Astronomers are often asked whether any animals can be living on the
moon. No observations we can make with the telescope can answer that
question directly. There are great plains to be seen on the moon, of
course, but even if there were elephants tramping over those plains,
our telescopes could not show them. Nor will our instruments pronounce
at once whether plants or trees flourish on the moon. The mammoth trees
of California are so big that a tunnel has been cut through the trunk
of one large enough to give passage for a carriage and pair. Even if
there were trees as big as this on the moon, they would not be visible
from the most famous observatories.
Let us think what we should ourselves experience if we could in some
marvellous manner be transferred from the earth to its satellite, and
tried to explore that new and wonderful country. Alas, we should find
it utterly impossible to live there for an hour, or even for a minute!
Troops of difficulties would immediately beset us. The very first would
be the want of air. Ponder for a moment on the invariable presence
of air around our own globe. Even if you climb to the top of a high
mountain, or if you take a lofty voyage in a balloon, you are all the
time bathed in air. It is air which supports the balloon, just as a
cork is buoyed up by water. In all circumstances, we must have air to
breathe. In that air is oxygen gas, and we must have oxygen incessantly
supplied to our lungs to reinvigorate our blood. We require, too, that
this oxygen shall be diluted with a much larger amount of nitrogen
gas, for our lungs and system of circulation are adapted for abode in
that particular mixture of gases which we find here. The atmosphere
becomes more and more rarefied the higher we ascend, and apparently
terminates altogether some two or three hundred miles over our heads.
Beyond the limits of the atmosphere it seems as if empty space would be
met with all the way from the earth to the moon. We could not procure
a single breath of air, and life would be, of course, impossible. Even
at a height of three or four miles, respiration becomes difficult,
and doubtless life could not possibly be sustained at a height of ten
miles.
It is therefore plain that for a voyage to the moon we should require
an ample supply of air, or, at least, of life-giving oxygen, which in
some way or other was to be inhaled during the progress of the journey.
When at length 240,000 miles had been traversed, and we were about
to land on the moon, we would first of all ascertain whether it was
surrounded with a coating of air. Most of the globes through space
are, so far as we can learn, covered and warmed with an enveloping
atmosphere of some kind; but, unhappily, the poor moon has been left
entirely, or almost entirely, without any such clothing. She is quite
bare of atmosphere at all comparable in density or in volume to that
which surrounds us, though possibly we do now and then perceive some
traces of air, or of some kind of gas, in small quantities in the lunar
valleys.
I am sure each intelligent boy or girl will want to know how we are
able to tell all this. We have never been at the moon, and how then can
we say that it is nearly destitute of air? Nor can our telescope answer
this question immediately, for you could hardly expect to see air,
even if it were there. How then are we able to make such assertions?
There are many different ways in which we have learned the absence of
air from the moon. I will tell you one of the easiest and the most
certain of these methods. First let me say that air is not perfectly
transparent. No doubt I can see you, and you can see me, though a good
many feet of air may lie between us; but when we deal with distances
much greater, there is a very simple way in which we can show that air
is not quite transparent. In the evening, when the sun is setting and
the sky is clear, you can look at him without discomfort; but in the
middle of the day you know that it is impossible to look at the sun
without shading your eyes with smoked glass or protecting them by some
similar contrivance. The reason is, that when the sun is either setting
or rising we look at it through an immense thickness of air, which not
being perfectly transparent stops some of the light. Thus it is that
the sun in these circumstances loses its dazzling brilliancy, and we
can view it without discomfort.
At the seaside you can notice the same effect in a different manner. Go
out on a fine and clear night, when the stars in their thousands are
glittering overhead, and then look down gradually towards the horizon,
and you will find the stars becoming fainter and fainter. Indeed, even
the brightest star cannot be seen when it is at the horizon, because an
immense thickness of the atmosphere is not transparent.
We can now state the argument by which we may prove that there is
little or no air on our satellite. The moon will frequently pass
between the earth and a star, and when the star is a really bright one
the observations that can be made are of great interest. Let me first
describe what we actually see. The star is shining brightly until the
moment when the moon eclipses it. Generally speaking, its disappearance
is instantaneous. But this would not be the case if the moon were
encircled with an atmosphere. If the moon were coated with air, the
light from the star would not be extinguished _instantly_; it would
gradually decline, according as it had to pass through more and more
of the moon’s atmosphere. Thus you would find that the star dwindled
down in brightness before the solid body of the moon had advanced far
enough to shut it out. The sudden extinction of the stars demonstrates
the airless state of our satellite.
There would be another insuperable difficulty in adopting the moon
as a residence, even supposing that you could get there. Water is
absent from its surface. We have examined every part of it, and we
find no evidences of seas or of oceans, of lakes or rivers; we never
see anything like clouds or mists, which are, of course, only water in
the vaporous form. We are, therefore, assured that, so far as water is
concerned, the moon is an absolute desert. This is, perhaps, the most
striking contrast between the aspect of the earth and the aspect of the
moon. Were an astronomer on the moon to look at our earth he would find
most of its surface concealed beneath clouds, and through the openings
in these clouds he would see that by far the greater part of this globe
was covered by the expanse of ocean; in fact, when the lunar astronomer
had realized the prevalence of water upon this earth, either in the
form of ocean or cloud, I feel sure he would come to the conclusion
that nothing could live here except seals or other amphibious animals.
Owing to the absence of air and water, the moon would be totally
disqualified for the support of life of those types in which we know
it. For air and water are necessary to every animal, from the humblest
animalcule up to whales or elephants. Air and water are necessary
for every form of vegetable life, from the lichen which grows on a
stone up to the noble old oak of the forest. But even supposing that
we could land on the moon, bearing with us an ample supply of oxygen
to breathe, and of water to drink, we should find ourselves perplexed
and embarrassed, to say the very least of it, by an extraordinary
difference that would immediately attract our notice. That familiar
experience of gravity, or the weights of things, which we have
acquired in our residence on a great globe like the earth, would seem
ludicrously altered when we began to walk about on a little globe
like the moon. We should be astonished at the transformation by which
the weight of everything was much lessened; when you pulled out your
watch you would hardly feel it at the end of the chain; it would seem
like a mere shell; but yet the watch is all right, it is going as well
as ever. Nothing has altered about it except its weight. A big stone
attracts your notice, and, to your amazement, you find that it does
not weigh so much as a piece of wood of the same size would weigh down
here. A stone that you could hardly stir on the earth, you can carry
about on the moon. Nor is this to be explained by any peculiarity in
the constitution of the lunar stone. Most probably it will be not very
dissimilar to some of the rocks on the earth. The relative lightness
of a lunar stone is not due to its being formed of some very special
material; we must seek for some other explanation. Every object on
the moon would be found only one-sixth as heavy as the same object on
the earth. A sturdy laborer at one of the docks can carry one sack
of corn on his back here, and he finds that this load is as much as
is convenient. He would, however, discover, were he placed on the
moon, that his load had suddenly become lightened to one-sixth part
(Fig. 45). The laborer would find that he could carry six sacks of
corn on the moon without making a greater effort than the support of
a single sack on the earth cost him. To explain how such a change as
this has occurred, look at these two pictures: one shows the laborer
on a small body like the moon, the other shows him on a great globe
like the earth. What the laborer actually does feel is not quite so
simple a thing as he imagines. He imagines that it is the weight of the
corn, and the corn alone, which produces that pressure on his shoulders
which he knows so well. But that is not exactly the manner in which
the philosopher will look at the same question. What the laborer does
actually feel is the attraction between the earth beneath his feet and
the corn on his back. It is this force which produces the pressure on
his shoulders. Its magnitude no doubt depends upon the quantity of corn
in the sack, but it also depends on the quantity of matter on the earth
beneath his feet. In fact, the force between two attracting bodies
depends upon the masses of both the attracting bodies. When the laborer
is transferred to the moon, of which the mass is so much less than that
of the earth, the attraction is less there than it is here, even though
the corn is the same in the two cases.
[Illustration: FIG. 45.--The Lessened Gravitation on the Moon.]
Many odd instances could be given of the extraordinary consequences
of life on a world where all weights are reduced to a sixth part. One
occurred to me the other day when I saw a postman going his rounds with
an amazing load of Christmas presents and parcels. I thought, how much
happier must be the lot of a postman on the moon, if such functionaries
are wanted there! All the presents of toys or more substantial
donations might be the same as before, the only alteration would be
that they would not feel nearly so heavy. A box which contains a pound
of chocolate bonbons might still contain exactly the same quantity of
sweetmeat on the moon, but the exertion of carrying it would be reduced
to one-sixth. It would only weigh as much as two or three ounces do
on the earth. Our streets provide another admirable illustration of
the drawbacks of our life here as compared with the facilities offered
by life on the moon. I feel quite confident that no perambulators can
be necessary there. I cannot indeed say that there are babies to be
found on the moon, but of this I am certain, that even if the lunar
babies were as plump and as sturdy as ours, they must still only weigh
about a sixth as much as ours do. A lunar nurse would scorn to use a
perambulator, even for a pair of twins; she might take them both out
on her arm for an airing, and even then only bear one-third of the
load that her terrestrial sister must sustain if she is carrying but a
single child.
The lightness of bodies in the moon would entirely transform many of
our most familiar games. In cricket, for instance, I don’t think the
bowling would be so much affected, but the hits on the moon would
be truly terrific. I believe an exceptionally good throw of the
cricket-ball here is about a hundred yards, but the same man, using
the same ball and applying the same force to it, would send the ball
six hundred yards on the moon. So, too, every hit would in the lunar
game carry the ball to six times the distance it does here. Football
would show a striking development in lunar play; a good kick would not
only send the ball over the cross-bar, but it would go soaring over the
houses, and perhaps drop in the next parish.
Our own bodies would, of course, participate in the general buoyancy,
so that, while muscular power remained unabated, we should be almost
able to run and jump as if we had on the famous seven-league boots. I
have seen an athlete in a circus jump over ten horses placed side by
side. The same athlete, making the same effort, would jump over sixty
horses on the moon.
A run with a pack of lunar foxhounds would indeed be a marvellous
spectacle. There need be no looking round by timid horsemen to find
open roads or easy gaps. The five-barred gate itself would be utterly
despised by a huntsman who could easily clear a hay-rick. It would
hardly be worth taking a serious jump to clear a canal unless there was
a road and a railway or so, which could be disposed of at the same time.
To illustrate this subject of gravitation in another way, suppose that
we were to be transferred from this earth to some globe much greater
than the earth--to a globe, for instance, as large and massive as
the sun. We can then show that the weight of every object would be
increased. Indeed, everything would weigh about twenty-seven times as
much as we find it does here. To pull out your watch would be to hoist
a weight of about five or six pounds out of your pocket. Indeed, I do
not see how you could draw out your watch, for even to raise your arm
would be impossible; it would feel heavier by far than if it were made
of solid lead. It is, perhaps, conceivable that you might stand upright
for a moment, particularly if you had a wall to lean up against; but of
this I feel certain, that if you once got down on the ground, it would
be utterly out of your power to rise again.
These illustrations will at least answer one purpose: they will show
how difficult it is for us to form any opinion as to the presence or
the absence of life on the other globes in space. We are just adapted
in every way for a residence on this particular earth of a particular
size and climate, and with atmosphere of a particular composition.
Within certain slender limits our vital powers can become accommodated
to change, but the conditions of other worlds seem to be so utterly
different from those we find here, that it would probably be quite
impossible for beings constituted as we are to remain alive for five
minutes on any other globe in space.
It is, however, quite another question as to whether there may not
be inhabitants of some kind on many of the other splendid globes. We
have through the wide extent of space inconceivable myriads of worlds,
presenting, no doubt, every variety of size and climate, of atmosphere
and soil. It seems quite preposterous to imagine that among all these
globes ours alone should be the abode of life. The most reasonable
conclusion for us to come to is that these bodies may be endowed with
life of types which are just as appropriate to the physical conditions
around them as is the life, both animal and vegetable, on this globe to
the special circumstances in which it is placed.