earth now barren and desolated under intense solar heat,--countries
which, for that very cause, will not improbably become the seat of
mechanical and thence of political power. Whoever finds the way to
make industrially useful the vast sun-power now wasted on the deserts
of North Africa or the shores of the Red Sea, will effect a greater
change in men’s affairs than any conqueror in history has done; for he
will once more people those waste places with the life that swarmed
there in the best days of Carthage and of old Egypt, but under another
civilization, where man no longer shall worship the sun as a god, but
shall have learned to make it his servant.
V.
THE PLANETS AND THE MOON.
When we look up at the heavens, we see, if we watch through the night,
the host of stars rising in the east and passing above us to sink
in the west, always at the same distance and in unchanging order,
each seeming a point of light as feeble as the glow-worm’s shine in
the meadow over which they are rising, each flickering as though the
evening wind would blow it out. The infant stretches out its hand to
grasp the Pleiades; but when the child has become an old man the “seven
stars” are still there unchanged, dim only in his aged sight, and
proving themselves the enduring substance, while it is his own life
which has gone, as the shine of the glow-worm in the night. They were
there just the same a hundred generations ago, before the Pyramids were
built; and they will tremble there still, when the Pyramids have been
worn down to dust with the blowing of the desert sand against their
granite sides. They watched the earth grow fit for man long before man
came, and they will doubtless be shining on when our poor human race
itself has disappeared from the surface of this planet.
Probably there is no one of us who has not felt this solemn sense of
their almost infinite duration as compared with his own little portion
of time, and it would be a worthy subject for our thought if we could
study them in the light that the New Astronomy sheds for us on their
nature. But I must here confine myself to the description of but a few
of their number, and speak, not of the infinite multitude and variety
of stars, each a self-shining sun, but only of those which move close
at hand; for it is not true of quite all that they keep at the same
distance and order.
Of the whole celestial army which the naked eye watches, there are five
stars which do change their places in the ranks, and these change in
an irregular and capricious manner, going about among the others, now
forward and now back, as if lost and wandering through the sky. These
wanderers were long since known by distinct names, as Mercury, Venus,
Mars, Jupiter, and Saturn, and believed to be nearer than the others;
and they are, in fact, companions to the earth and fed like it by the
warmth of our sun, and like the moon are visible by the sunlight which
they reflect to us. With the earliest use of the telescope, it was
found that while the other stars remained in it mere points of light
as before, these became magnified into disks on which markings were
visible, and the markings have been found with our modern instruments,
in one case at least, to take the appearance of oceans and snow-capped
continents and islands. These, then, are not uninhabitable self-shining
suns, but worlds, vivified from the same fount of energy that supplies
us, and the possible abode of creatures like ourselves.
[Illustration: FIG. 60.--SATURN. (FROM A DRAWING BY TROUVELOT).]
“Properly speaking,” it is said, “man is the only subject of interest
to man;” and if we have cared to study the uninhabitable sun because
all that goes on there is found to be so intimately related to us,
it is surely a reasonable curiosity which prompts the question so
often heard as to the presence of life on these neighbor worlds,
where it seems at least not impossible that life should exist. Even
the very little we can say in answer to this question will always be
interesting; but we must regretfully admit at the outset that it is
but little, and that with some planets, like Mercury and Venus, the
great telescopes of modern times cannot do much more than those of
Galileo, with which our New Astronomy had its beginning.
Let us leave these, then, and pass out to the confines of the planetary
system, where we may employ our telescopes to better advantage.
The outer planets, Neptune and Uranus, remain pale disks in the most
powerful instruments, the first attended by a single moon, the second
by four, barely visible; and there is so very little yet known about
their physical features, that we shall do better to give our attention
to one of the most interesting objects in the whole heavens,--the
planet Saturn, on which we can at any rate see enough to arouse a
lively curiosity to know more.
When Galileo first turned his glass on Saturn, he saw, as he thought,
that it consisted of three spheres close together, the middle one
being the largest. He was not quite sure of the fact, and was in a
dilemma between his desire to wait longer for further observation, and
his fear that some other observer might announce the discovery if he
hesitated. To combine these incompatibilities--to announce it so as to
secure the priority, and yet not announce it till he was ready--might
seem to present as great a difficulty as the discovery itself; but
Galileo solved this, as we may remember, by writing it in the sentence,
“Altissimum planetam tergeminum observavi” (“I have observed the
highest planet to be triple”), and then throwing it (in the printer’s
phrase) “into pi,” or jumbling the letters, which made the sentence
into the monstrous word
SMAJSMRMJLMEBOETALEVMJPVNENVGTTAVJRAS,
and publishing _this_, which contained his discovery, but under lock
and key. He had reason to congratulate himself on his prudence, for
within two years two of the supposed bodies disappeared, leaving only
one. This was in 1612; and for nearly fifty years Saturn continued to
all astronomers the enigma which it was to Galileo, till in 1656 it
was finally made clear that it was surrounded by a thin flat ring,
which when seen fully gave rise to the first appearance in Galileo’s
small telescope, and when seen edgewise disappeared from its view
altogether. Everything in this part of our work depends on the power
of the telescope we employ, and in describing the modern means of
observation we pass over two centuries of slow advance, each decade
of which has marked some progress in the instrument, to one of its
completest types, in the great equatorial at Washington, shown in Fig.
61.
[Illustration: FIG. 61.--THE EQUATORIAL TELESCOPE AT WASHINGTON.]
The revolving dome above, the great tube beneath, its massive piers,
and all its accessories are only means to carry and direct the great
lens at the further end, which acts the part of the lens in our own
eye, and forms the image of the thing to be looked at. Galileo’s
original lens was a single piece of glass, rather smaller than that of
our common spectacles; but the lens here is composed of two pieces,
each twenty-six inches in diameter, and collects as much light as a
human eye would do if over two feet across. But this is useless if the
lens is not shaped with such precision as to send every ray to its
proper place at the eye-piece, nearly thirty-five feet away; and, in
fact, the shape given its surface by the skilful hands of the Messrs.
Clark, who made it, is so exquisitely exact that all the light of a
star gathered by this great surface is packed at the distant focus into
a circle very much smaller than that made by the dot on this _i_, and
the same statement may be made of the great Lick glass, which is three
feet in diameter,--an accuracy we might call incredible were it not
certain. It is with instruments of such accuracy that astronomy now
works, and it is with this particular one that some of the observations
we are going to describe have been made.
In all the heavens there is no more wonderful object than Saturn, for
it preserves to us an apparent type of the plan on which all the worlds
were originally made. Let us look at it in this study by Trouvelot
(Fig. 60). The planet, we must remember, is a globe nearly seventy
thousand miles in diameter, and the outermost ring is over one hundred
and fifty thousand miles across, so that the proportionate size of our
earth would be over-represented here by a pea laid on the engraving.
The belts on the globe show delicate tints of brown and blue, and parts
of the ring are, as a whole, brighter than the planet; but this ring,
as the reader may see, consists of at least three main divisions, each
itself containing separate features. First is the gray outer ring, then
the middle one, and next the curious “crape” ring, very much darker
than the others, looking like a belt where it crosses the planet,
and apparently feebly transparent, for the outline of the globe has
been seen (though not very distinctly) _through_ it. The whole system
of rings is of the most amazing thinness, for it is probably thinner
in proportion to its size than the paper on which this is printed is
to the width of the page; and when it is turned edgewise to us, it
disappears to all but the most powerful telescopes, in which it looks
then like the thinnest conceivable line of light, on which the moons
have been seen projected, appearing like beads sliding along a golden
wire. The globe of the planet casts on the ring a shadow, which is
here shown as a broken line, as though the level of the rings were
suddenly disturbed. At other times (as in a beautiful drawing made with
the same instrument by Professor Holden) the line seems continuous,
though curved as though the middle of the ring system were thicker
than the edge. The rotation of the ring has been made out by direct
observations; and the whole is in motion about the globe,--a motion
so smooth and steady that there is no flickering in the shadow “where
Saturn’s steadfast shade sleeps on its luminous ring.”
[Illustration: FIG. 62.--JUPITER, MOON, AND SHADOW. (BY PERMISSION OF
WARREN DE LA RUE.)]
What is it? No solid could hold together under such conditions; we can
hardly admit the possibility of its being a liquid film extended in
space; and there are difficulties in admitting it to be gaseous. But if
not a solid, a liquid, or a gas, again what can it be? It was suggested
nearly two centuries ago that the ring might be composed of innumerable
little bodies like meteorites, circling round the globe so close
together as to give the appearance we see, much as a swarm of bees at
a distance looks like a continuous cloud; and this remains the most
plausible solution of what is still in some degree a mystery. Whatever
it be, we see in the ring the condition of things which, according
to the nebular hypothesis, once pertained to all the planets at a
certain stage of their formation; and this, with the extraordinary
lightness of the globe (for the whole planet would float on water),
makes us look on it as still in the formative stage of uncondensed
matter, where the solid land as yet is not, and the foot could find
no resting-place. Astrology figured Saturn as “spiteful and cold,--an
old man melancholy;” but if we may indulge such a speculation, modern
astronomy rather leads us to think of it as in the infancy of its
life, with every process of planetary growth still in its future, and
separated by an almost unlimited stretch of years from the time when
life under the conditions in which we know it can even begin to exist.
* * * * *
Like this appears also the condition of Jupiter (Fig. 62), the
greatest of the planets, whose globe, eighty-eight thousand miles in
diameter, turns so rapidly that the centrifugal force causes a visible
flattening. The belts which stretch across its disk are of all delicate
tints--some pale blue, some of a crimson lake; a sea-green patch has
been seen, and at intervals of late years there has been a great oval
red spot, which has now nearly gone, and which our engraving does not
show. The belts are largely, if not wholly, formed of rolling clouds,
drifting and changing under our eyes, though more rarely a feature
like the oval spot just mentioned will last for years, an enduring
enigma. The most recent observations tend to make us believe that the
equatorial regions of Jupiter, like those of the sun, make more turns
in a year than the polar ones; while the darkening toward the edge is
another sunlike feature, though perhaps due to a distinct cause, and
this is beautifully brought out when any one of the four moons which
circle the planet passes between us and its face, an occurrence also
represented in our figure. The moon, as it steals on the comparatively
dark edge, shows us a little circle of an almost lemon-yellow, but the
effect of contrast grows less as it approaches the centre. Next (or
sometimes before), the disk is invaded by a small and intensely black
spot, the shadow of the moon, which slides across the planet’s face,
the transit lasting long enough for us to see that the whole great
globe, serving as a background for the spectacle, has visibly revolved
on its axis since we began to gaze. Photography, in the skilful hands
of the late Professor Henry Draper, gave us reason to suspect the
possibility that a dull light is sent to us from parts of the planet’s
surface besides what it reflects, as though it were still feebly
glowing like a nearly extinguished sun; and, on the whole, a main
interest of these features to us lies in the presumption they create
that the giant planet is not yet fit to be the abode of life, but is
more probably in a condition like that of our earth millions of years
since, in a past so remote that geology only infers its existence, and
long before our own race began to be. That science, indeed, itself
teaches us that such all but infinite periods are needed to prepare a
planet for man’s abode, that the entire duration of his race upon it is
probably brief in comparison.
* * * * *
We pass by the belt of asteroids, and over a distance many times
greater than that which separates the earth from the sun, till we
approach our own world. Here, close beside it as it were, in comparison
with the enormous spaces which intervene between it and Saturn and
Jupiter, we find a planet whose size and features are in striking
contrast to those of the great globe we have just quitted. It is Mars,
which shines so red and looks so large in the sky because it is so
near, but whose diameter is only about half that of our earth. This is
indeed properly to be called a neighbor world, but the planetary spaces
are so immense that this neighbor is at closest still about thirty-four
million miles away.
[Illustration: FIG 63.--THREE VIEWS OF MARS.]
[Illustration: FIG 64.--MAP OF MARS.]
Looking across that great gulf, we see in our engraving (Fig.
63)--where we have three successive views taken at intervals of a few
hours--a globe not marked by the belts of Jupiter or Saturn, but with
outlines as of continents and islands, which pass in turn before our
eyes as it revolves in a little over twenty-four and a half of our
hours, while at either pole is a white spot. Sir William Herschel was
the first to notice that this spot increased in size when it was turned
away from the sun, and diminished when the solar heat fell on it; so
that we have what is almost proof that here is ice (and consequently
water) on another world. Then, as we study more, we discern forms which
move from day to day on the globe apart from its rotation, and we
recognize in them clouds sweeping over the surface,--not a surface of
still other clouds below, but of what we have good reason to believe to
be land and water.
By the industry of numerous astronomers, seizing every favorable
opportunity when Mars comes near, so many of these features have been
gathered that we have been enabled to make fairly complete maps of the
planet, one of which by Mr. Green is here given (Fig. 64).
Here we see the surface more diversified than that of our earth,
while the oceans are long, narrow, canal-like seas, which everywhere
invade the land, so that on Mars one could travel almost everywhere by
water. These canals seem also in some cases to exist in pairs or to be
remarkably duplicated. The spectroscope indicates water-vapor in the
Martial atmosphere, and some of the continents, like “Lockyer Land,”
are sometimes seen white, as though covered with ice: while one island
(marked on our map as Hall Island) has been seen so frequently thus,
that it is very probable that here some mountain or tableland rises
into the region of perpetual snow.
The cause of the red color of Mars has never been satisfactorily
ascertained. Its atmosphere does not appear to be dark enough to
produce such an effect, and perhaps as probable an explanation as any
is one the suggestion of which is a little startling at first. It is
that vegetation on Mars may be _red_ instead of green! There is no
intrinsic improbability in the idea, for we are even to-day unprepared
to say with any certainty why vegetation is green here, and it is quite
easy to conceive of atmospheric conditions which would make red the
best absorber of the solar heat. Here, then, we find a planet on which
we obtain many of the conditions of life which we know ourselves, and
here, if anywhere in the system, we may allowably inquire for evidence
of the presence of something like our own race; but though we may
indulge in supposition, there is unfortunately no prospect that with
any conceivable improvement in our telescopes we shall ever obtain
anything like certainty. We cannot assert that there are any bounds to
man’s invention, or that science may not, by some means as unknown to
us as the spectroscope was to our grandfathers, achieve what now seems
impossible; but to our present knowledge no such means exist, though we
are not forbidden to look at the ruddy planet with the feeling that it
may hold possibilities more interesting to our humanity than all the
wonders of the sun, and all the uninhabitable immensities of his other
worlds.
Before we leave Mars, we may recall to the reader’s memory the
extraordinary verification of a statement made about it more than a
hundred years ago. We shall have for a moment to leave the paths of
science for those of pure fiction, for the words we are going to quote
are those of no less a person than our old friend Captain Gulliver,
who, after his adventures with the Lilliputians, went to a flying
island inhabited largely by astronomers. If the reader will take down
his copy of Swift, he will find in this voyage of Gulliver’s to Laputa
the following imaginary description of what its imaginary astronomers
saw:--
“They have likewise discovered two lesser stars or satellites
which revolve about Mars, whereof the innermost is distant from
the centre of the primary planet exactly three of its diameters,
and the outermost five; the former revolves in the space of ten
hours, and the latter in twenty-one and a half.”
Now, compare this passage, which was published in the year 1727, with
the announcement in the scientific journals of August, 1877 (a hundred
and fifty years after), that two moons did exist, and had just been
discovered by Professor Hall, of Washington, with the great telescope
of which a drawing has been already given. The resemblance does not end
even here, for Swift was right also in describing them as very near the
planet and with very short periods, the actual distances being about
one and a half and seven diameters, and the actual times about eight
and thirty hours respectively,--distances and periods which, if not
exactly those of Swift’s description, agree with it in being less than
any before known in the solar system. It is certain that there could
not have been the smallest ground for a suspicion of their existence
when “Gulliver’s Travels” was written, and the coincidence--which is
a pure coincidence--certainly approaches the miraculous. We can no
longer, then, properly speak of “the snowy poles of moonless Mars,”
though it does still remain moonless to all but the most powerful
telescopes in the world, for these bodies are the very smallest known
in the system. They present no visible disks to measure, but look
like the faintest of points of light, and their size is only to be
guessed at from their brightness. Professor Pickering has carried on
an interesting investigation of them. His method depended in part on
getting holes of such smallness made in a plate of metal that the light
coming through them would be comparable with that of the Martial moons
in the telescope. It was found almost impossible to command the skill
to make these holes small enough, though one of the artists employed
had already distinguished himself by drilling a hole through a fine
cambric needle _lengthwise_, so as to make a tiny steel tube of it.
When the difficulty was at last overcome, the satellites were found to
be less than ten miles in diameter, and a just impression both of their
apparent size and light may be gathered from the statement that either
roughly corresponds to that which would be given by a human hand held
up at Washington, and viewed from Boston, Massachusetts, a distance of
four hundred miles.
We approach now the only planet in which man is certainly known to
exist, and which ought to have an interest for us superior to any which
we have yet seen, for it is our own. We are voyagers on it through
space, it has been said, as passengers on a ship, and many of us have
never thought of any part of the vessel but the cabin where we are
quartered. Some curious passengers (these are the geographers) have
visited the steerage, and some (the geologists) have looked under the
hatches, and yet it remains true that those in one part of our vessel
know little, even now, of their fellow-voyagers in another. How much
less, then, do most of us know of the ship itself, for we were all born
on it, and have never once been off it to view it from the outside!
No world comes so near us in the aerial ocean as the moon; and if we
desire to view our own earth as a planet, we may put ourselves in fancy
in the place of a lunar observer. “Is it inhabited?” would probably
be one of the first questions which he would ask, if he had the same
interest in us that we have in him; and the answer to this would call
out all the powers of the best telescopes such as we possess.
An old author, Fontenelle, has put in the mouth of an imaginary
spectator a lively description of what would be visible in twenty-four
hours to one looking down on the earth as it turned round beneath him.
“I see passing under my eyes,” he says, “all sorts of faces,--white and
black and olive and brown. Now it’s hats, and now turbans, now long
locks and then shaven crowns; now come cities with steeples, next more
with tall, crescent-capped minarets, then others with porcelain towers;
now great desolate lands, now great oceans, then dreadful deserts,--in
short, all the infinite variety the earth’s surface bears.” The truth
is, however, that, looking at the earth from the moon, the largest
moving animal, the whale or the elephant, would be utterly beyond our
ken; and it is questionable whether the largest ship on the ocean
would be visible, for the popular idea as to the magnifying power
of great telescopes is exaggerated. It is probable that under any
but extraordinary circumstances our lunar observer, with our best
telescopes, could not bring the earth within less than an apparent
distance of five hundred miles; and the reader may judge how large a
moving object must be to be seen, much less recognized, by the naked
eye at such a distance.
Of course, a chief interest of the supposition we are making lies in
the fact that it will give us a measure of our own ability to discover
evidences of life in the moon, if there are any such as exist here; and
in this point of view it is worth while to repeat, that scarcely any
temporary phenomenon due to human action could be even telescopically
visible from the moon under the most favoring circumstances. An army
such as Napoleon led to Russia might conceivably be visible if it moved
in a dark solid column across the snow. It is barely possible that such
a vessel as one of the largest ocean steamships might be seen, under
very favorable circumstances, as a moving dot; and it is even quite
probable that such a conflagration as the great fire of Chicago would
be visible in the lunar telescope, as something like a reddish star on
the night side of our planet; but this is all in this sort that could
be discerned.