one year with another, much however might have been done by our lunar
observer during this century. In its beginning, in comparison to the
vast forests which then covered the North American continent, the
cultivated fields along its eastern seaboard would have looked to him
like a golden fringe bordering a broad mantle of green; but now he
would see that the golden fringe has encroached upon the green farther
back than the Mississippi, and he would gather his best evidence of
change from the fact (surely a noteworthy one) that the people of
the United States have altered the features of the world during the
present century to a degree visible in another planet!
Our observer would probably be struck by the moving panorama of
forests, lakes, continents, islands, and oceans, successively gliding
through the field of view of his telescope as the earth revolved;
but, travelling along beside it on his lunar station, he would hardly
appreciate its actual flight through space, which is an easy thing to
describe in figures, and a hard one to conceive. If we look up at the
clock, and as we watch the pendulum recall that we have moved about
nineteen miles at every beat, or in less than three minutes, over a
distance greater than that which divides New York from Liverpool, we
still probably but very imperfectly realize the fact that (dropping
all metaphor) the earth is really a great projectile, heavier than the
heaviest of her surface rocks, and traversing space with a velocity of
over sixty times that of the cannon-ball. Even the firing of a great
gun with a ball weighing one or two hundred pounds is, to the novice at
least, a striking spectacle. The massive iron sphere is hoisted into
the gun, the discharge comes, the ground trembles, and, as it seems,
almost in the same instant, a jet rises where the ball has touched the
water far away. The impression of immense velocity and of a resistless
capacity of destruction in that flying mass is irresistible, and
justifiable too: but what is this ball to that of the earth, which is
a globe counting eight thousand miles in diameter, and weighing about
six thousand millions of millions of millions of tons; which, if our
cannon-ball were flying ahead a mile in advance of its track, would
overtake it in less than the tenth part of a second; and which carries
such a potency of latent destruction and death in this motion, that if
it were possible instantly to arrest it, then, in that instant, “earth
and all which it inherits would dissolve” and pass away in vapor?
Our turning sphere is moving through what seems to be all but an
infinite void, peopled only by wandering meteorites, and where warmth
from any other source than the sun can scarcely be said to exist; for
it is important to observe that whether the interior be molten or
not, we get next to no heat from it. The cold of outer space can only
be estimated in view of recent observations as at least four hundred
degrees Fahrenheit below zero (mercury freezes at thirty-nine degrees
below), and it is the sun which makes up the difference of all these
lacking hundreds of degrees to us, but indirectly, and not in the way
that we might naturally think, and have till very lately thought; for
our atmosphere has a great deal to do with it beside the direct solar
rays, allowing more to come in than to go out, until the temperature
rises very much higher than it would were there no air here. Thus,
since it is this power in the atmosphere of storing the heat which
makes us live, no less than the sun’s rays themselves, we see how the
temperature of a planet may depend on considerations quite beside its
distance from the sun; and when we discuss the possibility of life in
other worlds, we shall do well to remember that Saturn may be possibly
a warm world, and Mercury conceivably a cold one.
We used to be told that this atmosphere extended forty-five miles above
us, but later observation proves its existence at a height of many
times this; and a remarkable speculation, which Dr. Hunt strengthens
with the great name of Newton, even contemplates it as extending in
ever-increasing tenuity until it touches and merges in the atmosphere
of other worlds.
[Illustration: FIG. 65.--THE MOON.
(FROM A PHOTOGRAPH BY L. M. RUTHERFURD, 1873, PUBLISHED BY O. G.
MASON.)]
But if we begin to talk of things new and old which interest us in our
earth as a planet, it is hard to make an end. Still we may observe
that it is the very familiarity of some of these which hinders us from
seeing them as the wonders they really are. How has this familiarity,
for instance, made commonplace to us not only the wonderful fact that
the fields and forests, and the apparently endless plain of earth and
ocean, are really parts of a great globe which is turning round
(for this rotation we all are familiar with), but the less appreciated
miracle that we are all being hurled through space with an immensely
greater speed than that of the rotation itself. It needs the vision
of a poet to see this daily miracle with new eyes; and a great poet
has described it for us, in words which may vivify our scientific
conception. Let us recall the prologue to “Faust,” where the archangels
are praising the works of the Lord, and looking at the earth, not as we
see it, but down on it, from heaven, as it passes by, and notice that
it is precisely this miraculous swiftness, so insensible to us, which
calls out an angel’s wonder.
“And swift and swift beyond conceiving
The splendor of the world goes round,
Day’s Eden-brightness still relieving
The awful Night’s intense profound.
The ocean tides in foam are breaking,
Against the rocks’ deep bases hurled,
And both, the spheric race partaking,
Eternal, swift, are onward whirled.”[5]
[5] Bayard Taylor’s translation.
So, indeed, might an angel see it and describe it!
* * * * *
We may have been already led to infer that there is a kind of evolution
in the planets’ life, which we may compare, by a not wholly fanciful
analogy, to ours; for we have seen worlds growing into conditions
which may fit them for habitability, and again other worlds where we
may surmise, or may know, that life has come. To learn of at least one
which has completed the analogy, by passing beyond this term to that
where all life has ceased, we need only look on the moon.
* * * * *
The study of the moon’s surface has been continued now from the time
of Galileo, and of late years a whole class of competent observers has
been devoted to it, so that astronomers engaged in other branches have
oftener looked on this as a field for occasional hours of recreation
with the telescope than made it a constant study. I can recall one or
two such hours in earlier observing days, when, seated alone under
the overarching iron dome, the world below shut out, and the world
above opened, the silence disturbed by no sound but the beating of the
equatorial clock, and the great telescope itself directed to some hill
or valley of the moon, I have been so lost in gazing that it seemed as
though a look through this, the real magic tube, had indeed transported
me to the surface of that strange alien world. Fortunately for us, the
same spectacle has impressed others with more time to devote to it and
more ability to render it, so that we not only have most elaborate
maps of the moon for the professional astronomer, but abundance of
paintings, drawings, and models, which reproduce the appearance of
its surface as seen in powerful telescopes. None of the latter class
deserves more attention than the beautiful studies of Messrs. Nasmyth
and Carpenter, who prepared at great labor very elaborate and, in
general, very faithful models of parts of its surface, and then had
them photographed under the same illumination which fell on the
original; and I wish to acknowledge here the special indebtedness of
this part of what I have to lay before the reader to their work, from
which the following illustrations are chiefly taken.
Let us remember that the moon is a little over twenty-one hundred miles
in diameter; that it weighs, bulk for bulk, about two-thirds what the
earth does, so that, in consequence of this and its smaller size, its
total weight is only about one-eightieth of that of our globe; and
that, the force of gravity at its surface being only one-sixth what it
is here, eruptive explosions can send their products higher than in our
volcanoes. Its area is between four and five times that of the United
States, and its average distance is a little less than two hundred and
forty thousand miles.
[Illustration: FIG. 66.--THE FULL MOON.]
This is very little in comparison with the great spaces we have been
traversing in imagination; but it is absolutely very large, and across
it the valleys and mountains of this our nearest neighbor disappear,
and present to the naked eye only the vague lights and shades known to
us from childhood as “the man in the moon,” and which were the puzzle
of the ancient philosophers, who often explained them as reflections
of the earth itself, sent back to us from the moon as from a mirror.
It, at any rate, shows that the moon always turns the same face toward
us, since we always see the same “man,” and that there must be a back
to the moon which we never behold at all; and, in fact, nearly half of
this planet does remain forever hidden from human observation.
The “man in the moon” disappears when we are looking in a telescope,
because we are then brought so near to details that the general
features are lost; but he can be seen in any photograph of the full
moon by viewing it at a sufficient distance, and making allowance for
the fact that the contrasts of light and shade appear stronger in the
photograph than they are in reality. If the small full moon given in
Fig. 66, for instance, be looked at from across a room, the naked-eye
view will be recovered, and its connection with the telescopic ones
better made out. The best time for viewing the moon, however, is not
at the full, but at the close of the first quarter; for then we see,
as in this beautiful photograph (Fig. 65) by Mr. Rutherfurd, that the
sunlight, falling slantingly on it, casts shadows which bring out all
the details so that we can distinguish many of them even here,--this
photograph, though much reduced, giving the reader a better view than
Galileo obtained with his most powerful telescope. The large gray
expanse in the lower part is the Mare Serenitatis, that on the left the
Mare Crisium, and so on; these “seas,” as they were called by the old
observers, being no seas at all in reality, but extended plains which
reflect less light than other portions, and which with higher powers
show an irregular surface. Most of the names of the main features of
the lunar surface were bestowed by the earlier observers in the infancy
of the telescope, when her orb
“Through optic glass the Tuscan artist ‘viewed’
At evening from the top of Fiesole
Or in Valdarno, to descry new lands,
Rivers, or mountains in her spotty globe.”
Mountains there are, like the chain of the lunar Apennines, which the
reader sees a little below the middle of the moon, and to the right
of the Mare Serenitatis, and where a good telescope will show several
thousand distinct summits. Apart from the mountain chains, however, the
whole surface is visibly pitted with shallow, crater-like cavities,
which vary from over a hundred miles in diameter to a few hundred yards
or less, and which, we shall see later, are smaller sunken plains
walled about with mountains or hills.
One of the most remarkable, of these is Tycho, here seen on the
photograph of the full moon (Fig. 66), from which radiating streaks go
in all directions over the lunar surface. These streaks are a feature
peculiar to the moon (at least we know of nothing to which they can be
compared on the earth), for they run through mountain and valley for
hundreds of miles without any apparent reference to the obstacles in
their way, and it is clear that the cause is a deep-seated one. This
cause is believed by our authors to be the fact that the moon was once
a liquid sphere over which a hard crust formed, and that in subsequent
time the expansion of the interior before solidification cracked the
shell as we see. The annexed figure (Fig. 67) is furnished by them to
illustrate their theory, and to show the effects of what they believe
to be an analogous experiment, _in minimis_, to what Nature has
performed on the grandest scale; for the photograph shows a glass globe
actually cracked by the expansion of an enclosed fluid (in this case
water), and the resemblance of the model to the photograph of the full
moon on page 141 is certainly a very interesting one.
[Illustration: FIG. 67.--GLASS GLOBE, CRACKED.]
We are able to see from this, and from the multitude of craters shown
even on the general view, where the whole face of our satellite is
pit-marked, that eruptive action has been more prominent on the moon in
ages past than on our own planet, and we are partly prepared for what
we see when we begin to study it in detail.
We may select almost any part of the moon’s surface for this nearer
view, with the certainty of finding something interesting. Let us
choose, for instance, on the photograph of the half-full moon (Fig.
65), the point near the lower part of the Terminator (as the line
dividing light from darkness is called) where a minute sickle of light
seems to invade the darkness, and let us apply in imagination the power
of a large telescope to it. We are brought at once considerably within
a thousand miles of the surface, over which we seem to be suspended,
everything lying directly beneath us as in a bird’s-eye view, and what
we see is the remarkable scene shown in Fig. 68.
We have before us such a wealth of detail that the only trouble is
to choose what to speak of where every point has something to demand
attention, and we can only give here the briefest reference to the
principal features. The most prominent of these is the great crater
“Plato,” which lies in the lower right-hand part of the cut. It will
give the reader an idea of the scale of things to state that the
diameter of its ring is about seventy miles; so that he will readily
understand that the mountains surrounding it may average five to six
thousand feet in height, as they do. The sun is shining from the left,
and, being low, casts long shadows, so that the real forms of the
mountains on one side are beautifully indicated by these shadows, where
they fall on the floor of the crater. In the lower part of the mountain
wall there has been a land-slide, as we see by the fragments that have
rolled down into the plain, and of which a trace can be observed in our
engraving. The whole is quite unlike most terrestrial craters, however,
not only in its enormous size, but in its proportions; for the floor
is not precipitous, but flat, or partaking of the general curvature of
the lunar surface, which it sinks but little below. I have watched with
interest in the telescope streaks and shades on the floor of Plato, not
shown in our cut; for here some have suspected evidences of change,
and fancied a faint greenish tint, as if due to vegetation, but it is
probably fancy only. Notice the number of small craters around the
big one, and everywhere on the plate, and then look at the amazingly
rugged and tumbled mountain heaps on the left (the lunar Alps), cut
directly through by a great valley (the valley of the Alps), which is
at the bottom about six miles wide and extraordinarily flat,--flatter
and smoother even than our engraving shows it, and looking as though
a great engineering work, rather than an operation of Nature, were in
question. Above this the mountain shadows are cast upon a wide plain,
in which are both depressed pits with little mountain (or rather hill)
rings about them, and extraordinary peaks, one of which, Pico (above
the great crater), starts up abruptly to the height of eight thousand
feet, a lunar Matterhorn.
If Mars were as near as the moon, we should see with the naked eye
clouds passing over its face; and that we never do see these on the
moon, even with the telescope, is itself a proof that none exist there.
Now, this absence of clouds, or indeed of any evidence of moisture,
is confirmed by every one of the nearer views like those we are here
getting. We might return to this region with the telescope every month
of our lives without finding one indication of vapor, of moisture, or
even of air; and from a summit like Pico, could we ascend it, we should
look out on a scene of such absolute desolation as probably no
earthly view could parallel. If, as is conceivable, these plains were
once covered with verdure, and the abode of living creatures, verdure
and life exist here no longer, and over all must be the silence of
universal death. But we must leave it for another scene.
[Illustration: FIG. 68.--PLATO AND THE LUNAR ALPS.]
South of Plato extends for many hundred miles a great plain, which
from its smoothness was thought by the ancient observers to be water,
and was named by them the “Imbrian Sea,” and this is bounded on the
south and west by a range of mountains--the “lunar Apennines” (Fig.
69)--which are the most striking on our satellite. They are visible
even with a spy-glass, looking then like bread-crumbs ranged upon a
cloth, while with a greater power they grow larger and at the same
time more chaotic. As we approach nearer, we see that they rise
with a comparatively gradual slope, to fall abruptly, in a chain of
precipices that may well be called tremendous, down to the plain below,
across which their shadows are cast. Near their bases are some great
craters of a somewhat different type from Plato, and our illustration
represents an enlarged view of a part of this Apennine chain, of the
great crater Archimedes, and of its companions Aristillus and Autolycus.
Our engraving will tell, more than any description, of the contrast
of the tumbled mountain peaks with the level plain from which they
spring,--a contrast for which we have scarcely a terrestrial parallel,
though the rise of the Alps from the plains of Lombardy may suggest an
inadequate one. The Sierra Nevadas of California climb slowly up from
the coast side, to descend in great precipices on the east, somewhat
like this; but the country at their feet is irregular and broken, and
their highest summits do not equal those before us, which rise to
seventeen or eighteen thousand feet, and from one of which we should
look out over such a scene of desolation as we can only imperfectly
picture to ourselves from any experience of a terrestrial desert. The
curvature of the moon’s surface is so much greater than ours, that it
would hide the spurs of hills which buttress the southern slopes of
Archimedes, leaving only the walls of the great mountain ring visible
in the extremest horizon, while between us and them would extend what
some still maintain to have been the bed of an ancient lunar ocean,
though assuredly no water exists there now.
Among the many fanciful theories to account for the forms of the
ringed plains, one (and this is from a man of science whose ideas are
always original) invokes the presence of water. According to it, these
great plains were once ocean beds, and in them worked a coral insect,
building up lunar “atolls” and ring-shaped submarine mountains, as the
coral polyp does here. The highest summits of the great rings thus
formed were then low islands, just “a-wash” with the waves of the
ancient lunar sea, and, for aught we know, green with feathery palms.
Then came (in the supposition in question) a time when the ocean dried
up, and the mountains were left standing, as we see, in rings, after
the cause of their formation was gone. If it be asked where the water
went to, the answer is not very obvious on the old theories; but those
who believe in them point to the extraordinary cracks in the soil, like
those our engraving shows, as chasms and rents, by which the vanished
seas, and perhaps also the vanished air, have been absorbed into the
interior.
[Illustration: FIG. 69.--THE LUNAR APENNINES: ARCHIMEDES.]
If there was indeed such an ancient ocean, it would have washed the
very feet of the precipices on whose summits we are in imagination
standing, and below us their recesses would have formed harbors which
fancy might fill with commerce, and cities in which we might picture
life and movement where all is now dead. It need hardly be said that
no telescope has ever revealed their existence (if such ruins, indeed,
there are), and it may be added that the opinion of geologists is, as
a whole, unfavorable to the presence of water on the moon, even in
the past, from the absence of any clear evidence of erosive action;
but perhaps we are not yet entitled to speak on these points with
certainty, and are not forbidden to believe that water may have existed
here in the past by any absolute testimony to the contrary. The views
of those who hold the larger portion of the lunar craters to have
been volcanic in their formation are far more probable; and perhaps
as simple an evidence of the presumption in their favor as we can
give is directly to compare such a lunar region as this, the picture
of which was made for us from a model, with a similar model made from
some terrestrial volcanic region. Here (Fig. 70) is a photograph of
such a modelled plan of the country round the Bay of Naples, showing
the ancient crater of Vesuvius and its central cone, with other and
smaller craters along the sea. Here, of course, we _know_ that the
forms originated in volcanic action, and a comparison of them with our
moon-drawing is most interesting. To return to our Apennine region
(Fig. 69), we must admit, however, when we consider the vast size of
these things (Archimedes is fifty miles in diameter), that they are
very different in proportion from our terrestrial craters, and that
numbers of them present no central cone whatever; so that if some of
them seem clearly eruptive, there are others to which we have great
difficulties in making these volcanic theories apply. Let us look, for
instance, at still another region (Fig. 71). It lies rather above the
centre of the full moon, and may be recognized also on the Rutherfurd
photograph; and it consists of the group of great ring-plains, three of
which form prominent figures in our cut.
Ptolemy (the lower of these in the drawing) is an example of such a
plain, whose diameter reaches to about one hundred and fifteen miles,
so that it encloses an area of nearly eight thousand square miles
(or about that of the State of Massachusetts), within which there is
no central cone or point from which eruptive forces appear to have
acted, except the smaller craters it encloses. On the south we see
a pass in the mountain wall opening into the neighboring ring-plain
of Alphonsus, which is only less in size; and south of this again is
Arzachel, sixty-six miles in diameter, surrounded with terraced walls,
rising in one place to a height greater than that of Mont Blanc, while
the central cone is far lower. The whole of the region round about,
though not the roughest on the moon, is rough and broken in a way
beyond any parallel here, and which may speak for itself; but perhaps
the most striking of the many curious features--at least the only one
we can pause to examine--is what is called “The Railway,” an almost
perfectly straight line, on one side of which the ground has abruptly
sunk, leaving the undisturbed part standing like a wall, and forming a
“fault,” as geologists call it. This is the most conspicuous example of
its kind in the moon, but it is only one of many evidences that we are
looking at a world whose geological history has been not wholly unlike
our own. But the moon contains, as has been said, but the one-eightieth
part of the mass of our globe, and has therefore cooled with much
greater rapidity, so that it has not only gone through the epochs
of our own past time, but has in all probability already undergone
experiences which for us lie far in the future; and it is hardly less
than justifiable language to say that we are beholding here in some
respects what the face of our world may be when ages have passed away.
[Illustration: FIG. 70.--VESUVIUS AND NEIGHBORHOOD OF NAPLES.]