by Mark Wicks
CHAPTER V
WE VIEW THE LUNAR SCENERY IN THE NORTHERN HEMISPHERE
"Now, Professor," exclaimed M'Allister, jumping up with a shrug of theshoulders, "you've given our friend John a considerable amount ofinformation on a wee bit dry subject, so, mayhap, you will now give ussomething more interesting, and go on with the description of thenatural features of the moon down yonder."
"Yes do, please, Professor," said John; "M'Allister's own temperature isevidently rising rapidly. Strange, isn't it, that a douche of cold factsshould make our friend so warm!"
"Well, not altogether," I replied laughingly; "there should always be ahealthy reaction after a cold douche. Much depends on the intensity ofthe cold applied, and you know that if you touch extremely cold metal itburns you like hot iron!"
"Professor," chimed in M'Allister, "maybe I _was_ a bit warm, but reallyyour facts were not so cold as to make me hot."
"I'm glad to hear you say so," I answered.
"At all events, Professor," continued John, "whatever may beM'Allister's actual temperature, I'm simply burning to know somethingabout that very striking formation with the steel-grey colouredflooring which is situated not very far down from the North Pole, and alittle to the east of the central meridian."
"That," I said, "is a large walled plain called Plato, and, being on areceding curve of the moon, it is seen from the earth foreshortened, sothat it appears to be elliptical in shape. It is about sixty miles indiameter, and encloses an area of 2700 square miles, which is just aboutthe area of Lincolnshire. The general height of the mountain walls isover 3600 feet; one mountain on the east is nearly 7500 feet high, andothers on the north and west are but little lower.
"You will notice that there are several breaks in the walls, and a largeone on the south-west; whilst on the inner slope of the mountains youcan see where a great landslide has occurred.
"It is rather singular, John, that in your first selection you havechosen a formation which is one of the lunar mysteries!"
"Ah! Professor," said John, smiling, "I always was lucky! What is thisdreadful mystery?" he asked, with an assumed expression of awe.
"Oh, it's not a ghost story, John, nor anything to make your fleshcreep," I said rather grimly. "Usually the floor of a walled plainbecomes brighter as the sun rises higher and higher in the sky, butPlato actually becomes darker under a high sun. By some it has beenthought that this is merely the effect of contrast with the very brightsurroundings of this formation, and that there is no actual darkening ofthe tint. This is certainly not the case, for I have examined itcarefully myself with the telescope--shutting out all the brightsurroundings from the field of view, but the floor still appearedequally dark.
"Others have suggested that the hot sun causes the growth of some kindof vegetation all over the plain, the ripening of which makes the floordarker in tint. As regards this suggestion, it is the fact that uponMars the old sea-beds are the places where vegetation is most luxuriantat the present time; so, if Plato were at one time an enclosed sea, itmight not be impossible that vegetation in some low form might grow andbe nourished by the crude gaseous remains of a former atmosphere. Agreenish tint has occasionally been noticed by some observers, alsoseveral light streaks across the floor, as well as several smallcraterlets, which have been duly noted on the maps.
"But before we go any further we will have a better means of seeing, forit is rather uncomfortable looking directly down upon the moon. So,John, just lend a hand and we'll fetch one of those large mirrors."
This was done, and the mirror suspended with the upper part projectingforward, so that when adjusted at the proper angle we could sit and lookstraight into the mirror before us and see the reflection of all thatwas below. We could still look down at the objects, if we wished to doso, without shifting our position.
"There, John," I remarked, as we completed this arrangement, "I havealready arranged mirrors in the proper positions at the windows in theforepart of the vessel, so that in future M'Allister will be able to seewhat is nearly straight ahead of him. Now you will understand that I hada scientific use for the mirrors I provided, and did not require themmerely to admire my beautiful face in as you suggested."
John laughed as I recalled his suggestion, saying, "All right,Professor, I know you generally have a good reason for what you do."
Now, being more comfortably seated, I drew their attention to some smallisolated mountains on the area to the south of Plato, pointing out Pico,an isolated mountain over 8000 feet in height, and another with threepeaks not very far from it. To the north-east of these, some distanceaway, are the Teneriffe and Straight Ranges; also isolated groups.
"You will remember," I remarked, "that I said there were severalformations which seemed to me to owe their present appearance to theaction of water. Now look well at all this district before us--does itnot seem to bear out my contention? Those numerous small mountains andisolated groups were not, I think, originally isolated, but connectedwith the adjoining ranges. If we assume that Plato was once an enclosedsea, or lake, which burst through the mountain walls--possibly owing totheir being weakened or broken by volcanic action--there would have beena tremendous outrush of water, which must have carried away a good dealof the softer material of these hills and mountains; whilst, in afteryears, the continual wash of the waters, combined with aerialdenudation, would gradually have worn away all but the hardest parts ofthese formations.
"Most probably the whole of the surrounding area was also at some time asea, though volcanic action has since altered its surface conformation,and in places it bears evidence of having been covered with lava. It isnot unusual on our world for volcanoes to burst up from under the sea,so even the evidence of volcanic action does not, as some seem to think,negative the possibility of water ever existing here; and it may not beinappropriate to point out that our hydrographers have proved that ourocean-beds are not always smooth, but are often diversified by highhills and deep valleys."
M'Allister here interjected: "Professor, would you kindly tell ussomething about that fine range of mountains over yonder, just to theright hand?"
"Oh yes," I replied; "I was just about to mention that mountain range,which is called the Alps after those in Switzerland; and that peak onthe front portion, just south of the great valley you see, is named MontBlanc, and is about 12,000 feet in height.
"You will notice a very large number of peaks in this and the otherneighbouring ranges--in fact, several thousands have been marked on ourlarge maps.
"Cutting diagonally in a north-westerly direction, completely throughthe Alps, you will notice a long and deep valley. This is known as the'Great Alpine Valley,' and is over eighty miles long, and varies fromabout three miles to six and a half miles in width. At the eastern endit is some 11,000 feet deep, debouching on to the plain in severalcomparatively narrow passes, whilst at its north-western extremity it isvery shallow, and emerges on to what is known as the Sea of Cold, whichcovers an area of about 100,000 square miles. This valley seems toafford another example of formation by the action of water.
"Amongst the three thousand peaks comprised in the Apennine range justbelow the Alps, are several mountains of considerable altitude," Iremarked, pointing out Mount Huygens, nearly 20,000 feet high, MountHadley, 15,000 feet, and Mount Woolf, 12,000 feet in height. "This rangecurves round towards the east, and finishes with a fine ring-plaincalled Eratosthenes--some thirty-seven miles in diameter, with a floordepressed 8000 feet below the lunar surface. It encloses a centralmountain, and on the east wall there is one peak which rises 16,000 feetabove the floor.
"The ranges in this part of the moon are, perhaps, more like those onour earth than others to be found on its surface, but much more wild andrugged.
"Eastward and northward of these ranges is the Sea of Showers, on whichthere are several fine ring-mountains and walled plains--notablyAutolychus and Aristillus, two very perfect ring-mountains some 9000feet high.
"One of the most striking, on account of i
ts size and situation, is thatlarge one which is called Archimedes, and is about fifty miles indiameter; and you will notice that a rugged mass of mountains and highhills extends from it to a distance of over a hundred miles on thesouth. The floor of this walled plain is only about 600 feet below thegeneral level, and the mountain walls average about 4000 feet in height;but there is at least one peak some 7000 feet high.
"You will see a little below and westward of Archimedes the commencementof a system of large cracks or crevasses in the lunar surface which areknown as 'rills.' Many such systems are found in various parts of themoon; some of the cracks are comparatively shallow, but, according toProfessor Langley, others are known to be at least eight miles deep, andmay be infinitely deeper, though I cannot say I understand how thesegreat depths have been arrived at. The length of the cracks varies froma few miles to over three hundred miles, and from a few hundred yards tosome miles in width. They are attributed partly to volcanic action, butmainly to the contraction of the crust of the lunar globe as it becamecold. Being so much smaller, the moon would cool much more rapidly thanthe earth, and the disruptive effects would necessarily be greater."
John here touched my arm, and pointing to some mountains on the bordersof a large elongated oval area, close to the north-western terminatorwhere the sun was setting, asked me what they were. I explained that thedark area was known as the Mare Crisium, or Sea of Conflicts, and ispossibly the deepest of the large lunar depressions.
"It is about 280 miles long from north to south, and 355 miles wide fromeast to west, but, owing to its position, the width is seen from theearth very much foreshortened, so that it really looks nearly twice aslong as it is wide. It contains an area of about 75,000 square miles,thus being as large as the combined area of Scotland and Ireland, andthe five largest northern counties of England. It is surrounded bymountains, some being over 11,000 feet high, reckoning from the darkfloor."
I drew their attention to Proclus--a ring-mountain on the eastern sideof this sea--which is about eighteen miles in diameter, and the secondbrightest of the lunar formations. "From its neighbourhood severalbright streaks diverge in different directions, two extending a long wayacross the dark area, and there is a longer one striking towards thenorth and another towards the south at an angle of about 120 degreeswith each other.
"Seen through the telescope, these ray-streaks often appear verybrilliant under a high sun, looking in fact very like electricsearch-lights; though I notice that the Rev. T.W. Webb has rathercuriously remarked that these particular streaks are not very easilyseen. Similar ray-streaks, many enormously longer than these, are foundin various parts of the lunar surface, but their exact nature and originhas never yet been definitely settled. They only come into view when thesun is beginning to be high up in the lunar sky, and the higher the sun,the brighter the rays appear. Some of the shorter ones are ridges, butthis is evidently not the case with the others, for they cast noshadows, as ridges would when the sun is low. Very many radiate from alarge ring-mountain called Tycho, in the southern hemisphere; and one ofthem extends, with some breaks, nearly three thousand miles, passingnorthward over the Sea of Serenity and finally disappearing on themoon's north-western edge, or 'limb,' as it is termed.
"Professor Pickering assumes that these rays were caused by volcanicdust or other light reflecting material emitted from a series of smallcraters, and states that they are really made up of a series of shortrays placed or joined end to end. What I have observed myself seems tobear out this latter statement; but the opinion I have formed as totheir origin differs from the theory of Professor Pickering. It seems tome more probable that the volcanic dust was carried by a strong wind,split up into two or more separate currents by a succession of peaks.The wind currents swept clean the area over which they actually passed,but dust fell or drifted in the lines between the currents. Exactly thesame thing may be observed in connection with snow-storms on our earthwhen accompanied by a high wind. One part of the earth's surface will beswept clean by the wind current, whilst a long line of the adjoiningsurface is covered with a thick deposit of snow. I have also noticedthat where the ray-streaks impinge upon a mountain, or ring, there is anappearance of spreading out and heaping up of the bright material verymuch as snow would be spread out or drifted up in similar situations onthe earth."
M'Allister here interrupted with the remark that, when we wereapproaching the moon, he had particularly noticed that all appearance ofthe face of the "man in the moon" had vanished. He said he had expectedto see that more distinctly as we got nearer.
"That would not be the case, M'Allister," I answered. "The resemblanceto a human face which we see from the earth is caused by the combinedeffect of the bright and dusky areas on the lunar surface as seen from adistance. The depressed dark areas, which we call seas, form the eyes,nose, and mouth of the face, but when we had approached nearer to themoon the details of the surface configuration stood out so much moredistinctly that they entirely obliterated the general effect of themarkings as seen from a distance."
"Professor," exclaimed John, "I have read that before telescopes wereinvented it was thought by many that the markings seen on the moon werereally the features of our own earth reflected by the moon as in amirror. Is that correct?"
"Oh yes, John," I said. "It seems to have been a fairly general beliefin many parts of the world, and travellers tell us that, even withinvery recent times, they have found in some of the more out-of-the-wayparts of the world that the same idea is still held by uneducatedpeople!"
Objects of interest being so numerous on the lunar surface we could onlygive a comprehensive glance at many of them, and as we had so manyplaces to inspect, I now gave M'Allister the order to steer eastward.
He accordingly moved his switches and the _Areonal_ quickly passed overthe Sea of Tranquillity, which has an area of 140,000 square miles; thenover the Sea of Vapours, a smaller area, parts of which have a duskygreen tint, from whence to the northward we had a view over the Sea ofSerenity, another deep depression nearly as large as the Sea ofTranquillity, and much of which is a light green colour.
Then we came again to the Sea of Showers, a large "sea" having an areaof 340,000 square miles; and, still moving eastward, the great lunar"Ocean of Storms" soon came into view. This covers a very large portionof the eastern and north-eastern part of the moon's surface, and, withall its bays and indentations, is estimated to be two million squaremiles in extent.
I, however, again reminded them that, although these areas are termedseas and oceans, no water exists there now, whatever may have been thecase in the long distant past. They are now only large depressions, andnot often level but intersected by hills, ridges, and even mountains.
As we passed along I called their particular attention to themagnificent "Bay of Rainbows" on the north-eastern coast of the Sea ofShowers. "From Cape Laplace (9000 feet high) on the western extremity,to Cape Heraclides (4000 feet high) on the eastern extremity, this greatbay is about 140 miles across, the depth of its curvature being overeighty miles. It bears a very strong resemblance to many large bays onour sea-coasts in various parts of the world, but I am not aware of anysuch bay which is bordered by a mass of such lofty mountains as this is.
"We are looking at it now under a high sun, but when the sun has onlyjust risen sufficiently high to illuminate all those high mountains,whilst the lower surroundings are still in shadow, the great baypresents in the telescope the appearance of a brilliant luminous archspringing from the lighted part of the moon and extending far out overthe dark part of the disc.
"Farther eastward, and lower down on the Ocean of Storms, you willobserve what is admitted by all to be the very brightest large formationupon the moon, viz. Aristarchus--a ring-plain nearly thirty miles indiameter, the floor of which is 5000 feet below the surface level. Itpossesses a central mountain, very difficult to measure on account ofthe general brightness, but believed to be about 1300 feet high.Well-defined terraces are seen on the mountain walls enclosing the area,and
many external ridges are connected with the walls, especially to thesouth. This formation is evidently covered with some substance whichreflects light to a greater extent than that on similar formations;indeed it appears so bright that when the moon is new and the whole ofthis part of the disc is dark, Aristarchus can still be seen with atelescope, and this gave rise in the past to the idea that it was avolcano in actual eruption. The explanation is, however, more prosaic,because the mountain is really brought into view by earthshine on itsbright covering. When the moon is new the earth is almost fully lightedon the side toward the moon, and sheds a faint light on the dark portionof its disc, thus producing the phenomenon known as 'the old moon in thenew moon's arms.'
"Close to Aristarchus you will notice another ring-plain, which iscalled Herodotus, about twenty-three miles in diameter, with a floor7000 feet depressed; but this formation is not nearly so bright as itsneighbour. That high plateau between them is notable on account of theT-shaped cleft in it, which runs into that other long zig-zag cleft (insome parts two miles wide and 1600 feet in depth), whose directionchanges abruptly several times in its length of over one hundred miles.
"Turning from this towards the south-west you will see the most majesticformation to be found upon the moon--the great ring-plain called'Copernicus,' after the founder of our present system of astronomy. Itis about sixty miles in diameter, only roughly circular in shape, and asit stands isolated upon the great ocean-bed it is most favourablysituated for observation. A large number of very high ridges, separatedby deep valleys, radiate from it in all directions to a distance ofhundreds of miles, presenting the appearance of a grand system ofbuttresses to the mountain walls. These walls are high, and contain avery large number of peaks which, when seen through the telescope asthey catch the sunlight, look like a string of bright pearls shining onthe border of the ring. A peak on one side is 12,000 feet in altitude,on the other side is one only 1000 feet lower, whilst, rising from nearthe central part of the floor, are no less than five small mountainpeaks. Owing to its size, brightness, and isolated position, thissplendid ring-mountain can be seen from the earth without the aid of aglass; but even a field-glass will reveal much in this and similarformations which cannot be detected by the unaided eye.
"The Rev. T.W. Webb has termed Tycho, in the southern hemisphere, 'theMetropolitan Crater of the Moon,' but, in my opinion, Copernicus is,owing to its position and grandeur, much more worthy of that dignity.Tycho is fine in itself, but is not so favourably situated, beingsurrounded by other formations somewhat in the same way as St. Paul'sCathedral is surrounded and shut in, for the most part, by other andmeaner buildings.
"How much more should we appreciate the splendid proportions and majestyof our Metropolitan Cathedral if we could view it as an isolatedbuilding with a fine open space all around it!"
"I quite agree with that, Professor," remarked John, "and I have alwaysthought it a great pity that Sir Christopher Wren was not allowed tocarry out his original plan in this respect."
We were looking at the Carpathian range of mountains just to thenorthward of Copernicus, when M'Allister touched my arm, exclaiming,"Look, Professor, at all those tiny craters near the western side ofCopernicus. Why, there are so many of them that the ground for milesround looks like a honeycomb, and in some places there are straight rowsof them!"
"Yes," I said, "this part of the lunar surface is simply riddled withtiny craterlets, and some of them are utilised as tests for thedefinition of our telescopes. I have heard it remarked that a map ofthis part of the moon presents almost the appearance of the froth on aglass of stout when it has settled down, the very numerous tinyair-bubbles of different sizes representing the craterlets; and reallyit does bear such a resemblance.
"Almost due east of Copernicus is another bright and isolated ring-plainnamed Kepler, after the celebrated astronomer. This is some twenty-twomiles in diameter and surrounded by very bright streaks of light,extending in some directions over seventy miles, the whole nimbus oflight covering an area of nearly ten thousand square miles. These reallyare streaks, not ridges, for, as you will see, nearly all the surfacesurrounding this formation is flat and level.
"Some of the streaks from Kepler radiate in the direction ofAristarchus, others towards Copernicus, cutting right through the raysfrom those formations. From this it is gathered that Copernicus wasformed first, then Aristarchus, and Kepler still later on in the moon'shistory.
"The surrounding wall of Kepler is comparatively low with respect tothe lunar surface level, but the depth of the crater is nearly tenthousand feet below the mountain peaks. The whole formation is coveredwith the same light-reflecting material as the streaks which surroundit."
