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.”