me -than she ever was before. I shall always be conscious, -when looking at her face, that she is the -offspring of the earth, and that there exists between -these two bodies an intimacy that I had -never imagined possible. For me your tides and -your eclipses seem an inarticulate language, a -caressing exchange of communications between -these two celestial beings of one blood. To my -mind they are, in a certain sense, personalities, -and, as a creature of the earth, I feel now my -relationship to the moon.”</p> - -<p class='c009'>“Very good,” I replied. “All science and -all forms of knowledge are rooted in the imagination. -To-morrow we shall begin with the photographs, -and many most interesting things that -I have not yet mentioned will then naturally -present themselves before us.”</p> - -<p class='c009'>“Good night then,” said my companion, “and -to-morrow I shall count upon the delights of a -photographic journey in the moon.”</p> -<div class='pbb'> - <hr class='pb c000' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c002'> - <div><span class='pageno' id='Page_45'>45</span><span class='c019'>I</span></div> - <div class='c000'><span class='c019'>NEW MOON TO FIRST QUARTER</span></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_47'>47</span> - <h2 id='ch01' class='c010'>I<br /> <br />NEW MOON TO FIRST QUARTER</h2> -</div> -<p class='drop-capa0_25_0_7 c020'>AT breakfast the next morning I asked my -friend if she still had sufficient curiosity -concerning the moon to induce her to undertake -the contemplated journey amid lunar -scenes.</p> - -<p class='c009'>“Yes, surely,” she replied. “My dreams last -night were filled with wonderful spectacles; great -cones of shadow flitted continually through the -heavens, eclipsing, in turn, moon, sun, and stars; -and I stared, as it seemed, for hours at strange -faces veiled behind a maze of mathematical diagrams -covering the moon. I am not sure that -your discourses have made me scientifically much -wiser, but I feel that my imagination is sufficiently -aroused to enable me to enjoy the photographic -excursion that you have proposed, and -I am quite ready to start at once.”</p> - -<p class='c009'>“Excellent!” I said, producing my portfolio. -“Here then are the photographs which I trust -will enable us, in imagination, to spend an interesting -month upon the moon. These photographs -were made at the Yerkes observatory and they -<span class='pageno' id='Page_48'>48</span>represent the moon, as you will perceive, in all -of her principal phases, beginning with the narrow -crescent of the New Moon, and ending -with the similar, but reversed, sickle of the Old -Moon.”</p> - -<p class='c009'>“Let us take them out into the park under -the trees,” my friend suggested.</p> - -<p class='c009'>The shafts of morning sunshine, falling through -the branches and illuminating the broad lawns -and brilliant flower-beds, offered the greatest possible -contrast with the strange scenes of the preceding -night. We chose the shadow of a huge -elm, and had a table placed there for our accommodation. -On this I spread the photographs, and -my companion began to examine them with many -expressions of interest.</p> - -<p class='c009'>“It is not often,” I said, “that science finds -so flattering an audience.”</p> - -<p class='c009'>“And I hope, surely, never so small a one,” -she responded, laughing. “But you must admit -that science very seldom presents herself in so -attractive a form as that of these pictures.”</p> - -<p class='c009'>“They are indeed of the highest excellence,” -I replied. “It is the very moon herself that you -see there.”</p> - -<p class='c009'>“But are you certain that they have not been -embellished? Has not the hand of an artist retouched -and improved them—particularly these -large ones that seem to contain a thousand curious -<span class='pageno' id='Page_49'>49</span>things which I can hardly believe really exist -on the moon?”</p> - -<p class='c009'>“No,” I said, “there is nothing fictitious or -imaginary in what you see. The only art displayed -here is that of the astronomer-photographer, -whose greatest ambition is to make his -pictures absolutely true to nature. A defect in -one of his plates, producing the appearance of a -speck of light or shadow which does not actually -exist, causes him as much distress of mind as you -would experience upon hearing a false note from -your piano. Indeed, the astronomer is so desirous -of having nothing but the truth represented -in his pictures that he often prefers, for his own -study, the original negatives alone, because every -time that they are reversed to make a ‘positive’ -copy something is sure to be lost, and some slight -defect is certain to be introduced. Let us begin, -if you please, with the series of smaller pictures -showing the various phases, and the gradual advance -of daylight across the moon’s surface. -Take first the photograph which I have labeled -No. 1. It shows the New Moon when it is between -three and four days old. You must often have -seen it in that form in the western sky soon after -sunset. Photographs of the New Moon have been -made when the crescent is still narrower than -that here shown, but there is no such photograph -in this series, and it would possess little interest -<span class='pageno' id='Page_50'>50</span>for you because almost no details of mountains, -craters, and plains would be visible. It is hardly -possible to make a good photograph of the moon -when it is only one or two days from the sun -in its monthly journey, on account both of the -glare of the solar light in our atmosphere and -of the nearness of the moon to the horizon, where -the air lacks transparency and steadiness. In the -photograph before us you will observe a great -number of strange forms and shadings. I shall -tell you what these are presently, but first let me -call your attention to the fact that the picture -does not exhibit a phenomenon which you would -behold if you were actually looking at the moon -in the phase here represented. You see here the -New Moon very clearly, but not the Old Moon in -her arms.”</p> - -<p class='c009'>“Indeed! It is a pity that the photograph -does not show so interesting a sight.”</p> - -<p class='c009'>“Yes, it is a pity. The cause lies in the defect -of light from what I have called the ‘Old Moon.’ -The part that we see in the photograph is illuminated -with sunshine, while the remainder of the -moon reflects only the earthshine, which is too -faint to be photographed (at least with the amount -of exposure required to make a good picture of the -brightly lighted crescent); although, as I have -said, you would see it clearly if you were looking -at the New Moon herself.”</p> - -<div id='i050' class='figcenter id002'> -<img src='images/i050.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 1. February 19, 1904; Moon’s Age 3.85 Days.</span></p> -</div> -</div> - -<p class='c009'><span class='pageno' id='Page_51'>51</span>“But,” interrupted my companion, “do you -mean to tell me that the earth illuminates the -moon?”</p> - -<p class='c009'>“Surely it does. Why not?” I replied, smiling. -“You must remember that the earth is -simply a huge moon to our imagined inhabitants -of the lunar world. Our globe sends to the -moon about fourteen times as much reflected sunlight -as the moon sends to the earth. The consequence -is than an earthlit night on the moon is -far more brilliant than a moonlit night on the -earth.”</p> - -<p class='c009'>“Then why do we not always see the moon -shining with light from the earth?”</p> - -<p class='c009'>“It is a question of contrast. You cannot -see a faint light in the immediate presence of an -overpoweringly brighter light. The part of the -moon that the sun illuminates is in the full glare -of day, and this is so much more brilliant than -the reflected earthlight that that portion of the -moon which enjoys only the latter is not visible -to us, except for a few days after New Moon, when -the amount of light from the crescent is not yet -great enough to dazzle our eyes and hide the rest -from sight. I should advise you when the next -New Moon occurs—you can find the date in any -almanac—to look at it in the western sky. You -will see in addition to the bright crescent the full -round orb of the moon, shining faintly, with a -<span class='pageno' id='Page_52'>52</span>dull, rather copperish, tint, and you will find it -interesting, then, to remember that that light is -reflected from our earth.</p> - -<p class='c009'>“And now,” I continued, “let us examine our -photograph more closely. There is one remark -that I had expected which you have not made; -it concerns the position of the crescent. You observe -that it is bowed toward the left. If you saw -it with the naked eye in the sky it would be bowed -toward the right, or toward the place of sunset. -The reason is that the photograph presents the -moon as seen with a telescope, which reverses objects, -turning them top for bottom. In this picture, -and in all the others that we shall examine, -the southern part of the moon is at the top and -the northern part at the bottom, the western part -at the left and the eastern part at the right. The -first thing that you probably notice in the photograph -is a conspicuous oval plain, somewhat below -the center of the crescent.”</p> - -<p class='c009'>“Yes, and I see clearly why you call it a plain, -for it is perfectly flat and smooth.”</p> - -<p class='c009'>“Not quite so flat and smooth as you suppose. -This object is one of the most celebrated on the -moon. It is the so-called <i>Mare Crisium</i>, or Sea -of Crises, as we may translate the name given -to it by the astronomers of a couple of centuries -ago, many of whom knew more Latin than science. -Owing to its apparent smoothness of surface, as -<span class='pageno' id='Page_53'>53</span>well as to its form and general aspect, they took -it for a great lake or sea.”</p> - -<p class='c009'>“To tell you the truth,” said my friend, “if -I were an astronomer and had discovered this -curious place on the moon, I should certainly -believe just what your Latin-loving predecessors -believed, but I doubt if I should have been capable -of inventing so singular a name for it.”</p> - -<p class='c009'>“In the singularity of the names they chose -for objects on the moon,” I replied, “their invention -is unrivaled. We shall see some remarkable -examples. Of course they are not at all to -be blamed for thinking that this oval spot, and -other similar ones of much greater magnitude, -were seas and oceans. They simply judged by -appearance and by analogy. Finding mountains -on the moon, they saw no improbability in supposing -that there were bodies of water also. -They had not the means of knowing, as we know -to-day, that there is no water on the moon. Yet, -perhaps, they were not so far wrong after all. -The <i>Mare Crisium</i> certainly has the look of an -empty sea bed, and I should not be willing to assert -that ages ago it was not filled with water.”</p> - -<p class='c009'>“Like the Great Salt Lake, dried up,” suggested -my companion.</p> - -<p class='c009'>“Not exactly, for the Great Salt Lake dried -up would probably present a surface as white -as snow, whereas the <i>Mare Crisium</i> is very dark. -<span class='pageno' id='Page_54'>54</span>It must be admitted, however, that gradually the -white deposit would grow darker, and there may -be much significance in the fact, which some observers -have noticed, that, at times, parts of the -dark plains on the moon seem to glitter with -minute points of light. Your imagination is at -liberty to see deposits of salt there.”</p> - -<p class='c009'>“In that case,” said my companion, laughing, -“I should prefer to regard the <i>Mare Crisium</i> as -resembling that wonderful valley discovered by -Sindbad the Sailor, whose floor was sprinkled -with diamonds.”</p> - -<p class='c009'>“Well,” I replied, “science certainly cannot -deny the possibility of diamonds on the moon, for -she is <i>par excellence</i> the world of volcanoes, and -one of the most striking discoveries of recent -years is that of the intimate association existing -between ancient volcanic vents and deposits of -diamonds. The diamonds of South Africa are -found in lava rocks that cooled off ages ago.”</p> - -<p class='c009'>“Then I hope that no future Columbus will -find a way to the moon, for we should have too -many diamonds, and they would lose all their -charm.”</p> - -<p class='c009'>“That is true, but suppose that not only diamonds -but even more beautiful gems should be -discovered in the lunar world? You surely would -not object to a transethereal traffic bringing them -to our doors. However, there is not the slightest -<span class='pageno' id='Page_55'>55</span>prospect that we shall ever be able to go from the -earth to the moon. Let us resume our examination -of the photograph, and concentrate our attention -on the known facts.”</p> - -<p class='c009'>I then proceeded to tell my friend, whose interest -I was delighted to find had not yet begun -to flag even in the face of comparatively matter-of-fact -statements, that the <i>Mare Crisium</i> is a -profound depression, about 350 miles in length -by 280 in breadth. Exactly how far it lies below -the general level of the lunar surface we do not -know; but, at any rate, if it was ever filled with -water it formed a deep, navigable sea. Its encircling -mountains, which appear generally bright -in the photograph, especially along the eastern -border, where the sunlight strikes directly against -their slopes, are in many places steep and abrupt. -At one place, on the southwestern side, there is -a mountainous promontory 11,000 feet in height. -There are a number of small craters on the floor -of the <i>Mare Crisium</i>, but the scale of this photograph -is not large enough to show them clearly.</p> - -<p class='c009'>“You will notice,” I continued, “that there is -a kind of bay on the eastern side, which runs back -into the mountains, and is bordered with high, -steep cliffs. Near this point, on that part of the -moon over which the sun has not yet risen, there -is a very remarkable mountain which we shall see -in a later photograph. But let us finish with -<span class='pageno' id='Page_56'>56</span>this one. Look at the comparatively small oval -adjoining the <i>Mare Crisium</i> below (toward the -north). It is one of the great crater rings of the -moon, and is named Cleomedes. It is much -larger than it looks, being nearly 80 miles in its -greatest diameter, and there is a peak on its surrounding -wall 10,000 feet in height. Still farther -toward the north you will observe two or three -other smaller craters or rings, which are very -interesting when studied with the telescope.</p> - -<p class='c009'>“Now, please turn your attention to the photograph -bearing the number 2. You see again the -<i>Mare Crisium</i>, and nearly in the center of the -crescent, and just on the border line between day -and night, a perfect oval ring with a central peak. -It is called Langrenus. It is even larger than -Cleomedes, being about 90 miles across. It has -the form of an oval, as we see it, but that is an -effect of perspective, since it is so far round -the side of the lunar globe. In reality it is a -nearly circular circumvallation, or rather an almost -perfect hexagon, composed of gigantic -mountains including a valley, in the center of -which rises a cluster of peaks 3,000 feet in -height.”</p> - -<p class='c009'>“This second photograph,” interrupted my -friend, “was taken later than the first, I suppose, -since it shows more of the moon’s surface.”</p> - -<div id='i056' class='figcenter id002'> -<img src='images/i056.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 2. September 24, 1903; Moon’s Age 3.87 Days.</span></p> -</div> -</div> -<p class='c009'><span class='pageno' id='Page_57'>57</span>“I should have told you that,” I replied. -“Yes, it does represent the moon at a time when -more of its surface, visible to us, is illuminated -by the sun. In fact, we may regard it as a picture -of the moon made about a day later than the -other. But I must now tell you that these photographs -were not all taken in regular succession, -a day apart, or even two days apart. That was -impracticable for reasons that I need not explain. -Some of them were made at one season of the -year and some at another. Yet taken together -they form a sufficiently continuous series to enable -us, with their aid, to follow the changing aspects -of the moon during more than three weeks, -or all that part of a lunation in which the moon -is a conspicuous object in the sky.”<a id='r2' /><a href='#f2' class='c021'><sup>[2]</sup></a></p> - -<div class='fn'> - -<div class='footnote' id='f2'> -<p class='c022'><span class='label'><a href='#r2'>2</a>. </span>In addition to what is said in the text concerning the photographs -the reader should be informed that, in consequence of her “librations,” -the moon does not, all the time, present <i>exactly</i> the same -surface toward the earth. If she did we should never see more -than one half of her surface. In fact, however, at one time or -another, we see, in all (but never at the same time), about fifty-nine -per cent of her surface, leaving forty-one per cent which is forever -invisible because never turned in our direction. The librations, or -“balancings,” of the moon, which bring now one and now another -portion of the usually invisible hemisphere into view, are of three -kinds: First, the libration in latitude, arising from the combined -effects of the inclination of the moon’s orbit to the plane of the earth’s -orbit, and the inclination of her axis of rotation to the plane of her -own orbit. When added together these two inclinations make the -axis of the moon lean one way or the other with respect to the earth -about 6½°. But, since the inclination of the moon’s orbit to that of -the earth is continually varying to a small extent, the amount of -this libration is also variable. Its effect is to cause now the North -and now the South Pole of the moon to incline slightly toward the -observer on the earth, so that he can see alternately a little way -round the northern and the southern edges of the moon’s disk.</p> - -<p class='c022'>Second, the libration in longitude, which arises from the eccentricity -of the moon’s orbit, causing her to move a little faster when she -is nearer the earth, or in perigee, and a little slower when she is farther -from the earth, or in apogee. In consequence of this, she gets -alternately about 6° ahead of, or behind, the position which she -would have if her orbit were a perfect circle and her motion perfectly -uniform. But, inasmuch as her rotation on her axis is never either -faster or slower, she shows a little of her usually invisible hemisphere -on the western side when she is between perigee and apogee, and a -little on the eastern side when she is between apogee and perigee. -The accompanying diagram is designed to aid the reader in understanding -these effects.</p> - -<div id='i058' class='figcenter id002'> -<img src='images/i058.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>Effect of Moon, Varying Velocity in Orbit Producing Libration in Longitude.</p> -</div> -</div> - -<p class='c022'>Third, the diurnal libration, which arises from the fact that the -diameter of the earth bears a considerable proportion to the distance -of the moon. If the observer were at the center of the earth there -would be no effect of this kind, but being situated about 4,000 miles -from the center, there is a parallactic effect in consequence of which -we see a little around the western side of the moon when she is rising -and a little around the eastern side when she is setting. The -maximum diurnal libration is a little more than one degree. The -maximum libration in latitude is 6° 44´, and that in longitude 7° 45´. -An illustration of the results of libration will be found by comparing -photographs Nos. 1 and 2. They were both taken at nearly the -same “age of the moon,” about three days, twenty hours, but under -different librations, so that in No. 2 more of the western edge of the -moon is visible, and the crescent appears broader. Even more -remarkable examples of the results of libration are seen in Nos. 6 -and 7, and 8 and 9. In No. 6, the moon is actually “older” by about -half a day than in No. 7, yet, owing to libration, the “terminator,” -or line between day and night on the moon, is considerably farther -toward the east in the latter than in the former. A similar effect is -seen in comparing Nos. 8 and 9. The exact dates and ages of the -moon corresponding to these photographs are given in the -Appendix.</p> -</div> - -</div> - -<p class='c009'><span class='pageno' id='Page_58'>58</span>“If you will follow the curve of the terminator -toward the south (upward in the photograph), -<span class='pageno' id='Page_59'>59</span>you will perceive that there is a long line of ovals, -more or less resembling Langrenus. The first of -these, darker in appearance than Langrenus, is -named Vendelinus.”</p> - -<p class='c009'>“What extraordinary names!” exclaimed my -companion, “and how unpicturesque!”</p> - -<p class='c009'>“Yes, it is true that the invention of the old -astronomers who supplied these names seems to -have failed a little at times. They did exceedingly -well in naming the ‘seas’ and similar objects, -but for the mountains, craters, and ring -plains they could think of no better plan than -that of attaching to them their own names, and -<span class='pageno' id='Page_60'>60</span>the names of other <i>savants</i>, or supposed <i>savants</i> -of their time, or of preceding centuries. And -in Latinizing these names they gave them a -kind of uniformity, which is hardly pleasing to -our taste to-day. But let me continue. Vendelinus -is an extremely beautiful sight when the -sunlight strikes its broken walls in such a manner -as to bring into prominence, by contrast with -the deep shadows, the rugged peaks, precipices, -and ridges of which its very irregular ring is -composed. You should see it with a powerful -telescope, especially under the rays of the setting -sun. Then the bottom of the valley within -has been described by Mr. Eiger, an English student -of lunar phenomena, as appearing punctured -like a sieve with holes.”</p> - -<p class='c009'>“And what are they?”</p> - -<p class='c009'>“Volcanic craters, probably, long since extinct.”</p> - -<p class='c009'>“So many volcanoes in one place?”</p> - -<p class='c009'>“Oh, yes. You have been at Naples and have -seen Vesuvius. But probably you have not visited -the Phlægrean Fields which lie northwest of -Naples. If you had had a passion for geology -when you were in Italy you would have explored -that region, and there you would have found -something not altogether unlike the valley of -Vendelinus in the moon. There is a great number -of extinct volcanic craters near Naples, and they -<span class='pageno' id='Page_61'>61</span>show how similar in many ways the moon is, or -has been, to the earth.”</p> - -<p class='c009'>“But, dear me,” my friend exclaimed, “are we -going to see nothing but burned-out craters and -wild, ragged mountains on the moon? I am sure -that I should never have thought of visiting -Naples for the sake of looking at its Phlægrean -Fields.”</p> - -<p class='c009'>“Still,” I replied, “you must certainly know -that Pompeii and Herculaneum and the memories -of their tragic fate are the most vivid attraction -of Naples to-day, although the Pompeiians have -all been dead for almost 2,000 years. So in looking -at these spectacles in the moon we cannot but -be interested by the reflection that they are reminders -and relics of a wonderful history, whatever -its precise character may have been. The -moon seems to me to stand for the most affecting -of all tragedies—the passing of a world. When -I survey its extraordinary landscapes, it is like -looking upon a long-abandoned stage, whose actors -are in their graves, whose scenery is moldering -under a gaping roof, whose machinery is -broken, whose very traditions are forgotten, but -which yet retains a semblance of its former brilliance. -I do not have to imagine inhabitants in -the moon at the present day in order to find it -interesting. The possibility that it may once -have had inhabitants is enough, remembering its -<span class='pageno' id='Page_62'>62</span>nearness to the earth and the manner of its origin, -to make it the most fascinating thing that -the heavens contain.”</p> - -<p class='c009'>“Indeed, I had never thought of the moon -quite in that way,” was the reply. “If you can -read a history for me in these craters and ring -plains I believe I shall find them more interesting -than I expected.”</p> - -<p class='c009'>“I cannot promise you a history as full of romantic -details as that of Herodotus,” I said, -“but it may contain nearly as many actual facts. -However, we shall see about that as we go along. -Let us now return to the inspection of the photograph. -Be kind enough to look a little above Vendelinus. -You observe there another still larger -ring plain, or walled valley, with a conspicuous -mountain in the center. This is Petavius. It -belongs to the chain of similar formations which -includes Langrenus and Vendelinus, but it is more -wonderful than either of them. It is nearly a -hundred miles long from north to south. For -some reason, as with Vendelinus, its ruggedness -and complexity of structure are more conspicuous -in the lunar afternoon than in the lunar morning. -It is a question of the direction in which the light -falls across it. A curious thing about Petavius -is the convexity of its vast floor. The center is -about 800 feet higher than the edges along the -feet of the surrounding mountains.”</p> - -<p class='c009'><span class='pageno' id='Page_63'>63</span>“How do you know that?”</p> - -<p class='c009'>“The shadows tell the story. The height of -objects on the moon is measured by observing the -length of their shadows under a known inclination -of the sun’s rays. When I stand this book -upright on the table, allowing the sunlight to -strike it on one side, it casts a shadow on the -table. If I did not know the height of the book, -and could not measure it directly, I could find it -out by measuring the length of its shadow, other -simple trigonometrical data, easily ascertained, -being known. There is an enormous cleft not -clearly visible in the photograph, extending from -the central mountains of Petavius to the southwestern -wall of the valley. Still farther south, -above Petavius, you will notice another conspicuous -oval plain and several smaller ones near it. -The largest of these is named Furnerius. They -all lay in the morning sunshine, not far from the -terminator, when this photograph was taken.”</p> - -<p class='c009'>“Tell me, please, about the ‘terminator’ of -which you have spoken several times. As I understand -you it is the line between day and night -on the moon.”</p> - -<p class='c009'>“Yes, and a very wonderful line it is, too. -There is nothing just like it on the earth. Owing -to the effects of our atmosphere in dispersing the -light, day and night do not stand face to face with -one another on the earth in the same way that -<span class='pageno' id='Page_64'>64</span>they do on the moon. Here we have twilight in -the evening and dawn in the morning, and night -neither comes nor goes for us with the startling -suddenness that characterizes it on the moon. -For an hour or two after sunset and before sunrise, -we receive rays of reflected and refracted -light from the atmosphere above us, which spread -a soft, pleasing illumination over the landscape, -and render all objects more or less distinctly visible. -But if you were on the moon in certain situations, -the passage from day to night or from -night to-day would be as rapid as the falling or -rising of a curtain. Imagine yourself standing -on the western wall of Vendelinus or Petavius at -the time when this photograph was taken. You -would be in a blaze of pitiless, untempered sunshine, -but glancing down the precipice at your -feet you would seem to be looking into a gulf -of blackness. But for the light reflected back -from the eastern cliff, and that coming from the -earth, there would be scarcely a ray of illumination -on the rocks below you. You would look -down into inky darkness, and would scarcely dare -to make a step from fear of falling over the -edge of a bottomless pit. At the same time, -as I told you last night, you would see the -stars all about you in the sky, even close to -the sun.</p> - -<p class='c009'>“This is the reason,” I continued, “why the -<span class='pageno' id='Page_65'>65</span>march of day across the moon, always keeping -sharp on the heels of night, is a spectacle so imposing -and unparalleled. It is this wonderful -march that we are going to follow with the aid of -the photographs. I shall now ask you to give -your attention to <a href='#i066'>photograph No. 3</a>. It was made -more than a day and a half later than the others, -measured by the age of the moon, which, in this -case, was about five days and a half. You notice -how in the interval the sunlight has swept eastward -over the moon’s surface. The <i>Mare Crisium</i> -is recognizable in the lowest or most northerly, -of three large, dark plains. The small -white oval a considerable distance above it is our -old acquaintance Langrenus, whose floor and -walls are now very brilliant in the full sunshine, -which falls upon them at a high angle. Vendelinus -and Petavius are less conspicuous. The -broad, dark plain which has come into view eastward -from Langrenus is the <i>Mare Fœcunditatis</i>, -which we may translate ‘Sea of Fecundity’! -You certainly cannot aver that on this occasion -the invention of the old astronomers failed in the -matter of romantic suggestiveness. The name -calls up pictures of a great body of tranquil -water, fanned by gentle, stimulating breezes, filled -with fish of every variety, dotted with vine- and -flower-garlanded islets, and bordered by well-watered -shores, rich with vegetation, and supporting -<span class='pageno' id='Page_66'>66</span>a numerous and happy population. Some such -idea of the <i>Mare Fœcunditatis</i> may have been in -the minds of its sponsors a couple of centuries -ago. But telescopes have become too powerful -in our day to permit us to be any longer deceived -as to the actual nature of this singular lunar -region. Like the <i>Mare Crisium</i>, it may have been -the bed of a sea many years ago, but at the present -time it contains no water, and its shores present -an endless succession of fire-scarred cliffs, -peaks, and volcanoes. The only ‘islands’ in it -are extinct craters.”</p> - -<p class='c009'>“But,” said my companion, smiling, “where -then is its history?”</p> - -<p class='c009'>“Ah!” I replied, “is not this old sea itself -history enough? When it has receded sufficiently -into the past, all history loses its details, and -presents only its setting and its grand primary -elements. Suppose that, some ages in the future, -you should be an inhabitant of a distant planet, -surveying with a telescope the dried-up basin of -the Atlantic Ocean. Provided only that you were -convinced, in your own mind, that it had once -been an ocean, with fertile, inhabited shores, and -with ships sailing upon it, you would be singularly -lacking in imagination if you could not reconstruct -its history for yourself. The details -could safely be left to your invention and you -could change them from time to time to suit -<span class='pageno' id='Page_67'>67</span>your varying moods. Terrestrial historians have -sometimes done that.”</p> - -<div id='i066' class='figcenter id002'> -<img src='images/i066.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 3. July 29, 1903; Moon’s Age 5.54 Days.</span></p> -</div> -</div> - -<p class='c009'>“But do <i>you</i> believe that the <i>Mare Fœcunditatis</i> -was ever such a sea, and the scene of such -events?”</p> - -<p class='c009'>“That is certainly a very pointed question. -Questions of that kind are always in order when -one is treating of ascertained verifiable facts, but -just now, you know, we have wandered a little -aside from the straight path of scientific exactitude. -Still, I will be frank with you and say that -I really possess no settled opinion concerning the -former condition of the moon, except so far as -what we may call its ‘geological’ history is revealed -by its present state. I am sure that the -moon was once the seat of tremendous volcanic -action, and I think it not improbable that its great -depressed plains were once occupied by water, but -as to inhabitants, I know no more about them -than you do. Still, I am disposed to think that, -as we go on, <i>you</i>, at least, will reach the conclusion -that all life has not yet disappeared from the -moon. We are going to learn some very suggestive -and significant things before we are -through.</p> - -<p class='c009'>“Farther toward the south and closer toward -the terminator you will see in the photograph a -third dark plain with five sides, the northern -one convex and ill-defined. At its upper corner -<span class='pageno' id='Page_68'>68</span>is an incomplete ring plain. This region bears -a still more curious name than the <i>Mare Fœcunditatis</i>. -It is the <i>Mare Nectaris</i> or ‘Sea of -Nectar.’”</p> - -<p class='c009'>“Apparently your astronomers of old took the -moon for an abode of the gods.”</p> - -<p class='c009'>“Yes, or for their wine cellar. But we shall -get a better look at the surroundings of this Sea -of Nectar in a later photograph, and then I shall -have more to tell you about it. In the meantime -let us return to the <i>Mare Crisium</i>. To the east -(right-hand side) of the <i>Mare Crisium</i> you will -observe a diamond-shaped district, not very dark, -with a bright point at the corner which faces the -<i>Mare</i>. You could never guess its name. It is -called the <i>Palus Somnii</i>, which may be translated -‘Marsh of a Dream.’ It is a very singular place, -and, seen with the telescope, possesses a color -which is unique upon the moon, a kind of light -brown, quite unlike the hue of any of the other -plains or mountain regions. It is covered all -over with short, low ridges, as if its surface had -been broken up in a most irregular manner with -a giant plow. What the person who named it saw -there to lead him to connect it in his mind with -dreams I have never been able to imagine. The -bright point on its western edge is a remarkable -crater mountain, named Proclus. What -that mountain is made of nobody knows, but it -<span class='pageno' id='Page_69'>69</span>gleams with extraordinary brilliance when the -sun strikes it.”</p> - -<p class='c009'>“Why may it not be snow-covered?”</p> - -<p class='c009'>“That is a suggestion which has often been -made, but one great objection to it is that we have -reason for believing that snow, at least in such -a situation, cannot exist on the moon. Another -objection is that only a few of the lunar mountains -are comparable in brightness with Proclus, -and they are not the loftiest ones. Upon the -whole it is much more probable that the reflecting -power of Proclus is due to the composition of its -rocks, perhaps to broad crystalline surfaces exposed -in the sunshine.”</p> - -<p class='c009'>“It is a surprise to me, then, that that -‘earthly godfather’ of lunar wonders, who had a -sufficiently vivid fancy to invent the ‘Marsh of a -Dream’ close by, did not name this mountain for -some jewel, real or imaginary.”</p> - -<p class='c009'>“It would have been more poetic, indeed, but -as I have already told you, the mountains and volcanoes -of the moon nearly all bear very prosaic -designations, while a wealth of fancy has been -lavished in naming the ‘seas’ and plains. The -astronomer Riccioli is responsible for most of the -commonplace nomenclature that we find in lunar -charts. If you will now glance at the northern -(lower) ‘horn’ of the moon in the photograph -you will notice, near the terminator, about two -<span class='pageno' id='Page_70'>70</span>thirds of the way from the <i>Mare Crisium</i> to the -end of the horn, a pair of ring plains, or crater -rings, apparently almost touching one another. -They are Atlas and Hercules, the latter being the -smaller one on the right. A darker oval below -them near the bright edge of the moon is -Endymion.”</p> - -<p class='c009'>“That, at least,” exclaimed my companion, -delighted, “is a romantic and appropriate name! -I am enchanted to think that Endymion has not -been separated by your cold-hearted science from -her who loved him so well.”</p> - -<p class='c009'>“But if you should look at Endymion with a -telescope you would wonder what the moon could -find in him to admire. He has been turned into -a huge, broken-walled ring plain. You will observe -that the other, the southern or upper horn -of the moon in the photograph, appears extraordinarily -roughened. It is completely pitted with -craters and rings. There are so many of them, -and they are so entangled, that I shall not undertake -to indicate them by their individual names, -especially as there is none among them of the -very first importance. If, however, you will -bring your attention back to the <i>Mare Nectaris</i> -I shall be able to point out to you a very extraordinary -object, which lies just on the border between -day and night here, but will be seen in the -next photograph that we examine, in full morning -<span class='pageno' id='Page_71'>71</span>light. The object that I mean is a ring on the -right-hand edge of the <i>Mare Nectaris</i>. Its eastern -wall and the top of its central peak are -brightly illuminated by the rays of the rising sun; -while beyond it, to the eastward, everything, with -the exception of the tips of one or two high peaks, -is steeped in night. This is one of the mightiest -volcanic formations that the moon contains. Its -name is Theophilus. To see it and certain gigantic -neighbors that it has, fully displayed, we shall -turn, after this glance at its first appearance, to -photograph No. 4.</p> - -<p class='c009'>“In this photograph the sunrise line on the -moon has advanced so much farther eastward -that the <i>Mare Nectaris</i> lies well within the illuminated -part of the disk, and Theophilus has become -the most conspicuous object of the kind in -view. You now observe that it does not stand -alone, but is linked, so to speak, with another -similar ring on its southeastern side, while still -farther southward is a third less regular ring -which seems to belong to the same group.”</p> - -<p class='c009'>“Oh, yes,” cried my companion, “they certainly -do seem to be connected. They look like -three links of an enormous broken chain dropped -upon the moon.”</p> - -<p class='c009'>“The ring nearest to Theophilus,” I continued, -“and whose northwestern side has been destroyed -to give room for the full circle of the -<span class='pageno' id='Page_72'>72</span>wall of Theophilus, is named Cyrillus. The other -more distant one is Catharina. If you wish to -become a little learned in the geography of the -moon it is necessary that you should remember -these names. As to the objects that the names -designate, they are far too wonderful ever to be -forgotten, and it is impossible to confuse them -with any other features of the lunar world. -There is a great deal of ‘history’ connected with -these three enormous volcanic formations, but I -am going to reserve that for a while, because by -and by we shall examine a larger photograph -of these same objects in which you will see their -marvelous details displayed. Now let me direct -your attention to the first chain of mountains that -we have found upon the moon. Above Catharina -you will notice a thin, crinkled line of light passing -through a comparatively level district and -ending at another ring. It is a range of peaks -and cliffs named the Altai Mountains. They are -of no great height, and cannot be compared in -magnificence with the lunar Alps and the lunar -Apennines which we shall see in the photographs -taken a few days later, but they are nevertheless -very interesting. The ring mountain at which -the Altai range terminates is named Piccolomini. -It is another marvelous object for telescopic -study. The incomplete ring, with a dark interior, -which forms the southern corner of the <i>Mare Nectaris</i>, -<span class='pageno' id='Page_73'>73</span>resembling a semicircular bay, is Fracastorius. -It is a very curious object because close -inspection reveals that the missing part of its -ring has been submerged, but is still faintly visible -through the surface of the <i>Mare</i>.”</p> - -<div id='i072' class='figcenter id002'> -<img src='images/i072.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 4. November 24, 1903; Moon’s Age 5.74 Days.</span></p> -</div> -</div> - -<p class='c009'>“I suppose it cannot be water that has covered -it, since you have so often assured me that there -is no water on the moon.”</p> - -<p class='c009'>“No, it is not water, but rock or sand or -solidified lava, or some kind of solid matter. It -looks as though the whole bed of the <i>Mare Nectaris</i> -had welled up in one mighty convulsive outpouring -of liquid lava, which broke down the wall -of Fracastorius, inundated the interior, and then -hardened like a floor of cement. The probability -that a catastrophe of the kind I have described -has occurred here is heightened by the fact that -the bed of the <i>Mare Nectaris</i> is concave, sunken -in the center, as if it had broken and settled down -‘like ice upon a pond.’ Scattered more or less all -over its surface and particularly near its shores, -there are indications of this breaking down, and -of something that has been covered up.”</p> - -<p class='c009'>“To me it seems very mysterious,” said my -friend, “and very terrible also.”</p> - -<p class='c009'>“It is more or less mysterious to the astronomer -likewise. Still, geology shows that -there have been somewhat similar occurrences -on the earth. If you will now direct your eyes -<span class='pageno' id='Page_74'>74</span>to the lower (northern) part of the photograph -you will notice some additional things that have -come into view with the advance of the sunlight. -You observe that a vast somber region occupies -the inner portion of the crescent below the center. -This consists of two immense plains, one of which -sends a large ‘bay’ as far south as the ring of -Theophilus, where it is connected by a narrow -‘strait’ with the <i>Mare Nectaris</i>.</p> - -<p class='c009'>“Turning to <a href='#i074'>photograph No. 5</a> we see the two -plains to which I have referred more fully displayed. -The sun has now risen over their entire -surface. The upper one is the <i>Mare Tranquillitatis</i>, -‘Sea of Tranquillity’; and the lower one -the <i>Mare Serenitatis</i>, ‘Sea of Serenity.’”</p> - -<p class='c009'>“I have always thought that astronomers -must be happy persons,” said my companion, with -a smile, “and these names are convincing.”</p> - -<div id='i074' class='figcenter id002'> -<img src='images/i074.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 5. July 1, 1903; Moon’s Age 6.24 Days.</span></p> -</div> -</div> - -<p class='c009'>“Yes, perhaps, but then in bestowing the -names they may have been transferring to the -moon ideals of tranquillity and serenity which -they did not find realized upon the earth. I am -not going to talk about these two ‘seas’ at present -because they are better represented upon one of -the large photographs which we shall examine -later. I prefer to direct your attention just now -to some other things. In the first place look -once more at Theophilus and its companion rings, -and observe how they maintain their preëminence. -<span class='pageno' id='Page_75'>75</span>The entire surface of the moon to the eastward -and southward is broken and heaped up with -mountains, craters, and rings, but nowhere do we -see anything comparable with Theophilus except, -perhaps, far toward the south, where near the inner -border appear two still larger, but less regular, -rings lying in line at a right angle to the -terminator. The one on the left is Maurolycus, -and the other, still half obscured by night, is -Stöfler.”</p> - -<p class='c009'>“The names of old astronomers, I suppose.”</p> - -<p class='c009'>“Yes, astronomers sufficiently famous in their -day, but who would be virtually forgotten at the -present time if their friend Riccioli had not thus -immortalized them. You see it is a great piece -of good fortune to have your name in the moon. -It is a kind of revenge for the neglect of future -generations at home.”</p> - -<p class='c009'>“And it seems to me an equal good fortune -to have had an admirer willing to set your name -up in the moon.”</p> - -<p class='c009'>“Surely. But Riccioli’s own name is there -also. Afterwards I shall show you his lunar -monument, a truly magnificent one. Permit me -now to tell you that Maurolycus is much greater -in extent than any of the rings that we have yet -seen. Not by any means so perfect in form as -Theophilus, it covers a vast extent of surface, as -much as 150 miles across, with an amazing mass -<span class='pageno' id='Page_76'>76</span>of broken rings, walls, ramparts, ridges and -chasms. Some of its peaks are 14,000 or 15,000 -feet in height. It has a very lofty central mountain, -visible in the photograph, and whose peak -comes into view when the sun is rising long before -the surroundings have been illuminated, so -that it resembles a star glowing amid the blackest -night. The neighbor of Maurolycus, Stöfler, -is equally extensive and almost equally wild and -magnificent when the sunlight is leaping across it -from pinnacle to pinnacle and ridge to ridge. In -this photograph, however, it is too near the terminator -to be well seen. We shall presently pass -to photograph No. 6, where Stöfler appears in full -light, but before doing so let us glance at the -northern part of the moon as here pictured. -Close to the terminator, below the grand oval -form of the <i>Mare Serenitatis</i>, you will perceive -two rings, one above the other. They seem to be -the complement of the other pair, Atlas and Hercules, -which we looked at when the sun had recently -risen upon them in another photograph, -and which now appear far off toward the west. -You observe that Atlas and Hercules lie upon -an east and west line, and the others upon a -north and south line. The northernmost one is -named Aristoteles, and the other Eudoxus. They -are situated near the edge of a plain called the -<i>Mare Frigoris</i>, ‘Sea of Cold,’ thus named, I suppose, -<span class='pageno' id='Page_77'>77</span>because it lies so far north. Aristoteles -is about 60 miles in diameter, and its immense -wall is very high and splendidly terraced. Eudoxus, -equally deep, is only 40 miles in diameter.</p> - -<p class='c009'>“Turning to photograph No. 6, taken when the -moon was more than a day older than it was when -No. 5 was made, we have a striking example of -the effect of libration in presenting the moon at -perceptibly different angles to our line of sight -at corresponding phases. We have now arrived -at First Quarter, and behold all the western half -of the moon illuminated by the sun. You will -perceive that we now have in view, simultaneously, -six of the great plains called ‘seas,’ namely, -the <i>Mare Crisium</i>, the <i>Mare Fœcunditatis</i>, the -<i>Mare Nectaris</i>, the <i>Mare Tranquillitatis</i>, the <i>Mare -Serenitatis</i>, and the <i>Mare Frigoris</i>, while others -are beginning to emerge out of night on the east. -Maurolycus and Stöfler, the pair of giant rings -in the south, are better seen than before because -daylight has advanced farther across them. In -fact Stöfler now appears more imposing than its -great neighbor, and a smaller ring breaking the -continuity of its wall on the western side is visible. -Above these, in the direction of the south -pole of the moon, and around the pole itself, the -surface is marvelously rough and broken. It -looks as if it would be impossible to find a level -acre of ground in all that region. The rings and -<span class='pageno' id='Page_78'>78</span>craters are veritably innumerable. It is the -existence of these irregularities which causes the -terminator to appear so crooked and broken. At -some places you perceive small bright points -within the edge of the night half of the moon. -These, of course, are the summits of peaks, which -have just been touched by the sunlight while the -surface all around them is still covered with -darkness.</p> - -<p class='c009'>“Below Stöfler, all along the terminator, as -far as the middle of the moon, an irregular row -of rings appears. Three of these bear some resemblance -to the great group of which Theophilus -is the chief member. They are, counting from -south toward north, Aliacensis, Werner, and -Blanchinus. Below them two other much larger -ones are conspicuous, Albategnius, the more -southerly, and Hipparchus. These two are full of -moon history. Albategnius, the smaller, is very -deep and comparatively perfect in condition, -while Hipparchus, more than 90 miles across, has -been vividly described as a ‘wreck and ruin,’ its -walls, once possibly of great height, being now -low and broken, and traversed with gaps and valleys, -while a great cleft exists crossing a part of -the broad, irregular floor. It is probable that Hipparchus -is an older formation than Albategnius.”</p> - -<div id='i078' class='figcenter id002'> -<img src='images/i078.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 6. November 26, 1903; Moon’s Age 7.75 Days.</span></p> -</div> -</div> - -<p class='c009'>“Pardon me,” interrupted my companion, -“but I must cry for mercy. Really, these strange -<span class='pageno' id='Page_79'>79</span>names escape from my mind as fast as you mention -them. Is there not something a little more -romantic in the moon—something to relieve the -strain of all this nomenclature of words terminating -in ‘us,’ and this frightful lunar geology?”</p> - -<p class='c009'>“Yes,” I said, “I believe that on the other half -of the moon, which has not yet seen the sun rise, -we shall find something better to your taste. But -do not be too impatient. Reflect that these names -represent very wonderful things visible to us in -another world than ours, things the knowledge of -which has cost the lifelong labors of many gifted -men, and that will be remembered, studied, talked, -and written about centuries after we are dead. -Fortunately for your powers of attention the -eastern half of the moon, upon which day will -be seen gradually dawning in the next set of -photographs, has a general character quite different -from that of the western half. It contains -the greatest ranges of lunar mountains, yet upon -the whole it is more level, being covered to a -great extent with broad plains, in the midst and -along the borders of which stand the most remarkable -and interesting of all the lunar formations. -In and around some of them we shall -search for the evidences which some astronomers -think that they have found of life upon the moon.”</p> - -<p class='c009'>“Oh, that indeed will be interesting!” exclaimed -my friend with reviving animation.</p> - -<p class='c009'><span class='pageno' id='Page_80'>80</span>“But,” I added, “do not place your expectations -too high. Keep your imagination under -control, try always to be just a little ‘scientific’ -in your way of looking at things, and then I believe -you will not be disappointed.”</p> - -<p class='c009'>“Oh, please do not think that I have been disappointed,” -she said deprecatingly. “But positively -you must admit that ‘Albategnius,’ ‘Aliacensis,’ -‘Blanchinus,’ and ‘Maurolycus,’ are not -precisely captivating. Remember that I have -read little except poetry and romance, and those -histories that are full of stories.”</p> - -<p class='c009'>“You will find a deep vein of poetry and romance -in the moon,” I replied, “before we have -finished, and after you have reflected upon what -we have seen and what we have been saying.”</p> - -<p class='c009'>Leaving the remaining photographs to be examined -after lunch, we now entered the house.</p> -<div class='pbb'> - <hr class='pb c000' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c002'> - <div><span class='pageno' id='Page_81'>81</span><span class='c019'>II</span></div> - <div class='c000'><span class='c019'>FIRST QUARTER TO FULL MOON</span></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_83'>83</span> - <h2 id='ch02' class='c010'>II<br /> <br />FIRST QUARTER TO FULL MOON</h2> -</div> -<p class='drop-capa0_25_0_7 c020'>NOTWITHSTANDING the signs of impatience -which my friend had manifested -when we were passing, in our review of -the photographs, from one lunar ring mountain to -another, all more or less similar in appearance -and characteristics, I was gratified to see that her -mind was still attracted to the subject of the -moon, and during the lunch she, of her own accord, -began to talk of it.</p> - -<p class='c009'>“You have said so much about volcanic occurrences -on the moon,” she remarked, “that I -wonder why you do not call those immense mountains -‘volcanoes.’ I observe that you always -speak of them as ‘rings,’ or ‘mountain rings,’ -or ‘ring plains’; while to me, although to be sure -I am no geologist and have perhaps no right to -an opinion, they seem plainly to be just huge -volcanoes and nothing else.”</p> - -<p class='c009'>“Your observation is quite correct,” I replied, -“as far as superficial appearance goes, and I -may add that these great rings are often called -volcanoes. If we apply the proper adjective and -<span class='pageno' id='Page_84'>84</span>name them ‘lunar volcanoes,’ perhaps there can -be no objection to the term. But they are certainly -widely different from our terrestrial volcanoes. -The difference is not in size alone, -although in that regard it is enormous. There -is a far more significant difference, which you -could hardly be expected to notice in a simple -inspection of the photographs, although it is evident -when once pointed out. I refer to the fact -that what seem to be the craters of lunar volcanoes -are not situated on the tops of mountains. -They are immense plains, more or less irregular -in surface, and often having a peak or a group -of peaks in the center, while around these plains -always extends a mountain ring, steep on the inner -side, and having a gradual slope without. -But most significant fact of all, the plains, or -floors inside the ring, are almost invariably situated -thousands of feet below the general level -of the moon. If the terrestrial volcanoes were -formed on the plan of the lunar ones, when we -visit Vesuvius, instead of climbing up a mountain -rising out of the midst of a plain and capped -with a cone, having a funnel-shaped crater in the -center, we should find before us a relatively low, -circular elevation, on surmounting which there -would appear on the inside of the circle a great -basinlike hollow, far below the level of the surrounding -country. In the center of this, distant -<span class='pageno' id='Page_85'>85</span>from the lofty encircling walls, would be seen a -conical hill with smoke and vapor issuing from -a vent at its summit. The top of this crater hill -would be lower than the rim of the basin-shaped -hollow, so that the whole volcano with its immediate -surroundings would be inclosed and shut -off from the environing upper world by the sides -of the basin. While you finish your coffee I will -make a sketch which may render this difference -between lunar and terrestrial volcanoes evident -at a glance.”</p> - -<div id='i085a' class='figcenter id005'> -<img src='images/i085a.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>Lunar Volcano, in Section.</p> -</div> -</div> - -<div id='i085b' class='figcenter id005'> -<img src='images/i085b.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>Terrestrial Volcano, in Section.</p> -</div> -</div> - -<p class='c009'>Accordingly, after a few minutes, I presented -to her these two diagrams, remarking that it -should be borne in mind that the two sketches -were not made on the same relative scale. “I -was compelled,” I said, “to change the true proportions -in the section of the lunar volcano, for -if I had drawn them as they are in fact, the width -<span class='pageno' id='Page_86'>86</span>of the basin would have been enormous in proportion -to its depth. You will recall that I told you -that such rings as Albategnius and Maurolycus -are a hundred miles and even more in diameter, -while their depth does not exceed two or three -miles. It results from this necessary falsification -of proportions in the sketch that the terrestrial -volcano, although so widely different in form, appears -comparable in magnitude with the lunar -one. But the fact is that you could take a dozen -of the largest volcanic mountains on the earth -and throw them into one of the great lunar rings -without filling it.”</p> - -<p class='c009'>“I am the more astonished by what you say,” -remarked my friend, “because you have already -told me that the moon is so much smaller than -the earth. How does it happen, then, that her -volcanoes are so much larger? I should think -that in a little world all things would be small -in proportion.”</p> - -<p class='c009'>“It is quite natural to think so,” I replied, -“until you reflect upon the consequences of the -smaller force of gravitation on a small world. I -told you last evening that gravitation on the moon, -is only one sixth as powerful as it is on the earth, -and you will recall that one consequence which I -pointed out was that you would weigh only -twenty pounds if you were on the moon. Since -the same reasoning applies to all objects in the -<span class='pageno' id='Page_87'>87</span>lunar world, it is clear that a similar force exerted -there would be able to produce enormously -greater effects, as for instance in the formation -of vast hollows or depressions, by violent explosions, -the products of which would be thrown to -immense distances. Some selenographers, which -is a term applied to those who study the features -of the lunar world, have suggested that in this -cause alone is to be found the explanation of the -giant lunar ring mountains. At some remote -period of the past, according to them, the volcanic -forces of the moon reached a maximum of -activity and energy. The lava, cinders, ashes, -and other products of ejection, were hurled to a -height of scores of miles, and when this fell back -at a great distance from the centers of eruption -these were piled up in huge rings, fifty, eighty, -or a hundred miles in diameter, while the surface -of the moon within the rings sank in consequence -of the withdrawal of the material thus -ejected. To account for the existence of the central -mountains so often found in the middle of -the rings, it has been suggested that at a much -later period, when the volcanic energy had become -comparatively insignificant, as a result of the -cooling of the interior of the moon, less violent -explosions, not greater than many that have occurred -on the earth, took place, and by these the -central peaks were formed.”</p> - -<p class='c009'><span class='pageno' id='Page_88'>88</span>“You are going to think me too romantic, or -too imaginative, again,” said my friend, with a -smile, “but I cannot prevent myself from wondering -what the inhabitants of the moon did and -thought while all those marvelous things were -happening.”</p> - -<p class='c009'>“I have not said that there were inhabitants -of the moon.”</p> - -<p class='c009'>“No, but you have confessed that there might -have been inhabitants, some time, and I should -like to know whether they were there when those -terrible volcanoes were formed.”</p> - -<p class='c009'>“If they were,” I replied, “they could not -have survived such a universal upheaval as the -surface of the moon has undergone. You have -seen in the photographs that the great rings and -smaller craters are scattered thickly over the -moon. It is true that comparatively few are -found in the level expanses called ‘seas,’ but if -those regions were covered with water they could -only have been inhabited by beings provided with -gills and fins.”</p> - -<p class='c009'>“How long ago did these explosions occur?”</p> - -<p class='c009'>“I cannot tell you, except that it must have -been many ages in the past; so long ago, indeed, -that the whole course of human history seems -but a day in comparison.”</p> - -<p class='c009'>“Then,” said my friend with animation, -“there has been time enough <i>since</i> that dreadful -<span class='pageno' id='Page_89'>89</span>period for inhabitants to develop upon the moon, -has there not?”</p> - -<p class='c009'>“Yes, time enough, perhaps, provided that -sufficient water and air and other vital requisites -remained after the exhaustion of the volcanic -energies.”</p> - -<p class='c009'>“Oh, let us say that they did remain. I am -eager to believe that the moon has not always -been so desolate as she appears at present.”</p> - -<p class='c009'>“Very well, you are at liberty to believe that -if you like. No astronomer is likely positively -to contradict you, although he may smile a little -incredulously. Besides, as I have already told -you, there are certain rather inconclusive indications -of some kind of life, and of some kind of -activity, still on the moon.”</p> - -<p class='c009'>“Please show them to me, then, or tell me -about them. Perhaps I shall find them less inconclusive -than you do.”</p> - -<p class='c009'>“Everything in its turn,” I replied. “We -shall come to the indications that I have spoken -of after we resume the inspection of the photographs.”</p> - -<p class='c009'>“Then I am ready to resume at once.”</p> - -<p class='c009'>Accordingly we returned to the table and the -photographs under the pleasant shade of the elm. -Taking up the photograph numbered 7, I remarked -that it exhibited the moon as it appears -a little after First Quarter; that is to say, a trifle -<span class='pageno' id='Page_90'>90</span>more than half the face turned toward the earth -is in the sunlight. I called attention once more -to the six “seas,” which we had already remarked, -and to the continued conspicuousness of Theophilus -and its companions, a little above the middle -of the visible hemisphere.</p> - -<p class='c009'>“You observe now,” I continued, “how the -rotundity of the lunar globe begins to manifest -itself as the sunlight sweeps farther eastward. -The crescent shape is gone and the line between -day and night begins to be bowed outward, convexly. -The <i>Mare Crisium</i> is particularly well defined, -and also the diamond-shaped region called -the <i>Palus Somnii</i>. With the sun so nearly vertical -above it, the remarkable peak of Proclus, -between the <i>Palus Somnii</i> and the <i>Mare Crisium</i>, -has become very brilliant. In a telescope you -would see it glowing almost like a star. You observe -also that several long, straight, bright rays -proceed from it in several directions.”</p> - -<p class='c009'>“All the more reason, it seems to me,” said -my friend, “why your unimaginative astronomer, -Riccioli, should have named it for some brilliant -gem instead of attaching to so dazzling an object -the prosaic designation of ‘Proclus.’”</p> - -<p class='c009'>“After all,” I replied, “what’s in a name?” -Now that you are familiar with the appearance -of Proclus, its name will henceforth call up -to your mind an image as brilliant as if it -<span class='pageno' id='Page_91'>91</span>had been named ‘Mount Diamond’ or ‘Mount -Amethyst.’”</p> - -<div id='i090' class='figcenter id002'> -<img src='images/i090.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 7. July 2, 1903; Moon’s Age 7.24 Days.</span></p> -</div> -</div> - -<p class='c009'>“Pardon me,” said my friend, “but it was not -of names like those that I was thinking. Observe -how he who named the neighboring <i>Palus Somnii</i>, -‘Marsh of a Dream,’ exhibited an exquisite delicacy -of fancy. It suggests something indefinitely -strange, romantic, imaginative. That unknown -astronomer, unknown at least to me, put a little -of himself, a little of his inmost mind, into the -name, and I thank him for it. I shall never forget -the ‘Marsh of a Dream’ in the moon. It will -haunt my own dreams. I shall be all my life -seeking and never finding its meaning.”</p> - -<p class='c009'>“Since you are in so poetic a mood,” I responded, -“I rejoice that besides its bald facts, its -fireless volcanoes, and its dried-up plains, the -moon possesses many things that can stir the imagination -of the most sentimental observer. But, -in order that we may not wander too far from the -paths of science, let me recall your attention to the -photograph. We have been going over ground already -trodden by returning to the neighborhood of -the <i>Mare Crisium</i>. I shall now lead you back to the -terminator, where we shall find a little that is new. -Still nearly hidden in night we perceive many -great rings on which the sun is beginning to rise, -and four of the most important ranges of mountains -are coming into view. One of these, on the -<span class='pageno' id='Page_92'>92</span>southern border of the <i>Mare Serenitatis</i>, is visible -throughout its entire extent. It forms a portion -of the coquettish ornaments with which the -Moon Maiden has decorated her hair, as we shall -see clearly in the next photograph. This range -is named the Hæmus mountains. Near its center, -quite at the edge of the ‘sea,’ is a bright crater -ring, one of the most conspicuous on the moon. -It is called Menelaus.”</p> - -<p class='c009'>“Menelaus?” exclaimed my friend. “Ah, -then Riccioli did not confine his favoritism to the -astronomers and philosophers in putting their -names in the moon. Menelaus, if I remember -my classical reading correctly, was the husband -of Helen of Troy.”</p> - -<p class='c009'>“Yes, the brother of Agamemnon himself. -You must admit that Riccioli occasionally felt -his imagination a little awakened. He was not -altogether destitute of the spirit of poetry.”</p> - -<p class='c009'>“But did he also put Helen in the moon?”</p> - -<p class='c009'>“I am sorry to say that he did not. It would -have been a very suitable abode for her. However, -if you like, you may recognize Helen in the -Moon Maiden herself.”</p> - -<p class='c009'>“Thank you, that will be, indeed, an unexpected -pleasure.”</p> - -<p class='c009'>“Meanwhile allow me to point out to you that -there is a curious light streak, very faintly shown -in the photograph, which crosses the <i>Mare Serenitatis</i> -<span class='pageno' id='Page_93'>93</span>from Menelaus to the opposite shore, and reappears -more distinctly, on the lighter-colored -plain toward the north. This streak comes all -the way from a great ring mountain named Tycho -in the southern part of the moon. It is more than -2,000 miles long, and is one of the greatest mysteries -of the lunar world. Tycho, which lies just -on the sunrise line, is not well seen in this photograph. -It has a great number of these strange -streaks or rays proceeding from it in all directions. -We shall study them in one of the photographs -which are to come. One word in regard -to the plain north of the <i>Mare Serenitatis</i> of -which I have just spoken. It, too, has a name -that is calculated to appeal to your lively imagination. -It is called the <i>Lacus Somniorum</i>, -which if my knowledge of Latin is correct, means -‘Lake of the Sleepers.’”</p> - -<p class='c009'>“Then your old friend Riccioli certainly did -not bestow the appellation.”</p> - -<p class='c009'>“No, it was one of his more fanciful, or, if -you prefer, more poetical predecessors, perhaps -the same who imagined the ‘Marsh of a Dream.’”</p> - -<p class='c009'>“Oh, that gives me another reason to think -of him with admiration and gratitude. He, at -least, had a soul that rose above mere prosaic -facts.”</p> - -<p class='c009'>“Perhaps. But do not think too lightly of -the facts of the moon. After all the human mind -<span class='pageno' id='Page_94'>94</span>must base itself upon the solid ground of fact. -Without that we should become mere dreamers, -and be suited only to inhabit your favorite -‘Marsh.’”</p> - -<p class='c009'>“The other mountain ranges of which I have -spoken,” I continued, “are faintly distinguishable -eastward from the <i>Mare Serenitatis</i>. They are -the Apennines, the Caucasus, and the Alps. But -perhaps we had better turn at once to photograph -No. 8 where they are much more clearly seen, because -the sunrise there has advanced a couple -of hundred miles farther east.”</p> - -<p class='c009'>“But, dear me, how slowly the sun rises on -the moon! Was this photograph taken a day -later than the other?”</p> - -<div id='i094' class='figcenter id002'> -<img src='images/i094.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 8. August 31, 1903; Moon’s Age 9.22 Days.</span></p> -</div> -</div> - -<p class='c009'>“Almost exactly two days later. When it -was made the moon was nearly nine and a -quarter days old, and its age at the time No. 7 was -made was only seven and a quarter days. But, -owing to the effects of libration, an explanation -of which I have put into a note for your private -reading when you feel like it, [see p. <a href='#Page_57'>57</a>, footnote], -the difference of phase amounts to less -than two days. You are right, however, in remarking -that sunrise is a very slow process on -the moon. It requires about two weeks to pass -from the western side of the moon to the eastern -side, and both day and night at any point on the -moon last about a fortnight. This results from -<span class='pageno' id='Page_95'>95</span>the fact that, as I have told you, the moon does -not turn rapidly on its axis like our own globe, -but keeps always the same side directed toward -the earth. Accordingly, a lunar day and night -are together about a month long.”</p> - -<p class='c009'>“And was it so when, as I must persist in believing, -there were inhabitants on the moon?”</p> - -<p class='c009'>“Probably, although it may have been shorter -then. The consequences of these excessively long -days and nights would be very serious to beings -fashioned upon the terrestrial plan. In the practical -absence of an atmosphere the heat of the -sun’s rays, pouring down without interruption -and without the intervention of any clouds or -vapors for fourteen days at a time, must be -simply overpowering. And then, during the -equally long night that ensues, the radiation into -open space must quickly leave the surface of the -moon exposed to the most frightful degree of -cold, comparable with the absolute zero of empty -space!”</p> - -<p class='c009'>“But think, what a merciless environment you -are picturing for my inhabitants of the moon. -Please do not forget that I insist that their comfort -shall be considered.”</p> - -<p class='c009'>“Oh, as for that, you know you were content -a little while ago to relegate your inhabitants to -a remote period in the past, after the volcanic -fury of the lunar world had ceased, and before -<span class='pageno' id='Page_96'>96</span>its present airless and waterless condition had -supervened. Possibly at that time things were -not so uncomfortable for them. They may have -had clouds to temper the sunshine, rains to cool -the days and dews the nights, and shady parks -like yours for philosophic and scientific contemplation.”</p> - -<p class='c009'>“Do not forget the poets.”</p> - -<p class='c009'>“Certainly not. But is not the moon herself -the very spirit of poetry? What in nature is -more poetical in its suggestions than the moon -wading through fleecy clouds on a serene summer’s -night? But pardon me, we are forgetting -my mountains, upon which I insist as strongly -as you do upon your inhabitants. The mountains -have this advantage that they are very real, -and no exercise of the imagination is required -to bring them clearly before us. In photograph -No. 8 they are all visible. The Apennines, the -greatest of them, start from the eastern end of -the <i>Mare Serenitatis</i>, and run in a slightly curved -line southeastward, a distance of about 450 miles. -They form the singular ornament which the Moon -Maiden (or shall we now call her Helen of Troy?) -wears upon her forehead. Turn the photograph -upside down so that the moon is presented as the -naked eye sees it in the sky, and you will find that, -although he aimed only to be scientifically exact -and to exclude everything but the real facts, Mr. -<span class='pageno' id='Page_97'>97</span>Wallace has produced an excellent picture of this -wonderful face in the moon.”</p> - -<p class='c009'>“But what is that face?”</p> - -<p class='c009'>“It is humanity projected upon the moon. It -is a lesson on the powers of the imagination. We -perceive a certain collocation of mountains, peaks, -and plains on the disk of the moon, and our fancy -sees in them a human likeness. We should congratulate -ourselves that we are able to do this. -It is a kind of proof of superiority. Many brute -animals do not recognize even their own likenesses -in a mirror, much less in a picture. But the Moon -Maiden is perhaps as real as your inhabitants.”</p> - -<p class='c009'>“I am not prepared to confess that yet.”</p> - -<p class='c009'>“Very well, let us go on. The lunar Caucasus -is the broader, but shorter, range of mountains -at the northeastern corner of the <i>Mare Serenitatis</i>, -and the Alps extend eastward from the Caucasus -to a conspicuous dark oval close to the terminator, -which is one of the most remarkable formations -on the moon, and which, when we come to study -it in one of the larger photographs, will probably -interest you deeply because it is one of the places -where recent studies have discovered indications -of what may possibly be some form of lunar life. -I wish now to direct your attention to the central -and upper parts of the photograph. Running -downward from the south, a little west of the terminator, -you will perceive a double row of immense -<span class='pageno' id='Page_98'>98</span>rings and ring plains. They are not only -remarkable individually, but quite as remarkable -for their juxtaposition in two long ranges. -Among them, in the westernmost row, are three -or four whose names you may remember—Maurolycus, -Stöfler, Aliacensis and Werner. Still -larger ones are included in the eastern row, the -largest of all being at the bottom. It is rather -a hexagon than a circle. It is 115 miles in diameter, -and the flat plain inside the bordering -mountains contains about 9,000 square miles. By -close inspection you will perceive a small crater -mountain near the northwestern side. This immense -walled plain is named Ptolemæus after a -great astronomer of antiquity, the author of the -Ptolemæic system, which treated the earth as the -center of the universe.</p> - -<p class='c009'>“Still more interesting are the things visible -farther south. You cannot fail to remark a very -beautiful ring, a perfect circle, brightly illuminated -on the eastern side, and having a bright point -symmetrically placed in the exact center. It is -named Tycho, after another great astronomer, -and is generally regarded as the most perfect -crater ring on the moon. It is 54 miles in diameter, -and its walls are about 17,000 feet high on -the inner side, more than a thousand feet higher -than Mt. Blanc, the giant of the terrestrial Alps. -Its central mountain is 5,000 feet high. The most -<span class='pageno' id='Page_99'>99</span>remarkable thing about Tycho is the vast system -of ‘rays’ or bands which seem to shoot out from -it in all directions, traversing the surface of the -moon, north, south, east, and west for hundreds -of miles, and never turning aside on account of -any obstacle. They lie straight across mountains, -valleys, and plains. We have already seen one -of them, the largest of all perhaps, crossing the -<i>Mare Serenitatis</i> and the <i>Lacus Somniorum</i>, in -the northern hemisphere of the moon. Nobody -knows exactly what these rays mean or what they -consist of. We shall from this time on see them -in all the photographs that we examine, and later -I shall have more to say about them, and the -speculations to which they have given rise.</p> - -<p class='c009'>“About half way between Tycho and the south -pole of the moon, you will see an enormous irregular -plain, with lofty broken walls, interrupted -by a number of crater rings. Several similar -rings also appear in the interior of the plain. If -Tycho is the most perfect in form of the lunar -crater rings, this great inclosure, which is named -Clavius, is the finest example of the walled valleys. -It is more than 140 miles across, and covers an -area of not less than 16,000 square miles. Two of -the rings within it, which seem so small in comparison, -are 25 miles across. A smaller walled -plain, yet one of really immense size, is seen half -way between Tycho and Clavius, and farther from -<span class='pageno' id='Page_100'>100</span>the terminator than either of them. This is Maginus, -and it possesses the peculiarity that at full -moon it practically disappears!”</p> - -<p class='c009'>“But how can that be possible? I see nothing -behind which it can be hidden.”</p> - -<p class='c009'>“It is the sunlight that hides it. You must -have noticed already that the rings and mountains -are best seen when at no great distance from the -terminator, because there the sunlight strikes -across them at a low angle, and their shadows are -thrown sharply upon the adjoining slopes and -levels. Look at the western part of the moon in -the photograph before us. Many of the huge -rings and walled plains that were so striking in -appearance when the sun was rising upon them -are now barely visible. Langrenus and Petavius, -for instance, have become no more than whitish -blotches, and even Theophilus is no longer conspicuous. -The reason is because when the sunlight -falls vertically upon any part of the moon -there are no shadows there, and without shadows -there can be no appearance of relief. Then the -mightiest mountains are almost lost from sight -in the universal glare. The same thing would -be apparent if you were suspended above the -earth at a great height in a balloon and looking -down upon the tops of the snowclad Rockies. -Without shadows serving to reveal their true -character and to throw their outlines in silhouette -<span class='pageno' id='Page_101'>101</span>upon the adjacent plains, they would resemble -only white spots and lines on the generally darker -expanse of the continent. But Maginus is an -extreme case. Owing to the relatively small elevation -of its walls, and their broken-up state, and -owing also, probably, to a similarity of color between -the mountain ring and the inclosed plain, -when the light is vertical upon them, as at the -time of Full Moon, they blend together and become -barely distinguishable from one another, and -from the surrounding surface of the moon.</p> - -<p class='c009'>“Take now photograph No. 9. The age of the -moon here is actually less than it was in the photograph -that we last examined, yet, in consequence -of libration, which has caused the moon, -in effect, to roll a little to one side, the sunlight -is farther advanced toward the east, and we see -many features of the lunar world that before had -not yet emerged from night. Clavius you will notice -is much more fully illuminated. See how -distinctly the shadow of its vast western wall -is cast upon the floor of the valley within, while -the opposite eastern wall with its immense cliffs -and precipices glows in full sunshine, its shadow, -thrown toward the east, blending with the darkness -of night still covering that side of the moon. -Southeast of Tycho, which is beautifully shown -here, two other great walled plains have come into -view. The uppermost of these is Longomontanus -<span class='pageno' id='Page_102'>102</span>and the other Wilhelm I. For a considerable -distance below these (toward the north) the surface -continues broken with rings and craters, but -at length these give place to a dark, level expanse. -This is a part of the <i>Mare Nubium</i>, or ‘Sea of -Clouds.’”</p> - -<p class='c009'>“Not quite so romantic a name as some of the -others,” remarked my friend, “but still I think -I can be sure that Riccioli had nothing to do with -the selection. There is certainly something poetic -in the idea of a sea of clouds.”</p> - -<p class='c009'>“It is a very beautiful region when examined -with a telescope,” I continued, “and its mountainous -shores contain many interesting formations. -Farther north, you will observe, near the terminator, -and apparently lying in the midst of the -<i>Mare Nubium</i>, a large ring, as perfect in form as -Tycho itself. This is a very famous object, and -it bears the name of the great astronomer Copernicus, -who overthrew the Ptolemæic system and -established in its place the true idea of the solar -system, namely, that the sun is its center, while -the earth and the other planets revolve as satellites -around him.”</p> - -<p class='c009'>“Surely,” said my friend, “Copernicus deserved -to have his name placed in the moon, and -very conspicuously, too.”</p> - -<div id='i102' class='figcenter id002'> -<img src='images/i102.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 9. August 2, 1903; Moon’s Age 8.97 Days.</span></p> -</div> -</div> - -<p class='c009'>“It could not have been made more conspicuous,” -I replied, “for the situation of the great -<span class='pageno' id='Page_103'>103</span>ring mountain called Copernicus, in the midst of -an immense level expanse, makes it one of the -most marked features of the lunar world. Copernicus -is the subject of one of the larger photographs -that we are going to examine later, and I -reserve a description of its peculiarities. North -of Copernicus you will observe apparently a continuation -of the <i>Mare Nubium</i>. But it is really -another ‘sea’ that we are looking upon there, the -<i>Mare Imbrium</i>, ‘Sea of Rains.’ The baylike -projection that runs out into the bright highlands -west of Copernicus bears the name of the -<i>Sinus Medii</i>, ‘Central Gulf,’ and the one just below -it is the <i>Sinus Æstuum</i>, ‘Gulf of Heats,’ -which is certainly suggestive of dog days on the -moon. Observe that the <i>Sinus Æstuum</i> merges -on the west with a dark, oval area, which is called -the <i>Mare Vaporum</i>, ‘Sea of Mists.’ It is one of -the darkest districts on the moon. If you will -now turn the photograph upside down you will -find that the <i>Sinus Medii</i> constitutes the dark eye -of the Moon Maiden, while the <i>Sinus Æstuum</i> -and the <i>Mare Vaporum</i> form that portion of her -hair which droops upon her forehead.”</p> - -<p class='c009'>“Why not frankly call it frizzed?”</p> - -<p class='c009'>“Because I feared that you would not consider -that a sufficiently poetic term.”</p> - -<p class='c009'>“But I find poetry enough in the names ‘Gulf -of Heats’ and ‘Sea of Mists.’ My admiration -<span class='pageno' id='Page_104'>104</span>for the man who could think of such appellations -continually increases.”</p> - -<p class='c009'>“Then please reverse the photograph, for we -must not lose ourselves in dreams. You will -notice that the range of the lunar Apennines runs -between the <i>Mare Vaporum</i> and the <i>Sinus Æstuum</i> -on one side, and the <i>Mare Imbrium</i> on -the other. The entire chain of the Apennines -is beautifully shown here. They are exceedingly -steep on the side facing the <i>Mare Imbrium</i>, and -gigantic peaks standing upon their long wall cast -immense shadows over the ‘sea.’ Their southwestern -slopes are comparatively gentle, rising -gradually from the level of the <i>Mare Vaporum</i>. -At their upper or southern end, in the direction -of Copernicus, they suddenly terminate with a -beautiful ring, which is called Eratosthenes. -This is a fine example of the disk or cup shape -of the lunar volcano. The bottom of Eratosthenes -lies 8,000 feet below the level of the surrounding -<i>Mare</i>, while peaks on its wall are as much as -15,000 or 16,000 feet in height. Between the -lower end of the Apennines and the upper end of -the Caucasus Mountains a strait opens a broad, -level way between the <i>Mare Imbrium</i> and the -<i>Mare Serenitatis</i>. On one of the large photographs -these two ‘seas’ and the strait connecting -them are represented in all their picturesque details, -as you will see when we come to study them. -<span class='pageno' id='Page_105'>105</span>I promise you at that time a free rein to your -imagination and plenty of room for its flights. -On the northern border of the <i>Mare Imbrium</i> and -close to the terminator we see once more the remarkable -oval valley to which I referred when -pointing out the lunar Alps, and which bears the -name of Plato. I call your attention to it and -also, again, to Copernicus, in order that you may -compare their appearance here with that which -they present in the next photograph, taken when -the moon’s age was eleven and three-quarter -days.”</p> - -<div id='i106' class='figcenter id002'> -<img src='images/i106.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 10. November 30, 1903; Moon’s Age 11.78 Days.</span></p> -</div> -</div> - -<p class='c009'>We hereupon turned to photograph No. 10.</p> - -<p class='c009'>“Now,” I continued, “observe the difference -that some two days’ advance of the sunlight has -produced. Plato is far within the illuminated -part of the disk, and it looks darker than before. -Copernicus, on the other hand, which appeared -as a sharp ring with one border dark when it -was near the sunrise line, has now become a round, -white spot, somewhat darker in the center, with -a great grayish splatter surrounding it upon the -surface of the <i>Mare</i>. In the meantime, over -nearly the whole extent of the <i>Mare Imbrium</i> the -sun has risen and two other <i>mares</i> have made -their appearance, one of which, extending across -half the width of the eastern hemisphere, might -be called the Pacific Ocean of the moon, if it had -any water. It is named the <i>Oceanus Procellarum</i>, -<span class='pageno' id='Page_106'>106</span>the ‘Ocean of Tempests,’ while at its southern -extremity a very dark nearly circular expanse, -inclosed with mountains, bears the name of the -<i>Mare Humorum</i>, ‘Sea of Humors.’”</p> - -<p class='c009'>“Evidently the astronomer who bestowed -that name was not in a joking mood else he would -surely have called it the ‘Sea of Humor.’”</p> - -<p class='c009'>“No, apparently he was in deep earnest. But -what kind of humors he was thinking of I cannot -tell. Perhaps the name occurred to him because -the <i>Mare Humorum</i> is the darkest of all the great -levels on the moon. It is very conspicuous to -the naked eye at Full Moon. You will perceive -that Tycho has now become the most prominent -of all the rings on the moon. It will maintain -this distinction and continue to gain in conspicuousness -up to the time of Full Moon. Seen as -we now see it, Tycho manifestly merits the appellation -sometimes bestowed upon it of the ‘metropolitan -crater of the moon.’ Notice how bright -the mysterious bands radiating from it have become. -The higher the sun rises upon them the -more brilliantly they glow, almost as if they were -streaks of new-fallen snow. They spread over -the whole of the southwestern quarter of the -moon, hiding rings and mountains with their -brightness. One very notable ray runs down into -the <i>Mare Nubium</i>, and a fainter one parallel with -it produces the semblance of a long, walled way.</p> - -<p class='c009'><span class='pageno' id='Page_107'>107</span>“The South Pole of the moon lies in the midst -of a marvelously upheaved and tumbled region, -where one huge ring is seen breaking into another -on every hand. One of these rings, named Newton—it -lies just on the upper edge of the disk, -south of Clavius—surrounds the deepest known -depression on the moon. Its bottom sinks to a -depth of 24,000 feet below the highest point on -the wall. This gigantic hole is so profound that, -situated where it is, close to the pole, where the -sun can never rise very high, its depths remain -forever buried in night. It is the very ideal of -a dungeon, for if you were imprisoned at the bottom -you would never see either the sun or the -earth.”</p> - -<p class='c009'>“You make me shudder! Truly, after all, the -moon appears to be a world filled with dreadful -things. Who would ever imagine it, seeing how -serene and beautiful she is in a calm night?”</p> - -<p class='c009'>“Yet is there not a kind of beauty even in -those things, like the abyss of Newton, which appall -you only when you know the real facts about -them? There is a certain grace in their shapes -and outlines, and a great attraction for the eye -in their contrasts of light and shadow. It is the -same sort of attraction which we find in such terrestrial -scenes as the Yosemite Valley viewed -from Inspiration Point, or the awful depths and -chasms of the Grand Cañon of the Colorado. -<span class='pageno' id='Page_108'>108</span>The presence of man and his works is not always -essential in order to fix our attention upon the -wonders of nature. Their very grandeur exalts -us until we forget our little race and its ephemeral -achievements.”</p> - -<p class='c009'>“Still, I hope that you will show me something -on the moon less awe-inspiring and suited to -awaken more quiet thoughts, and especially to reassure -me concerning my lunarians, as I suppose -you would call them.”</p> - -<p class='c009'>“You shall not be kept long in expectation. -Turn your eyes once more to the <i>Mare Imbrium</i>. -You will observe that its northern shore consists -of a series of curves, each terminating with a -promontory projecting into the sea. When looking -at it I am often reminded of an entrancing -view which I once enjoyed from the summit of Mt. -Etna over the island of Sicily. From that great -elevation nearly the whole eastern and southeastern -coast of the island was visible as upon a map. -The indented shore stretched away in long, graceful -curves, where the blue Mediterranean contrasted -sharply with the yellow sands, and the -eye, wandering from Catania to Syracuse, was -enchanted with the beauty of those geometric -lines. But the winding coast of the <i>Mare Imbrium</i> -is far longer than the shores of Sicily, and -the mountains and cliffs bordering it are more -wonderful than any corresponding scenes on the -<span class='pageno' id='Page_109'>109</span>earth. I wish, particularly, to have you look at -the easternmost of the indentations on the northern -side of the <i>mare</i>. It bears a designation -that must surely please your imagination. It is -the <i>Sinus Iridum</i>, ‘Gulf or Bay of Rainbows.’”</p> - -<p class='c009'>“I recognize the work of my old friend the unknown -astronomer. Verily he had a poetic soul! -And he has written his poem on the chart of the -moon, for those to read who can.”</p> - -<p class='c009'>“It is a charming landscape that the telescope -reveals there,” I said, “even though no rainbows -are visible.”</p> - -<p class='c009'>“But you will not deny that they may once -have spanned that bay and its shores with their -exquisite arches?”</p> - -<p class='c009'>“No, I shall not deny so pleasing a possibility. -I will only say that it lies beyond the ken, -and even outside the field, of science.”</p> - -<p class='c009'>“Then I regard it as fortunate that <i>he</i> was -not too exclusive in his devotion to science, for -then he could never have seen the rainbows with -the eye of fancy, and your charts would not have -been adorned with so delightful a name.”</p> - -<p class='c009'>“Let me tell you about this bay or gulf,” I -said, tapping the photograph to recall her from -her reverie. “You observe that it terminates at -each end with a promontory. That at the western -end is named Laplace, and the other Heraclides. -The latter is the more picturesque. If ever you -<span class='pageno' id='Page_110'>110</span>have an opportunity to see the moon with a good -telescope do not fail to look at the promontory -of Heraclides, for if you are fortunate in the -choice of the time of observation when the setting -sun is throwing its shadow over the adjoining -‘bay,’ you will find that the serrated outlines of -the promontory represent, in a very striking manner, -the profile of a woman, more sharply defined -than the face of our familiar Moon Maiden, but a -mere miniature in relative size. The shores of -the <i>Sinus Iridum</i> are bordered with high cliffs, -behind which rise the peaks of a mighty mountain -mass. Just back of the center of the great -bowed shore of the ‘bay’ appears, in the photograph, -a small, bright crater ring. This bears the -name of Bianchini. It is a lunar volcano, 18 -miles in diameter, rising out of the midst of many -ranges of nearly parallel hills and mountains, the -general direction of which corresponds with that -of the shore of the ‘bay.’ If there is any place -on the moon where one is tempted to think that -the scenes of a living world might once have been -witnessed it is the <i>Sinus Iridum</i> and its neighborhood. -Its latitude is between 40° and 50° -north, corresponding with the most thickly populated -zone of our own globe. The surface of the -‘bay’—once its bottom, if we admit that it was -ever filled with water—is gently undulating, with -winding ridges that suggest the action of tides -<span class='pageno' id='Page_111'>111</span>and currents in sweeping to and fro deposits of -sand and gravel, and piling them in long rows of -bars and shallows. One can hardly help picturing -in the mind’s eye waves breaking on the curving -beach and dashing against the projecting -rocks of the promontories; a white city seated -just at the center of the shore of the ‘bay,’ near -Bianchini, like Naples at the feet of Vesuvius; a -rich vegetation covering the slopes of the mountain -valleys, and romantic sails dotting the ‘bay’ -and the neighboring ‘sea.’”</p> - -<p class='c009'>“I am very glad to observe,” interrupted my -friend, “that you are not hopelessly prejudiced -against my opinion that the moon has not always -been ‘dead,’ as you call it.”</p> - -<p class='c009'>“I am so far from it,” I replied, “that I am -half disposed to admit that she is not altogether -dead even yet. But it is my duty to keep you as -close as possible to the known facts. We shall -see the <i>Mare Imbrium</i> and the neighborhood of -the ‘Bay of Rainbows’ again. Meanwhile, suppose -we turn to the next photograph of the series, -No. 11. The age of the moon here is about thirteen -days. She is fast approaching the phase of -Full Moon. The first thing to which I would -direct your attention now is the exceedingly brilliant -point of light which has come into view -near the terminator, a little north of east where -the <i>Mare Imbrium</i> merges into the <i>Oceanus Procellarum</i>. -<span class='pageno' id='Page_112'>112</span>In several ways this is the most noteworthy -object on the moon. It led the famous -English astronomer, Sir William Herschel, to believe -that he had seen an active volcano on our -satellite. He naïvely wrote in his notebook on -a certain occasion: ‘The volcano glows more -brightly to-night!’ Yet it is no more active than -the other craters and crater rings in the lunar -world. It is only extraordinarily, almost incredibly -brilliant—by far the most dazzling point on -the moon. It is a ring mountain, and is named -Aristarchus. It has a near neighbor, barely visible -in this photograph, close by toward the east -named Herodotus. Herodotus is by no means remarkable -for brilliancy. The central peak and a -part of the floor and the east wall of Aristarchus -consist of some material—nobody can tell what it -is—which gleams in the sunlight, I had almost -said like diamonds, although that would be an exaggeration. -There are three or four other crater -rings on the moon, including Proclus, which are -also very brilliant, but not one of them can be regarded -as a rival of Aristarchus. Its power of -reflection is so great that it is even visible with a -telescope in the lunar night, when the only light -of any consequence that reaches it is that sent -from the earth. It was, indeed, this fact which -misled Herschel. He saw Aristarchus shining on -the night side of the moon, and naturally thought -<span class='pageno' id='Page_113'>113</span>that only the fires of an active volcano could have -rendered it thus visible.”</p> - -<div id='i112' class='figcenter id002'> -<img src='images/i112.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 11. December 1, 1903; Moon’s Age 12.98 Days.</span></p> -</div> -</div> - -<p class='c009'>“And are you sure that he was mistaken?”</p> - -<p class='c009'>“Positively. There is no fire in Aristarchus, -and has been none for ages.”</p> - -<p class='c009'>“But why do not astronomers undertake to -find out what it is that makes Aristarchus so -brilliant, then?”</p> - -<p class='c009'>“They have almost no data to go upon. You -should be informed that even the greatest telescopes, -with their highest powers, are unable to -bring the moon within less than an apparent distance -of say forty miles. At such a distance it -is manifestly impossible to tell of what a lunar -formation consists. We cannot analyze the moon -with the spectroscope as we can the sun and the -stars, because she does not shine with her own inherent -light. We can only infer that a large part -of the substance of Aristarchus consists of something -which reflects a very great proportion of the -light that falls upon it. If a mountain on the -earth were composed of a vast mass of crystals, -or of bare polished metal, we might expect it to -present, when seen from the moon, some such -appearance as we notice when we look at -Aristarchus.</p> - -<p class='c009'>“In this photograph the <i>Sinus Iridum</i>, having -the sun higher above it, is more brilliantly illuminated -than in No. 10. Particularly you will -<span class='pageno' id='Page_114'>114</span>notice the brightness of the line of cliffs along -its eastern curve, terminating at the promontory -of Heraclides.”</p> - -<p class='c009'>“That is the promontory which presents the -profile of a woman’s face, if I recall correctly -what you told me.”</p> - -<p class='c009'>“Yes. Please observe also that the oval of -Plato is as dark as ever, while Copernicus has, -if possible, increased in brightness, and the great -splatter of broken rays around it seems to have -extended farther over the surrounding maria. -Almost directly east of Copernicus, in the -<i>Oceanus Procellarum</i>, appears a much smaller -crater ring, Kepler, which resembles a miniature -of Copernicus because it, too, is encircled with a -kind of corona of short, bright rays. Copernicus, -Kepler, and Aristarchus mark the corners of a -large triangle. Speaking of rays recalls us to -Tycho. You will see that, as I told you, this wonderful -formation grows in relative prominence when -the period of Full Moon approaches. Its ringed -wall and central mountain are obscured by their -own brilliance, while the gigantic system of bright -bands, or rays, which have their center of origin -at Tycho, is gradually becoming the master feature -of the bright part of the moon.</p> - -<p class='c009'>“I have told you that the <i>Mare Humorum</i>, -which is very sharply defined in the picture before -us, is the darkest of all the level areas that -<span class='pageno' id='Page_115'>115</span>go under the name of ‘seas.’ It is not, however, -the darkest <i>spot</i> on the moon. There are several -places where the surface appears, at times, much -duskier than in any part of the <i>Mare Humorum</i>. -Three or four of these are clearly discernible in -this photograph. They lie westward from Copernicus -in the <i>Sinus Medii</i>, the <i>Sinus Æstuum</i>, and -the <i>Mare Vaporum</i>. Their dusky hue strikes the -eye at once. They give the impression of sink -holes. No special name is attached to them, but -they must have been evident to the first observers, -with the smallest telescopes, and it is rather surprising -they should have escaped special designation -on the lunar charts. A fact which will -especially interest you is that some observers look -upon these and other dusky areas on the moon -as being, possibly, indications of the existence of -some kind of vegetation there.”</p> - -<p class='c009'>“But if there is vegetation there may be other -kinds of life also, may there not?”</p> - -<p class='c009'>“Ah, I have not said positively that there <i>is</i> -vegetation, but <i>if</i> there is then your conclusion as -to other life may be correct. Glance next at the -upper part of the disk along the terminator. -Two or three broad oval rings have come into -view there. The largest of these with its long -eastern wall lying exactly on the line between -day and night is an extremely interesting formation, -bearing the name of Schickard. The plain -<span class='pageno' id='Page_116'>116</span>within the ring is almost large enough to have -been called a ‘sea’ or at least a ‘lake.’ It is -about 134 miles in diameter, and is in reality -much more nearly circular than it appears to be. -Like all similar formations situated near the -‘limb’ of the moon, by which we mean the edge -as viewed from the earth, it is greatly foreshortened -by perspective. The scale of the photograph -is, unfortunately, not large enough to reveal -an unique thing in the immediate neighborhood -of Schickard, toward the southeast. I refer -to what, as far as its telescopic appearance goes, -might be described as an enormous bubble—a -bubble 54 miles in diameter. Unlike the other -formations the surface of this singular ring is -elevated above the general level of the moon. -When we come to examine it in detail it hardly -answers, perhaps, to my designation of a bubble, -since the edges are a little higher than the center, -giving it the form of a shallow dish. If we could -visit it we should find on approaching that we -were climbing the slopes of what would seem to -be a chain of low mountains, and on reaching the -summit we should see before us an elevated circular -plain, sinking gradually toward the middle. -Filled with water it would form a shallow lake -lying on the top of a broad, flat mountain. There -is nothing else quite like it on the moon and certainly -nothing on the earth.”</p> - -<p class='c009'><span class='pageno' id='Page_117'>117</span>“It must have been a great curiosity in the -days when the moon was inhabited, and I suppose -that scientific ‘lunarians’ organized expeditions -to explore it.”</p> - -<p class='c009'>“Perhaps, if you choose to regard it in that -way. Now look again at the <i>Mare Humorum</i>. -You perceive that its eastern side is lined with -mountains and crater rings, while near the center -of the northern border there is a conspicuous ring -with a bright line running from the southern -edge to the center. This is one of the most beautiful -of lunar formations, and is named Gassendi. -It is a favorite object for those who study the -moon with telescopes on account of the great variety -and singularity of the details visible within -the ring. When you become a selenographer and -possess your own telescope you will find few -things more interesting to study than Gassendi.</p> - -<p class='c009'>“Next let us take up photograph No. 12. -Here the moon is once more a little ‘older’ than -before, and the sunrise line has again advanced -a little eastward. This advance does not appear -so rapid when the terminator is near the moon’s -limb, because, on account of the rounding away -of the lunar globe, the illuminated surface is foreshortened -from our point of view on the earth. -In this photograph you perceive that the wonderful -shining mountain Aristarchus has become -even brighter than it was before, or at least it is -<span class='pageno' id='Page_118'>118</span>more conspicuous on account of the appearance -of what seems to be a short ray shooting out from -it in a southeasterly direction. There is also a -light spot just below it which is caused by a little -mountain group called the Harbinger Mountains. -The bright ray connects Aristarchus with its -neighbor Herodotus, of which I spoke a little -while ago. There is a very remarkable feature -of the moon here, not shown in the photograph, -but to which I must briefly refer. It is an enormous -cleft, or crack, or, if you please, cañon, -which starts from Herodotus, whose northern -wall seems to have been broken through to give -passage to it, and goes winding across the surface -of the <i>Oceanus Procellarum</i> with several sharp -turns and angles for a total distance of nearly a -hundred miles. What produced this remarkable -chasm on the moon it is difficult to say. Some -have suggested that it may once have been the -bed of a river, but there are many serious objections -to that view. Nevertheless, there seems to -be little doubt that if we were to visit the moon -we should find, in many ways, a striking resemblance -between this prodigious cañon and that of -the Colorado River.”</p> - -<p class='c009'>“And are not all these things so ancient, as -far as you can tell, that, like the terrible volcanic -rings, they might have been formed before the appearance -of inhabitants upon the moon?”</p> - -<div id='i118' class='figcenter id002'> -<img src='images/i118.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 12. September 4, 1903; Moon’s Age 13.27 Days.</span></p> -</div> -</div> - -<p class='c009'><span class='pageno' id='Page_119'>119</span>“They certainly seem to be very ancient, and -I cannot deny the <i>possibility</i> of what you say.”</p> - -<p class='c009'>“Very well, then, I, for my part, am convinced -that curious eyes, filled with the light of intelligence, -have peered down from the verge of that -chasm into its fearful depths. If you will not -permit me this flight of imagination I shall refuse -to take any further interest in the moon.”</p> - -<p class='c009'>“Oh, I should not think of refusing. Imagine -what you will, and draw your own inferences, only -remembering that they are not supported by <i>ascertained</i> -facts, and probably never will be. Yet -for all that they may have an element of truth.”</p> - -<p class='c009'>“Pardon me for saying that your astronomical -science, as far as it concerns the moon at -least, does not seem to me quite satisfying. You -are not bold enough in drawing conclusions.”</p> - -<p class='c009'>“On the contrary many astronomers think -that some of their brethren are altogether too -bold in that respect. However, it must be freely -confessed that astronomical science, except perhaps -in its mathematics, is not satisfying even -to those who have created it. Nobody would rejoice -more sincerely than the astronomer at the -discovery of evidence of the former, or even the -present, habitability of the moon. It is surely a -great disappointment that we have not been able -to settle so apparently simple a question in regard -to our nearest neighbor in the sky.”</p> - -<p class='c009'><span class='pageno' id='Page_120'>120</span>“Then if I were a multimillionaire I should -certainly devote several of my millions to the construction -of a telescope great and powerful -enough to reveal so interesting a secret.”</p> - -<p class='c009'>“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 <i>see</i> -inhabitants on the moon, even if they existed.”</p> - -<p class='c009'>“Not if it magnified the moon a million -times?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“That is not much. I am sure I can see -people at that distance.”</p> - -<p class='c009'>“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, -<span class='pageno' id='Page_121'>121</span>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 -<span class='pageno' id='Page_122'>122</span>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 <i>Mare Serenitatis</i> -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 -<span class='pageno' id='Page_123'>123</span>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 <i>mares</i> are clearly -visible. On the right the <i>Mare Crisium</i>, the <i>Mare -Fœcunditatis</i>, the <i>Mare Nectaris</i> and the <i>Mare -Tranquillitatis</i>; in the center, above, the <i>Mare -Serenitatis</i>; on the left the <i>Mare Imbrium</i>, the -<i>Mare Vaporum</i>, the <i>Mare Nubium</i>, the <i>Mare -Humorum</i>, and the <i>Oceanus Procellarum</i>. The -two bright spots on the right, lower than the <i>Mare -Fœcunditatis</i>, are Petavius and a neighboring -ring. Vendelinus forms a less brilliant spot at -the western edge of an extension of the <i>Mare -Fœcunditatis</i>, and Langrenus is distinctly seen -on the western shore of the main body of that -<i>mare</i>. Proclus and the remarkable diamond of -the ‘Marsh of a Dream’ are very plain just under -the large oval of the <i>Mare Crisium</i>. The -mountains and cliffs encircling the <i>Mare Imbrium</i> -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 -<i>Mare Frigoris</i>, whose eastern end merges into the -broad <i>Oceanus Procellarum</i>. Aristarchus appears -as a very bright point in this ‘ocean,’ and far -<span class='pageno' id='Page_124'>124</span>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.</p> - -<div id='i122' class='figcenter id002'> -<img src='images/i122.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 13. September 5, 1903; Moon’s Age 14.40 Days.</span></p> -</div> -</div> - -<p class='c009'>“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 -<span class='pageno' id='Page_125'>125</span>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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“But,” I said, “even if I grant what you wish, -you must admit that the greatest tragedy of all -succeeded.”</p> - -<p class='c009'>“What do you mean?”</p> - -<p class='c009'>“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?”</p> - -<p class='c009'>“But that disappearance was gradual, was -it not?”</p> - -<p class='c009'>“Very likely it was, if it depended upon the -slow withdrawal of the atmosphere and water.”</p> - -<p class='c009'>“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. -<span class='pageno' id='Page_126'>126</span>I think I have read that some of your <i>savants</i> -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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>By this time the afternoon had waned and the -trees were lengthening their shadows upon the -lawns of the park.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_127'>127</span>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.”</p> - -<p class='c009'>“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.”</p> -<div class='pbb'> - <hr class='pb c005' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c002'> - <div><span class='pageno' id='Page_129'>129</span><span class='c019'>III</span></div> - <div class='c000'><span class='c019'>FULL MOON TO OLD MOON</span></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_131'>131</span> - <h2 id='ch03' class='c010'>III<br /> <br />FULL MOON TO OLD MOON</h2> -</div> -<p class='drop-capa0_25_0_7 c020'>AFTER dinner, in the brilliantly lighted -drawing-room, we once more spread out -the photographs on a table.</p> - -<p class='c009'>“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 <i>Mare Crisium</i> and the <i>Mare -Fœcunditatis</i>, which I expect you to recognize -on sight by this time, darkness has already -fallen, and the edge of the moon in that direction -<span class='pageno' id='Page_132'>132</span>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 <i>Mare -Imbrium</i>, and Grimaldi near the bright eastern -limb, are all conspicuous.”</p> - -<div id='i132' class='figcenter id002'> -<img src='images/i132.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 14. August 26, 1904; Moon’s Age 15.65 Days.</span></p> -</div> -</div> - -<p class='c009'>“But look!” exclaimed my friend, putting her -finger upon the photograph. “Here is something -that you have not mentioned at all. I believe -<span class='pageno' id='Page_133'>133</span>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.”</p> - -<p class='c009'>“I confess,” I replied, “that I am not acquainted -with her, and do not even see her. -Please point her out to me.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“Positively I do not see her.”</p> - -<p class='c009'>“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 <i>Mare -Nubium</i>—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 <i>Mare Humorum</i> constitutes her -chignon. She has a short neck, and a humped -back, consisting of the <i>Oceanus Procellarum</i>. -Copernicus resembles a starry badge that she -wears on her breast, and Aristarchus glitters -<span class='pageno' id='Page_134'>134</span>on the inner side of the elbow of her long arm. -The <i>Mare Imbrium</i> 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 <i>Mare Tranquillitatis</i>.”</p> - -<p class='c009'>“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 <i>Mare Crisium</i> and the <i>Mare Fœcunditatis</i>; -for you will see them no more, until another -lunar day has dawned.”</p> - -<p class='c009'>We next picked up photograph No. 15.</p> - -<div id='i134' class='figcenter id002'> -<img src='images/i134.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 15. August 28, 1904; Moon’s Age 17.41 Days.</span></p> -</div> -</div> - -<p class='c009'><span class='pageno' id='Page_135'>135</span>“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 <i>Mare Nectaris</i> -and the <i>Mare Tranquillitatis</i>. 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 <i>Mare -Nectaris</i>, 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 <i>Mare Tranquillitatis</i> -and the <i>Mare Serenitatis</i> it is late afternoon, -and your favorite ‘Marsh of a Dream’ has become -a true dreamland.”</p> - -<p class='c009'>“This oncoming of night,” said my friend, -“seems to me more imposing, and more suggestive -of mystery than was the advance of day.”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_136'>136</span>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 <i>Mare Tranquillitatis</i>. 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 -<span class='pageno' id='Page_137'>137</span>about upon the earth a lowering of temperature -comparable with that which occurs during the -lunar night.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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.</p> - -<p class='c009'>“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 <i>Mare Imbrium</i>. 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 -<span class='pageno' id='Page_138'>138</span><a href='#i138'>photograph No. 16</a>, 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 <i>Mare Nectaris</i>, -and more than half across the <i>Mare Tranquillitatis</i>, -while only the mountain tops along the -western edge of the <i>Mare Serenitatis</i> remain to -indicate its outlines in that direction. Theophilus, -Cyrillus, and Catharina, on the eastern border -of the <i>Mare Nectaris</i>, 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 <i>Mare Serenitatis</i>, 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 -<span class='pageno' id='Page_139'>139</span>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.”</p> - -<div id='i138' class='figcenter id002'> -<img src='images/i138.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 16. August 29, 1904; Moon’s Age 18.62 Days.</span></p> -</div> -</div> - -<p class='c009'>“Then the other side of the moon may not -be very different from the side that is turned -toward us.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“What a pity that so interesting a theory -should have been abandoned!”</p> - -<p class='c009'><span class='pageno' id='Page_140'>140</span>“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.”</p> - -<p class='c009'>“But surely you do not mean to aver that -science has no other business than that of recording -facts.”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_141'>141</span>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.</p> - -<p class='c009'>“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 <i>Mare Serenitatis</i> is -buried in night, and only a little of the eastern -edge of the <i>Mare Tranquillitatis</i> 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 -<span class='pageno' id='Page_142'>142</span>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 <i>mares</i> 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 -<i>Mare Imbrium</i> 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 -<span class='pageno' id='Page_143'>143</span>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 <i>Mare Imbrium</i> and the -<i>Mare Serenitatis</i>.</p> - -<div id='i142' class='figcenter id002'> -<img src='images/i142.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 17. October 10, 1903; Moon’s Age 20.06 Days.</span></p> -</div> -</div> - -<p class='c009'>“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 <i>Mare Serenitatis</i> and the <i>Mare Vaporum</i>, -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 -<span class='pageno' id='Page_144'>144</span><i>Mare Imbrium</i> 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.</p> - -<p class='c009'>“Yet, although the <i>Mare Imbrium</i> 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.”</p> - -<p class='c009'>“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.”</p> - -<div id='i144' class='figcenter id002'> -<img src='images/i144.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 18. September 29, 1904; Moon’s Age 20.50 Days.</span></p> -</div> -</div> - -<p class='c009'>“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 <i>Mare Imbrium</i> -<span class='pageno' id='Page_145'>145</span>to a change in the color of the—what shall I say, -grass?—covering it.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“Oh, I do support you with all my heart!” -she replied. “Pray go on, and tell me about the -lunar grass.”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_146'>146</span>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.</p> - -<p class='c009'>“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. -<span class='pageno' id='Page_147'>147</span>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 <i>Mare -Humorum</i>, is Byrgius, a walled plain near which -exists a small system of bright streaks resembling -those surrounding Copernicus and Kepler, -but much less extensive.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_148'>148</span>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.”</p> - -<p class='c009'>“Yes, that is no doubt true. Still, I wish that -Riccioli had possessed a little more imagination.”</p> - -<p class='c009'>“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 <i>Mare Nubium</i> 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 -<span class='pageno' id='Page_149'>149</span>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.”</p> - -<p class='c009'>“Oh, you interest me deeply! If Venus is -supplied with such an abundance of air, I suppose -she is inhabited?”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_150'>150</span>of the new and waxing moon. Only two of the -‘seas’ now remain completely in view—the <i>Mare -Humorum</i> and the <i>Oceanus Procellarum</i>.”</p> - -<p class='c009'>“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?”</p> - -<div id='i150' class='figcenter id002'> -<img src='images/i150.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 19. August 16, 1903; Moon’s Age 23.81 Days.</span></p> -</div> -</div> - -<p class='c009'>“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 -<i>Mare Humorum</i> are finely shown. Notice how -the floor of that little ‘sea,’ which is about the -<span class='pageno' id='Page_151'>151</span>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 <i>mare</i>. You can even see the comparatively -small crater that crowns the northern wall of the -ring. Southeast of the <i>Mare Humorum</i> 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.</p> - -<p class='c009'>“The <i>Oceanus Procellarum</i> is beautifully illuminated -in this picture. In several places, particularly -north of the <i>Mare Humorum</i>, parts of -<i>submerged</i> 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 <i>Mare Nectaris</i>.”</p> - -<p class='c009'>“Did that catastrophe occur after the formation -of the huge lunar volcanoes?”</p> - -<p class='c009'>“It is difficult to say just when it occurred, -but the appearances generally favor the view -<span class='pageno' id='Page_152'>152</span>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 <i>mares</i>, 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 <i>mares</i>, practically -in the state in which we see them, have -been true sea beds.</p> - -<p class='c009'>“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 <i>Oceanus Procellarum</i>. 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 -<span class='pageno' id='Page_153'>153</span>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 <i>Oceanus Procellarum</i> 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.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_154'>154</span>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:</p> - -<p class='c009'>“0° = Black (example, the shadows of mountains).</p> - -<p class='c009'>“1° = Gray black (example, darkest places -in the walled plains of Grimaldi and Riccioli).</p> - -<p class='c009'>“2° = Dark gray (example, the floor of -Endymion).</p> - -<p class='c009'>“3° = Medium gray (example, interior of -Theophilus).</p> - -<p class='c009'>“4° = Yellowish gray (example, interior of -Manilius).</p> - -<p class='c009'>“5° = Pure light gray (example, surface -around Kepler).</p> - -<p class='c009'>“6° = Light whitish gray (example, walls of -Macrobius).</p> - -<p class='c009'>“7° = Grayish white (example, Kepler).</p> - -<p class='c009'>“8° = Pure white (example, walls of Copernicus).</p> - -<p class='c009'>“9° = Glittering white (example, Proclus).</p> - -<p class='c009'>“10° = Dazzling white (sole example, the central -peak of Aristarchus).”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“You would be still more surprised,” I replied, -“if I could present to you a similar table -<span class='pageno' id='Page_155'>155</span>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 <i>mares</i> -and walled inclosures. Some of them appear to -be variable, and some are only to be detected under -particular illuminations.”</p> - -<p class='c009'>“Are not such colors an indication of something -living there?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“Oh, it was not the ‘grass’ that amused me, -but your unexpected way of introducing it. I -<i>want</i> 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 -<span class='pageno' id='Page_156'>156</span>roots giving way disclosed a glittering mass of -silver. Why not let me imagine that the peak of -Aristarchus is composed of pure silver?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“Why not say marble—a gigantic Carrara -mountain on the moon?”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_157'>157</span>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.</p> - -<p class='c009'>“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.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_158'>158</span>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.”</p> - -<p class='c009'>“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.”</p> - -<div id='i158' class='figcenter id002'> -<img src='images/i158.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 20. August 17, 1903; Moon’s Age 24.84 Days.</span></p> -</div> -</div> - -<p class='c009'><span class='pageno' id='Page_159'>159</span>“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 <i>Oceanus Procellarum</i>.</p> - -<p class='c009'>“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 -<i>Sinus Roris</i>, ‘Gulf of Dew.’ It connects the <i>Mare -Frigoris</i> with the <i>Oceanus Procellarum</i>. It is -<span class='pageno' id='Page_160'>160</span>another legacy from your friend the imaginative -astronomer.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“I hope that I have not been destroying any -of yours.”</p> - -<p class='c009'>“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.’”</p> - -<p class='c009'>“That element will not be diminished by what -I am about to point out. Look far over near the -eastern border of the <i>Oceanus Procellarum</i>, 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 -<span class='pageno' id='Page_161'>161</span>the southern border of the <i>Oceanus Procellarum</i>, -almost directly north of Gassendi. The latter is -very clearly shown at the lower end of the <i>Mare -Humorum</i>, 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 <i>Mare Humorum</i> -appear more ragged with mountains and -crater rings than before.”</p> - -<p class='c009'>“And have all these mountains and craters -names?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“It is mainly because we are on the earth that -we find such great difficulty in making accurate -<span class='pageno' id='Page_162'>162</span>maps of it. We cannot look at the earth as a -whole, but we have to crawl over its surface, making -measurements as we go, and afterwards translating -those measurements into lines and angles -on paper. Thus we are still uncertain about the -precise distance between many important points -on our globe, while for points on the moon no corresponding -uncertainty exists. The moon hangs -before us in the sky, with no clouds except those -in our own atmosphere to obscure it, and it is only -necessary carefully to observe the position of particular -points, and with the proper instruments -to measure their distance and directions from one -another. But even this is not a thing that can -be accomplished without much pains and much -knowledge. The astronomer, no matter what -field he chooses, is necessarily a hard worker, and -his motto, above everything else, is accuracy. -No one is more tempted than he by the sublimity -and the extraordinary character of the objects -of his study, to give rein to the imagination, and -yet imagination is the thing of all others from -whose vagaries he must most carefully guard -himself. So you must not blame him too severely -if he has not dotted the shores of the moon with -cities, and populated its plains with industrious -farmers.”</p> - -<p class='c009'>“If you will permit me to wander a little -aside from our photographic studies for a few -<span class='pageno' id='Page_163'>163</span>minutes,” said my friend, “I should like to ask -you about two or three things concerning the -moon which have long puzzled me. From my earliest -days, living the greater part of the time in -the country, I have heard that the moon exercises -a decided influence over the weather, and over -the growth of vegetation. I have neighbors who -would never think of planting certain things except -‘in the New of the moon’! Some will not cut -timber except ‘in the Old of the Moon,’ as they say -that the sap is drawn up by the moon’s influence -when she is growing. Is there really any truth -in all this?”</p> - -<p class='c009'>“Not the least. At any rate there is no scientific -evidence whatever for such statements, and -no probability that they are based on facts. -They are the result of faulty observation, misled -by coincidences. It is <i>imaginable</i> that the light -of the moon might have some influence upon -vegetable growth if it were an original kind of -light coming from the moon herself. But moonlight -is only reflected sunlight, and when we examine -it with the spectroscope we do not find that -the rays of light in visiting the moon and returning -thence to the earth have had either anything -added to or anything taken away from them, except -intensity. The total amount of light reflected -from the moon upon the earth is estimated -to be about 1/618000 of the total amount that -<span class='pageno' id='Page_164'>164</span>comes to us from the sun. Curiously enough -the moon appears to reflect proportionally more -heat than light, the amount of lunar heat received -by the earth being reckoned at 1/185000 of the -amount coming from the sun. The popular idea -that the moon affects the movement of sap in -plants is equally illusory.”</p> - -<p class='c009'>“But about the weather? I know people who -believe that a change of the moon from one phase -to another brings about a change of weather. Is -that true?”</p> - -<p class='c009'>“Certainly it is not true. The moon is changing -its apparent form all the time. There is no -sudden alteration at any phase. The popular -belief, however, has always been so firmly fixed -that many investigations have been made to ascertain -whether there is, in reality, any foundation -for it. These investigations have shown that no -measurable effect of the kind exists.”</p> - -<p class='c009'>“And the Full Moon does not drive away -clouds, as some assert?”</p> - -<p class='c009'>“Surely she does not. I will now tell you -something that the persons who plant and sow -and cut timber according to the phases of the -moon, and who believe that she exercises a kind -of magic control over the clouds, probably have -never heard of, although if they knew it they -might use it as an argument in favor of lunar -influences. It is this: The alternate approach -<span class='pageno' id='Page_165'>165</span>and retreat of the moon with respect to the earth, -as she travels round her elliptical orbit, produce -measurable, although slight, disturbances of the -magnetism of our planet. The distance of the -moon varies to the extent of about 30,000 miles. -Now, if it could be shown that these magnetic -disturbances were reflected in the character of -the weather, then the supposed influence of the -moon would be established. But that has not -been shown, and if it were shown it would still -be found that the phases of the moon had no relation -to the fact, for the moon may be at its -greatest or its least distance from the earth, or -at any intermediate distance during any possible -phase.”</p> - -<p class='c009'>“You will, perhaps, think me very persistent -in asking foolish questions, but there is one other -on my mind that I should like to put, now that -we have gone so far. It is this: I have read, since -the great earthquakes at San Francisco and Valparaiso, -and the great eruption of Vesuvius in -the same year, 1906, that the moon has an influence -over such things. Is this another unfounded -popular superstition?”</p> - -<p class='c009'>“It is not a notion of <i>popular</i> origin at all,” -I replied. “It originated rather from scientific -considerations, and there may possibly be a germ -of truth in it, although it yet remains to be demonstrated, -and the evidence concerning it is confusingly -<span class='pageno' id='Page_166'>166</span>contradictory. You will recall, I trust, -what has been said about the sun and the moon -producing tides in the oceans. We have also seen -that before our globe had assumed its present -condition, while it was yet more or less plastic -throughout its whole mass, and before the birth -of the moon, great tides were produced in the -body of the earth. The <i>tendency</i> to the production -of such bodily tides still exists, and now that -the moon has become a near-by attendant of the -earth, she acts more effectively in this regard -than does the sun. If the earth were still plastic -the moon would produce bodily tides in it. In -other words the earth would be deformed by the -attraction of the moon. The question has arisen -whether or not the tendency to the production of -such tides, now that the earth has become rigid, -may not disturb its crust sufficiently to induce -earthquakes and volcanic eruptions. Some students -of the subject have thought that they could -detect evidence that this is the case. It has frequently -happened that such phenomena have occurred -on a large scale, at or very close to, the periods -of New and of Full Moon. Those are the times, -as we saw when we were talking of the oceanic -tides, when the sun and the moon pull together. -If all great eruptions and earthquakes occurred -at these conjunctions there would be little doubt -of the correctness of the theory. But, unfortunately -<span class='pageno' id='Page_167'>167</span>for the clearness of our conceptions, this -is by no means the case. There have been many -earthquakes and volcanic outbursts when the sun -and the moon were not thus combining their tidal -attractions. Thus the evidence is found to be -contradictory or inconsistent, and the question -remains unsettled. It is, however, a very interesting -one, and the time will come, it is to be -hoped, when it will be answered decisively one -way or the other.”</p> - -<p class='c009'>After this digression we returned to the study -of the photographs.</p> - -<p class='c009'>“Photograph No. 20, which we have just been -examining,” I said, “represents the moon at the -age of about twenty-four days and twenty hours. -The next, and the last of the series showing the -moon in progressive phases, is No. 21. Here the -age of the moon is about twenty-six days and -twenty hours. It is the fast waning sickle of the -Old Moon which we behold. You perceive that it -is relatively uninteresting when compared with -No. 20, because very little except the eastern limb -is illuminated. Nearly all the great circular and -oval formations and craters, and all the ‘seas,’ -have passed into the lunar night. Only the eastern -verge of the <i>Oceanus Procellarum</i> remains in -sight, dulling the brilliance of the inner curve of -the sickle. The dark walled plain above the center -is Riccioli, and just below it appears Hevel, a -<span class='pageno' id='Page_168'>168</span>smaller, but yet large formation, with a low central -mountain. It is hardly worth our while to -attempt to identify the other features shown in -the photograph. They include none that we have -previously studied. Yet this picture has an interest -all its own because it is an excellent representation -of the moon at a time when she is so -near to the sun. Do not forget that, as I warned -you when we began with the crescent of the New -Moon, in these photographs the moon appears reversed -top for bottom. Seen in the sky in the -early morning this sickle would have its rounded -edge toward the left hand and directed more or -less downward, according to the position of the -sun. A great deal of confusion exists in the -minds of well-educated people concerning the position -of the sickle of the New and the Old Moon. -You have, of course, heard of the classic instances -in which artists have drawn the New Moon with -the concave side toward the sun! It is only necessary -to remember that a line drawn straight from -the center of the convex side of the sickle, whether -it be the New Moon or the Old Moon, always extends -directly toward the place occupied by the -sun.”</p> - -<div id='i168' class='figcenter id002'> -<img src='images/i168.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>No. 21. August 19, 1903; Moon’s Age 26.89 Days.</span></p> -</div> -</div> - -<p class='c009'>“There is,” said my friend, “an interesting -old superstition which I have often heard—I suppose -it must of course be a superstition—concerning -‘wet moons’ and ‘dry moons.’ As I recall it -<span class='pageno' id='Page_169'>169</span>they say that when the sickle of the New Moon -appears nearly upright in the sky that is a sign -of dry weather, because the moon is then like an -overturned cup, but when the sickle has its ends -turned upward that is a sign of wet weather, -because then the cup can hold water. I suppose -that these various positions of the moon actually -occur, but I do not know how they are brought -about.”</p> - -<p class='c009'>“The supposed influence of the position of -the New Moon on the weather,” I replied, “is too -gross a superstition to be worthy of any notice, -but the different attitudes of the sickle are interesting. -They arise from the changes in the position -of the moon as seen from the earth with -respect to the direction of the sun, and these -changes depend in turn on the inclination of the -moon’s path in the sky to the plane of the earth’s -equator as well as to the plane of the ecliptic or -the earth’s orbit. The ecliptic has an inclination -of about 23½° to the plane of the equator, and -the moon’s orbit is inclined a little over 5° to the -ecliptic. The moon may, in consequence, appear -more than 28° above or below the equator. But -since, as I told you in the beginning, the orbit of -the moon itself turns slowly about in space, the -distance of the moon above or below the equator -is not constant. It may be only a little more than -18°. In consequence of these changes of relative -<span class='pageno' id='Page_170'>170</span>position the situation of the horns of the crescent -moon varies. But you need never be in doubt as -to what position they will occupy at any time if -you will simply remember that a straight line -drawn from the point of one horn to that of the -other must always form a right angle with the -direction of the sun.</p> - -<div id='i170' class='figcenter id002'> -<img src='images/i170.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>Diagram Showing Why the Winter Moon Runs High.</p> -</div> -</div> - -<p class='c009'>“There is another very interesting fact about -the position of the moon in the sky which we -should not neglect to notice. Did you ever observe -the superior brilliancy of the light of the -Full Moon in winter? It is one of the compensations -that nature offers us. Since the Full Moon -is necessarily situated opposite to the point occupied -by the sun, and since the sun is far south -of the equator in midwinter, it follows that at the -same season the Full Moon appears high above -the equator in the northern hemisphere. You -<span class='pageno' id='Page_171'>171</span>will, perhaps, permit me to show you a diagram -intended to explain this phenomenon.</p> - -<p class='c009'>You observe that the sun being south of the -equator, in the direction indicated by the dotted -line, the Full Moon is correspondingly situated -north of the equator, and must necessarily appear -high in the sky at midnight, when the sun is at its -lowest declination. This is the reason why the -winter Full Moons are so brilliant, making the -snow-clad hills gleam with a splendor that sometimes -dazzles the eyes of the beholders. In the -Arctic regions the long winter night, when the sun -does not rise for months, is periodically brightened -by the presence of the Full Moon. Just the -opposite condition of affairs exists in summer. -Then the sun being north of the equator the Full -Moon is south of it, and ‘runs low,’ appearing -in high latitudes to skim along the southern -horizon.”</p> - -<p class='c009'>“Thank you, and now I will ask you one more -question,” said my friend. “I have often heard -of the ‘Harvest Moon’ and the ‘Hunter’s Moon.’ -Will you not kindly explain what is meant by -these terms and when the ‘Harvest Moon’ can be -seen? There is a poetic suggestiveness in the -name that appeals to me.”</p> - -<p class='c009'>“I will try with pleasure,” I said, “but I fear -that I shall have to trouble you with another diagram, -or perhaps with two.”</p> - -<p class='c009'><span class='pageno' id='Page_172'>172</span>“Oh, I shall not mind that at all. I have -grown used to diagrams as well as to the nomenclature -of the moon.”</p> - -<p class='c009'>“Well, if my diagrams conduct your thoughts -to things as interesting as many that lie concealed -behind the prosaic names on the moon I shall be -content. To begin, then, I must remind you that -in her monthly journey around the earth the -moon moves from west toward east in her orbit, -and thus she gets a little over 12° farther east -every twenty-four hours, as reckoned from the -position of the sun. The earth turning on its axis -in the same direction causes the moon to appear -to rise in the east and set in the west once every -twenty-four hours. But in consequence of the -constant eastward motion of the moon she rises -at a later hour every night. Here is a graphic -representation of what I mean:</p> - -<p class='c009'>“The earth is turning on its axis in the direction -represented by the arrows, and simultaneously -the moon is moving in its orbit in the -same direction, as is shown by the large arrow. -Suppose that some night the moon is seen -rising at a particular hour from the point A -on the earth. Then, the following night, when -the observer has again arrived at A, with the rotation -of the earth, the moon will have advanced -from M<sup>1</sup> to M<sup>2</sup>, and will not be seen rising until -the point occupied by the observer has arrived -<span class='pageno' id='Page_173'>173</span>at B. This retardation of the hour of moonrise -is variable on account of changes in the position -of the moon, arising from the inclination of her -orbit to the plane of the equator, and from the -inequalities of her motion, to which I have before -referred. On the average it amounts to fifty-one -minutes daily. It varies also with the distance of -the observer from the equator, the variation being -greater in high latitudes. In the latitude of New -York the retardation of moonrise may be as great -as an hour and a quarter, or as little as twenty-three -minutes.</p> - -<div id='i173' class='figcenter id002'> -<img src='images/i173.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>Diagram Showing Why Moon Rises Later Every Night.</p> -</div> -</div> - -<p class='c009'>“Now it is upon this variation that the phenomenon -of the ‘Harvest’ and the ‘Hunter’s -Moon’ depends. If I had a celestial globe here I -could show you that at the time of the Autumn -Equinox, September 22d, when the sun crosses the -<span class='pageno' id='Page_174'>174</span>equator moving southward, the apparent path of -the moon in the sky intersects the eastern horizon -at a comparatively small inclination. In other -words the moon at that time instead of rising -steeply from the horizon rises on a long slope almost -parallel with the horizon. The consequence -is that for several evenings in succession the Full -Moon near the time of the Autumn Equinox may -be seen rising just after sunset at almost the -same hour. Look at this second diagram and you -will see why this is so.</p> - -<div id='i174' class='figcenter id002'> -<img src='images/i174.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p>Diagram Illustrating the Harvest Moon.</p> -</div> -</div> - -<p class='c009'>“The little circles M show the moon at several -successive positions in her orbit, just twenty-four -hours apart. You perceive that in consequence of -the slight inclination to the eastern horizon the -sinking of the latter caused by the earth’s -rotation will bring the moon into view night -after night at almost the same hour. In fact, -in high northern latitudes like those of Norway -and Sweden the moon’s path at this time of -<span class='pageno' id='Page_175'>175</span>the year may actually coincide with the horizon, -so that for several evenings she will rise at -exactly the same hour. The name ‘Harvest Moon’ -explains itself, since it always occurs at the time -of the autumn harvests and the vintage, and -seems to supplement the fading daylight for the -benefit of late laborers in the fields. The ‘Harvest -Moon’ does not occur every year at precisely -the same date. It is very rare that Full Moon -happens to fall just on September 22d. It usually -either precedes or follows that date. The -‘Harvest Moon’ is the Full Moon which occurs -nearest to the Autumn Equinox, either before -or after. The ‘Hunter’s Moon’ is the first Full -Moon which follows the ‘Harvest Moon.’ Like -the former it rises for several successive evenings -near the same hour, but this phenomenon is less -marked in the case of the ‘Hunter’s Moon,’ because -it is farther from the Equinox.”</p> - -<p class='c009'>“Thank you, again,” said my friend. “I -shall never henceforth look at the moon without -thinking of circles, straight lines, and arrows as -well as of ‘ring mountains’ and ‘seas.’”</p> - -<p class='c009'>“Then you are making good progress toward -science,” I replied. “One last look, now, at the -photograph of the Old Moon’s sickle, and then -we had better postpone our examination of the -large photographs, showing certain particularly -interesting districts on the moon, until to-morrow -<span class='pageno' id='Page_176'>176</span>morning. There is here another interesting point -for artists to note. The convex side of the sickle -of the Old Moon, or the New Moon, is always an -arc of a circle, but the concave side is never circular -although it is often thus represented. The -concave side, neglecting its irregularities arising -from the differences of level and of brilliancy of -the lunar surface, is elliptical in outline, that is -to say, it is a semicircle viewed obliquely.”</p> - -<p class='c009'>“Whatever its geometry may be,” replied my -friend, “it is certainly very beautiful. Good -night, and I shall demand to see those large photographs -before the sun is very high to-morrow.”</p> -<div class='pbb'> - <hr class='pb c005' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c002'> - <div><span class='pageno' id='Page_177'>177</span><span class='c019'>IV</span></div> - <div class='c000'><span class='c019'>GREAT SCENES ON THE MOON</span></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_179'>179</span> - <h2 id='ch04' class='c010'>IV<br /> <br />GREAT SCENES ON THE MOON</h2> -</div> -<p class='drop-capa0_25_0_7 c020'>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.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_180'>180</span><i>Mare Nubium</i>, in the southeastern quarter of the -moon. You certainly must remember the <i>Mare -Nubium</i>, 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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_181'>181</span>of sunrise ran just along the border between the -<i>Mare Nubium</i> and the <i>Oceanus Procellarum</i>. -The <i>Mare Humorum</i> 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 <i>Mare Nubium</i> 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 -<span class='pageno' id='Page_182'>182</span>ring 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 <i>Mare Nubium</i> 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.”</p> - -<div id='i182' class='figcenter id002'> -<img src='images/i182.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>Bullialdus and the</span> <i>Mare Nubium</i>.</p> -</div> -</div> - -<p class='c009'>“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 -<span class='pageno' id='Page_183'>183</span>more fascinating than that of any puny race of -beings, passing their ephemeral lives upon its -wonderful surface, could possibly be.”</p> - -<p class='c009'>“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 -<i>Mare Humorum</i>. 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 -<span class='pageno' id='Page_184'>184</span>form 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 <i>Mare Nubium</i>. The whole system -bears some resemblance to a gigantic buckle.”</p> - -<p class='c009'>“What is that curious object below Bullialdus -which resembles an old-fashioned gold earring?”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_185'>185</span>probably greater in their vicinity than it was farther -eastward.</p> - -<p class='c009'>“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.</p> - -<p class='c009'>“South of Kies, at the edge of the <i>Mare Nubium</i>, -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. -<span class='pageno' id='Page_186'>186</span>Between 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.</p> - -<p class='c009'>“Near the southern shore of the <i>Mare Nubium</i> -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.</p> - -<p class='c009'>“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 <i>Mare Nubium</i>, 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 -<span class='pageno' id='Page_187'>187</span>one 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.”</p> - -<p class='c009'>“Have I not heard of something similar in -connection with the California earthquake in -1906?” asked my friend.</p> - -<p class='c009'>“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 <i>Mare Nubium</i>. -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 -<span class='pageno' id='Page_188'>188</span>part 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.</p> - -<p class='c009'>“The crater pit in the <i>Mare Nubium</i>, 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 -<span class='pageno' id='Page_189'>189</span>the lower end of the ‘Straight Wall’ and -Lassell, and over the bridge of the ‘nose,’ a -wedge-shaped mountain runs out into the <i>mare</i>. -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 <i>Mare Nubium</i>. -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 -<span class='pageno' id='Page_190'>190</span>at its northern end, and known as the Riphæan -Mountains.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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, -<span class='pageno' id='Page_191'>191</span>you should not be surprised at finding that nature -does not vary from her rule of uniformity on the -moon.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_192'>192</span>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.”</p> - -<p class='c009'>“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.”</p> - -<div id='i192' class='figcenter id002'> -<img src='images/i192.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>Tycho, Clavius, and their Surroundings.</span></p> -</div> -</div> - -<p class='c009'>“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 -<span class='pageno' id='Page_193'>193</span>small 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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'><span class='pageno' id='Page_194'>194</span>“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?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“Thank you, again. You have saved my lunarians. -And now please tell me what is that -frightful black chasm above Clavius?”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_195'>195</span>and imagine yourself entangled in that labyrinth! -You would have but a small chance for escape, I -fancy.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“For what William was it named?”</p> - -<p class='c009'>“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 <i>Mare Nubium</i>, 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 -<span class='pageno' id='Page_196'>196</span>eastern 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.’</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_197'>197</span>possessed 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 <i>Mare Nubium</i>, 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.”</p> - -<p class='c009'>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.</p> - -<p class='c009'><span class='pageno' id='Page_198'>198</span>“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.”</p> - -<p class='c009'>“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.”</p> - -<div id='i198' class='figcenter id002'> -<img src='images/i198.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>The Great Southwest on the Moon.</span></p> -</div> -</div> - -<p class='c009'>“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 <i>Mare Nectaris</i>, 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 -<span class='pageno' id='Page_199'>199</span>diameter, 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.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_200'>200</span>on 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 -<span class='pageno' id='Page_201'>201</span>geologist, 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 -<span class='pageno' id='Page_202'>202</span>arrangement 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.”</p> - -<p class='c009'>My friend had listened to me in silence for a -<span class='pageno' id='Page_203'>203</span>long 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?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'><span class='pageno' id='Page_204'>204</span>“Well,” she replied, with a sigh, ending with -a smile, “go on. After all I believe I am really -interested.”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_205'>205</span>while 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.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_206'>206</span>in 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.”</p> - -<p class='c009'>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.</p> - -<p class='c009'>“Dear me,” she exclaimed, “the moon becomes -more terrible every moment! Positively, -I almost shrink from the sight.”</p> - -<div id='i206' class='figcenter id002'> -<img src='images/i206.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>The Giant Ring Mountains, Theophilus and its Neighbors.</span></p> -</div> -</div> - -<p class='c009'>“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 -<span class='pageno' id='Page_207'>207</span>the 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 <i>Mare Nectaris</i> -on the west. Notice the huge mountain fold -<span class='pageno' id='Page_208'>208</span>which 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.</p> - -<p class='c009'>“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. -<span class='pageno' id='Page_209'>209</span>From 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.”</p> - -<p class='c009'>“I no longer wish to visit the moon,” interrupted -my friend, shaking her head.</p> - -<p class='c009'>“Not if you were assured of a safe return?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'><span class='pageno' id='Page_210'>210</span>“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 -<span class='pageno' id='Page_211'>211</span>walls 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.”</p> - -<p class='c009'>We came now to the large picture of Copernicus, -and my friend took it in her hands to examine -it.</p> - -<p class='c009'>“It is a marvelous thing to look upon,” she -said, “but it doesn’t frighten me as Theophilus -did.”</p> - -<p class='c009'>“No, Copernicus is rather sublime than terrifying -in aspect. Its comparatively lone situation, -with the <i>Mare Nubium</i>, the <i>Oceanus Procellarum</i> -and the <i>Mare Imbrium</i> 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 -<span class='pageno' id='Page_212'>212</span>uniform 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 -<span class='pageno' id='Page_213'>213</span>of 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 -<span class='pageno' id='Page_214'>214</span>photograph 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.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_215'>215</span>three or four times the initial velocity which some -modern guns are capable of imparting to their -projectiles.”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“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 <i>Mare Imbrium</i>, 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 -<span class='pageno' id='Page_216'>216</span>southward 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.</p> - -<p class='c009'>“Near the eastern end of the Carpathians -the mountains make their greatest advance into -the <i>Mare Imbrium</i>, 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. -<span class='pageno' id='Page_217'>217</span>These 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 -<i>Mare Imbrium</i> below.</p> - -<p class='c009'>“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 <i>Mare Nubium</i>. 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 <i>mare</i> both south and north of -Gambart. Those on the north are remarkable for -the darkness of the surface, especially in the -northwestern part.</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_218'>218</span>evidently 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.”</p> - -<p class='c009'>“I regret that he was deceived.”</p> - -<div id='i218' class='figcenter id002'> -<img src='images/i218.jpg' alt='' class='ig001' /> -<div class='ic002'> -<p><span class='sc'>Two Great Lunar “Seas”</span><br />The <i>Mare Serenitatis</i> and a Part of the <i>Mare Imbrium</i>.</p> -</div> -</div> - -<p class='c009'>“So do I. We shall now leave Copernicus -and its marvelous surroundings, and turn to the -last photograph in our series, representing the -<i>Mare Serenitatis</i> in its full extent, and a large -<span class='pageno' id='Page_219'>219</span>part of the <i>Mare Imbrium</i>. Is it not a beautiful -picture?”</p> - -<p class='c009'>“It is, indeed, but so strange!”</p> - -<p class='c009'>“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 <i>Mare Serenitatis</i> 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 <i>Mare Imbrium</i>; on the -northwest, where another strait opens into the -<i>Lacus Somniorum</i>, 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 <i>Mare Tranquillitatis</i>. The <i>Mare -Serenitatis</i> 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 -<span class='pageno' id='Page_220'>220</span>light which are never seen on this vast lunar -plain.”</p> - -<p class='c009'>“Oh, but it <i>must</i> 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.”</p> - -<p class='c009'>“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 <i>mares</i> 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 -<i>Mare Serenitatis</i> 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 -<span class='pageno' id='Page_221'>221</span>southern shore of the strait leading into the -<i>Mare Imbrium</i>. 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 <i>Mare Serenitatis</i> and the <i>Lacus -Somniorum</i>, to the <i>Mare Frigoris</i>. 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 <i>mare</i> 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.’</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_222'>222</span>situation of the bright crater just in the center -of the bow. Menelaus and the streak from Tycho -can be seen at Full Moon with no greater optical -aid than that of a good binocular. On the edge -of the ‘sea,’ off a lofty headland of the Hæmus -chain, another lone little crater is visible, Sulpicius -Gallus by name. It, too, is remarkable for -its brilliant reflective power. Behind the mountains, -directly back of Sulpicius Gallus, and lying -in an upraised part of the <i>Mare Vaporum</i>, 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 <i>Mare Imbrium</i>. -They contain one notable crater ring named -Marco Polo, which lies just above a great square -<i>massif</i>, 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, -<span class='pageno' id='Page_223'>223</span>off this cape, is an array of small mountain peaks, -which must have been islands, if the lunar ‘seas’ -were once true seas.</p> - -<p class='c009'>“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 <i>Mare Serenitatis</i>, 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 <i>Mare Serenitatis</i> for nearly 200 miles to a -sharp promontory which shuts off the <i>Lacus Somniorum</i> -on one side from the <i>mare</i>. West of -Aristoteles and Eudoxus the mountain mass extends -<span class='pageno' id='Page_224'>224</span>to a curious sharp-angled plain, which it -skirts on the north and south.</p> - -<p class='c009'>“The western shore of the <i>Mare Serenitatis</i> -beyond the strait opening into the <i>Lacus Somniorum</i> -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 <i>Mare Tranquillitatis</i>, -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 <i>Mare Serenitatis</i>.</p> - -<p class='c009'>“We return to the Caucasus region. These -mountains front the <i>Mare Imbrium</i> 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 -<span class='pageno' id='Page_225'>225</span>ring plain dark with shadow on one of its -sides. This is Theætetus, interesting as the scene -of an alleged display of ‘smoke,’ reported to have -been witnessed by a French observer with his -telescope a few years ago. Several occurrences -of this kind have been reported on the moon, but -more or less doubt attaches in every instance -the accuracy of the observations, or at least to -that of the conclusions drawn from them. Below -Theætetus is an oval ring almost entirely filled -up, with two craters within it. This is named -Cassini. Below Cassini begins another mass of -mountains, the lunar Alps. These are by no -means as extensive as the Caucasus, but they contain -some lofty peaks, and are traversed by one of -the most remarkable valleys on the moon. It is -not very distinctly shown in this picture, but you -may recognize it by a dark band commencing opposite -a small bay which sets back into the mountains. -The valley continues through the mountains -and the adjoining hilly regions nearly to -the shore of the narrow <i>Mare Frigoris</i>, 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 <i>Mare Imbrium</i>, -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 -<span class='pageno' id='Page_226'>226</span>by high cliffs. In the photograph all of -the encircling wall is illuminated on the inner side -except at the east end, where the shadows extend -a short distance upon the floor. Plato looks as -though it might once have been a ring mountain -of the usual type, which has been partly filled in -the interior by a local uprush of molten lava. -The diameter of the ring is 60 miles, but the inclosure -sinks only about half as deep beneath the -crest of the wall, as is the rule with formations -of similar outline. A central peak, a group of -mountains, may be buried there.</p> - -<p class='c009'>“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:</p> - -<p class='c009'>“‘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.’</p> - -<p class='c009'>“The white marks to which Professor Pickering -refers are but faintly indicated in the photograph -before us, but with the telescope, when the -<span class='pageno' id='Page_227'>227</span>illumination is favorable, they are plainly seen. -There are a number of very small crater pits -scattered over the floor of Plato, and around these -changes of color occur which have been ascribed -to the emission of some substance from the pits -and to the presence of vegetation, nourished by -the gases and vapors, and springing into renewed -life every time the sun rises upon the plain. -Broad areas of the inclosure gradually change -color as the sun rises, and again as the sun sets, -and these phenomena have also been ascribed to -the presence of vegetation. You may, if you wish, -regard Plato as a kind of mountain-ringed prairie, -covered with something analogous to prairie grass -and shrubs, which depends for its existence, -partly, upon the supply of gases spreading over -the surface from the crater pits.”</p> - -<p class='c009'>“So this, then, is your ‘lunar grass’?”</p> - -<p class='c009'>“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 <i>mares</i> 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.’”</p> - -<p class='c009'>“Does this vegetation resemble that of the -earth?”</p> - -<p class='c009'><span class='pageno' id='Page_228'>228</span>“I cannot tell you.”</p> - -<p class='c009'>“But where vegetation exists animal life is -possible, is it not?”</p> - -<p class='c009'>“Yes, it is <i>possible</i>.”</p> - -<p class='c009'>“What forms would it have?”</p> - -<p class='c009'>“I cannot tell you. But I certainly should -not expect to find manlike creatures there.”</p> - -<p class='c009'>“Oh, men are not <i>necessary</i> 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.”</p> - -<p class='c009'>“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 -<span class='pageno' id='Page_229'>229</span>quantities of the gases constituting the air we -breathe. In fact we may look forward to a time, -fortunately for us extremely remote, when the -interior rocks of the earth will, in this manner, -absorb perhaps all of its atmosphere.”</p> - -<p class='c009'>“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?”</p> - -<p class='c009'>“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 <i>all</i> 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 -<span class='pageno' id='Page_230'>230</span>planet’s atmosphere in a day as escape from it -there can be no decrease of the total amount of -air. If more escape than enter, the atmosphere -will diminish. If more enter than escape, the atmosphere -will grow. Finally if none escape the -atmosphere may increase indefinitely. This, as -far as the effect of gravitation is concerned, -should be the case on the sun, for the solar attraction -is more than sufficient to retain any gas -known to us. In consequence, the sun’s atmosphere -may be increasing in extent and density. -Even the earth’s atmosphere may be slowly increasing -from this cause, and herein may lie the -explanation of the enormous atmosphere surrounding -the great planet Jupiter.</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“But,” interjected my friend, “is not this -that you have been telling me in contradiction -<span class='pageno' id='Page_231'>231</span>to what you said about the cause of the sharp -division between day and night on the moon, and -about the visibility of the stars there in the -daytime?”</p> - -<p class='c009'>“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.</p> - -<p class='c009'>“But we have not yet finished with our photograph. -We were looking at the plain of Plato, -you will recollect. Notice, now, the <i>Mare Imbrium</i> -off the coast that adjoins Plato on the -south. You see there several bright spots resembling -islands. Islands they must have been -if the <i>mare</i> 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 -<span class='pageno' id='Page_232'>232</span>Cape Laplace, at the western end of the ‘Bay of -Rainbows.’</p> - -<p class='c009'>“We now turn to the southwestern border of -the <i>Mare Imbrium</i>, 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.</p> - -<p class='c009'>“Let us now pass this strait and enter the -<i>Mare Serenitatis</i>. 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 -<span class='pageno' id='Page_233'>233</span>indications of that wonderful lunar world of remote -antiquity which lies buried in the grave of a -planet. Directly opposite the opening of the -strait, a small, round, light spot is seen in the -midst of the sea. This is Linné, very famous for -its strange and suggestive history. Here, if anywhere -on the moon, changes visible to human eyes -have taken place, and, in the opinion of Professor -Pickering, are still taking place every fortnight. -In the center of the light spot is a minute crater, -and from this crater there seems to issue some -kind of vapor which spreads over the surrounding -surface, alternately expanding and shrinking in -extent. A remarkable change in the form and -appearance of Linné was recorded by the astronomer -Schmidt, at Athens, in 1866. What had occurred -has been explained by some as the falling -in of a crater floor some six miles in diameter. -But the observations of Professor Pickering are -more interesting and suggestive. According to him -the bright patch about the crater pit extends during -the lunar night and diminishes by day, indicating -that something issues from the pit and -is deposited over the surrounding plain in the -form of hoar frost, which melts away in the sunshine. -He has even recorded an apparent expansion -of the white area during a lunar eclipse -when the cold shadow of the earth tends to condense -the vapors. If this is true it seems rather -<span class='pageno' id='Page_234'>234</span>surprising that many more similar phenomena -are not visible elsewhere.</p> - -<p class='c009'>“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?”</p> - -<p class='c009'>“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.”</p> - -<p class='c009'>“Perhaps,” I suggested, “the lunarians, whom -<span class='pageno' id='Page_235'>235</span>you have reconstructed in your fancy, reached, -before the catastrophe came that ended their existence, -a higher state of civilization than ours, -and learned to substitute electrically driven vessels -for white-winged ships.”</p> - -<p class='c009'>“That would be like the introduction of vulgar -steamboats on the canals of Venice,” she replied.</p> - -<p class='c009'>“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.”</p> - -<hr class='c023' /> - -<p class='c009'>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:</p> - -<p class='c009'>“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 <i>Mare Serenitatis</i>. -But my fancy remains faithful to the -<span class='pageno' id='Page_236'>236</span>‘Marsh of a Dream,’ which still represents for me -the culmination of lunar ideality.</p> - -<p class='c009'>“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.”</p> -<div class='pbb'> - <hr class='pb c005' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c002'> - <div><span class='pageno' id='Page_237'>237</span><span class='c019'>APPENDIX</span></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_239'>239</span> - <h2 id='apndx' class='c010'>APPENDIX</h2> -</div> -<p class='c011'><span class='sc'>Dates</span>, and age of the moon, when the twenty-one -serial photographs were made at the Yerkes -Observatory, by Mr. Wallace, with the 12-inch -telescope and a special color filter constructed by -him:</p> - -<table class='table3' summary=''> -<colgroup> -<col width='14%' /> -<col width='39%' /> -<col width='45%' /> -</colgroup> - <tr> - <td class='c016'><a href='#i050'>No. 1</a>,</td> - <td class='c016'>February 19, 1904;</td> - <td class='c024'>Moon’s Age 3.85 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i056'>No. 2</a>,</td> - <td class='c016'>September 24, 1903;</td> - <td class='c024'>Moon’s Age 3.87 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i066'>No. 3</a>,</td> - <td class='c016'>July 29, 1903;</td> - <td class='c024'>Moon’s Age 5.54 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i072'>No. 4</a>,</td> - <td class='c016'>November 24, 1903;</td> - <td class='c024'>Moon’s Age 5.74 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i074'>No. 5</a>,</td> - <td class='c016'>July 1, 1903;</td> - <td class='c024'>Moon’s Age 6.24 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i078'>No. 6</a>,</td> - <td class='c016'>November 26, 1903;</td> - <td class='c024'>Moon’s Age 7.75 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i090'>No. 7</a>,</td> - <td class='c016'>July 2, 1903;</td> - <td class='c024'>Moon’s Age 7.24 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i094'>No. 8</a>,</td> - <td class='c016'>August 31, 1903;</td> - <td class='c024'>Moon’s Age 9.22 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i102'>No. 9</a>,</td> - <td class='c016'>August 2, 1903;</td> - <td class='c024'>Moon’s Age 8.97 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i106'>No. 10</a>,</td> - <td class='c016'>November 30, 1903;</td> - <td class='c024'>Moon’s Age 11.78 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i112'>No. 11</a>,</td> - <td class='c016'>December 1, 1903;</td> - <td class='c024'>Moon’s Age 12.98 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i118'>No. 12</a>,</td> - <td class='c016'>September 4, 1903;</td> - <td class='c024'>Moon’s Age 13.27 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i122'>No. 13</a>,</td> - <td class='c016'>September 5, 1903;</td> - <td class='c024'>Moon’s Age 14.40 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i132'>No. 14</a>,</td> - <td class='c016'>August 26, 1904;</td> - <td class='c024'>Moon’s Age 15.65 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i134'>No. 15</a>,</td> - <td class='c016'>August 28, 1904;</td> - <td class='c024'>Moon’s Age 17.41 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i138'>No. 16</a>,</td> - <td class='c016'>August 29, 1904;</td> - <td class='c024'>Moon’s Age 18.62 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i142'>No. 17</a>,</td> - <td class='c016'>October 10, 1903;</td> - <td class='c024'>Moon’s Age 20.06 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i144'>No. 18</a>,</td> - <td class='c016'>September 29, 1904;</td> - <td class='c024'>Moon’s Age 20.50 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i150'>No. 19</a>,</td> - <td class='c016'>August 16, 1903;</td> - <td class='c024'>Moon’s Age 23.81 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i158'>No. 20</a>,</td> - <td class='c016'>August 17, 1903;</td> - <td class='c024'>Moon’s Age 24.84 Days</td> - </tr> - <tr> - <td class='c016'><a href='#i168'>No. 21</a>,</td> - <td class='c016'>August 19, 1903;</td> - <td class='c024'>Moon’s Age 26.89 Days</td> - </tr> -</table> -<div class='pbb'> - <hr class='pb c005' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c002'> - <div><span class='pageno' id='Page_241'>241</span><span class='c019'>INDEX</span></div> - </div> -</div> - -<div class='pbb'> - <hr class='pb c002' /> -</div> -<div class='chapter'> - <span class='pageno' id='Page_242'>242</span> - <h2 id='idx' class='c010'>INDEX</h2> -</div> - -<ul class='index c005'> - <li class='c025'>Abenezra, <a href='#Page_205'>205</a>.</li> - <li class='c025'>Abulfeda, <a href='#Page_200'>200</a>.</li> - <li class='c025'>Air on the moon, <a href='#Page_230'>230</a>.</li> - <li class='c025'>Albategnius, <a href='#Page_78'>78</a>.</li> - <li class='c025'>Aliacensis, <a href='#Page_78'>78</a>, <a href='#Page_205'>205</a>.</li> - <li class='c025'>Almamon, <a href='#Page_205'>205</a>.</li> - <li class='c025'>Alps, <a href='#Page_97'>97</a>. - <ul> - <li>remarkable valley in, <a href='#Page_225'>225</a>.</li> - </ul> - </li> - <li class='c025'>Altai Mountains, <a href='#Page_72'>72</a>, <a href='#Page_200'>200</a>. - <ul> - <li>chain of small craters near, <a href='#Page_200'>200</a>.</li> - </ul> - </li> - <li class='c025'>Animal life on the moon, <a href='#Page_228'>228</a>.</li> - <li class='c025'>Apennines, <a href='#Page_10'>10</a>, <a href='#Page_96'>96</a>, <a href='#Page_104'>104</a>, <a href='#Page_137'>137</a>, <a href='#Page_143'>143</a>, <a href='#Page_222'>222</a>, <a href='#Page_232'>232</a>.</li> - <li class='c025'>Apennines and Caucasus, strait between, <a href='#Page_234'>234</a>.</li> - <li class='c025'>Apianus, <a href='#Page_205'>205</a>.</li> - <li class='c025'>Archimedes, 143, <a href='#Page_232'>232</a>.</li> - <li class='c025'>Aristarchus, <a href='#Page_117'>117</a>, <a href='#Page_153'>153</a>. - <ul> - <li>astonishing brilliance of, <a href='#Page_112'>112</a>.</li> - <li>cause of brilliance of, <a href='#Page_155'>155</a>.</li> - <li>possible composition of, <a href='#Page_113'>113</a>.</li> - </ul> - </li> - <li class='c025'>Aristoteles, <a href='#Page_76'>76</a>, <a href='#Page_138'>138</a>.</li> - <li class='c025'>Atlas, <a href='#Page_70'>70</a>.</li> - <li class='c025'>Atmosphere, lunar, <a href='#Page_31'>31</a>. - <ul> - <li>disappearance of, <a href='#Page_228'>228</a>.</li> - <li>what has become of it, <a href='#Page_32'>32</a>.</li> - </ul> - </li> - <li class='c025'>Atmospheres, how they may grow or decrease, <a href='#Page_230'>230</a>.</li> - <li class='c025'>Azophi, <a href='#Page_205'>205</a>.</li> - <li class='c005'>Barry, <a href='#Page_189'>189</a>.</li> - <li class='c025'>“Bay of Rainbows,” <a href='#Page_109'>109</a>, <a href='#Page_111'>111</a>, <a href='#Page_142'>142</a>, <a href='#Page_157'>157</a>, <a href='#Page_158'>158</a>.</li> - <li class='c025'>Bessel, <a href='#Page_221'>221</a>.</li> - <li class='c025'>Bianchini, <a href='#Page_110'>110</a>.</li> - <li class='c025'>Birt, <a href='#Page_188'>188</a>.</li> - <li class='c025'>Blancanus, <a href='#Page_78'>78</a>, <a href='#Page_194'>194</a>.</li> - <li class='c025'>Bonpland, <a href='#Page_189'>189</a>.</li> - <li class='c025'>Bubbles on the moon, <a href='#Page_186'>186</a>.</li> - <li class='c025'>Bullialdus, <a href='#Page_180'>180</a>-<a href='#Page_182'>182</a>, <a href='#Page_183'>183</a>. - <ul> - <li>mountains near, <a href='#Page_183'>183</a>.</li> - </ul> - </li> - <li class='c025'>Byrgius, <a href='#Page_147'>147</a>.</li> - <li class='c005'>Calippus, <a href='#Page_223'>223</a>.</li> - <li class='c025'>Campanus, <a href='#Page_185'>185</a>.</li> - <li class='c025'>Capuanus, <a href='#Page_185'>185</a>, <a href='#Page_196'>196</a>.</li> - <li class='c025'>Carpathian Mountains, <a href='#Page_215'>215</a>.</li> - <li class='c025'>Cassini, <a href='#Page_225'>225</a>.</li> - <li class='c025'>Catharina, <a href='#Page_72'>72</a>, <a href='#Page_138'>138</a>, <a href='#Page_199'>199</a>, <a href='#Page_206'>206</a>. - <ul> - <li>remarkable valleys near, <a href='#Page_199'>199</a>-<a href='#Page_200'>200</a>.</li> - </ul> - </li> - <li class='c025'>Caucasus Mountains, <a href='#Page_97'>97</a>, <a href='#Page_223'>223</a>.</li> - <li class='c025'>Caucasus and Apennines, strait between, <a href='#Page_234'>234</a>.</li> - <li class='c025'>“Cavern life” on moon, <a href='#Page_229'>229</a>.</li> - <li class='c025'>Cichus, <a href='#Page_185'>185</a>, <a href='#Page_196'>196</a>.</li> - <li class='c025'>Clavius, <a href='#Page_99'>99</a>, <a href='#Page_101'>101</a>, <a href='#Page_146'>146</a>, <a href='#Page_192'>192</a>. - <ul> - <li>length of great wall of, <a href='#Page_193'>193</a>.</li> - </ul> - </li> - <li class='c025'>Cleft near shore of <i>Mare Nubium</i>, <a href='#Page_186'>186</a>.</li> - <li class='c025'><span class='pageno' id='Page_243'>243</span>Clefts on moon, resemblance of, to geological “faults,” <a href='#Page_187'>187</a>.</li> - <li class='c025'>Cleomedes, <a href='#Page_56'>56</a>.</li> - <li class='c025'>Color on moon, <a href='#Page_155'>155</a>.</li> - <li class='c025'>Colorado Cañon, possible likeness of, to cleft on moon, <a href='#Page_118'>118</a>.</li> - <li class='c025'>Copernicus, <a href='#Page_102'>102</a>, <a href='#Page_211'>211</a>. - <ul> - <li>an argument for the volcanic theory, <a href='#Page_212'>212</a>.</li> - <li>buried ring near, <a href='#Page_217'>217</a>-<a href='#Page_218'>218</a>.</li> - <li>crater pits near, <a href='#Page_213'>213</a>.</li> - <li>hexagonal form of, <a href='#Page_212'>212</a>.</li> - </ul> - </li> - <li class='c025'>Craters, lunar, formation of, ascribed to falling masses, <a href='#Page_201'>201</a>. - <ul> - <li>theory of, advanced by W. K. Gilbert, <a href='#Page_200'>200</a>.</li> - </ul> - </li> - <li class='c025'>Cyrillus, <a href='#Page_72'>72</a>, <a href='#Page_138'>138</a>, <a href='#Page_199'>199</a>, <a href='#Page_206'>206</a>, <a href='#Page_210'>210</a>.</li> - <li class='c005'>“Dark woman” in moon, <a href='#Page_133'>133</a>.</li> - <li class='c025'>Darwin, Prof. George, <a href='#Page_6'>6</a>.</li> - <li class='c025'>Dawes, <a href='#Page_224'>224</a>.</li> - <li class='c025'>Day and night on moon, <a href='#Page_63'>63</a>.</li> - <li class='c025'>Day on moon, length of, <a href='#Page_95'>95</a>.</li> - <li class='c005'>Earth, light of, on moon, <a href='#Page_50'>50</a>. - <ul> - <li>shadow of, effects of, as shown by Prof. William H. Pickering, <a href='#Page_28'>28</a>.</li> - <li>shadow of, its size and length, <a href='#Page_18'>18</a>.</li> - </ul> - </li> - <li class='c025'>Eclipse, lunar, <a href='#Page_17'>17</a>-<a href='#Page_18'>18</a>. - <ul> - <li>earth’s atmosphere and, <a href='#Page_27'>27</a>.</li> - <li>moon visible during, <a href='#Page_26'>26</a>.</li> - </ul> - </li> - <li class='c025'>Eclipses, lunar, colors visible during, <a href='#Page_29'>29</a>. - <ul> - <li>fix historic dates, <a href='#Page_29'>29</a>.</li> - <li>number of, in year, <a href='#Page_42'>42</a>.</li> - <li>when annular, <a href='#Page_41'>41</a>.</li> - </ul> - </li> - <li class='c025'>Eclipses, why they do not occur every month, <a href='#Page_38'>38</a>. - <ul> - <li>solar, different from lunar, <a href='#Page_27'>27</a>.</li> - <li>number of, in year, <a href='#Page_42'>42</a>.</li> - <li>why of greater scientific value than lunar, <a href='#Page_28'>28</a>.</li> - </ul> - </li> - <li class='c025'>Endymion, <a href='#Page_70'>70</a>, <a href='#Page_132'>132</a>.</li> - <li class='c025'>Eratosthenes, <a href='#Page_104'>104</a>.</li> - <li class='c025'>Eudoxus, <a href='#Page_76'>76</a>, <a href='#Page_138'>138</a>.</li> - <li class='c005'>Fracastorius, <a href='#Page_73'>73</a>.</li> - <li class='c025'>Fra Mauro, <a href='#Page_189'>189</a>.</li> - <li class='c025'>Full Moon in winter, why it runs high, <a href='#Page_170'>170</a>.</li> - <li class='c025'>Furnerius, <a href='#Page_63'>63</a>.</li> - <li class='c005'>Gases, escape of, from moon, <a href='#Page_229'>229</a>. - <ul> - <li>from planets, <a href='#Page_33'>33</a>.</li> - <li>molecular velocity of, <a href='#Page_33'>33</a>, <a href='#Page_229'>229</a>.</li> - </ul> - </li> - <li class='c025'>Gassendi, <a href='#Page_117'>117</a>.</li> - <li class='c025'>Gauricus, <a href='#Page_196'>196</a>.</li> - <li class='c025'>Gay Lussac, <a href='#Page_216'>216</a>.</li> - <li class='c025'>Gemma Frisius, <a href='#Page_202'>202</a>.</li> - <li class='c025'>“Geology” of moon, <a href='#Page_67'>67</a>.</li> - <li class='c025'>“Giantism” on the moon, <a href='#Page_193'>193</a>.</li> - <li class='c025'>Gilbert, W. K., theory of lunar craters advanced by, <a href='#Page_200'>200</a>.</li> - <li class='c025'>Gravitation on moon, <a href='#Page_34'>34</a>-<a href='#Page_36'>36</a>.</li> - <li class='c025'>Grimaldi, <a href='#Page_121'>121</a>, <a href='#Page_132'>132</a>.</li> - <li class='c005'>Hæmus Mountains, <a href='#Page_92'>92</a>, <a href='#Page_220'>220</a>.</li> - <li class='c025'>Hansen, theory of, in regard to the other side of moon, <a href='#Page_139'>139</a>.</li> - <li class='c025'>Harbinger Mountains, <a href='#Page_118'>118</a>.</li> - <li class='c025'>“Harvest Moon,” <a href='#Page_171'>171</a>.</li> - <li class='c025'>Heat of moon compared with that of sun, <a href='#Page_164'>164</a>.</li> - <li class='c025'>Helen of Troy, <a href='#Page_92'>92</a>.</li> - <li class='c025'>Hell, <a href='#Page_196'>196</a>.</li> - <li class='c025'><span class='pageno' id='Page_244'>244</span>Hercules, <a href='#Page_70'>70</a>.</li> - <li class='c025'>Herodotus, <a href='#Page_112'>112</a>, <a href='#Page_158'>158</a>. - <ul> - <li>cleft near, <a href='#Page_118'>118</a>.</li> - </ul> - </li> - <li class='c025'>Herschel, Sir William, his supposed discovery of active lunar volcano, <a href='#Page_112'>112</a>.</li> - <li class='c025'>Hipparchus, <a href='#Page_78'>78</a>.</li> - <li class='c025'>Hoar frost on moon, <a href='#Page_34'>34</a>.</li> - <li class='c025'>“Hunter’s Moon,” <a href='#Page_171'>171</a>.</li> - <li class='c005'>Inhabitants of moon, <a href='#Page_31'>31</a>-<a href='#Page_32'>32</a>, <a href='#Page_88'>88</a>, <a href='#Page_95'>95</a>. - <ul> - <li>would not be visible with most powerful telescope, <a href='#Page_120'>120</a>.</li> - <li>why they might be giants, <a href='#Page_193'>193</a>.</li> - </ul> - </li> - <li class='c005'>Kepler, <a href='#Page_114'>114</a>, <a href='#Page_141'>141</a>, <a href='#Page_152'>152</a>.</li> - <li class='c025'>Kies, <a href='#Page_185'>185</a>.</li> - <li class='c005'><i>Lacus Somniorum</i>, <a href='#Page_93'>93</a>, <a href='#Page_219'>219</a>.</li> - <li class='c025'>Landsberg, <a href='#Page_217'>217</a>.</li> - <li class='c025'>Langrenus, <a href='#Page_56'>56</a>, <a href='#Page_123'>123</a>, <a href='#Page_132'>132</a>.</li> - <li class='c025'>Lava floods on moon, <a href='#Page_73'>73</a>, <a href='#Page_152'>152</a>.</li> - <li class='c025'>Libration, effects of, on visibility of parts of moon, <a href='#Page_57'>57</a>-<a href='#Page_58'>58</a>, <i>Note</i>.</li> - <li class='c025'>Life on the moon, <a href='#Page_230'>230</a>.</li> - <li class='c025'>Light of moon compared with that of sun, <a href='#Page_163'>163</a>.</li> - <li class='c025'>Lindenau, <a href='#Page_202'>202</a>.</li> - <li class='c025'>Linné, changes in, <a href='#Page_233'>233</a>. - <ul> - <li>observations of, by Professor Pickering, <a href='#Page_233'>233</a>.</li> - <li>observations of, by Schmidt, <a href='#Page_233'>233</a>.</li> - </ul> - </li> - <li class='c025'>Loewy and Puiseux, opinion of, on lunar “seas,” <a href='#Page_220'>220</a>.</li> - <li class='c025'>Longomontanus, <a href='#Page_101'>101</a>, <a href='#Page_146'>146</a>, <a href='#Page_150'>150</a>, <a href='#Page_195'>195</a>.</li> - <li class='c025'>Lubiniesky, <a href='#Page_184'>184</a>.</li> - <li class='c025'>Lunar charts, their relative accuracy, <a href='#Page_161'>161</a>.</li> - <li class='c025'>Lunar history, <a href='#Page_62'>62</a>.</li> - <li class='c025'>Lunar month, <a href='#Page_12'>12</a>.</li> - <li class='c025'>Lunar nomenclature, <a href='#Page_59'>59</a>, <a href='#Page_147'>147</a>. - <ul> - <li>number of objects bearing names, <a href='#Page_161'>161</a>.</li> - <li>singularity of, <a href='#Page_203'>203</a>.</li> - </ul> - </li> - <li class='c025'>Lunar plains, darkening of, near sunset, <a href='#Page_144'>144</a>.</li> - <li class='c025'>Lunar sickle, rule to determine position of, <a href='#Page_168'>168</a>.</li> - <li class='c025'>Lunar vegetation, <a href='#Page_32'>32</a>.</li> - <li class='c005'>Maginus, <a href='#Page_100'>100</a>, <a href='#Page_146'>146</a>, <a href='#Page_196'>196</a>.</li> - <li class='c025'>Manilius, <a href='#Page_122'>122</a>, <a href='#Page_222'>222</a>.</li> - <li class='c025'>Marco Polo, <a href='#Page_222'>222</a>.</li> - <li class='c025'><i>Mare Crisium</i>, <a href='#Page_52'>52</a>, <a href='#Page_55'>55</a>.</li> - <li class='c025'><i>Mare Fœcunditatis</i>, <a href='#Page_65'>65</a>.</li> - <li class='c025'><i>Mare Frigoris</i>, <a href='#Page_76'>76</a>.</li> - <li class='c025'><i>Mare Humorum</i>, <a href='#Page_106'>106</a>, <a href='#Page_117'>117</a>, <a href='#Page_150'>150</a>.</li> - <li class='c025'><i>Mare Imbrium</i>, <a href='#Page_103'>103</a>, <a href='#Page_142'>142</a>, <a href='#Page_144'>144</a>, <a href='#Page_224'>224</a>. - <ul> - <li>irregularities in the floor of, <a href='#Page_232'>232</a>.</li> - <li>islands in, <a href='#Page_231'>231</a>.</li> - </ul> - </li> - <li class='c025'><i>Mare Nectaris</i>, <a href='#Page_68'>68</a>, <a href='#Page_135'>135</a>.</li> - <li class='c025'><i>Mare Nubium</i>, <a href='#Page_102'>102</a>, <a href='#Page_148'>148</a>, <a href='#Page_180'>180</a>.</li> - <li class='c025'><i>Mare Serenitatis</i>, <a href='#Page_74'>74</a>, <a href='#Page_135'>135</a>, <a href='#Page_219'>219</a>, <a href='#Page_232'>232</a>. - <ul> - <li>bordering cliffs of, <a href='#Page_220'>220</a>.</li> - <li>ridges in the floor of, <a href='#Page_234'>234</a>.</li> - </ul> - </li> - <li class='c025'><i>Mare Tranquillitatis</i>, <a href='#Page_74'>74</a>, <a href='#Page_135'>135</a>.</li> - <li class='c025'><i>Mare Vaporum</i>, <a href='#Page_103'>103</a>.</li> - <li class='c025'>“Marsh of a Dream,” <a href='#Page_68'>68</a>, <a href='#Page_91'>91</a>.</li> - <li class='c025'>Mass of moon, <a href='#Page_35'>35</a>.</li> - <li class='c025'>Maurolycus, <a href='#Page_75'>75</a>, <a href='#Page_142'>142</a>, <a href='#Page_204'>204</a>.</li> - <li class='c025'>Menelaus, <a href='#Page_92'>92</a>, <a href='#Page_221'>221</a>.</li> - <li class='c025'>Mercator, <a href='#Page_185'>185</a>.</li> - <li class='c025'>Month, lunar, <a href='#Page_12'>12</a>.</li> - <li class='c025'><span class='pageno' id='Page_245'>245</span>Moon, birth of, and Pacific Ocean, <a href='#Page_6'>6</a>. - <ul> - <li>distance of, from earth, <a href='#Page_8'>8</a>.</li> - <li>greatest distance of, from earth, <a href='#Page_8'>8</a>.</li> - <li>influence of, on growth of vegetation, <a href='#Page_163'>163</a>.</li> - <li>least distance of, from earth, <a href='#Page_8'>8</a>.</li> - <li>life on, <a href='#Page_230'>230</a>.</li> - <li>other side of, <a href='#Page_139'>139</a>.</li> - <li>seen by daylight, <a href='#Page_149'>149</a>.</li> - <li>separation of, from the earth, <a href='#Page_6'>6</a>.</li> - <li>turning of same face of, toward earth, <a href='#Page_19'>19</a>.</li> - </ul> - </li> - <li class='c025'>Moon and earthquakes, <a href='#Page_165'>165</a>.</li> - <li class='c025'>Moon and the weather, <a href='#Page_164'>164</a>.</li> - <li class='c025'>Moon and volcanoes, <a href='#Page_165'>165</a>.</li> - <li class='c025'>“Moon Maiden,” <a href='#Page_10'>10</a>, <a href='#Page_96'>96</a>, <a href='#Page_103'>103</a>, <a href='#Page_122'>122</a>.</li> - <li class='c025'>Mount Hadley, <a href='#Page_222'>222</a>.</li> - <li class='c005'>New Moon, photograph of, <a href='#Page_49'>49</a>.</li> - <li class='c025'>New Moon and the weather, <a href='#Page_169'>169</a>.</li> - <li class='c025'>Newton, deepest crater on moon, <a href='#Page_107'>107</a>.</li> - <li class='c025'>Nicollet, <a href='#Page_188'>188</a>.</li> - <li class='c025'>Night, advance of, over moon, <a href='#Page_131'>131</a>. - <ul> - <li>length of, on moon, <a href='#Page_95'>95</a>.</li> - <li>lunar, coldness of, <a href='#Page_136'>136</a>.</li> - </ul> - </li> - <li class='c025'>Nodes of moon and their revolution, <a href='#Page_38'>38</a>-<a href='#Page_39'>39</a>.</li> - <li class='c005'><i>Oceanus Procellarum</i>, <a href='#Page_105'>105</a>, <a href='#Page_150'>150</a>. - <ul> - <li>submerged rays in, <a href='#Page_151'>151</a>.</li> - </ul> - </li> - <li class='c025'>Orbit of moon, <a href='#Page_8'>8</a>.</li> - <li class='c025'>Origin of moon, <a href='#Page_6'>6</a>.</li> - <li class='c005'>Pacific Ocean and birth of moon, <a href='#Page_6'>6</a>.</li> - <li class='c025'><i>Palus Somnii</i>, <a href='#Page_68'>68</a>.</li> - <li class='c025'>Path of moon about sun, <a href='#Page_16'>16</a>-<a href='#Page_17'>17</a>, <i>Note</i>.</li> - <li class='c025'>Petavius, <a href='#Page_62'>62</a>, <a href='#Page_123'>123</a>.</li> - <li class='c025'>Phases of moon explained, <a href='#Page_13'>13</a>-<a href='#Page_16'>16</a>.</li> - <li class='c025'>Phlægrean Fields, <a href='#Page_60'>60</a>.</li> - <li class='c025'>Photographs, lunar, <a href='#Page_47'>47</a>-<a href='#Page_49'>49</a>. - <ul> - <li>in series, <a href='#Page_57'>57</a>.</li> - <li>peculiar tone of, <a href='#Page_145'>145</a>.</li> - <li>why they are reversed, <a href='#Page_52'>52</a>.</li> - </ul> - </li> - <li class='c025'>Photometry, lunar, <a href='#Page_153'>153</a>-<a href='#Page_154'>154</a>.</li> - <li class='c025'>Piccolomini, <a href='#Page_72'>72</a>, <a href='#Page_200'>200</a>.</li> - <li class='c025'>Pickering, Prof. William H., observations of Linné by, <a href='#Page_233'>233</a>. - <ul> - <li>on effects of earth’s shadow on moon, <a href='#Page_28'>28</a>.</li> - <li>opinion of, regarding changes in Plato, <a href='#Page_226'>226</a>.</li> - <li>theory of Tycho’s rays by, <a href='#Page_126'>126</a>.</li> - </ul> - </li> - <li class='c025'>Pico, <a href='#Page_231'>231</a>.</li> - <li class='c025'>Pitatus, <a href='#Page_186'>186</a>, <a href='#Page_195'>195</a>.</li> - <li class='c025'>Plato, <a href='#Page_105'>105</a>, <a href='#Page_114'>114</a>, <a href='#Page_132'>132</a>, <a href='#Page_225'>225</a>. - <ul> - <li>changes observed in, opinion of Prof. William H. Pickering regarding, <a href='#Page_226'>226</a>.</li> - <li>vegetation in, <a href='#Page_227'>227</a>.</li> - </ul> - </li> - <li class='c025'>Plinius, <a href='#Page_224'>224</a>.</li> - <li class='c025'>Poetry of the moon, <a href='#Page_96'>96</a>.</li> - <li class='c025'>Posidonius, <a href='#Page_224'>224</a>.</li> - <li class='c025'>Prism binoculars for viewing moon, <a href='#Page_122'>122</a>.</li> - <li class='c025'>Proclus, <a href='#Page_68'>68</a>. - <ul> - <li>remarkable brilliance of, <a href='#Page_90'>90</a>.</li> - </ul> - </li> - <li class='c025'>Projectile force on moon, <a href='#Page_37'>37</a>.</li> - <li class='c025'>Promontorium Ænarium, <a href='#Page_189'>189</a>.</li> - <li class='c025'>Promontory Acherusia, <a href='#Page_224'>224</a>.</li> - <li class='c025'>Promontory Heraclides, <a href='#Page_109'>109</a>.</li> - <li class='c025'>Promontory Laplace, <a href='#Page_109'>109</a>.</li> - <li class='c025'><span class='pageno' id='Page_246'>246</span>Ptolemæus, <a href='#Page_98'>98</a>.</li> - <li class='c025'>Pytheas, <a href='#Page_216'>216</a>.</li> - <li class='c005'>Rabbi Levi, <a href='#Page_202'>202</a>.</li> - <li class='c025'>Reinhold, <a href='#Page_217'>217</a>.</li> - <li class='c025'>Riccioli, nomenclature of, for lunar objects, <a href='#Page_69'>69</a>.</li> - <li class='c025'>Rings, ranges of, on moon, <a href='#Page_97'>97</a>-<a href='#Page_98'>98</a>.</li> - <li class='c025'>Riphæan Mountains, <a href='#Page_190'>190</a>.</li> - <li class='c025'>Rotation of moon “braked” by tides, <a href='#Page_20'>20</a>.</li> - <li class='c025'>Rotation of moon, illustrated, <a href='#Page_19'>19</a>-<a href='#Page_20'>20</a>.</li> - <li class='c005'>Sacrobosco, <a href='#Page_206'>206</a>.</li> - <li class='c025'>Schickard, <a href='#Page_115'>115</a>.</li> - <li class='c025'>Schmidt, observation of Linné by, <a href='#Page_233'>233</a>.</li> - <li class='c025'>Schröter, “lunar city” discovered by, <a href='#Page_218'>218</a>.</li> - <li class='c025'>“Seas,” lunar, character of beds of, <a href='#Page_142'>142</a>.</li> - <li class='c025'>Shadow of moon during eclipse, <a href='#Page_40'>40</a>. - <ul> - <li>length of, <a href='#Page_40'>40</a>.</li> - </ul> - </li> - <li class='c025'>Shadows on moon, topography revealed by, <a href='#Page_100'>100</a>-<a href='#Page_101'>101</a>. - <ul> - <li>used to measure heights on moon, <a href='#Page_63'>63</a>.</li> - </ul> - </li> - <li class='c025'>Sidereal revolution of moon, <a href='#Page_11'>11</a>.</li> - <li class='c025'><i>Sinus Æstuum</i>, <a href='#Page_103'>103</a>.</li> - <li class='c025'><i>Sinus Iridum</i>, <a href='#Page_109'>109</a>.</li> - <li class='c025'><i>Sinus Medii</i>, <a href='#Page_103'>103</a>.</li> - <li class='c025'><i>Sinus Roris</i>, <a href='#Page_159'>159</a>.</li> - <li class='c025'>Size of moon, <a href='#Page_8'>8</a>.</li> - <li class='c025'>Sky as seen from moon, <a href='#Page_29'>29</a>.</li> - <li class='c025'>Snow, can it exist on the moon? <a href='#Page_69'>69</a>.</li> - <li class='c025'><span class='pageno' id='Page_247'>247</span>Snow, non-existence of, on moon, <a href='#Page_69'>69</a>.</li> - <li class='c025'>South polar region of moon, <a href='#Page_77'>77</a>.</li> - <li class='c025'>South pole of moon, <a href='#Page_106'>106</a>.</li> - <li class='c025'>Stadius, <a href='#Page_218'>218</a>.</li> - <li class='c025'>Stöfler, <a href='#Page_75'>75</a>. - <ul> - <li>row of rings near, <a href='#Page_204'>204</a>.</li> - </ul> - </li> - <li class='c025'>“Straight wall,” <a href='#Page_187'>187</a>.</li> - <li class='c025'>Strait between Apennines and Caucasus, <a href='#Page_234'>234</a>.</li> - <li class='c025'>Sulpicius Gallus, <a href='#Page_222'>222</a>.</li> - <li class='c025'>Sunrise, slow progress of, on moon, <a href='#Page_94'>94</a>.</li> - <li class='c025'>Sunshine, effects of, when vertical on moon, <a href='#Page_100'>100</a>.</li> - <li class='c025'>Surface of moon, nature of, <a href='#Page_9'>9</a>. - <ul> - <li>size of, <a href='#Page_9'>9</a>.</li> - </ul> - </li> - <li class='c025'>Synodic revolution of, <a href='#Page_11'>11</a>-<a href='#Page_12'>12</a>.</li> - <li class='c005'>Tacitus, <a href='#Page_200'>200</a>.</li> - <li class='c025'>Telescopic power, limits of, <a href='#Page_120'>120</a>.</li> - <li class='c025'>Teneriffe Mountains, <a href='#Page_231'>231</a>.</li> - <li class='c025'>“Terminator,” meaning of, <a href='#Page_63'>63</a>.</li> - <li class='c025'>Theætetus, <a href='#Page_225'>225</a>.</li> - <li class='c025'>Theophilus, <a href='#Page_71'>71</a>, <a href='#Page_138'>138</a>, <a href='#Page_198'>198</a>, <a href='#Page_206'>206</a>. - <ul> - <li>crater pits near, <a href='#Page_211'>211</a>.</li> - <li>grandeur of appearance of, when highly magnified, <a href='#Page_207'>207</a>.</li> - <li>great mountain fold near, <a href='#Page_207'>207</a>-<a href='#Page_208'>208</a>.</li> - <li>what would be seen from wall of, near sunset, <a href='#Page_208'>208</a>.</li> - </ul> - </li> - <li class='c025'>Tidal attraction, forcing moon away in reaction of, <a href='#Page_6'>6</a>.</li> - <li class='c025'>“Tidal friction,” <a href='#Page_20'>20</a>.</li> - <li class='c025'>Tides, causing of, by moon and sun, <a href='#Page_21'>21</a>. - <ul> - <li>effect of earth’s rotation on, <a href='#Page_25'>25</a>.</li> - <li><span class='pageno' id='Page_248'>248</span>service rendered by, <a href='#Page_22'>22</a>.</li> - <li>simultaneous occurrence of, on opposite sides of earth, <a href='#Page_23'>23</a>.</li> - <li>when highest, <a href='#Page_21'>21</a>.</li> - <li>when lowest, <a href='#Page_22'>22</a>.</li> - </ul> - </li> - <li class='c025'>Twilight, why none on moon, <a href='#Page_64'>64</a>.</li> - <li class='c025'>Tycho, <a href='#Page_10'>10</a>, <a href='#Page_98'>98</a>, <a href='#Page_106'>106</a>, <a href='#Page_146'>146</a>, <a href='#Page_191'>191</a>. - <ul> - <li>longest ray of, <a href='#Page_93'>93</a>, <a href='#Page_221'>221</a>.</li> - <li>ray system of, <a href='#Page_124'>124</a>.</li> - <li>rays of, <a href='#Page_99'>99</a>. - <ul> - <li>theory of Nasmyth, <a href='#Page_124'>124</a>-<a href='#Page_125'>125</a>.</li> - <li>theory of Pickering, <a href='#Page_126'>126</a>.</li> - </ul> - </li> - </ul> - </li> - <li class='c005'>Vegetation on moon, <a href='#Page_32'>32</a>, <a href='#Page_115'>115</a>, <a href='#Page_142'>142</a>, <a href='#Page_144'>144</a>, <a href='#Page_227'>227</a>.</li> - <li class='c025'>Vendelinus, <a href='#Page_59'>59</a>, <a href='#Page_123'>123</a>.</li> - <li class='c025'>Venus seen by daylight, <a href='#Page_149'>149</a>.</li> - <li class='c025'>Verne, Jules, “Trip to the Moon,” <a href='#Page_4'>4</a>.</li> - <li class='c025'>Volcanic craters on moon, <a href='#Page_60'>60</a>.</li> - <li class='c025'>Volcanoes, lunar, <a href='#Page_54'>54</a>. - <ul> - <li>contrasted with those of earth, <a href='#Page_84'>84</a>.</li> - <li>effects of gravitation on size of, <a href='#Page_86'>86</a>.</li> - </ul> - </li> - <li class='c005'>Water on the moon, <a href='#Page_53'>53</a>.</li> - <li class='c025'>“Weathering” on the moon, <a href='#Page_197'>197</a>.</li> - <li class='c025'>Weight on the moon, <a href='#Page_36'>36</a>.</li> - <li class='c025'>Werner, <a href='#Page_78'>78</a>, <a href='#Page_205'>205</a>.</li> - <li class='c025'>Wilhelm I., <a href='#Page_102'>102</a>, <a href='#Page_195'>195</a>.</li> - <li class='c005'>Zagut, <a href='#Page_202'>202</a>.</li> -</ul> -<div class='pbb'> - <hr class='pb c005' /> -</div> - -<div class='nf-center-c0'> -<div class='nf-center c005'> - <div><span class='pageno' id='Page_249'>249</span><b><span class='large'>BOOKS BY GARRETT P. 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