to scientific _induction_. Speculation is a kind of mental mirror, that
before now has anticipated or supplemented the visions of sense.
Not being practical astronomers ourselves, we have to follow the
counsel of that unknown authority who bids us believe the expert.
But expertness being the fruit of experience, we may be puzzled to
tell who have attained that rank. We will inquire, however, with due
docility, of the oracles of scientific research. It is agreed on all sides
that to render the moon habitable by beings at all akin with our own
kind, there must be within or upon that body an atmosphere, water,
changing seasons, and the alternations of day and night. We know
that changes occur in the moon, from cold to heat, and from
darkness to light. But the lunar day is as long as 291 of ours; so that
each portion of the surface is exposed to, or turned from, the sun for
nearly 14 days. This long exposure produces excessive heat, and the
long darkness excessive cold. Such extremities of temperature are
unfavourable to the existence of beings at all like those living upon
the earth, especially if the moon be without water and atmosphere.
As these two desiderata seem indispensable to lunar inhabitation,
we may chiefly consider the question, Do these conditions exist? If
so, inductive reasoning will lead us to the inference, which
subsequent experience will strengthen, that the moon is inhabited
like its superior planet. But if not, life on the satellite similar to life
on the earth, is altogether improbable, if not absolutely impossible.
The replies given to this query will be by no means unanimous. But,
for the full understanding of the state of the main question, and to
assist us in arriving at some sort of verdict, we will hear several
authorities on both sides of the case. The evidence being
cumulative, we pursue the chronological order, and begin with La
Place. He writes: "The lunar atmosphere, if any such exists, is of an
extreme rarity, greater even than that which can be produced on the
surface of the earth by the best constructed air-pumps. It may be
inferred from this that no terrestrial animal could live or respire at
the surface of the moon, and that if the moon be inhabited, it must
be by animals of another species." [428] This opinion, as Sir David
Brewster points out, is not that the moon has no atmosphere, but
that if it have any it is extremely attenuated. Mr. Russell Hind's
opinion is similar with respect to water. He says: "Earlier
selenographists considered the dull, grayish spots to be water, and
termed them the lunar seas, bays, and lakes. They arc so called to
the present day, though we have strong evidence to show that if
water exist at all on the moon, it must be in very small quantity."
[429] Mr. Grant tells us that "the question whether the moon
be surrounded by an atmosphere has been much discussed by
astronomers. Various phenomena are capable of indicating such an
atmosphere, but, generally speaking, they are found to be
unfavourable to its existence, or at all events they lead to the
conclusion that it must be very inconsiderable." [430] Humboldt
thinks that Schroeter's assumptions of a lunar atmosphere and lunar
twilight are refuted, and adds: "If, then, the moon is without any
gaseous envelope, the entire absence of any diffused light must
cause the heavenly bodies, as seen from thence, to appear projected
against a sky _almost black_ in the day-time. No undulation of air
can there convey sound, song, or speech. The moon, to our
imagination, which loves to soar into regions inaccessible to full
research, is a desert where silence reigns unbroken." [431] Dr.
Lardner considers it proven "that there does not exist upon the moon
an atmosphere capable of reflecting light in any sensible degree,"
and also believes that "the same physical tests which show the
non-existence of an atmosphere of air upon the moon are equally
conclusive against an atmosphere of vapour." [432] Mr. Breen is
more emphatic. He writes: "In the want of water and air, the
question as to whether this body is inhabited is no longer equivocal.
Its surface resolves itself into a sterile and inhospitable waste, where
the lichen which flourishes amidst the frosts and snows of Lapland
would quickly wither and die, and where no animal with a drop of
blood in its veins could exist." [433] The anonymous author of the
Essay on the _Plurality of Worlds_ announces that astronomers are
agreed to negative our question without dissent. We shall have to
manifest his mistake. His words are: "Now this minute examination
of the moon's surface being possible, and having been made by
many careful and skilful astronomers, what is the conviction which
has been conveyed to their minds with regard to the fact of her
being the seat of vegetable or animal life? Without exception, it
would seem, they have all been led to the belief that the moon is not
inhabited; that she is, so far as life and organization are concerned,
waste and barren, like the streams of lava or of volcanic ashes on the
earth, before any vestige of vegetation has been impressed upon
them; or like the sands of Africa, where no blade of grass finds
root." [434] Robert Chambers says: "It does not appear that our
satellite is provided with an atmosphere of the kind found upon
earth; neither is there any appearance of water upon the surface. . . .
These characteristics of the moon forbid the idea that it can be at
present a theatre of life like the earth, and almost seem to declare
that it never can become so." [435] Schoedler's opinion is
concurrent with what has preceded. He writes: "According to the
most exact observations it appears that the moon has no atmosphere
similar to ours, that on its surface there are no great bodies of water
like our seas and oceans, so that the existence of water is doubtful.
The whole physical condition of the lunar surface must, therefore,
be so different from that of our earth, that beings organized as we
are could not exist there." [436] Another German author says: "The
observations of Fraunhofer (1823), Brewster and Gladstone (1860),
Huggins and Miller, as well as Janssen, agree in establishing the
complete accordance of the lunar spectrum with that of the sun. In
all the various portions of the moon's disk brought under
observation, no difference could be perceived in the dark lines of the
spectrum, either in respect of their number or relative intensity.
From this entire absence of any special absorption lines, it must be
concluded that there is no atmosphere in the moon, a conclusion
previously arrived at from the circumstance that during an
occultation no refraction is perceived on the moon's limb when a
star disappears behind the disk." [437] Mr. Nasmyth follows in the
same strain. Holding that the moon lacks air, moisture, and
temperature, he says, "Taking all these adverse conditions into
consideration, we are in every respect justified in concluding that
there is no possibility of animal or vegetable life existing on the
moon, and that our satellite must therefore be regarded as a barren
world." [438] A French astronomer holds a like opinion, saying:
"There is nothing to show that the moon possesses an atmosphere;
and if there was one, it would be perceptible during the occultations
of the stars and the eclipses of the sun. It seems impossible that, in
the complete absence of air, the moon can be peopled by beings
organized like ourselves, nor is there any sign of vegetation or of
any alteration in the state of its surface which can be attributed to a
change of seasons." [439] On the same side Mr. Crampton writes
most decisively, "With what we _do_ know, however, of our
satellite, I think the idea of her being inhabited may be dismissed
_summarily_; _i.e._ her inhabitation by intelligent beings, or an
animal creation such as exist here." [440] And, finally, in one of
Maunder's excellent _Treasuries_, we read of the moon, "She has no
atmosphere, or at least none of sufficient density to refract the rays
of light as they pass through it, and hence there is no water on her
surface; consequently she can have no animals like those on our
planet, no vegetation, nor any change of seasons." [441] These
opinions, recorded by so many judges of approved ability and
learning, have great weight; and some may regard their premisses
and conclusions as irresistibly cogent and convincing. The case
against inhabitation is certainly strong. But justice is impartial.
_Audi alteram partem_.
Judges of equal erudition will now speak as respondents. We go
back to the seventeenth century, and begin with a work whose
reasoning is really remarkable, seeing that it is nearly two hundred
and fifty years since it was first published. We refer to the
_Discovery of a New World_ by John Wilkins, Bishop of Chester;
in which the reverend philosopher aims to prove the following
propositions:--"1. That the strangeness of this opinion (that the
moon may be a world) is no sufficient reason why it should be
rejected; because other certain truths have been formerly esteemed
as ridiculous, and great absurdities entertained by common consent.
2. That a plurality of worlds does not contradict any principle of
reason or faith. 3. That the heavens do not consist of any such pure
matter which can privilege them from the like change and
corruption, as these inferior bodies are liable unto. 4. That the moon
is a solid, compacted, opacous body. 5. That the moon hath not any
light of her own. 6. That there is a world in the moon, hath been the
direct opinion of many ancient, with some modern mathematicians;
and may probably be deduced from the tenets of others. 9. That
there are high mountains, deep valleys, and spacious plains in the
body of the moon. 10. That there is an atmosphoera, or an orb of
gross vaporous air, immediately encompassing the body of the
moon. 13. That 'tis probable there may be inhabitants in this other
world; but of what kind they are, is uncertain." [442] We go on to
1686, and listen to the French philosopher, Fontenelle, in his
Conversations with the Marchioness. "'Well, madam,' _said I_, 'you
will not be surprised when you hear that the moon is an earth too,
and that she is inhabited as ours is.' 'I confess,' _said she_, 'I have
often heard talk of the world in the moon, but I always looked upon
it as visionary and mere fancy.' 'And it may be so still,' _said I_. 'I
am in this case as people in a civil war, where the uncertainty of
what may happen makes them hold intelligence with the opposite
party; for though I verily believe the moon is inhabited, I live civilly
with those who do not believe it; and I am still ready to embrace the
prevailing opinion. But till the unbelievers have a more considerable
advantage, I am for the people in the moon.'" [443] Whatever may
be thought of his philosophy, no one could quarrel with the
Secretary of the Academy on the score of his politeness or his
prudence. A more recent and more reliable authority appears in Sir
David Brewster. He tells us that "MM. Maedler and Beer, who have
studied the moon's surface more diligently than any of their
predecessors or contemporaries, have arrived at the conclusion that
she has an atmosphere." Sir David himself maintains that "_every
planet and satellite in the solar system must have an atmosphere_."
[444] Bonnycastle, whilom professor of mathematics in the Royal
Military Academy, Woolwich, writes: "Astronomers were formerly
of opinion that the moon had no atmosphere, on account of her
never being obscured by clouds or vapours; and because the fixed
stars, at the time of an occultation, disappear behind her
instantaneously, without any gradual diminution of their light. But if
we consider the effects of her days and nights, which are near thirty
times as long as with us, it may be readily conceived that the
phenomena of vapours and meteors must be very different. And
besides, the vaporous or obscure part of our atmosphere is only
about the one thousand nine hundred and eightieth part of the earth's
diameter, as is evident from observing the clouds, which are seldom
above three or four miles high; and therefore, as the moon's
apparent diameter is only about thirty-one minutes and a half, or one
thousand eight hundred and ninety seconds, the obscure part of her
atmosphere, supposing it to resemble our own, when viewed from
the earth, must subtend an angle of less than one second; which is so
small a space, that observations must be extremely accurate to
determine whether the supposed obscuration takes place or not."
[445] Dr. Brinkley, at one time the Astronomer-Royal of Ireland,
writes: "Many astronomers formerly denied the existence of an
atmosphere at the moon; principally from observing no variation of
appearance on the surface, like what would take place, did clouds
exist as with us; and also, from observing no change in the light of
the fixed stars on the approach of the dark edge of the moon. The
circumstance of there being no clouds, proves either that there is no
atmosphere similar to that of our earth, or that there are no waters on
its surface to be converted into vapour; and that of the lustre of the
stars not being changed, proves that there can be no dense
atmosphere. But astronomers now seem agreed that an atmosphere
does surround the moon, although of small density when compared
with that of our earth. M. Schroeter has observed a small twilight in
the moon, such as would arise from an atmosphere capable of
reflecting the rays at the height of about one mile." [446] Dr.
Brinkley is inaccurate in saying that astronomers are agreed as to
the lunar atmosphere. Like students in every other department of
inquiry, spiritual as well as physical, they fail at present to see "eye
to eye"; which is not surprising, seeing that the eye is so restricted,
and the object so remote.
Dr. Dick, whose productions have done much to popularize the
study of the heavens, and to promote its reverent pursuit, says: "On
the whole it appears most probable that the moon is surrounded with
a fluid which serves the purpose of an atmosphere; although this
atmosphere, as to its nature, composition, and refractive power, may
be very different from the atmosphere which surrounds the earth. It
forms no proof that the moon, or any of the planets, is destitute of
an atmosphere, because its constitution, its density, and its power of
refracting the rays of light are different from ours. An atmosphere
may surround a planetary body, and yet its parts be so fine and
transparent that the rays of light, from a star or any other body, may
pass through it without being in the least obscured, or changing their
direction. In our reasonings on this subject, we too frequently
proceed on the false principle, that everything connected with other
worlds must bear a resemblance to those on the earth." [447] Mr.
Neison, who has written one of the latest contributions to the
science of selenography, says, "Of the present non-existence of
masses of water upon the surface of the moon, there remains no
doubt, though no evidence of its entire absence from the lunar crust
can be adduced; and similarly, many well-established facts in
reference to the moon afford ample proof of the non-existence of a
lunar atmosphere, having a density equal to, or even much less than,
that of the earth; but of the absence of an atmosphere, whose mass
should enable it to play an important part in the moulding of the
surface of the moon, and comparable almost to that of the terrestrial
atmosphere, in their respective ratios to the masses of their planets,
little, if any, trustworthy evidence exists." On another page of the
same work, the author affirms "that later inquiries have shown that
the moon may possess an atmosphere that must be regarded as fully
capable of sustaining various forms of vegetation of even an
advanced type; and, moreover, it does not appear how it can justly
be questioned that the lunar surface in favourable positions may yet
retain a sufficiency of moisture to support vegetation of many kinds;
whilst in a very considerable portion of the entire surface of the
moon, the temperature would not vary sufficiently to materially
affect the existence of vegetable life." [448] Some of these writers
may appear to be travelling rather too fast or too far, and their
assumptions may wear more of the aspect of plausibility than of
probability. But on their atmospheric and aqueous hypothesis,
vegetation in abundance is confessedly a legitimate consequence. If
a recent writer has liberty to condense into a sentence the conclusion
from the negative premiss in the argument by saying, "As there is
but a little appearance of water or air upon the moon, the conclusion
has been inferred that there exists no vegetable or animal life on that
globe," [449] other writers, holding opposite views of the moon's
physical condition, may be allowed to expatiate on the luxuriant
life which an atmosphere with water and temperature would
undoubtedly produce. Mr. Proctor's tone is temperate, and his
language that of one who is conscious with Hippocrates that "art is
long and life is short." He says, in one of his contributions to lunar
science, "It may safely be asserted that the opportunities presented
during the life of any single astronomer for a trustworthy
investigation of any portion of the moon's surface, under like
conditions, are few and far between, and the whole time so
employed must be brief, even though the astronomer devote many
more years than usual to observational research." [450] This
prepares us to find in another of the same author's works the
following suggestive sentence: "With regard to the present
habitability of the moon, it may be remarked that we are not
justified in asserting positively that no life exists upon her surface.
Life has been found under conditions so strange, we have been so
often mistaken in assuming that _here_ certainly, or _there_, no
living creatures can possibly exist, that it would be rash indeed to
dogmatise respecting the state of the moon in this respect." [451]
Narrien, one of the historians of the science, may be heard, though
his contribution might be cast into either scale. He writes: "The
absence of those variations of light and shade which would be
produced by clouds floating above her surface, and the irregularities
of the ground, visible at the bottom and on the sides of her cavities,
have given reason to believe that no atmosphere surrounds her, and
that she is destitute of rivers and seas. Such are the opinions
generally entertained concerning the moon; but M. Schroeter, a
German astronomer, ventures to assert that our satellite is the abode
of living and intellectual beings; he has perceived some indications
of an atmosphere which, however, he admits, cannot exceed two
miles in height, and certain elevations which appear to him to be
works of art rather than of nature. He considers that a uniformity of
temperature must be produced on her surface by her slow rotation
on her axis, by the insensible change from day to night, and the
attenuated state of her atmosphere, which is never disturbed by
storms; and that light vapours, rising from her valleys, fall in the
manner of a gentle and refreshing dew to fertilize her fields." [452]
Dr. H. W. M. Olbers is fully persuaded "that the moon is inhabited
by rational creatures, and that its surface is more or less covered
with a vegetation not very dissimilar to that of our own earth." Dr.
Gruithuisen, of Munich, maintains that he has descried through his
large achromatic telescope "great artificial works in the moon
erected by the lunarians," which he considers to be "a system of
fortifications thrown up by the selenitic engineers." We should have
scant hope of deciding the dispute by the dicta of the ancients, were
these far more copious than we find them to be. Yet reverence for
antiquity may justify our quoting one of the classic fathers. Plutarch
says, "The Pythagoreans affirme, that the moone appeereth
terrestriall, for that she is inhabited round about, like as the earth
wherein we are, and peopled as it were with the greatest living
creatures, and the fairest plants." Again, "And of all this that hath
been said (my friend _Theon_) there is nothing that doth proove and
show directly, this habitation of men in the moon to be impossible."
[453] Here we close the argument based on _induction_, and sum
up the evidence in our possession. On the one hand, several
scientific men, whose names we need not repeat, having surveyed
the moon, deny it an atmosphere, water, and other conditions of life.
Consequently, they disbelieve in its inhabitation, solely because
they consider the fact undemonstrable; none of them being so
unscientific as to believe it to be absolutely impossible. On the other
hand, we have the valuable views of Maedler and Beer, whose lunar
labours are unsurpassed, and whose map of the moon is a marvel
and model of advanced selenography. They do not suppose the
conditions on our satellite to be exactly what they are on this globe.
In their own words, the moon is "no copy of the earth, much less a
colony of the same." They merely believe her to be environed with
air, and thus habitable. And when we recall our own Sir David
Brewster, Professor Bonnycastle, Dr. Brinkley, Dr. Dick, Mr.
Neison, and Mr. Proctor; and reckon with them the continental
astronomers, Dr. Gruithuisen, Dr. Olbers, and Schroeter, all of
whom attempted to fix the idea of planetary inhabitation on the
popular mind, we must acknowledge that they, with their opponents,
have a strong claim on our attention. The only verdict we are able
just now to render, after hearing these conflicting testimonies, is the
Scotch one, _Not proven_. We but append the legal indorsement
_ignoramus_, we do not know. The subject must remain _sub
judice_; but what we know not now, we hope to know hereafter.