STABILITY OF THE STAR-SYSTEM: IMPORTANCE OF OUR CENTRAL POSITION: SUMMARY
AND CONCLUSION
One of the greatest difficulties with regard to the vast system of stars
around us is the question of its permanence and stability, if not
absolutely and indefinitely, yet for periods sufficiently long to allow for
the many millions of years that have certainly been required for our
terrestrial life-development. This period, in the case of the earth, as I
have sufficiently shown, has been characterised throughout by extreme
uniformity, while a continuance of that uniformity for a few millions of
years in the future is almost equally certain.
But our mathematical astronomers can find no indications of such stability
of the stellar universe as a whole, if subject to the law of gravitation
alone. In reply to some questions on this point, my friend Professor George
Darwin writes as follows:--'A symmetrical annular system of bodies might
revolve in a circle with or without a central body. Such a system would be
unstable. If the bodies are of unequal masses and not symmetrically
disposed, the break-up of the system would probably be more rapid than in
the ideal case of symmetry.'
This would imply that the great annular system of the Milky Way is
unstable. But if so, its existence at all is a greater mystery than ever.
Although in detail its structure is very irregular, as a whole it is
wonderfully symmetrical; and it seems quite impossible that its generally
circular ring-like form can be the result of the chance aggregation of
matter from any pre-existing different form. Star-clusters are equally
unstable, or, rather, nothing is known or can be predicated about their
stability or instability, according to Professors Newcomb and Darwin.
Mr. E.T. Whittaker (Secretary to the Royal Astronomical Society), to whom
Professor G. Darwin sent my questions, writes:--'I doubt whether the
principal phenomena of the stellar universe are consequences of the law of
gravitation at all. I have been working myself at spiral nebulæ, and have
got a first approximation to an explanation--but it is electro-dynamical
and not gravitational. In fact, it may be questioned whether, for bodies of
such tremendous extent as the Milky Way or nebulæ, the effect which we call
gravitation is given by Newton's law; just as the ordinary formulæ of
electrostatic attraction break down when we consider charges moving with
very great velocities.'
Accepting these statements and opinions of two mathematicians who have
given special attention to similar problems, we need not limit ourselves to
the laws of gravitation as having determined the present form of the
stellar universe; and this is the more important because we may thus escape
from a conclusion which many astronomers seem to think inevitable, viz.
that the observed proper motions of the stars cannot be explained by the
gravitative forces of the system itself. In chapter VIII. of this work I
have quoted Professor Newcomb's calculation as to the effect of gravitation
in a universe of 100 million stars, each five times the mass of our sun,
and spread over a sphere which it would take light 30,000 years to cross;
then, a body falling from its outer limits to the centre could at the
utmost acquire a velocity of twenty-five miles a second; and therefore, any
body in any part of such a universe having a greater velocity would pass
away into infinite space. Now, as several stars have, it is believed, much
more than this velocity, it follows not only that they will inevitably
escape from our universe, but that they do not belong to it, as their great
velocity must have been acquired elsewhere. This seems to have been the
idea of the astronomer who stated that, even at the very moderate speed of
our sun, we should in five million years be deep in the actual stream of
the Milky Way. To this I have already sufficiently replied; but I now wish
to bring before my readers an excellent illustration of the importance of
the late Professor Huxley's remark, that the results you got out of the
'mathematical mill' depend entirely on what you put into it.
In the _Philosophical Magazine_ (January 1902) is a remarkable article by
Lord Kelvin, in which he discusses the very same problem as that which
Professor Newcomb had discussed at a much earlier date, but, starting from
different assumptions, equally based on ascertained facts and probabilities
deduced from them, brings out a very different result.
Lord Kelvin postulates a sphere of such a radius that a star at its
confines would have a parallax of one-thousandth part of a second (0".001),
equivalent to 3215 light-years. Uniformly distributed through this sphere
there is matter equal in mass to 1000 million suns like ours. If this
matter becomes subject to gravitation, it all begins to move at first with
almost infinite slowness, especially near its centre; but nevertheless, in
twenty-five million years many of these suns would have acquired velocities
of from twelve to twenty miles a second, while some would have less and
some probably more than seventy miles a second. Now such velocities as
these agree generally with the measured velocities of the stars, hence Lord
Kelvin thinks there may be as much matter as 1000 million suns within the
above-named distance. He then states that if we suppose there to be 10,000
million suns within the same sphere, velocities would be produced very much
greater than the known star-velocities; hence it is probable that there is
very much less matter than 10,000 million times the sun's mass. He also
states that if the matter were not uniformly distributed within the sphere,
then, whatever was the irregularity, the acquired motions would be greater;
again indicating that the 1000 million suns would be ample to produce the
observed effects of stellar motion. He then calculates the average distance
apart of each of the 1000 million stars, which he finds to be about 300
millions of millions of miles. Now the nearest star to our sun is about
twenty-six million million of miles distant, and, as the evidence shows, is
situated in the denser part of the solar cluster. This gives ample
allowance for the comparative emptiness of the space between our cluster
and the Milky Way, as well as of the whole region towards the poles of the
Milky Way (as shown by the diagrams in chapter IV.), while the comparative
density of extensive portions of the Galaxy itself may serve to make up the
average.
Now, previous writers have come to a different conclusion from the same
general line of argument, because they have started with different
assumptions. Professor Newcomb, whose statement made some years back is
usually followed, assumed 100 million stars each five times as large as our
sun, equal to 500 million suns in all, and he distributed them equally
throughout a sphere 30,000 light-years in diameter. Thus he has half the
amount of matter assumed by Lord Kelvin, but nearly five times the extent,
the result being that gravity could only produce a maximum speed of
twenty-five miles a second; whereas on Lord Kelvin's assumption a maximum
speed of seventy miles a second would be produced, or even more. By this
latter calculation we find no insuperable difficulty in the speed of any of
the stars being beyond the power of gravitation to produce, because the
rates here given are the direct results of gravitation acting on bodies
almost uniformly distributed through space. Irregular distribution, such as
we see everywhere in the universe, might lead to both greater and less
velocities; and if we further take account of collisions and near
approaches of large masses resulting in explosive disruptions, we might
have almost any amount of motion as the result, but as this motion would
be produced by gravitation within the system, it could equally well be
controlled by gravitation.
[Illustration: DIAGRAM OF STELLAR UNIVERSE (Plan). 1. Central part of Solar
Cluster. 2. Sun's Orbit (Black spot). 3. Outer limit of Solar Cluster. 4.
Milky Way.]
In order that my readers may better understand the calculations of Lord
Kelvin, and also the general conclusions of astronomers as to the form and
dimensions of the stellar universe, I have drawn two diagrams, one showing
a plan on the central plane of the Milky Way, the other a section through
its poles. Both are on the same scale, and they show the total diameter
across the Milky Way as being 3600 light-years, or about half that
postulated by Lord Kelvin for his hypothetical universe. I do this because
the dimensions given by him are those which are sufficient to lead to
motions near the centre such as the stars now possess in a minimum period
of twenty-five million years after the initial arrangement he supposes, at
which later epoch which we are now supposed to have reached, the whole
system would of course be greatly reduced in extent by aggregations
towards and near the centre. These dimensions also seem to accord
sufficiently with the actual distances of stars as yet measured. The
smallest parallax which has been determined with any certainty, according
to Professor Newcomb's list, is that of Gamma Cassiopeiæ, which is
one-hundredth of a second (0".01), while Lord Kelvin gives none smaller
than 0".02, and these will all be included within the solar cluster as I
have shown it.
[Illustration: DIAGRAM OF STELLAR UNIVERSE (Section). Section through Poles
of Milky Way.]
It must be clearly understood that these two illustrations are merely
diagrams to show the main features of the stellar universe according to the
best information available, with the proportionate dimensions of these
features, so far as the facts of the distribution of the stars and the
views of those astronomers who have paid most attention to the subject can
be harmonised. Of course it is not suggested that the whole arrangement is
so regular as here shown, but an attempt has been made by means of the
dotted shading to represent the comparative densities of the different
portions of space around us, and a few remarks on this point may be needed.
The solar cluster is shown very dense at the central portion, occupying
one-tenth of its diameter, and it is near the outside of this dense centre
that our sun is supposed to be situated. Beyond this there seems to be
almost a vacuity, beyond which again is the outer portion of the cluster
consisting of comparatively thinly scattered stars, thus forming a kind of
ring-cluster, resembling in shape the beautiful ring-nebula in Lyra, as has
been suggested by several astronomers. There is some direct evidence for
this ring-form. Professor Newcomb in his recent book on _The Stars_ gives
a list of all stars of which the parallax is fairly well known. These are
sixty-nine in number; and on arranging them in the order of the amount of
their parallax, I find that no less than thirty-five of them have
parallaxes between 0".1 and 0".4 of a second, thus showing that they
constitute part of the dense central mass; while three others, from 0".4 to
0".75, indicate those which are our closest companions at the present time,
but still at an enormous distance. Those which have parallaxes of less than
the tenth and down to one-hundredth of a second are only thirty-one in all;
but as they are spread over a sphere ten times the diameter, and therefore
a thousand times the cubic content of the sphere containing those above
one-tenth of a second, they ought to be immensely more numerous even if
very much more thinly scattered. The interesting point, however, is, that
till we get down to a parallax of 0".06, there are only three stars as yet
measured, whereas those between 0".02 and 0".06, an equal range of
parallax, are twenty-six in number, and as these are scattered in all
directions they indicate an almost vacant space followed by a moderately
dense outer ring.
In the enormous space between our cluster and the Milky Way, and also above
and below its plane to the poles of the Galaxy, stars appear to be very
thinly scattered, perhaps more densely in the plane of the Milky Way than
above and below it where the irresolvable nebulæ are so numerous; and there
may not improbably be an almost vacant space beyond our cluster for a
considerable distance, as has been supposed, but this cannot be known till
some means are discovered of measuring parallaxes of from one-hundredth to
one five-hundredth of a second.
These diagrams also serve to indicate another point of considerable
importance to the view here advocated. By placing the solar system towards
the outer margin of the dense central portion of the solar cluster (which
may very possibly include a large proportion of dark stars and thus be much
more dense towards the centre than it appears to us), it may very well be
supposed to revolve, with the other stars composing it, around the centre
of gravity of the cluster, as the force of gravity towards that centre
might be perhaps twenty or a hundred times greater than towards the very
much less dense and more remote outer portions of the cluster. The sun, as
indicated on the diagrams, is about thirty light-years from that centre,
corresponding to a parallax of a little more than one-tenth of a second,
and an actual distance of 190 millions of millions of miles, equal to about
70,000 times the distance of the sun from Neptune. Yet we see that this
position is so little removed from the exact centre of the whole stellar
universe, that if any beneficial influences are due to that central
position in regard to the Galaxy, it will receive them perhaps to as full
an extent as if situated at the actual centre. But if it is situated as
here shown, there is no further difficulty as to its proper motion carrying
it from one side to the other of the Milky Way in less time than has been
required for the development of life upon the earth. And if the solar
cluster is really sub-globular, and sufficiently condensed to serve as a
centre of gravity for the whole of the stars of the cluster to revolve
around, all the component stars which are not situated in the plane of its
equator (and that of the Milky Way) must revolve obliquely at various
angles up to an angle of 90°. These numerous diverging motions, together
with the motions of the nearer stars outside the cluster, some of which may
revolve round other centres of gravity made up largely of dark bodies,
would perhaps sufficiently account for the apparent random motions of so
many of the stars.
UNIFORM HEAT-SUPPLY DUE TO CENTRAL POSITION
We now come to a point of the greatest interest as regards the problem we
are investigating. We have seen how great is the difference in the
estimates of geologists and those of physicists as to the time that has
elapsed during the whole development of life. But the position we have now
found for the sun, in the outer portion of the central star-cluster, may
afford a clue to this problem. What we require is, some mode of keeping up
the sun's heat during the enormous geological periods in which we have
evidence of a wonderful uniformity in the earth's temperature, and
therefore in the sun's heat-emission. The great central ring-cluster with
its condensed central mass, which presumably has been forming for a much
longer period than our sun has been giving heat to the earth, must during
all this time have been exerting a powerful attraction on the diffused
matter in the spaces around it, now apparently almost void as compared with
what they may have been. Some scanty remnants of that matter we see in the
numerous meteoric swarms which have been drawn into our system. A position
towards the outside of this central aggregation of suns would evidently be
very favourable for the growth by accretion of any considerable mass. The
enormous distance apart of the outer components (the outer ring) of the
cluster would allow a large amount of the inflowing meteoritic matter to
escape them, and the larger suns situated near the surface of the inner
dense cluster would draw to themselves the greater part of this matter.[23]
The various planets of our system were no doubt built up from a portion of
the matter that flowed in near the plane of the ecliptic, but much of that
which came from all other directions would be drawn towards the sun itself
or to its neighbouring suns. Some of this would fall directly into it;
other masses coming from different directions and colliding with each other
would have their motion checked, and thus again fall into the sun; and so
long as the matter falling in were not in too large masses, the slow
additions to the sun's bulk and increase of its heat would be sufficiently
gradual to be in no way prejudicial to a planet at the earth's distance.
The main point I wish to suggest here is, that by far the greater portion
of the matter of the whole stellar universe has, either through gravitation
or in combination with electrical forces, as suggested by Mr. Whittaker,
become drawn together into the vast ring-formed system of the Milky Way,
which is, presumably, slowly revolving, and has thus been checked in its
original inflow toward the centre of mass of the stellar universe. It has
also probably drawn towards itself the adjacent portions of the scattered
material in the spaces around it in all directions.
Had the vast mass of matter postulated by Lord Kelvin acquired no motion of
revolution, but have fallen continuously towards the centre of mass, the
motions developed when the more distant bodies approached that centre would
have been extremely rapid; while, as they must have fallen in from every
direction, they would have become more and more densely aggregated, and
collisions of the most catastrophic nature would frequently have occurred,
and this would have rendered the central portion of the universe the
_least_ stable and the _least_ fitted to develop life.
But, under the conditions that actually prevail, the very reverse is the
case. The quantity of matter remaining between our cluster and the Milky
Way being comparatively small, the aggregation into suns has gone on more
regularly and more slowly. The motions acquired by our sun and its
neighbours have been rendered moderate by two causes: (1) their nearness to
the centre of the very slowly aggregating cluster where the motion due to
gravitation is least in amount; and (2) the slight differential attraction
away from the centre by the Milky Way on the side nearest to us. Again,
this protective action of the Milky Way has been repeated, on a smaller
scale, by the formation of the outer ring of the solar cluster, which has
thus preserved the inner central cluster itself from a too abundant direct
inflow of large masses of matter.
But although the matter composing the outer portion of the original
universe has been to a large extent aggregated into the vast system of the
Milky Way, it seems probable, perhaps even certain, that some portion would
escape its attractive forces and would pass through its numerous open
spaces--indicated by the dark rifts, channels, and patches, as already
described--and thus flow on unchecked towards the centre of mass of the
whole system. The quantity of matter thus reaching the central cluster from
the enormously remote spaces beyond the Milky Way might be very small in
comparison with what was retained to build up that wonderful star-system;
but it might yet be so large in total amount as to play an important part
in the formation of the central group of suns. It would probably flow
inwards almost continuously, and when it ultimately reached the solar
cluster, it would have attained a very high velocity. If, therefore, it
were widely diffused, and consisted of masses of small or moderate size as
compared with planets or stars, it would furnish the energy requisite for
bringing these slowly aggregating stars to the required intensity of heat
for forming luminous suns.
Here, then, I think, we have found an adequate explanation of the very
long-continued light and heat-emitting capacity of our sun, and probably of
many others in about the same position in the solar cluster. These would at
first gradually aggregate into considerable masses from the slowly moving
diffused matter of the central portions of the original universe; but at a
later period they would be reinforced by a constant and steady inrush of
matter from its very outer regions, and therefore possessing such high
velocities as to materially aid in producing and maintaining the requisite
temperature of a sun such as ours, during the long periods demanded for
continuous life-development. The enormous extension and mass of the
original universe of diffused matter (as postulated by Lord Kelvin) is thus
seen to be of the greatest importance as regards this ultimate product of
evolution, because, without it, the comparatively slow-moving and cool
central regions might not have been able to produce and maintain the
requisite energy in the form of heat; while the aggregation of by far the
larger portion of its matter in the great revolving ring of the galaxy was
equally important, in order to prevent the too great and too rapid inflow
of matter to these favoured regions.
It appears, then, that if we admit as probable some such process of
development as I have here indicated, we can dimly see the bearing of all
the great features of the stellar universe upon the successful development
of life. These are, its vast dimensions; the form it has acquired in the
mighty ring of the Milky Way; and our position near to, but not exactly in,
its centre. We know that the star-system _has_ acquired these forms,
presumably from some simple and more diffused condition. We know that we
_are_ situated near the centre of this vast system. We know that our sun
_has_ emitted light and heat, almost uniformly, for periods incompatible
with rapid aggregation and the equally rapid cooling which physicists
consider inevitable. I have here suggested a mode of development which
would lead to a very slow but continuous growth of the more central suns;
to an excessively long period of nearly stationary heat-giving power; and
lastly, an equally long period of very gradual cooling--a period the
commencement of which our sun may have just entered upon.
Descending now to terrestrial physics, I have shown that, owing to the
highly complex nature of the adjustments required to render a world
habitable and to retain its habitability during the æons of time requisite
for life-development, it is in the highest degree improbable that the
required conditions and adaptations should have occurred in any other
planets of any other suns, which _might_ occupy an equally favourable
position with our own, and which were of the requisite size and heat-giving
power.
Lastly, I submit that the whole of the evidence I have here brought
together leads to the conclusion that our earth is almost certainly the
only inhabited planet in our solar system; and, further, that there is no
inconceivability--no improbability even--in the conception that, in order
to produce a world that should be precisely adapted in every detail for the
orderly development of organic life culminating in man, such a vast and
complex universe as that which we know exists around us, may have been
absolutely required.
SUMMARY OF ARGUMENT
As the last ten chapters of this volume embody a connected argument leading
to the conclusion above stated, it may be useful to my readers to summarise
rather fully the successive steps of this argument, the facts on which it
rests, and the various subsidiary conclusions arrived at.
(1) One of the most important results of modern astronomy is to have
established the unity of the vast stellar universe which we see around us.
This rests upon a great mass of observations, which demonstrate the
wonderful complexity in detail of the arrangement and distribution of stars
and nebulæ, combined with a no less remarkable general symmetry, indicating
throughout a single inter-dependent system, not a number of totally
distinct systems so far apart as to have no physical relations with each
other, as was once supposed.
(2) This view is supported by numerous converging lines of evidence, all
tending to show that the stars are not infinite in number, as was once
generally believed, and which view is even now advocated by some
astronomers. The very remarkable calculations of Lord Kelvin, referred to
in the early part of this chapter, give a further support to this view,
since they show that if the stars extended much beyond those we see or can
obtain direct knowledge of, and with no very great change in their average
distance apart, then the force of gravitation towards the centre would have
produced on the average more rapid motions than the stars generally
possess.
(3) An overwhelming consensus of opinion among the best astronomers
establishes the fact of our nearly central position in the stellar
universe. They all agree that the Milky Way is nearly circular in form.
They all agree that our sun is situated almost exactly in its medial plane.
They all agree that our sun, although not situated at the exact centre of
the galactic circle, is yet not very far from it, because there are no
unmistakable signs of our being nearer to it at any one point and farther
away from the opposite point. Thus the nearly central position of our sun
in the great star-system is almost universally admitted.
On the question of the solar-cluster there is more difference of opinion;
though here, again, all are agreed that there is such a cluster. Its size,
form, density, and exact position are somewhat uncertain, but I have, as
far as possible, been guided by the best available evidence. If we adopt
Lord Kelvin's general idea of the gradual condensation of an enormous
diffused mass of matter towards its common centre of gravity, that centre
would be approximately the centre of this cluster. Also, as gravitational
force at and near this centre would be comparatively small, the motions
produced there would be slow, and collisions, being due only to
differential motions, when they did occur would be very gentle. We might
therefore expect many dark aggregations of matter here, which may explain
why we do not find any special crowding of visible stars in the direction
of this centre; while, as no star has a sensible disc, the dark stars if at
great distances would hardly ever be seen to occult the bright ones. Thus,
it seems to me, the controlling force may be explained which has retained
our sun in approximately the same orbit around the centre of gravity of
this central cluster during the whole period of its existence as a sun and
our existence as a planet; and has thus saved us from the
possibility--perhaps even the certainty--of disastrous collisions or
disruptive approaches to which suns, in or near the Milky Way, and to a
less extent elsewhere, are or have been exposed. It seems quite probable
that in that region of more rapid and less controlled motions and more
crowded masses of matter, no star can remain in a nearly stable condition
as regards temperature for sufficiently long periods to allow of a complete
system of life-development on any planet it may possess.
(4) The various proofs are next stated that assure us of the almost
complete uniformity of matter, and of material physical and chemical laws,
throughout our universe. This I believe no one seriously disputes; and it
is a point of the greatest importance when we come to consider the
conditions required for the development and maintenance of life, since it
assures us that very similar, if not identical, conditions must prevail
wherever organic life is or can be developed.
(5) This leads us on to the consideration of the essential characteristics
of the living organism, consisting as it does of some of the most abundant
and most widely distributed of these material elements, and being always
subject to the general laws of matter. The best authorities in physiology
are quoted, as to the extreme complexity of the chemical compounds which
constitute the physical basis for the manifestation of life; as to their
great instability; their wonderful mobility combined with permanence of
form and structure; and the altogether marvellous powers they possess of
bringing about unique chemical transformations and of building up the most
complicated structures from simple elements.
I have endeavoured to put the broad phenomena of vegetable and animal life
in a way that will enable my readers to form some faint conception of the
intricacy, the delicacy, and the mystery of the myriad living forms they
see everywhere around them. Such a conception will enable them to realise
how supremely grand is organic life, and to appreciate better, perhaps, the
absolute necessity for the numerous, complex and delicate adaptations of
inorganic nature, without which it is impossible for life either to exist
now, or to have been developed during the immeasurable past.
(6) The general conditions which are absolutely essential for life thus
manifested on our planet are then discussed, such as, solar light and heat;
water universally distributed on the planet's surface and in the
atmosphere; an atmosphere of sufficient density, and composed of the
several gases from which alone protoplasm can be formed; some alternations
of light and darkness, and a few others.
(7) Having treated these conditions broadly, and explained why they are
important and even indispensable for life, we next proceed to show how they
are fulfilled upon the earth, and how numerous, how complex, and often how
exact are the adjustments needed to bring them about, and maintain them
almost unchanged throughout the vast æons of time occupied in the
development of life. Two chapters are devoted to this subject; and it is
believed that they contain facts that will be new to many of my readers.
The combinations of causes which lead to this result are so varied, and in
several cases dependent on such exceptional peculiarities of physical
constitution, that it seems in the highest degree improbable that they can
_all_ be found again combined either in the solar system or even in the
stellar universe. It will be well here just to enumerate these conditions,
which are all essential within more or less narrow limits:--
Distance of planet from the sun.
Mass of planet.
Obliquity of its ecliptic.
Amount of water as compared with land.
Surface distribution of land and water.
Permanence of this distribution, dependent probably on the
unique origin of our moon.
An atmosphere of sufficient density, and of suitable component
gases.
An adequate amount of dust in the atmosphere.
Atmospheric electricity.
Many of these act and react on each other, and lead to results of great
complexity.
(8) Passing on to other planets of the solar system, it is shown that none
of them combine all the complex conditions which are found to work
harmoniously together on the earth; while in most cases there is some one
defect which alone removes them from the category of possible
life-producing and life-supporting planets. Among these are the small size
and mass of Mars, being such that it cannot retain aqueous vapour; and the
fact that Venus rotates on its axis in the same time as it takes to revolve
round the sun. Neither of these facts was known when Proctor wrote upon the
question of the habitability of the planets. All the other planets are now
given up--and were given up by Proctor himself--as possible life-bearers in
their present stage; but he and others have held that, if not suitable now,
some of them may have been the scene of life-development in the past,
while others will be so in the future.
In order to show the futility of this supposition, the problem of the
duration of the sun as a stable heat-giver is discussed; and it is shown
that it is only by reducing the periods claimed by geologists and
biologists for life-development upon the earth, and by extending the time
allowed by physicists to its utmost limits, that the two claims can be
harmonised. It follows that the whole period of the sun's duration as a
light and heat-giver has been required for the development of life upon the
earth; and that it is only upon planets whose phases of development
synchronise with that of the earth that the evolution of life is possible.
For those whose material evolution has gone on quicker or slower, there has
not been, or will not be, time enough for the development of life.
(9) The problem of the stars as possibly having life-supporting planets is
next dealt with, and reasons are given why in only a minute portion of the
whole is this possible. Even in that minute portion, reduced probably to a
few of the component suns of the solar-cluster, a large proportion seems
likely to be ruled out by being close binary systems, and another large
portion by being in process of aggregation. In those remaining, whether
they may be reckoned by tens or by hundreds we cannot say, the chances
against the same complex combination of conditions as those which we find
on the earth occurring on any planet of any other sun are enormously great.
(10) I then refer, briefly, to some recent measurements of star-radiation,
and suggest that they may thus possibly have important effects on the
development of vegetable and animal life; and, finally, I discuss the
problem of the stability of the stellar universe and the special advantage
we derive from our central position, suggested by some of the latest
researches of our great mathematician and physicist--Lord Kelvin.
CONCLUSIONS
Having thus brought together the whole of the available evidence bearing
upon the questions treated in this volume, I claim that certain definite
conclusions have been reached and proved, and that certain other
conclusions have enormous probabilities in their favour.
The conclusions reached by modern astronomers are: (1) That the stellar
universe forms one connected whole; and, though of enormous extent, is yet
finite, and its extent determinable.
(2) That the solar system is situated in the plane of the Milky Way, and
not far removed from the centre of that plane. The earth is therefore
nearly in the centre of the stellar universe.
(3) That this universe consists throughout of the same kinds of matter, and
is subjected to the same physical and chemical laws.
The conclusions which I claim to have shown to have enormous probabilities
in their favour are--
(4) That no other planet in the solar system than our earth is inhabited or
habitable.
(5) That the probabilities are almost as great against any other sun
possessing inhabited planets.
(6) That the nearly central position of our sun is probably a permanent
one, and has been specially favourable, perhaps absolutely essential, to
life-development on the earth.
* * * * *
These latter conclusions depend upon the combination of a large number of
special conditions, each of which must be in definite relation to many of
the others, and must all have persisted simultaneously during enormous
periods of time. The weight to be given to this kind of reasoning depends
upon a full and fair consideration of the _whole_ evidence as I have
endeavoured to present it in the last seven chapters of this book. To this
evidence I appeal.
* * * * *
This completes my work as a connected argument, founded wholly on the facts
and principles accumulated by modern science; and it leads, if my facts are
substantially correct and my reasoning sound, to one great and definite
conclusion--that man, the culmination of conscious organic life, has been
developed here only in the whole vast material universe we see around us. I
claim that this is the logical outcome of the evidence, if we consider and
weigh this evidence without any prepossessions whatever. I maintain that it
is a question as to which we have no right to form _a priori_ opinions not
founded upon evidence. And evidence opposed to this conclusion, or even as
to its improbability, we have absolutely none whatever.
But, if we admit the conclusion, nothing that need alarm either the
scientific or the religious mind necessarily follows, because it can be
explained or accounted for in either of two distinct ways. One
considerable body, including probably the majority of men of science, will
admit that the evidence does apparently lead to this conclusion, but will
explain it as due to a fortunate coincidence. There might have been a
hundred or a thousand life-bearing planets, had the course of evolution of
the universe been a little different, or there might have been none at all.
They would probably add, that, as life and man _have_ been produced, that
shows that their production was possible; and therefore, if not now then at
some other time, if not here then in some other planet of some other sun,
we should be sure to have come into existence; or if not precisely the same
as we are, then something a little better or a little worse.
The other body, and probably much the largest, would be represented by
those who, holding that mind is essentially superior to matter and distinct
from it, cannot believe that life, consciousness, mind, are products of
matter. They hold that the marvellous complexity of forces which appear to
control matter, if not actually to constitute it, are and must be
mind-products; and when they see life and mind apparently rising out of
matter and giving to its myriad forms an added complexity and unfathomable
mystery, they see in this development an additional proof of the supremacy
of mind. Such persons would be inclined to the belief of the great
eighteenth century scholar, Dr. Bentley, that the soul of one virtuous man
is of greater worth and excellency than the sun and all his planets and all
the stars in the heavens; and when they are shown that there are strong
reasons for thinking that man _is_ the unique and supreme product of this
vast universe, they will see no difficulty in going a little further, and
believing that the universe was actually brought into existence for this
very purpose.
With infinite space around us and infinite time before and behind us, there
is no incongruity in this conception. A universe as large as ours for the
purpose of bringing into existence many myriads of living, intellectual,
moral, and spiritual beings, with unlimited possibilities of life and
happiness, is surely not _more_ out of proportion than is the complex
machinery, the life-long labour, the ingenuity and invention which we have
bestowed upon the production of the humble, the trivial, _pin_. Neither is
the apparent waste of energy so great in such a universe, comparatively, as
the millions of acorns, produced during its life by an oak, every one of
which might grow to be a tree, but of which only _one_ does actually, after
several hundred years, produce the _one_ tree which is to replace the
parent. And if it is said that the acorns are food for bird and beast, yet
the spores of ferns and the seeds of orchids are not so, and countless
millions of these go to waste for every one which reproduces the parent
form. And all through the animal world, especially among the lower types,
the same thing is seen. For the great majority of these entities _we_ can
see no use whatever, either of the enormous variety of the species, or the
vast hordes of individuals. Of beetles alone there are at least a hundred
thousand distinct species now living, while in some parts of sub-arctic
America mosquitoes are sometimes so excessively abundant that they obscure
the sun. And when we think of the myriads that have existed through the
vast ages of geological time, the mind reels under the immensity of, to
us, apparently useless life.
All nature tells us the same strange, mysterious story, of the exuberance
of life, of endless variety, of unimaginable quantity. All this life upon
our earth has led up to and culminated in that of man. It has been, I
believe, a common and not unpopular idea that during the whole process of
the rise and growth and extinction of past forms, the earth has been
preparing for the ultimate--Man. Much of the wealth and luxuriance of
living things, the infinite variety of form and structure, the exquisite
grace and beauty in bird and insect, in foliage and flower, may have been
mere by-products of the grand mechanism we call nature--the one and only
method of developing humanity.
And is it not in perfect harmony with this grandeur of design (if it be
design), this vastness of scale, this marvellous process of development
through all the ages, that the material universe needed to produce this
cradle of organic life, and of a being destined to a higher and a permanent
existence, should be on a corresponding scale of vastness, of complexity,
of beauty? Even if there were no such evidence as I have here adduced for
the unique position and the exceptional characteristics which distinguish
the earth, the old idea that all the planets were inhabited, and that all
the stars existed for the sake of other planets, which planets existed to
develop life, would, in the light of our present knowledge, seem utterly
improbable and incredible. It would introduce monotony into a universe
whose grand character and teaching is endless diversity. It would imply
that to produce the living soul in the marvellous and glorious body of
man--man with his faculties, his aspirations, his powers for good and
evil--that this was an easy matter which could be brought about anywhere,
in any world. It would imply that man is an animal and nothing more, is of
no importance in the universe, needed no great preparations for his advent,
only, perhaps, a second-rate demon, and a third or fourth-rate earth.
Looking at the long and slow and complex growth of nature that preceded his
appearance, the immensity of the stellar universe with its thousand million
suns, and the vast æons of time during which it has been developing--all
these seem only the appropriate and harmonious surroundings, the necessary
supply of material, the sufficiently spacious workshop for the production
of that planet which was to produce first, the organic world, and then,
Man.
In one of his finest passages our great world-poet gives us _his_
conception of the grandeur of human nature--'What a piece of work is man!
How noble in reason! How infinite in faculty! In form and moving, how
express and admirable! In action how like an angel! In apprehension how
like a god!' And for the development of such a being what is a universe
such as ours? However vast it may seem to our faculties, it is as a mere
nothing in the ocean of the infinite. In infinite space there may be
infinite universes, but I hardly think they would be all universes of
matter. That would indeed be a low conception of infinite power! Here, on
earth, we see millions of distinct species of animals, millions of
different species of plants, and each and every species consisting often
of many millions of individuals, no two individuals exactly alike; and when
we turn to the heavens, no two planets, no two satellites alike; and
outside our system we see the same law prevailing--no two stars, no two
clusters, no two nebulæ alike. Why then should there be other universes of
the _same_ matter and subject to the _same_ laws--as is implied by the
conception that the stars are infinite in number, and extend through
infinite space?
Of course there may be, and probably are, other universes, perhaps of other
kinds of matter and subject to other laws, perhaps more like our
conceptions of the ether, perhaps wholly non-material, and what we can only
conceive of as spiritual. But, unless these universes, even though each of
them were a million times vaster than our stellar universe, were also
infinite in number, they could not fill infinite space, which would extend
on all sides beyond them, so that even a million million such universes
would shrink to imperceptibility when compared with the vast beyond!
Of infinity in any of its aspects we can really know nothing, but that it
exists and is inconceivable. It is a thought that oppresses and overwhelms.
Yet many speak of it glibly as if they _knew_ what it contains, and even
use that assumed knowledge as an argument against views that are
unacceptable to themselves. To me its existence is absolute but
unthinkable--that way madness lies.
'O night! O stars, too rudely jars
The finite with the infinite!'
I will conclude with one of the finest passages relating to the infinite
that I am acquainted with, from the pen of the late R.A. Proctor:
'Inconceivable, doubtless, are these infinities of time and space, of
matter, of motion, and of life. Inconceivable that the whole universe can
be for all time the scene of the operation of infinite power, omnipresent,
all-knowing. Utterly incomprehensible how Infinite Purpose can be
associated with endless material evolution. But it is no new thought, no
modern discovery, that we are thus utterly powerless to conceive or
comprehend the idea of an Infinite Being, Almighty, All-knowing,
Omnipresent, and Eternal, of whose inscrutable purpose the material
universe is the unexplained manifestation. Science is in presence of the
old, old mystery; the old, old questions are asked of her--"Canst thou by
searching find out God? Canst thou find out the Almighty unto perfection?
It is as high as heaven; what canst thou do? deeper than hell; what canst
thou know?" And science answers these questions as they were answered of
old--"As touching the Almighty we cannot find Him out."'
* * * * *
The following beautiful lines--among the latest products of Tennyson's
genius--so completely harmonise with the subject-matter of the present
volume, that no apology is needed for quoting them here:--
(_The Question_)
Will my tiny spark of being
Wholly vanish in your deeps and heights?
Must my day be dark by reason,
O ye Heavens, of your boundless nights,
Rush of Suns and roll of systems,
And your fiery clash of meteorites?
(_The Answer_)
'Spirit, nearing yon dark portal
At the limit of thy human state,
Fear not thou the hidden purpose
Of that Power which alone is great,
Nor the myriad world, His shadow,
Nor the silent Opener of the Gate.'
FOOTNOTE:
[23] Since writing this chapter I have seen a paper by Luigi d'Auria
dealing mathematically with 'Stellar Motion, etc.,' and am pleased to see
that, from quite different considerations, he has found it necessary to
place the solar system at a distance from the centre not very much more
remote than the position I have given it. He says: 'We have good reasons to
suppose that the solar system is rather near the centre of the Milky Way,
and as this centre would, according to our hypothesis, coincide with the
centre of the Universe, the distance of 159 light years assumed is not too
great, nor can it be very much smaller.'--_Journal of the Franklin
Institute_, March 1903.
INDEX
Adrianus Tollius on stone axes, 203.
Air criminally poisoned by us, 260.
Albedo explained, 162.
Algol and its companion, 39;
change of colour of, 41.
Allen, Prof. F.J., on living matter, 193;
on importance of nitrogen, 195;
on physical conditions essential for life, 196.
Alpha Centauri, nearest star, 74.
Ammonia, importance of, to life, 195.
Anaximander's cosmic theory, 2.
Angles of a minute and second, 80.
Arcturus, rapid motion of, 172.
Argument of book, summary of, 310.
Astronomers, the first, 2.
Astronomy, the new, 24.
Astrophysics, a new science, 32.
Atmosphere, qualities requisite for life, 210;
requisite composition of, 212;
aqueous vapour in, 214;
and life, 243;
effects of density of, 245;
a complex structure, 259;
its vital importance to us, 260.
Ball, Sir R., on dark stars, 143;
_Time and Tide_, 233.
Barnham, S.W., on double stars, 123.
Blue of sky due to dust, 251.
Boeddicker's map of Milky Way, 164.
Brewster, Sir D., against Whewell, 15.
Campbell, Prof., on spectroscopic binaries, 125;
on uncertainty of sun's motions, 179;
on number of binary systems, 286.
Carbon compounds, vast numbers of, 194.
Carbonic acid gas essential for life, 196.
Central position of sun, importance of, 305.
Chaldeans the first astronomers, 2.
Chalmers Dr., on plurality of worlds, 13.
Chamberlin, T.C., origin of nebulæ, 120;
on stellar disruption, 186.
Chromosphere, the sun's, 107.
Clerke, Miss A.M., on limits of star system, 138;
on Milky Way, 158, 160;
on solar cluster, 165;
on uncertainty of the sun's motion, 177.
Climate, persistence of mild, 222.
Clouds, importance of, to life, 248.
Clusters in relation to Galaxy, 67.
Comte, on impossibility of real knowledge of the stars, 25.
Conclusions of the book, 317;
bearing of, on science and on religion, 319.
Corona of sun, 108.
Criticisms of article in _Fortnightly Review_, 168, 180.
Darwin, Prof. G., on meteoritic hypothesis, 133;
on origin of moon, 233;
on instability of annular systems, 295.
Day and night, uses of, 215.
Diagrams of star-distribution, 62, 66.
Diffraction-gratings, 30.
Disruption of stellar bodies, 187.
Doppler principle, the, 37.
Double stars, evolution of, 123;
not fitted for life, 286.
Dust, importance of, 249.
Dust-free air, results of, 254.
Earth, first measured, 5;
in relation to life, 218;
the only habitable planet, 262;
cannot retain hydrogen, 264;
supposed extreme conditions of, 271.
Earth's mass, how related to life, 265.
Ecliptic, obliquity of, in relation to life, 219.
Electricity, effects of atmospheric, 257;
atmospheric, how caused, 258.
Elements, change in spectra of, 129;
in the sun, 184;
in meteorites, 185;
in organic structures, 201.
Empedocles an early astronomer, 3.
Eudoxus on motions of planets, 3.
Evolution of the stars, 128.
Explanations of life-processes, 202.
Faculæ of sun, 105.
Fisher, Rev. O., on oceanic basins, 234;
on thin sub-oceanic crust, 237.
Fizeau measures speed of light, 79.
Flammarion, C., on universality of life, 274, 281.
Fontenelle on plurality of worlds, 9.
Galileo on star measurement, 74.
Geological climates, 222.
Geologists on duration of sun's heat, 275.
Germinal vesicle, M'Kendrick on, 202.
Gill, Sir D., on systematic star-motions, 178.
Globular clusters, stability of, 126;
and variables, 127.
Gore, Mr. J.E., on stars in Galaxy, 60;
on mass of binary stars, 97;
on remoteness of bright stars, 140;
on limits of star system, 145;
on limited number of stars, 151;
on life on planets of other suns, 282, 289.
Gould on solar cluster, 165.
Gould's map of Milky Way, 164.
Gravitation, motions produced by, on Lord Kelvin's hypothesis, 298.
Haliburton, Professor W.D., on proteids, 200.
Heat and cold on earth's surface, 207.
Heat-supply, our long-continued, accounted for, 305.
Herschel, Sir J., on Milky Way, 50;
on limits of the star-system, 147.
Heliometer, description of, 89.
Huggins, Sir W., on spectra of stars, 32;
measures radial motion, 37.
Huxley, Prof., on protoplasm, 198;
on duration of life, 278.
Hydrogen, why not in atmosphere, 240;
escapes from earth, 264.
Infinity, unknowable, 323;
Proctor on, 324.
Jupiter's satellites show speed of light, 79.
Kapteyn on solar cluster, 166.
Kelvin, Lord, on the sun's age, 279;
on a suggested primitive form of star-system, 298.
Kirchhoff, discovers spectrum-analysis, 28.
Laws of matter uniform throughout universe, 187.
Leaves, importance of, 197.
Lee, Dr., on origin of double stars, 123.
Lewis, on remote bright stars, 141.
Life, unity of organic, 189;
definitions of, 191;
conditions essential for, 206;
water essential for, 210;
atmosphere for, 210;
dependent on temperature, 218;
now improbable in stars, 288;
conditions essential for, summarised, 314.
Life-processes, explanations of, 202.
Light, velocity of measured, 79;
necessity of solar, 209;
from sky due to dust, 252.
Light-journey explained, 75.
Light-ratio shows stars to be limited, 152.
Living bodies, essential points in, 192.
Lockyer, Sir. N., on inorganic evolution, 117;
on evolution of stars, 130;
on Milky Way, 159;
on position of solar system, 161.
Luigi d'Auria on stellar motion, 306.
M'Kendrick, Prof., on germinal vesicle, 202.
Magnetism and sun-spots, 106.
Man, Shakespeare on, 322.
Mars, has no water, 266;
excessive temperatures on, 267.
Matter of universe uniform, 183.
Maunder on dark stars, 143.
Maxwell Hall, Mr., on star-motions, 178.
Measurement of star-distances, 85;
difficulty of, 86.
Mercury not habitable, 266.
Meteorites, elements in, 185;
not primitive bodies, 186.
Meteoritic hypothesis, 113;
Proctor on, 114;
explains nebulæ, 116;
Dr. Roberts on, 119.
Milky Way, the, 48;
form of, 51, 159;
description of, 52;
telescopic view of, 57;
stars in relation to, 59;
Mr. Gore on, 60;
density of stars in, 61;
clusters and nebulæ in relation to, 67;
probable distance of, 96;
forms a great circle, 157, 162;
Prof. Newcomb on, 158;
probably no life in, 284;
diagrams of, 300;
revolution of, important to us, 307.
Million, how to appreciate a, 82.
Minchin, G.M., on radiation from stars, 290.
Monck, Mr. W.H.S., on non-infinity of stars, 144;
on uncertainty of sun's motion, 177.
Moon, why no atmosphere, 263.
Moon's supposed origin, 233.
Motion, in line of sight, 35.
Motions, imperceptible, 39.
Nebulæ, with gaseous spectra, 43;
in relation to Galaxy, 66;
distribution of, 69;
many forms of, 70;
gaseous, 71;
meteoritic theory of, 116;
planetary and annular, 175;
Dr. Roberts on spiral, 117, 174;
Chamberlin on origin of, 120.
Nebular hypothesis, 98, 111;
objection to, 112.
Newcomb, Prof. S., on star distribution, 61;
on parallax of stars, 94;
on stability of star clusters, 126;
on scarcity of single stars, 128;
on limits of star system, 138;
on Milky Way, 158, 160;
on solar cluster, 167;
on star velocities, 171;
on average small mass of stars, 285;
on star-motions, 297.
Newton, Sir Isaac, on sun's habitability, 9.
Nichols, E.F., on heat of stars, 290.
Nitrogen, its importance to life, 195.
Non-habitability of great planets, 272.
Ocean and land, diagram of, 228.
---- basins, permanence of, 229.
---- ---- symmetry of, 238.
---- depths, how produced, 232.
Oceans, effect of, on temperature, 239;
curious relations of, 264.
Organic products, diversity of, 195.
Photographic astronomy, 43;
measures of star-distances, 89.
Photosphere, the, 105.
Physicists on sun's duration, 278.
Pickering's measurements of Algol, 40.
Planets, supposed habitability of, 266, 269;
the great, uninhabitable, 272;
internal heat of great, 273;
a last argument for habitability of, 274;
have probably no life, 315.
Planets' motions first explained, 3;
mass and atmosphere, 262.
Pleiades, number of stars in, 67;
a drifting cluster, 177.
Plurality of worlds, early writers on, 9;
Proctor on, 18.
Posidonius measures the earth, 5.
Pritchard's photographic measures of star-distance, 89.
Proctor, R.A., on other worlds, 18;
on form of Galaxy, 51;
on Herschel's views, 101;
on stellar universe, 103;
on meteoritic theory, 114;
on infinities, 136;
on star-drift, 176;
on life under varied conditions, 271;
on infinity, 324.
Proctor's _Old and New Astronomy_, 46;
chart of stars, 60.
Prominences of sun, 107.
Proteids, formation of, 199;
Prof. Haliburton on, 200.
Protoplasm, complexity of, 194;
a mechanism, 198;
sensibility of, to heat, 208.
Ptolemaic system of the heavens, 4.
Radial motion, 35.
Radiation from stars, 290.
Rain in the Carboniferous age, 225;
dependent on dust, 249.
Ramsay, Prof., on geological climates, 278.
Ranyard, on star-discs, 98;
on infinite universe, 137;
on mass of Orion nebula, 173.
Religious bearing of my conclusions, 319.
Reproduction, marvel of, 201.
Reversing layer of sun, 107.
Roberts, A.W., on birth of double stars, 123.
---- Dr. I., on limits of star-system, 148;
on spiral nebulæ, 117;
on meteoritic theory, 119;
photographs of nebulæ, 45, 174.
Roche limit explained, 120, 187.
Sanderson, Prof. Burdon, on living matter, 192.
Scientific and agnostic opinion on my conclusions, 318.
Secchi's classification of stars, 33.
Single stars perhaps rare, 128.
Solar apex, position of, 176.
Solar cluster, the, 165;
diagram showing, 300;
evidence for, 302;
importance to us, 306-7, 312.
Solar system, position of, 304.
Sorby on constitution of meteorites, 186.
Spectra, varieties of, 34;
of elements, changes in, 129.
Spectroscopic binaries, abundance of, 125;
great numbers of, 286.
Spectrum analysis, discovery of, 26.
Spencer, H., on status of nebulæ, 102.
Spiral nebulæ, origin of, 120.
Stars, proved to be suns, 32;
invisible, 39;
classification of, 33;
spectroscopic double, 42;
distribution of the, 47;
number of visible, 48;
description of Milky Way, 52;
in relation to Milky Way, 59;
distances of, 74;
measurement of distance of, 85;
mass of binary, 97;
evolution of double, 122;
spectroscopic double, 123;
clusters of, 125;
evolution of the, 128;
classification of, 130;
the hottest, 131;
when cooling give more heat, 132;
cycle of evolution and decay, 133;
supposed infinite number of, 135;
not infinite, 138;
law of diminishing numbers of, 149;
systematic motions of, 178;
in relation to life, 282, 287;
possible use of their emanations, 289.
Star-clusters and variables, 127.
Star-density, diagram of, 66.
Star-drift, Proctor on, 176.
Starlight, electrical measure of, 290;
possible uses of, 292.
Star-motions, Prof. Newcomb on, 297.
Star-system, limited, 145;
stability of, 295;
supposed primitive form of, 297.
Stellar motion, Luigi d'Auria on, 306.
---- universe, shape of, 49;
unity of, 100;
evolution of, 103;
diagrams of, 300.
Stoney, Dr., on atmospheres and gravity, 263.
Sun, a typical star, 104;
brightness of, 104;
heat of, 104;
surface of, 105;
surroundings of, 106-110;
corona of, 108;
colour of, 111;
elements in, 184.
Sun's distance, measure of, 76.
---- heat, supposed limits of, 275.
---- life, all required to develop earth-life, 280.
---- motion through space, 91, 169.
---- ---- uncertain, 177.
Sun-spots, nature of, 105.
Symmetry of oceans, cause of, 238.
Temperature, essential for life, 206;
equalised by water, 239;
as regards life on planets, 267.
Tennyson on man and the universe, 325.
Uniformity of matter, 183.
Unity of stellar universe, 100.
Universe of stars, how its form has affected our sun and earth, 308.
Universe not disproportionate if man is its sole product, 320.
VENUS, radial motions of, 38;
diagram of transit of, 77;
life barely possible on, 266;
adverse climatic conditions of, 268.
WATER, an essential for life, 210;
its amount and distribution, 227;
an equaliser of temperature, 239.
Wave-lengths, how measured, 31.
Whewell, on plurality of worlds, 8, 15;
on man as the highest product of the universe, 14.
Whittaker, Mr. E.T., on gravitative and electro-dynamical forces, 296.
Winds, importance of, to life, 246.
ZODIACAL light, 109.
Printed by T. and A. CONSTABLE, Printers to His Majesty,
at the Edinburgh University Press
[Illustration: THE NEBULÆ AND CLUSTERS OF THE NORTHERN HEAVENS. Drawn upon
an equal surface projection from Dr. DREYER'S catalogue of 1888 The Milky
Way from a Dr. BOEDDICKER'S Drawing by SIDNEY WATERS]
[Illustration: THE NEBULÆ AND CLUSTERS OF THE SOUTHERN HEAVENS. Drawn upon
an equal surface projection from Dr. DREYER'S catalogue of 1888 The Milky
Way from URANOMETRIA ARGENTINA by SIDNEY WATERS]
_WORKS BY THE SAME AUTHOR._
TRAVELS ON THE AMAZON AND RIO-NEGRO.
PALM-TREES OF THE AMAZON, AND THEIR USES (_out of print_).
THE MALAY ARCHIPELAGO.
NATURAL SELECTION AND TROPICAL NATURE.
THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS. _2 vols._
ISLAND LIFE, OR INSULAR FAUNAS AND FLORAS.
DARWINISM.
AUSTRALASIA. _2 vols._
BAD TIMES--CAUSES OF DEPRESSION OF TRADE (_out of print_).
LAND NATIONALISATION, ITS NECESSITY AND ITS AIMS.
VACCINATION A DELUSION.
MIRACLES AND MODERN SPIRITUALISM.
THE WONDERFUL CENTURY (_New and Illustrated Edition_).
THE WONDERFUL CENTURY READER.
STUDIES SCIENTIFIC AND SOCIAL.
* * * * *
Transcriber's Notes:
Obvious punctuation and spelling errors repaired.
Inconsistent hyphenation has been repaired.
The oe and ae ligatures in the text has been left as it appears in the
original book.
Italic text is denoted by _underscores_ and bold text by =equal signs=.
In ambiguous cases, the text has been left as it appears in the original
book. In particular, many mismatched quotation marks have not been changed.
The remaining corrections made:
Page v, "Fort-nightly" changed to "Fortnightly".
Page 106, "terrestial" changed to "terrestrial".
End of Project Gutenberg's Man's Place in the Universe, by Alfred R. Wallace