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II.Sr., JH.I1.. Jf.S.1L
J\fAN'S PLACE IN THE UNIVERSE
MAN'S PLACE IN
THE UNIVERSE
A Study of the Results of Scientific Research
in Relation to the Unity or Plurality
of \V orIds
BY
ALFRED R. VV ALLACE
LL.D., D.C.L., F.R.S., ETC.
· 0, glittering host! 0, golden line!
I would I had an angers ken,
Your deepest secrets to divine,
And read your mysteries to men. '
THIRD EDITIO.Y
LONDON
CHAPMAN AND HALL
LIl\IITED
19 0 4
, 1 said unto my inmost heart t
Shall I don corslet, helm, and shield,
And shall 1 with a Giant strive,
And charge a Dragon on the field? '
J. H. DELL.
JUN g
1958
PREFACE
THIS work has been written in consequence of the
great interest excited by my article, under the same
title t which appeared simultaneously in The Fort-
nightly Review and the New York Illdeþe'lldcllt.
T\vo friends who read the manuscript \vere of
opinion that a volume, in which the evidence could
be given much more fully, \vould be desirable, and
the result of the publication of the article confirmed
their view.
I ,vas led to a study of the subject ,vhen writing
four new chapters on Astronomy for a nevI edition
of The Wonderful Centur)'. I then found that
almost all writers on general astronomy, from Sir
John Herschel to Professor Simon Newcomb and
Sir Norman Lockyer, stated, as an indisputable
fact, that our sun is situated ,in the plane of the great
ring of the Milky Way, and also very nearly in the
centre of that ring. The most recent researches also
showed that there was little or no proof of there
being any stars or nebulæ very far beyond the
Milky Way, which thus seemed to be the limit, In
that direction, of the stellar universe.
"
vi MAN'S PLACE IN THE UNIVERSE
Turning to the earth and the other planets of the
Solar System, I found that the most recent re-
searches led to the conclusion that no other planet
was likely to be the seat of organic life, unless
perhaps of a very low type. For many years I had
paid special attention to the problem of the measure-
ment of geological timet and also that of the mild
climates and generally uniform conditions that had
prevailed throughout all geological epochs; and on
considering the number of concurrent causes and
the delicate balance of conditions required to main-
tain such uniformity, I became still more convinced
that the evidence was exceedingly strong against the
probability or possibility of any other planet being
inhabited.
Having long been acquainted with most of the
works dealing with the question of the supposed
Plurality of Worlds, I was quite aware of the very
superficial treatment the subject had received, even
in the hands of the most able writers, and this made
me the more willing to set forth the whole of the
available evidence - astronomical t physical, and
biological-in such a way as to show both what was
proved and what suggested by it.
The present vvork is the result, and I venture to
think that those who will read it carefully will admit
that it is a book that was worth writing. It is founded
almost entirely on the marvellous body of facts and
PREFACE
vii
conclusions of the New Astronomy together with those
reached by modern physicists, chemists, and biolo-
gists. I ts novelty consists in combining the various
results of these different branches of science into
a connected whole, so as to show their bearing upon
a single problem-a problem which is of very great
interest to ourselves.
This problem is, whether or no the logical
inferences to be drawn from the various results
of modern science lend support to the view that our
earth is the only inhabited planet, not only in the
Solar System but in the whole stellar universe.
Of course it is a point as to which absolute demon-
stration, one \vay or the other, is impossible. But
in the absence of any direct proofs, it is clearly
rational to inquire into probabilities; and these
probabilities must be determined not by our pre-
possessions for any particular view, but by an
absolutely impartial and unprejudiced examination
of the tendency of the evidence.
As the book is written for the general t educated
body of readers, many of whom may not be
acquainted with any aspect of the subject or with the
\vonderful advance of recent knowledge in that
department often termed the New Astronomy, a
popular account has been given of all those branches
of it which bear upon the special subject here
discussed, This part of the work occupies the first
viii MAN'S PLACE IN THE UNIVERSE
six chapters. Those who are fairly acquainted
with modern astronomical literature t as given in
popular works, may begin at my seventh chapter,
which marks the commencement of the considerable
body of evidence and of argument I have been able
to adduce.
To those of my readers who may have been
influenced by any of the adverse criticisms on my
views as set forth in the article already referred to,
I must again urge, that throughout the \vhole of this
work, neither the facts nor the more obvious con-
clusions from the facts are given on my own
authority, but always on that of the best astronomers,
mathematicians, and other men of science to whose
works I have had access, and whose names, with
exact references, I generally give.
What I claim to have done is, to have brought
together the various facts and phenomena they have
accumulated; to have set forth the hypotheses by
which they account for them, or the results to
which the evidence clearly points; to have judged
between conflicting opinions and theories; and
lastly, to have combined the results of the various
widely-separated departments of science, and to have
shown how they bear upon the great problem \vhich
I have here endeavoured, in sonle slight degree,
to elucidate.
As such a large body of facts and arguments from
PREFACE
IX
distinct sciences have been here brought together,
I have given a rather full summary of the whole
argument, and have stated my final conclusions in
six short sentences. I then briefly discuss the two
aspects of the whole problem-those from the
materialistic and from the spiritualistic points of view;
and I conclude \vith a few general observations on
the almost unthinkable problems raised by ideas
of Infinity-problems which some of my critics
thought I had attempted in some degree to deal with t
but which, I here point out, are altogether above and
beyond the questions I have discussed, and equally
above and beyond the highest po\vers of the human
in tellect.
BROADSTONE, DORSET,
September 1903.
b
, The wilder'd mind is tost and lost,
o sea, in thy eternal tide;
The reeling brain essays in vain,
o stars, to grasp the vastness wide !
The terrible tremendous scheme
That glimmers in each glancing light,
o night, 0 stars, too rudely jars
The finite with the infinite! '
.T. H. DELL
CONTENTS
CHA P.
I. EARLY IDEAS,
II. !vIODERN IDEAS,
III. THE NEW ASTRONOMY,
IV. THE DISTRIBUTION OF THE STARS,
v. DISTANCES OF STARS: THE SUN'S MOTION>> .
VI. UNITY A
D EVOLUTION OF THE STAR-SYSTEM,
VII. ARE THE STARS INFINITE?
VIII. OUR RELATION TO THE 1vIILKY 'V AY,
IX. THE UNIFORMITY OF MATTER AND ITS LAWS,
X. THE ESSENTIAL CHARACTERS OF ORGANISMS
XI. PHYSICAL CONDITIONS ESSENTIAL FOR LIFEt
XII. THE EARTH IN RELATION TO LIFE,
XIII. THE ATMOSPHERE IN RELATION TO LIFE, ·
XIV. THE OTHER PLANETS ARE NOT HABITABLE,
PAGE
. I
7
24
47
73
99
135
15 6
18 3
19 1
206
218 v"
243
262
XV. THE STARS: HAVE THEY PLANETS? ARE THEY
USEFUL TO US? . 282
XVI. STABILITY OF THE STAR-SYSTEM: IMPORTANCE OF
CENTRAL POSITION: SUMMARY AND CONCLUSION, 295
INDEX, 3 26
EIGHT DIAGRAAfS IN THE TEXT AND
TWO STAR CHARTS AT END.
xi
, Who is man, and what his place?
Anxious asks the heart, perplext
In this recklessness of space,
Worlds with worlds thus intermixt :
What has he, this atom creature,
In the infinitude of Nature? '
F. T. PALGRAVE.
MAN'S PLACE IN THE UNIVERSE
CHAPTER I
EARLY IDEAS AS TO THE UNIVERSE AND ITS
RELA TION TO MAN
W HEN men attained to sufficient intelligence for
speculations as to their own nature and that of the
earth on which they lived, they must have been pro-
foundly impressed by the nightly pageant of the
starry heavens. The intense sparkling brilliancy of
Sirius and Vega, the more massive and steady lumin-
osity of Jupiter and Venus, the strange grouping of
the brighter stars into constellations to which fantastic
names indicating their resemblance to various animals
or terrestrial objects seemed appropriate and were
soon generally adopted, together with the apparently
innumerable stars of less and less brilliancy scattered
broadcast over the sky, many only being visible on
the clearest nights and to the acutest vision, consti-
tuted altogether a scene of marvellous and impressive
splendour of which it must have seemed almost im-
possible to attain any real knowledge, but which
afforded an endless field for the imagination of the
observer.
The relation of the stars to the sun and moon in
their respective motions was one of the earliest pro-
"'-
2 MAN'S PLACE IN THE UNIVERSE [CHAP.
blems for the astronomer, and it was only solved by
careful and continuous observation, which showed
that the invisibility of the former during the day was
whoIIy due to the blaze of light, and this is said to
have been proved at an early period by the observed
fact that from the bottom of very deep wells stars
can be seen while the sun is shining. During total
eclipses of the sun also the brighter stars become
visible, and, taken in connection with the fixity of
position of the pole-star, and the course of those
circumpolar stars which never set in the latitudes of
Greece, Egypt, and Chaldea, it soon became possible
to frame a simple hypothesis which supposed the
earth to be suspended in space, while at an unknown
distance from it a crystal sphere revolved upon an
axis indicated by the pole-star, and carried with it
the whole host of heavenly bodies. This was the
theory of Anaximander (540 B.C.), and it served
as the starting-point for the more complex theory
which continued to be held in various forms and
with endless modifications down to the end of the
sixteenth century.
I t is believed that the early Greeks obtained some
kno\vledge of astronomy from the Chaldeans, who
appear to have been the first systematic observers of
the heavenly bodies by means of instruments, and
who are said to have discovered the cycle of eighteen
years and ten days after which the sun and moon
return to the same relative positions as seen from
the earth. The Egyptians perhaps derived their
knowledge from the same source, but there is no
proof that they were great observers, and the accu-
rate orientation, proportions, and angles of the Great
I.]
EARLY IDEAS
3
Pyramid and its inner passages may perhaps indicate
a Chaldean architect.
The very obvious dependence of the whole life of
the earth upon the sun, as a giver of heat and light,
sufficiently explains the origin of the belief that the
latter was a mere appanage of the former; and as
the moon also illuminates the night, while the stars
as a whole also give a very perceptible amount of
light, especiaIIy in the dry climate and clear atmo-
sphere of the East, and \\
hen compared with the
pitchy darkness of cloudy nights \vhen the n100n
is below the horizon, it seemed clear that the
whole of these grand luminaries-sun, moon, stars,
and planets-were but parts of the terrestrial system,
and existed solely for the benefit of its inhabitants.
Empedocles (444 B.C.) is said to have been the
first who separated the planets from the fixed stars,
by observing their very peculiar n10tions, \vhile
Pythagoras and his followers determined correctly
the order of their succession from IVlercury to Saturn.
No attempt was made to explain these motions tiIl
a century later t when Eudoxus of Cnidos, a con-
temporary of Plato and of Aristotle, resided for some
time in Egypt, where he became a skilful astronomer.
He was the .first who systematicalIy worked out and
eXplained the various motions of the heavenly bodies
on the theory of circular and uniform motion round
the earth as a centre, by means of a series of con-
centric spheres, each revolving at a different rate
and on a different axis, but so united that all shared
in the motion round the polar axis. The moon,
for example, was supposed to be carried by three
spheres, (he first revolved paranel to the equator
4 MAN'S PLACE IN THE UNIVERSE [CHAP.
and accounted for the diurnal motion-the rIsing
and setting-of the moon; another moved parallel
to the ecliptic and eXplained the monthly changes of
the moon; while the third revolved at the same rate
but more obliquely, and eXplained the inclination of
the moon's orbit to that of the earth. I n the same
way each of the five planets had four spheres, two
moving like the first two of the moon, another one
also moving in the ecliptic was required to explain
the retrograde motion of the planets, while a fourth
oblique to the ecliptic was needed to explain the
diverging motions due to the different obliquity of
the orbit of each planet to that of the earth. This
was the celebrated Ptolemaic system in the simplest
form needed to account for the more obvious motions
of the heavenly bodies. But in the course of ages the
Greek and Arabian astronomical observers discovered
small divergences due to the various degrees of
excentricity of the orbits of the moon and planets
and their consequent varying rates of motion; and to
explain these other spheres were added, together
with smaller circles sometimes revolving excentri-
cally, so that at length about sixty of these spheres,
epicycles and excentrics were required to account
for the various motions observed with the rude
instruments, and the rates of motion determined by
the very imperfect time-measurers of those early
ages. And although a few great philosophers had
at different times rejected this cumbrous system and
had endeavoured to promulgate more correct ideas,
their views had no influence on public opinion even
among astronomers and mathematicians, and the
Ptolemaic system held full sway down to the time of
I.]
EARLY IDEAS
s
Copernicus, and was not finally given up till I{epler's
La'lvs and Galileo's Dialogues compelled the adoption
of simpler and more intelligible theories.
\Ve are no\v so accustomed to look upon the main
facts of astronomy as mere elementary knowledge
that it is difficult for us to picture to ourselves the
state of almost complete ignorance which prevailed
even among the most civilised nations throughout
antiquity and the l\iiddle Ages. The rotundity of the
earth was held by a few at a very early period, and
\vas fairly well established in later classical times.
The rough determination of the size of our globe
followed soon after; and when instrumental observa-
tions became more perfect, the distance and size of
the moon were measured with sufficient accuracy to
show that it was very much smaller than the earth.
But this ,vas the farthest limit of the determination
of astronomical sizes and distances before the dis-
covery of the telescope. Of the sun's real distance
and size nothing ,vas known except that it was much
farther fronl us and much larger than the moon; but
even in th
century before the commencement of the
Christian era Posidonius determined the circumference
of the earth to be 240,000 stadia, equal to about 28,600
miles, a wonderfully close approximation considering
the very imperfect data at his command. He is also
said to have calculated the sun's distance, making it
only one-third less than the true amount, but this
must have been a chance coincidence, since he had
no means of measuring angles more accurately than
to one degree, whereas in the determination of the
sun's distance instruments are required which measure
to a second of arc.
6 MAN'S PLACE IN THE UNIVERSE [CHAP. I.
Before the discovery of the telescope the sizes of
the planets were quite unknown, \vhile the most that
could be ascertained about the stars was, that they
were at a very great distance from us. This being
the extent of the knowledge of the ancients as to the
actual dimensions and constitution of the visible uni-
verse, of which, be it remembered, the earth was held
to be the centre, we cannot be surprised at the almost
universal belief that this universe existed solely for
the earth and its inhabitants. In classical times it
was held to be at once the dwelling-place of the
gods and their gift to man, while in Christian ages
this belief \vas but slightly, if at all, changed; and in
both it \vould have been considered impious to main-
tain that the planets and stars did not exist for the
service and delight of mankind alone but in all pro-
bability had their own inhabitants, who might in
some cases be even superior in intellect to man him-
self. But apparently, during the whole period of
which we are now treating, no one was so daring as
even to suggest that there were other worlds with
other inhabitants, and it was no doubt because of the
idea that we occupied the world, the very centre of
the whole surrounding universe which existed solely
for us, that the discoveries of Copernicus, Tycho
Brahé, Kepler, and Galileo excited so much anta-
gonism and ,vere held to be impious and altogether
incredible. They seemed to upset the whole accepted
order of nature, and to degrade man by removing his
dwelling-place, the earth, from the commanding cen..
tral position it had al\vays before occupied.
CHAPTER II
MODERN IDEAS AS TO MAN'S RELATION TO THE UNIVERSE
THE beliefs as to the subordinate position held by
sun, moon, and stars in relation to the earth, ,vhich
,vere almost universal do\vn to the time of Coper-
nicus, began to give way when the discoveries of
Kepler and the revelations of the telescope demon-
strated that our earth was not specially distinguished
from the other planets by any superiority of size or
position. The idea at once arose that the other
planets might be inhabited; and when the rapidly
increasing po\ver of the telescope, and of astrononlical
instruments generally, revealed the \\"onders of the
solar system and the ever-increasing numbers of the
fixed stars, the belief in other inhabited ,vorlds
became as general as the opposite belief had been in
all preceding ages, and it is still held in modified
forms to the present day.
But it may be truly said that the later like the
earlier belief is founded more upon religious ideas
than upon a scientific and careful examination of the
whole of the facts both astronomical, physical, and
biological, and \ve must agree with the late Dr.
WhewelI, that the belief that other planets are
inhabited has been generally entertained, not in con-
sequence of physical reasons but in spite of them.
8 MAN'S PLACE IN THE UNIVERSE [CHAP.
And he adds :-' It was held that Venus, or that
Saturn was inhabited, not because anyone could
devise, with any degree of probability, any organised
structure which would be suitable to animal existence
on the surfaces of those planets; but because it was
conceived that the greatness or goodness of the
Creator, or His wisdom, or some other of His attri-
butes, would be manifestly imperfect, if these planets
were not tenanted by living creatures.' Those
persons who have only heard that many eminent
astronomers down to our own day have upheld the
belief in a 'Plurality of Worlds' will naturally
suppose that there must be some very cogent argu-
ments in its favour, and that it must be supported by
a considerable body of more or less conclusive facts.
They will therefore probably be surprised to hear
that any direct evidence which may be held to
support the view is almost wholly wanting, and that
the greater part of the arguments are weak and
flimsy in the extreme.
Of late years, it is true, some few writers have
ventured to point out how many difficulties there are
in the way of accepting the belief: but even these
have never examined the question from the various
points of view which are essential to a proper
consideration of it ; while, so far as it is still upheld,
it is thought sufficient to show, that in the case of
some of the planets, there seem to be such condi-
tions as to render life possible. I n the millions of
planetary systems supposed to exist it is held to be
incredible that there are not great numbers as well
fitted to be inhabited by animals of all grades,
including some as high as man or even higher, and
II.]
MODERN IDEAS
9
that we must, therefore, believe that they are so
inhabited. As in the present ,vork I propose to
show, that the probabilities and the weight of direct
evidence tend to an exactly opposite conclusion, it
,vill be ,vell to pass briefly in review the various
writers on the subject, and to give some indication of
the arguments they have used and the facts they
have set forth. F or the earlier upholders of the
theory I am indebted to Dr. \Vhewell, who, in his
Dialogue on the Pluralzïy of TVorlds-a Supplement
to his well-known volume on the subject-refers to
all writers of importance known to him.
The earliest are the great astronomers Kepler and
H uygens, and the learned Bishop Wilkins, who all
believed that the moon ,vas or might probably be
inhabited; and of these \Vhewell considers \\Tilkins
to have been by far the most thoughtful and earnest
in supporting his views. Then we have Sir Isaac
N e,vton himself who, at considerable length, argued
that the sun was probably inhabited. But the first
regular work devoted to the subject appears to have
been written by 1\1:. Fontenelle, Secretary to the
Academy of Sciences in Paris, who in 1686 published
his Conversations OIl the Plurality of TV01,lds. The
book consisted of five chapters, the first eXplaining
the Copernican Theory; the second maintaining that
the moon is a habitable ,vorld; the third gives
particulars as to the moon, and argues that the other
planets are also inhabited; the fourth gi ves details as
to the worlds of the five planets; while the fifth
declares that the fixed stars are suns, and that each
illuminates a world. This work was so ,veIl ,vritten,
and the subject proved so attractive, that it was
10 MAN'S PLACE IN THE UNIVERSE [CHAP.
translated into all the chief European languages,
while the astronomer Lalande edited one of the
French editions. Three English translations were
published, and one of these went through six editions
down to the year 1737. The influence of this work
was very great and no doubt led to that general
acceptance of the theory by such men as Sir William
Herschel, Sir John Herschel, Dr. Chalmers, Dr.
Dick, Dr. Isaac Taylor, and M. Arago, although it
was wholly founded on pure speculation, and there
,vas nothing that could be called evidence on one
side or the other.
This was the state of public opinion when an
anonymous work appeared (in I
53) under the some-
what misleading title of The Plurality of Worlds:
An Essay. This was written, as already stated, by
Dr. \Vhewell, who, for the first time, ventured to
doubt the generally accepted theory, and showed
that all the evidence at our command led to the con-
clusion that some of the planets were certaz'1zly not
habitable, that others were probably not so, while in
none was there that close correspondence with
terrestrial conditions which seemed essential for their
habitability by the higher animals or by man. The
book was ably written and showed considerable
kno\vledge of the science of the time, but it was very
diffuse, and the larger part of it \vas devoted to
showing that his views were not in any way opposed
to religion. One of his best arguments was founded
on the proposition that 'the Earth's Orbz"! z's the
Tel1zþerate Zone of the Solar Systenz,' that there only
is it possible to have those moderate variations of
heat and cold, dryness and moisture, which are suit-
II.]
rvl0DERN IDEAS
II
able for animal life. He suggested that the outer
planets of the system consisted mainly of water,
gases, and va pour, as indicated by their low specific
gravity, and were therefore quite unsuitable for
terrestrial life ; while those near the sun were equally
unsuited, because, owing to the great amount of solar
heat, water could not exist on their surfaces. He
devotes a great deal of space to the evidence that
there is no animal life on the moon, and taking this
as proved, he uses it as a counter argument against
the other side. They always urge that, the earth
being inhabited, we must suppose the other planets
to be so too; to \vhich he replies :-We know that
the moon is not inhabited though it has all the
advantage of proximity to the sun that the earth has;
why then should not other planets be equally
uninhabited?
He then comes to l\lars and admits that this
planet is very like the earth so far as we can judge,
and that it may therefore be inhabited, or as the
author expresses it, 'may have been judged worthy
of inhabitants by its Maker.' But he urges the small
size of l\lars, its coldness owing to distance from the
sun, and that the annual melting of its polar ice-caps
will keep it cold all through the summer. If there
are animals they are probably of a low type like the
saurians and iguanodons of our seas during the
\Vealden epoch; but, he argues, as even on our earth
the long process of preparation for man was carried
on for countless millions of years, we need not dis-
cuss whether there are intelligent beings on Mars
till \ve have some better evidence that there are any
living creatures at all.
12 MAN'S PLACE IN THE UNIVERSE [CHAP.
Several of the early chapters are devoted to an
attempt to minimise the difficulties of those religious
persons who feel oppressed by the immensity and
complexity of the material universe as revealed by
modern astronomy; and by the almost infinite insig-
nificance of man and his d wellin g-place, the earth, in
comparison with it, an insignificance vastly increased
if not only the planets of the solar system, but also
those which circle around the myriads of suns, are
also theatres of life. And these persons are further
disquieted because the very same facts are used by
sceptics of various kinds in their attacks upon
Christianity. Such writers point out the irrationality
and absurdity of supposing that the Creator of all
this unimaginable vastness of suns and systems, fill-
ing for all we know endless space, should take any
special interest in so mean and pitiful a creature as
man, the imperfectly developed inhabitant of one of
the smaller worlds attached to a second or third-rate
sun, a being whose whole history is one of war and
bloodshed, of tyranny, torture, and death; whose
a ,vful record is pictured by himself in such books as
Josephus' Hz'story of the Jews, the Decline a1zd Fall
of the ROma11, En'tþ'ire, and even more forcibly
summarised in that terrible picture of human
fiendishness and misery, The Martyrdo1lz of Matt;
while their character is indicated by one of the
kindest and simplest of their poets in the restrained
but expressive lines :-
, Man's inhumanity to man
Makes countless thousands mourn.'
I t is for such a being as this, they say, that God
II.]
MODERN IDEAS
13
should have specially revealed His will some
thousands of years ago, and finding that His com-
mands were not obeyed, His will not fulfilled, yet
ordained for their benefit the necessarily unique
sacrifice of H is Son, in order to save a small portion
of these 'miserable sinners' from the natural and
\vell-deserved consequence of their stupendous follies,
their unimaginable crimes? Such a belief they
maintain is too absurd, too incredible, to be held by
any rational being, and it becomes even less credible
and less rational if we maintain that there are count-
less other inhabited worlds.
I t is very difficult for the religious man to make
any adequate reply to such an attack as this, and as
a result many have felt their position to be untenable
and have accordingly lost all faith in the special
dogmas of orthodox Christianity. They feel them-
selves really to be between the horns of a dilemma.
If there are myriads of other worlds, it seems
incredible that they should each be the object of a
special revelation and a special sacrifice. If, on the
other hand, we are the only intelligent beings that
exist in the material universe, and are really the
highest creative product of a Being of infinite wisdom
and power, they cannot but wonder at the vast
apparent disproportion between the Creator and the
created, and are sometimes driven to Atheism from
the hopelessness of comprehending so mean and
petty a result as the sole outcome of infinite power.
\Vhe,vell tells us that the great preacher, Dr..
Chalmers, in his Astronomical Discourses, attempted
a reply to these difficulties, but, in his opinion, not
a very successful one; and a large part of hw own
14 MAN'S PLACE IN THE UNIVERSE [CHAP.
work is devoted to the same purpose. His main
point seems to be that we know too little of the
universe to arrive at any definite conclusions on the
question at issue, and that any ideas that we may
have as to the purposes of the Creator in forming the
vast system we see around us are almost sure to be
erroneous. We must therefore be content to remain
ignorant, and must rest satisfied in the belief that
the Creator had a purpose although we are not yet
permitted to know what it was. And to those who
urge that in other worlds there may be other laws of
nature which may render them quite as habitable by
intelligent beings as our world is for us, he replies,
that if we are to suppose new laws of nature in order
to render each planet habitable, there is an end of all
rational inquiry on the subject, and we may maintain
and believe that animals may live on the moon
without air or water, and on the sun exposed to heat
which vaporises earths and metals.
His concluding argument, and perhaps one of his
strongest, is that founded upon the dignity of man,
as conferring a pre-eminence upon the planet which
has produced him. 'I f,' he says, 'man be not merely
capable of Virtue and Duty, of universal Love and
Self- Devotion, but be also immortal; if his being be
of infinite duration, his soul created never to die;
then, indeed, we may well say that one soul out\veighs
the \vhole unintelligent creation.) And then, addres-
sing the religious world, he urges that, if, as they
believe, God has redeemed man by the sacrifice of
H is Son, and has given to hÍ111 a revelation of His
will, then indeed no other conception is possible
than that he is the sole and highest product of the
II. ]
MODERN IDEAS
15
universe. 'The elevation of millions of intellectual,
moral, religious t spiritual creatures, to a destiny so
prepared, consummated, and developed, is no un-
worthy occupation of all the capacities of space, time,
and matter.' Then with a chapter on 'The Unity
of the World/ and one on 'The Future,' neither of
\vhich contains anything \vhich adds to the force of
his argument, the book ends.
The publication of this able if rather vague and
diffuse work, contesting popular opinions, was followed
by a burst of indignant criticism on the part of a man
of considerable eminence in some branches of physics
-Sir David Brewster, but \vho was very inferior,
both in general knowledge of science and in literary
skill, to the \vriter whose views he opposed. The
purport of the book in \vhich he set forth his objec-
tions is indicated by its title-More Worlds than
Oue, the Creed of the Ph'ilosoþher and the Hoþe of the
Chrl:slia1Z. Though written with much force and
conviction it appeals mainly to religious prejudices,
and assumes throughout that every planet and star
is a special creation, and that the peculiarities of each
were designed for some special purpose. ' If,' he
says, 'the moon had been destined to be merely a
lamp to our earth, there was no occasion to variegate
its surface with lofty mountains and extinct volcanoes,
and cover it with large patches of matter that reflect
different quantities of light and give its surface the
appearance of continents and seas. It would have
been a better lamp had it been a smooth piece of
lime or of chalk.' I t is, therefore, he thinks, prepared
for inhabitants; and then he argues that all the
other satellites are also inhabited. Again he says
16 MAN'S PLACE IN THE UNIVERSE [CHAP.
that 'when it was found that Venus was about the
same size as the Earth, with mountains and valleys,
days and nights, and years analogous to our own, the
absurdity of believing that she had no inhabitants,
when no other rational purpose could be assigned for
her creation t became an argument of a certain amount
that she was, like the Earth, the seat of animal and
vegetable life.' Then, when it was found that Jupiter
was so gigantic 'as to require four moons to give
him light, the argument from analogy that he was
inhabited became stronger also, because it extended
to two planets.' And thus each successive planet
having certain points of analogy with the others
becomes an additional argument; so that when we
take account of all the planets, with atmosphere, and
clouds, and arctic snows, and trade-winds, the argu-
ment from analogy becomes, he urges, very powerful;
-' and the absurdity of the opposite opinion, that
planets should have moons and no inhabitants,
atmospheres with no creatures to breathe in them,
and currents of air without life to be fanned, became
a formidable argument which few minds, if any, could
. ,
resIst.
The work is full of such weak and fallacious
rhetoric and even, if possible, still weaker. Thus
after describing double stars, he adds-' But no
person can believe that two suns could be placed in
the heavens for no other purpose than to revolve
round their common centre of gravity'; and he con-
cludes his chapter on the stars thus :-' \Vherever
there is matter there must be Life; Life Physical to
enjoy its beauties-Life l\10ral to worship its l\Iaker,
and Life Intellectual to proclaim His wisdom and
Jr.]
MODERN IDEAS
17
His po\ver. And again-' A house ,vithottt tenants,
a city without citizens, presents to our minds the
same idea as a planet \vithout life, and a universe
without inhabitants. \Vhy the house was built, why
the city was founded, \vhy the planet was made, and
why the universe was created, it would be difficult
even to conjecture.' Arguments of this kind, which
in almost every case beg the question at issue, are
repeated ad nauseant. But he also appeals to the
Old Testament to support his views, by quoting the
fine passage in the Psalms-' \\Then I consider Thy
heavens the work of Thy fingers, the moon and the
stars which Thou hast ordained; what is man that
Thou art mindful of him?' on \vhich he remarks-
, \Ve cannot doubt that inspiration revealed to him
[David] the magnitude, the distances, and the final
cause, of the glorious spheres which fixed his admira-
tion.' And after quoting various other passages from
the prophets, all as he thinks supporting the same
view, he sets forth the extraordinary idea as a con-
firmatory argument, that the planets or some of them
are to be the future abode of man. For, he says-
'Man in his future state of existence is to consist,
as at present, of a spiritual nature residing in a
corporeal frame. He must live, therefore, upon a
material planet, subject to all the laws of matter.'
And he concludes thus :-' If there is not roonl, then,
on our globe for the millions of millions of beings
who have lived and died on its surface, we can
scarcely doubt that their future abode must be on
some of the primary or secondary planets of the
solar system, whose inhabitants have ceased to
exist, or upon planets which have long been in a
B
18 MAN'S PLACE IN THE UNIVERSE [CHAP.
state of preparation, as our earth was, for the ad ven t
of intellectual life.'
I t is pleasant to turn from such weak and trivial
arguments to the only other modern works which
deal at some length with this subject, the late Richard
A. Proctor's Other Worlds than Ours, and a volume
published five years later under the title-Our Place
Anzong ItzjÙzz'ties. \Vritten as these were by one
of the most accomplished astronomers of his day,
remarkable alike for the acuteness of his reasoning
and the clearness of his style, we are always inter-
ested and instructed even \vhen we cannot agree with
his conclusions. In the first work mentioned above,
he assumes, like Sir David Brewster, the antecedent
probability that the planets are inhabited and on
much the same theological grounds. So strongly
does he feel this that he continually speaks as if the
planets 1JZUSt be inhabited unless we can show very
good reason that they cannot be so, thus throwing
the burden of proving a negative on his opponents,
while he does not attempt to prove his positive con-
tention that they are inhabited, except by purely
hypothetical considerations as to the Creator's purpose
in bringing them into existence.
But starting from this point he endeavours to show
how \Vhe\vell's various difficulties may be overcome,
and here he always appeals to astronomical or physical
facts, and reasons well upon them. But he is quite
honest; and, coming to the conclusion that Jupiter
and Saturn, Uranus and Neptune, cannot be habit-
able, he adduces the evidence and plainly states the
result. But then he thinks that the satellites of
Jupiter and Saturn 1nay be habitable, and if they may
II.]
l\IODERN IDEAS
19
be, then he concludes that they ?/lust. One great
oversight in his whole argument is, that he is satisfied
\vith sho\ving the possibility that life may exist now,
but never deals with the -question of \vhether life
could have been developed fronl its earliest rudiments
up to the production of the higher vertebrates and
man; and this, as I shall show later, is the crux of
the ,,-hole problem.
\Vith regard to the other planets, after a careful
examination of all that is kno\vn about them, he
arrives at the conclusion that if l\Iercury is protected
by a cloud-laden atmosphere of a peculiar kind it
may possibly, but not probably, support high forms
of animal life. But in the case of Venus and l\lars
he finds so much resemblance to and so many ana-
logies ,vith our earth, that he concludes that they
almost certainly are so.
I n the case of the fixed stars, now that we kno\v
by spectroscopic observations that they are true suns,
many of which closely resemble our sun and give out
light and heat as he does, :l\lr. Proctor argues, that
'The vast supplies of heat thus el11itted by the stars
not only suggest the conclusion that there must be
worlds around these orbs for which these heat-
supplies are intended, but point to the existence of
the various forms of force into \yhich heat may be
transmuted. \Ve kno\v that the sun's heat poured
upon our earth is stored up in vegetable and animal
forms of life; is present in all the phenomena of
nature-in winds and clouds and rain, in thunder
and lightning, storm and hail; and that even the
,vorks of man are perfornled by virtue of the solar
heat-supplies. Thus the fact that the stars send forth
20 MAN'S PLACE IN THE UNIVERSE [CHAP.
heat to the worlds which circle around them suggests
at once the thought that on those worlds there must
exist animal and vegetable forms of life.' We may
note that in the first part of this passage the presence
of worlds or planets is 'suggested,' while later on
, the worlds which circle round them' is spoken of as
if it were a proved fact from which the presence of
vegetable and animal life may be inferred. A sug-
gestion depending on a preceding suggestion is not
a very firm basis for so vast and wide-reaching a
conclusion.
In the second work referred to above there is one
chapter entitled, 'A New Theory of Life in other
Worlds,' where the author gives his more matured
views of the question, which are briefly stated in the
preface as being' that the weight of evidence favours
my theory of the (relative) paucity of worlds.' His
views are largely founded on the theory of probabili-
ties, of which subject he had made a special study.
Taking first our earth, he shows that the period
during which life has existed upon it is very small in
comparison with that during which it must have been
slowly forming and cooling, and its atmosphere con-
- densing so as to form land and water on its surface.
And if we consider the time the earth has been
occupied by man, that is a very minute part, perhaps
not the thousandth part, of the period during which it
has existed as a planet. I t follows that even if we
consider only those planets whose physical condition
seems to us to be such as to be able to sustain
life, the chances are perhaps hundreds to one
against their being at that particular stage when
life has begun to be developed, or if it has begun
II.]
MODERN IDEAS
21
has reached as high a development as on our
earth.
vVith regard to the stars, the argument is still
stronger, because the epochs required for their forma-
tion are altogether unkno,vn, \vhile as to the condi-
tions required for the formation of planetary systems
around them we are totally ignorant. To this I
would add that we are equally ignorant as to the
probability or even possibility of many of these suns
producing planets which, by their position, size,
atnlosphere, or other physical conditions can possibly
become life-producing \vorlds. And, as we shall see
later, this point has been overlooked by all writers,
including l'vIr. Proctor himself. His conclusion is,
then, that although the worlds which possess life at
all approaching that of our earth may be relatively
few in number, yet considering the universe as prac-
tically infinite in extent, they may be really very
numerous.
I t has been necessary to give this sketch of the
views of those who have written specially on the
question of the Plurality of Worlds, because the
works referred to have been very widely read and
have influenced educated opinion throughout the
world. l\loreover, l\fr. Proctor, in his last work on
the subject, speaks of the theory as being' identified
with modern astronomy'; and in fact popular \vorks
still discuss it. But all these follow the same general
line of argument as those already referred to, and
the curious thing is that ,vhile overlooking many of
the most essential conditions they often introduce
others which are by no means essential-as, for
instance, that the atmosphere must have the same
22 MAN'S PLACE IN THE UNIVERSE [CHAP.
proportion of oxygen as our o\vn. They seem to
think that if any of our quadrupeds or birds taken
to another planet could not live there, no animals
of equally high organisation could inhabit it ; entirely
overlooking the very obvious fact that, supposing, as
is almost certain, that oxygen is necessary for life,
then, whatever proportion of oxygen within certain
limits was present, the forms of life that arose would
necessarily be organised in adaptation to that propor-
tion, which might be considerably less or greater than
on the earth.
The present volume will show how extremely
inadequate has been the treatment of this question,
which involves a variety of important considerations
hitherto altogether overlooked. These are extremely
numerous and very varied in their character, and the
fact that they all point to one conclusion-a conclu-
sion which so far as I am aware no previous \vriter
has reached-renders it at least worthy of the careful
consideration of all unbiassed thinkers. The whole
subject is one as to which no direct evidence is.
obtainable, but I venture to think that the conver-
gence of so many probabilities and indications towards
a single definite theory, intimately connected with
the nature and destiny of man himself, raises this
theory to a very much higher level of probability
than the vague possibilities and theological sugges-
tions which are the utmost that have been adduced
by previous writers.
In order to make every step of my argument
clearly intelligible to all educated readers, it will be
necessary to refer continually to the marvellous ex-
tension of our kno\vledge of the universe obtained
11.]
MODERN IDEAS
23
during the last half-century, and constituting what is
termed the N e\v Astronomy. The next chapter will
therefore be devoted to a popular exposition of the
new methods of research, so that the results reached,
\vhich will have to be referred to in succeeding
chapters, may be not only accepted, but clearly un-
derstood.
CHAPTER III
THE NEW ASTRONOMY
DURING the latter half of the nineteenth century
discoveries were made which extended the powers of
astronomical research into entirely new and unex-
pected regions, comparable to those which were
opened up by the discovery of the telescope more
than two centuries before. The older astronomy for
more than two thousand years was purely mechanical
and mathematical, being limited to observation and
measurement of the apparent motions of the heavenly
bodies, and the attempts to deduce, from these ap-
parent motions, their real motions, and thus deter-
mine the actual structure of the solar system. This
,vas first done when Kepler established his three
celebrated laws: and later, when Newton showed
that these laws were necessary consequences of
the one law of gravitation, and when succeeding
observers and mathematicians proved that each fresh
irregularity in the motions of the planets was explic-
able by a more thorough and minute application of
the same laws, this branch of astronomy reached its
highest point of efficiency and left very little more to
be desired.
Then, as the telescope became successively Im-
proved, the centre of interest was shifted to the
CH. III.]
THE NEW ASTRONOMY
2S
surfaces of the planets and their satellites, which were
\vatched and scrutinised with the greatest assiduity in
order if possible to attain some alTIOunt of kno\vledge
of their physical constitution and past history. A
similar minute scrutiny was given to the stars and
nebulæ, their distribution and grouping, and the
whole heavens were mapped out, and elaborate cata-
logues constructed by enthusiastic astronomers in
every part of the world. Others devoted themselves
to the immensely difficult problem of determining
the distances of the stars, and by the middle of the
century a few such distances had been satisfactorily
measured.
Thus, up to the middle of the nineteenth century
it appeared likely that the future of astronomy would
rest almost entirely on the improvement of the tele-
scope, and of the various instruments of measurement
by means of which more accurate determinations of
distances might be obtained. Indeed, the author of
the Positive Philosophy, Auguste Comte, felt so sure
of this that he deprecated all further attention to the
stars as pure waste of time that could never lead to
any useful or interesting result. I n his PhilosoPhical
Trealise on Popular Astro1lomy published in 1844,
he wrote very strongly on this poi nt. He there tells
us that, as the stars are only accessible to us by sight
they must always remain very imperfectJy known.
\Ve can know Ii ttJe more than their mere existence.
Even as regards so simple a phenomenon as their
temperature this must always be inappreciable to a
purely visual examination. Our knowledge of the
stars is for the most part purely negative, that is,
we can determine only that they do not belong to our
26 11:AN'S PLACE IN THE UNIVERSE [CHAP.
system. Outside that system there exists, in as-
tronomy, only obscurity and confusion, for want of
indispensable facts; and he concludes thus :-' I tis,
then, in vain that for half a century it has been
endeavoured to distinguish two astronomies, the one
solar the other sidereal. In the eyes of those for
whom science consists of real laws and not of in-
coherent facts, the second exists only in name, and
the first alone constitutes a true astronomy; and
I am not afraid to assert that it will always be
so.' And he adds that-' all efforts directed to this
subject for half a century have only produced an
accumulation of incoherent empirical facts which can
only interest an irrational curiosity.'
Seldom has a confident assertion of finality in sci-
ence received so crushing a reply as was given to the
above statements of Comte by the discovery in 1860
(only three years after his death) of the method of
spectrum-analysis which, in its application to the stars,
has revolutionised astronomy, and has enabled us to
obtain that very kind of knowledge which he declared
must be for ever beyond our reach. Through it we
have acquired accurate information as to the physics
and chemistry of the stars and nebulæ, so that we
now know really more of the nature, constitution, and
temperature of the enormously distant suns which we
distinguish by the general term stars, than we do of
most of the planets of our own system. I t has also
enabled us to ascertain the existence of numerous
invisible stars, and to determine their orbits, their
rate of motion, and even, approximately, their mass.
The despised stellar astronomy of the early part of
the century has no,v taken rank as the most pro-
III. ]
THE NEW ASTRONOMY
27
foundly interesting department of that grand science,
and the branch which offers the greatest promise of
future discoveries. As the results obtained by means
of this powerful instrument will often be referred to,
a short account of its nature and of the principles on
which it depends must here be given.
The solar spectrum is the band of coloured light
seen in the rainbow and, partially, in the de\v-drop,
but more completely when a ray of sunlight passes
through a prism-a piece of glass having a triangular
section. The result is, that instead of a spot of \vhite
light we have a narrow band of brilliant colours \vhich
succeed each other in regular order, from violet at
one end through blue, green, and yellow to red at
the other. We thus see that light is not a simple
and uniform radiation from the sun, but is made up
of a large number of separate rays, each of which
produces in our eyes the sensation of a distinct
colour. Light is now eXplained as being due to
vibrations of ether, that mysterious substance which
not only permeates all matter, but which fills space
at least as far as the remotest of the visible stars and
nebulæ. The exceedingly minute waves or vibrations
of the ether produce all the phenomena of heat, light,
and colour, as well as those chemical actions to which
photography owes its wonderful powers. By in-
genious experiments the size and rate of vibration of
these waves have been measured, and it is found
that they vary considerably, those forming the red
light, which is least refracted, having a \vave-Iength
of about 32"trlr-oo of an inch, while the violet rays at
the other end of the spectrum are only about half
that length or l)gO
of an inch. The rate at which
28 MAN'S PLACE IN THE UNIVERSE [CHAP.
the vibrations succeed each other is from 302 millions
of millions per second for the extreme red rays, to
737 millions of millions for those at the violet end of
the spectrum. These figures are given to show the
wonderful minuteness and rapidity of these heat and
light waves on which the whole life of the world, and
all our knowledge of other worlds and other suns,
directly depends.
But the mere colours of the spectrum are not the
most important part of it. Very early in the nine-
teenth century a close examination showed that it
was everywhere crossed by black lines of various
thicknesses, sometimes single, sometimes grouped
together. Many observers studied them and made
accurate drawings or maps showing their positions
and thicknesses, and by combining several prisms,
so that the beam of sunlight had to pass through
them successively, a spectrum could be produced sev-
eral feet long, and more than 3000 of these dark lines
were counted in it. But what they were and how
they were caused remained a mystery, till, in the year
1860, the German physicist Kirchhoff discovered the
secret and gave to chen1ists and astronomers a new
and quite unexpected engine of research.
It had already been observed that the chemical
elements and various compounds, when heated to
incandescence, produced spectra consisting of coloured
lines or bands which were constant for each element,
so that the elements could at once be recognised by
their characteristic spectra; and it had also been
noticed that some of these bands, especially the
yellow band produced by sodium, corresponded in
position with certain black lines in the solar spectrum.
III. ]
THE NEW ASTRONOMY
29
Kirchhoff's discovery consisted in showing that, when
the light from an incandescent body passes through
the same substance in a state of vapour or gas, so
much of the light is absorbed that the coloured lines
or bands become black. The mystery of n10re than
half a century was thus solved; and the thousands of
black lines in the solar spectrum were shown to be
caused by the light from the incandescent matter of
the sun's surface passing through the heated gases
or vapours immediately above it, and thereby having
the bright coloured lines of their spectra changed,
by absorption, to comparative blackness.
Chemists and physicists immediately set to work
examining the spectra of the elements, fixing the
position of the several coloured lines or bands by
accurate measurement, and comparing them with the
dark lines of the solar spectrum. The results were
in the highest degree satisfactory. I n a large pro-
portion of the elements the coloured bands corre-
sponded exactly with a group of dark lines in the
spectrum of the sun, in which, therefore, the same
terrestrial elements were proved to exist. Among
the elements first detected in this manner were
hydrogen, sodium, iron, copper, magnesium, zinc,
calcium, and many others. N early forty of the
elements have now been found in the sun, and it
seems highly probable that all our elements really
exist there, but as some are very rare and are present
in very minute quantities they cannot be detected.
Some of the dark lines in the sun were found not to
correspond to any known element, and as this was
thought to indicate an element peculiar to the sun it
was named Helium; but quite recently it has been
30 MAN'S PLACE IN THE UNIVERSE [CHAP.
discovered in a rare mineral. Many of the elements
are represented by a great number of lines, others
by very few. Thus iron has more than 2000, while
lead and potassium have only one each.
The value of the spectroscope both to the chemist
in discovering new elements and to the astronomer in
determining the constitution of the heavenly bodies,
is so great, that it became of the highest importance
to have the posi tion of all the dark lines in the solar
spectrum, as well as the bright lines of all the elements,
detertnined with extreme accuracy, so as to be able
to make exact comparisons between different spectra.
A t first this was done by means of very large-scale
drawings showing the exact position of every dark
or bright line. But this was found to be both in-
convenient and not sufficiently exact; and it was
therefore agreed to adopt the natural scale of the
wave-lengths of the different parts of the spectrum,
\vhich by means of what are termed diffraction-grat-
ings can now be measured with great accuracy.
Diffraction-gratings are forn1ed of a polished surface
of hard metal ruled with excessively fine lines, some-
times as many as 20,000 to an inch. When sun-
light falls upon one of these gratings it is reflected,
and by interferenèe of the rays from the spaces be-
tween the fine grooves, it is spread out into a
beautiful and well-defined spectrum, which, when the
lines are very close, is several yards in ]ength. In
these diffraction spectra many dark lines are seen
which can be shown in no other way, and they also
give a spectrum which is far more uniform than that
produced by glass prisms in which minute differences
in the composition of the glass cause some rays
III. ]
THE NEW ASTROKOMY
3 1
to be refracted more and others less than the normal
amount.
The spectra produced by diffraction-gratings are
double; that is, they are spread out on both sides of
the central line of the ray which remains ,vhite, and
the several coloured or dark lines are so clearly
defined that they can be thrown on a screen at a
considerable distance, giving a great length to the
spectrum. The data for obtaining the ,vave-Iengths
are the distance apart of the lines, the distance of the
screen, and the distance apart of the first pair of
dark lines on each side of the central bright line.
All these can be measured with extreme accuracy by
means of telescopes with micrometers and other
contrivances, and the result is an accuracy of deter-
mination of wave-lengths which can probably not be
equalled in any other kind of measurement.
As the wave-lengths are so excessively minute, it
has been found convenient to fix upon a still smaller
unit of measurement, and as the millimetre is the
smallest unit of the metric system, the ten-millionth
of a millimetre (technically termed 'tenth meter') is
the unit adopted for the measurement of wave-
lengths, which is equal to about the 250 millionth
of an inch. Thus the \vave-Iengths of the red and
blue lines characteristic of hydrogen are 6563 '07 and
4 861 '5 1 respectively. This excessively minute scale
of wave-lengths, once determined by the most refined
measurement, is of very great importance. Having
the ,,,ave-lengths of any t,vo lines of a spectrum so
determined, the space between then1 can be laid down
on a diagram of any length, and all the lines that
occur in any other spectrum between these t\VO lines
32 MAN'S PLACE IN THE UNIVERSE [CHAP.
can be marked in their exact relative positions. Now,
as the visible spectrum consists of about 300,000 rays
of light, each of different wave-lengths and therefore
of different refrangibilities, if it is laid down on such
a scale as to be of a length of 3000 inches (250 feet),
each wave-length will be l
O of an inch long, a space
easily visible by the naked eye.
The possession of an instrument of such wonder-
ful delicacy, and with powers which enable it to
penetrate into the inner constitution of the remotest
orbs of space, rendered it possible, within the next
quarter of a century, to establish what is practically
a new science-Astrophysics-often popularly termed
the New Astronomy. A brief outline of the main
achievements of this science must now be given.
The first great discovery made by Spectrum-
analysis, after the interpretation of the sun's spectrum
had been obtained, was, the real nature of the fixed
stars. I t is true they had long been held by astro-
nomers to be suns, but this was only an opinion
of the accuracy of which it did not seem possible to
obtain any proof. The opinion was founded on two
facts-their enormous distance from us, so great that
the whole diameter of the earth's orbit did not lead
to any apparent change of their relative positions,
and their intense brilliancy which at such distances
could only be due to an actual size and splendour
comparable with our sun. The spectroscope at once
proved the correctness of this opinion. As one after
another was examined, they were found to exhibit
spectra of the same general type as that of the sun-
a band of colours crossed by dark lines. The very
first stars examined by Sir William Huggins showed
III.]
THE NEW ASTRONOl\iY
33
the existence of nine or ten of our elements. Very
soon all the chief stars of the heavens were spectro-
scopically examined, and it was found that they
could be classed in three or four groups. The first
and largest group contains more than half the visible
stars t and a still larger proportion of the most
brilliant, such as Sirius, Vega, Regulus, and Alpha
Crucis in the Southern Hemisphere. They are
characterised by a white or bluish light, rich in the
ultra-violet rays, and their spectra are distinguished
by the breadth and intensity of the four dark bands
due to the absorption of hydrogen, while the various
black lines which indicate metallic vapours are com-
paratively fe\v, though hundreds of them can be
discovered by careful examination.
The next group, to which Capella and Arcturus
belong, is also very numerous, and forms the solar
type of stars. Their light is of a yellowish colour,
and their spectra are crossed throughout by innumer-
able fine dark lines more or less closely correspon-
ding with those in the solar spectrum.
The third group consists of red and variable stars,
which are characterised by fluted spectra. Such
spectra show like a range of Doric columns seen in
perspective, the red side being that most illumi-
nated.
The last group, consisting of fe\v and com-
paratively small stars, has also fluted spectra, but
the light appears to come from the opposite direc-
tion.
These groups were established by Father Secchi,
the Roman astronomer, in 1867, and have been
adopted with some modifications by Vogel of the
c
34 MAN'S PLACE IN THE UNIVERSE [CHAP.
Astrophysical Observatory at Pots dam. The exact
interpretation of these different spectra is somewhat
uncertain, but there can be little doubt that they
coincide primarily with differences of temperature
and wi th corresponding differences in the composition
and extent of the absorptive atmospheres. Stars
with fluted spectra indicate the presence of vapours
of the metalloids or of compound substances, while
the reversed flutings indicate the presence of carbon.
These conclusions have been reached by careful
laboratory experiments which are now carried on at
the same time as the spectral examination of the
stars and other heavenly bodies, so that each
peculiarity of their spectra, however puzzling and
apparently unmeaning, has been usually explained,
by being shown to indicate certain conditions of
chemical constitution or of temperature.
But whatever difficulty there may be in explaining
details, there remains no dOll bt whatever of the
fundamental fact that all the stars are true suns,
differing no doubt in size, and their stage of develop-
ment as indicated by the colour or intensity of their
light or heat, but all alike possessing a photosphere
or light-emitting surface, and absorptive atmospheres
of various qualities and density.
I nnumerable other details, such as the often con-
trasted colours of double stars, the occasional varia-
bility of their spectra, their relations to the nebulæ,
the various stages of their development and other
problems of equal interest, have occupied the con-
tinued attention of astronomers, spectroscopists, and
chemists; but further reference to these difficult
questions would be out of place here. The present
III.]
THE KE\V ASTRONOMY
35
sketch of the nature of spectrum-analysis applied to
the stars is for the purpose of making its principle
and method of observation intelligible to every
educated reader, and to illustrate the marvellous
precision and accuracy of the results attained by it.
So confident are astronOtners of this accuracy that
nothing less than perfect correspo1zde11ce of the various
bright lines in the spectrum of an element in the
laboratory with the dark lines in the spectrum of the
sun or of a star is required before the presence of
that element is accepted as proved. As Miss Clerke
tersely puts it-' Spectroscopic coincidences admit of
no compromise. Either they are absolute or they
are \vorthless.'
l\IEASURE
IENT OF MOTION IN THE LINE OF SIGHT
We must now describe another and quite distinct
application of the spectroscope, which is even more
marvellous than that already described. I t is the
method of measuring the rate of motion of any of the
visible heavenly bodies in a direction either directly
to,vards us, or directly away from us, technically
described as 'radial motion,' or by the expression-
, in the line of sight.' And the extraordinary thing is
that this power of measurement is altogether inde-
pendent of distance, so that the rate of motion in
miles per second of the remotest of the fixed stars, if
sufficiently bright to show a distinct spectrum, can be
measured with as much certainty and accuracy as in
the case of a much nearer star or a planet.
I n order to understand how this is possible we
36 MAN'S PLACE IN THE UNIVERSE [CHAP.
have again to refer to the wave-theory of light; and
the analogy of other wave-motions will enable us
better to grasp the principle on which these calcula-
tions depend. I f on a nearly calm day ,ve count the
waves that pass each minute by an anchored steam-
boat, and then travel in the direction the waves come
from, we shall find that a larger number pass us in
the same time. Again, if we are standing near
a railway, and an engine comes towards us whistling,
we shall notice that it changes its tone as it passes
us; and as it recedes the sound will be in a lower
key, although the engine may be at exactly the same
distance from us as when it was approaching. Yet
the sound does not change to the ear of the engine-
driver, the cause of the change being that the
sound-waves reach us in quicker succession as the
source of the waves is approaching us than when it
is retreating from us. N ow, just as the pitch of
a note depends upon the rapidity ,vith which the
successive air-vibrations reach our ear, so does the
colour of a particular part of the spectrum depend
upon the rapidity with which the ethereal waves
which produce colour reach our eyes; and as this
rapidity is greater when the source of the light is
approaching than when it is receding from us, a
slight shifting of the position of the coloured bands,
and therefore of the dark lines, \vill occur, as com-
pared with their position in the spectrum of the sun
or of any stationary source of light, if there is any
motion sufficient in amount to produce a perceptible
shift.
That such a change of colour would occur \vas
pointed out by Professor Doppler of Prague in 1842,
III.]
TIlE NEW ASTROXOrvIY
37
and It IS hence usually spoken of as the 'Doppler
principle'; but as the changes of colour were so
minute as to be in1possible of measurement it was not
at that time of any practical importance in astronomy.
But ,vhen the dark lines in the spectrum were care-
fully mapped, and their positions determined with
minute accuracy, it was seen that a means of measur-
ing the changes produced by motion in the line of
sight existed, since the position of any of the dark
or coIoured lines in the spectra of the heavenly bodies
could be compared with those of the corresponding
lines produced artificially in the laboratory. This
was first done in 1868 by Sir William Huggins, who,
by the use of a very powerful spectroscope constructed
for the purpose, found that such a change did occur
in the case of many stars, and that their rate of
motion towards us or a,vay from us-the radial
motion-could be calculated. As the actual distance
of some of these stars had been measured, and their
change of position annually (their proper motion)
determined, the additional factor of the amount of
motion in the direction of our line of sight completed
the data required to fix their true line of motion
among the other stars. The accuracy of this method
under favourable conditions and with the best instru-
ments is very great, as has been proved by those
cases in which we have independent means of calcu-
lating the real motion. The motion of Venus towards
or away from us can be calculated ,vith great accuracy
for any period, being a resultant of the combined
motions of the planet and of our earth in their re-
spective orbits. The radial motions of Venus were
determined at the Lick Observatory in August and
38 MAN'S PLACE IN THE UNIVERSE [CHAP.
September 1890, by spectroscopic observations, and
also by calculation, to be as follows :-
By Observation.
Aug. 16th. 7'3 miles per second.
" 22nd. 8"9 H " "
" 3 0 th. 7'3 H " U
Sep. 3rd. 8"3 " " "
,,4 th . 8'2 " " It
By Calculation.
8' I miles per second.
8'2 " " "
8'3 " " "
8'3 " " "
8'3 " " "
showing that the maximum error was only one mile
per second, while the mean error ,vas about a quarter
of a mile. I n the case of the stars the accuracy of
the method has been tested by observations of the
same star at times when the earth's motion in its
orbit is towards or away from the star, whose
apparent radial velocity is, therefore, increased or
diminished by a known amount. Observations of
this kind were made by Dr. Vogel, Director of the
Astrophysical Observatory at Potsdam, showing, in
the case of three stars, of which ten observations
were taken, a mean error of about two miles per
second; but as the stellar motions are more rapid
than those of the planets, the proportionate error is
no greater than in the example given above.
The great importance of this mode of determining
the real motion of the stars is, that it gives us a
knowledge of the scale on which such motions are
progressing; and when in the course of time we
discover whether any of their paths are rectilinear
or curved, we shall be in a position to learn something
of the nature of the changes that are going on and of
the laws on which they depend.
III.]
THE NE\V ASTRONOMY
39
INVISIBLE STARS AND IMPERCEPTIBLE l\10TIONS
But there is another result of this power of deter-
mining radial motion which is even more unexpected
and marvellous, and which has extended our know-
ledge of the stars in quite a new direction. By its
means it is possible to determine the existence of
invisible stars and to measure the rate of otherwise
imperceptible motions; that is of stars \vhich are
invisible in the most powerful modern telescopes, and
whose motions have such a limited range that no
telescope can detect them.
Double or binary stars forming systems which
revolve around their common centre of gravity were
discovered by Sir William Herschel, and very great
numbers are known; but in most cases their periods
of revolution are long, the shortest being about
twelve years, while many extend to several hundred
years. These are, of course, all visible binaries, but
many are now known of which one star only is
visible while the other is either non-lun1Înous or is so
close to its companion that they appear as a single
star in the most powerful telescopes. Many of the
variable stars belong to the former class, a good
example of which is Algol in the constellation
Perseus, which changes from the second to the fourth
magnitude in about four and a half hours, and in
about four and a half hours more regains its bril-
liancy till its next period of obscuration which occurs
regularly every two days and twenty-one hours.
The name Algol is from the Arabic At Ghoul, the
familiar' ghoul' of the Arabian Nights, so named-
'The Demon '-from its strange and weird behaviour.
40 l\1AN'S PLACE IN THE UNIVERSE [CHAP.
I t had long been conjectured that this obscuration
was due to a dark companion which partially eclipsed
the bright star at every revolution, showing that the
plane of the orbit of the pair was almost exactly
directed towards us. The application of the spectro-
scope made this conjecture a certainty. At an equal
time before and after the obscuration, motion in the
line of sight was shown, towards and away from us,
at a rate of twenty-six miles per second. From these
scanty data and the laws of gravitation which fix the
period of revolution of planets at various distances
from their centres of revolution, Professor Pickering
of the Harvard Observatory was able to arrive at
the follo,ving figures as highly probable, and they
may be considered to be certainly not far from the
truth.
Diameter of Algol, .
Diameter of dark companion,
Distance between their centres,
Orbital speed of Algol, .
Orbital speed of companion, .
Mass of Algol,
Mass of companion,
. 1,061,000 miles.
83 0 ,000 "
3,23 0 ,000 "
26.3 miles per sec.
55'4" " "
.
mass of our Sun.
2
. 1f "
"
"
When it is considered that these figures relate
to a pair of stars only one of which has ever been
seen, that the orbital motion even of the visible star
cannot be detected in the most powerful telescopes,
when, further, we take into account the enormous dis-
tance of these objects from us, the great results of
spectroscopic observation will be better appreciated.
But besides the marvel of such a discovery by such
simple means, the facts discovered are themselves in
the highest degr
e marvellous. AlI that we had
known of the stars through telescopic observation
III.]
THE NEW ASTRONOl\iY
4 1
indicated that they were at very great distances from
each other however thickly they may appear scattered
over the sky. This is the case even with close
telescopic double stars, owing to their enormous
remoteness from us. I t is no,v estimated that even
stars of the first magnitude are, on a general average,
about eighty millions of millions of miles distant;
,vhile the closest double stars that can be distinctly
separated by large telescopes are about half a second
apart. These, if at the above distance, will be about
15 00 millions of miles from each other. But in the
case of Algol and its companion, we have t\VO bodies
both larger than our sun, yet with a distance of only
2t millions of miles between their surfaces, a distance
not much exceeding their combined diameters. \Ve
should not have anticipated that such huge bodies
could revolve so closely to each other, and as we
now know that the neighbourhood of our sun-and
probably of all suns-is full of meteoric and cometic
matter, it would seem probable that in the case of
t\VO suns so near together the quantity of such matter
\vould be very great, and would lead probably by
continued collisions to increase of their bulk, and
perhaps to their final coalescence into a single giant
orb. I t is said that a Persian astronomer in the
tenth century calls Algol a red star, while it is now
white or somewhat yellowish. This would imply an
increase of temperature caused by collisions or friction,
and increasing proximity of the pair of stars.
A considerable number of double stars with dark
companions have been discovered by means of the
spectroscope, although their motion is not directly in
the line of sight, and therefore there is no obscura-
4 2 MAN'S PLACE IN THE UNIVERSE [CHAP.
tion. I n order to discover such pairs the spectra of
large numbers of stars are taken on photographic
plates every night and for considerable periods-
for a year or for several years. These plates are
then carefully examined with a high magnifying
power to discover any periodical displacement of the
lines, and it is astonishing in how large a number of
cases this has been found to exist and the period of
revolution of the pair determined.
But besides discovering double stars of which one
is dark and one bright, many pairs of bright stars
have been discovered by the same means. The
method in this case is rather different. Each com-
ponent star, being luminous, will give a separate
spectrum, and the best spectroscopes are so powerful
that they will separate these spectra when the stars
are at their maximum distance although no telescope
in existence, or ever likely to be made, can separate
the component stars. The separation of the spectra
is usually shown by the most prominent lines becom-
ing double and then after a time single, indicating
that the plane of revolution is more or less obliquely
towards us, so that the two stars if visible would
appear to open out and then get nearer together
every revolution. Then, as each star alternately
approaches and recedes from us the radial velocity
of each can be determined, and this gives the relative
mass. In this way not only doubles, but triple and
multiple systems, have been discovered. The stars
proved to be double by these two methods are so
numerous that it has been estimated by one of the
best observers that about one star in every thirteen
shows inequality in its radial motion and is therefore
really a :1ouble "tar.
III.]
THE NEW ASTRONOMY
43
THE NEBULÆ
One other great result of spectrum-analysis, and
in some respects perhaps the greatest, is its demon-
stration of the fact that true nebulæ exist, and that
they are not all star-clusters so remote as to be
irresolvable, as was once supposed. They are shown
to have gaseous spectra, or sometimes gaseous and
stellar spectra combined, and this, in connection with
the fact that nebulæ are frequently aggregated around
nebulous stars or groups of stars, renders it certain
that the nebulæ are in no way separated in space
from the stars, but that they constitute essential parts
of one vast stellar universe. There is, indeed, good
reason to believe that they are really the material out
of which stars are made, and that in their forms,
aggregations, and condensations, we can trace the
very process of evolution of stars and suns.
PHOTOGRAPHIC ASTRONOM:V
But there is yet another powerful engine of re-
search which the new astronomy possesses, and
which, either alone or in combination ,vith the spec-
troscope, had produced and will yet produce in the
future an amount of kno\vledge of the stellar universe
which could never be attained by any other nleans.
I t has already been stated ho\v the discovery of new
variable and binary stars has been rendered possible
by the preservation of the photographic plates on
which the spectra are self-recorded, night after night,
with every line, whether dark or coloured, in true
position, so as to bear magnification, and, by com-
44 MAN'S PLACE IN TI-IE UNIVERSE [CHAP.
parison with others of the series, enabling the most
minute changes to be detected and their amount
accurately measured. Without the preservation of
such comparable records, which is in no other way
possi ble, by far the larger portion of spectroscopic
discoveries could never have been made.
But there are two other uses of photography of
quite a different nature which are equally and
perhaps in their final outcome may be far more
important. The first is, that by the use of the photo-
graphic plate the exact positions of scores, hundreds,
or even thousands of stars can be self-mapped simul-
taneously with extreme accuracy, while any number
of copies can be made of these star-maps. This en-
tirely obviates the necessity for the old method of fix-
ing the position of each star by repeated measurement
by means of very elaborate instruments, and their
registration in laborious and expensive catalogues.
So important is this now seen to be, that specially
constructed cameras are made for stellar photography,
and by means of the best kinds of equatorial mount-
ing are made to revolve slowly so that the image of
each star remains stationary upon the plate for
several hours.
Arrangements have been now made among all the
chief observatories of the world to carry out a photo-
graphic survey of the heavens with identical instru-
ments, so as to produce maps of the whole star-
system on the same scale. These will serve as fixed
data for future astronomers, who will thus be able to
determine the moven1ents of stars of all n1agnitudes
with a certainty and accuracy hitherto unattainable.
The other important use of photography depends
III. ]
THE NEW ASTRONOMY
45
upon the fact that with a longer exposure within cer-
tain limits we increase the light-collecting power. It
,viII surprise many persons to learn that an ordinary
good portrait-camera with a lens three or four inches
in diameter, if properly mounted so that an exposure
of several hours can be made, will show stars so
minute that they are invisible even in the great Lick
telescope. In this ,yay the camera will often reveal
double-stars or small groups which can be made
visible in no other way.
Such photographs of the stars are no,v constantly
reproduced in works on Astronomy and in popular
magazine articles, and although some of them are
very striking, many persons are disappointed with
them, and cannot understand their great value, be-
cause each star is represented by a \vhite circle often
of considerable size and \vith a somewhat undefined
outline, not by a minute point of light as stars appear
in a good telescope. But the essential matter in all
such photographs is not so much the smallness, as
the roundness, of the star - images, as this proves
the extreme precision with which the image of every
star has been kept by the clockwork motion of the
instrument on the same point of the plate during the
whole exposure. F or exam pie, in the fine photo-
graph of the Great Nebula in Andromeda, taken
29 th December 1888, by Dr. Isaac Roberts, with an
exposure of four hours, there are probably over a
thousand stars large and small to be seen, everyone
represented by an almost exactly circular white dot
of a size dependent on the magnitude of the star.
These round dots can be bisected by the cross hairs
of a micrometer with very great accuracy, and thus
,
4 6 MAN'S PLACE IN THE UNIVERSE [CHAP. III.
the distance between the centres of any of the pairs,
as well as the direction of the line joining their
centres, can be determined as accurately as if each
was represented by a point only. But as a minute
white speck would be almost invisible on the maps,
and would convey no information as to the approxi-
mate magnitude of the star, mistakes would be much
more easily made, and it would probably be found
necessary to surround each star with a circle to
indicate its magnitude, and to enable it to be easily
seen. I t is probable, therefore, that the supposed
defect is really an important advantage. The above-
mentioned photograph is beautifully reproduced in
Proctor's Old and New Astronomy, published after
his greatly lamented death.
But besides the amount of altogether new know-
ledge obtained by the methods of research here
briefly explained, a great deal of light has been
thro\vn on the distribution of the stars as a whole t
and hence on the nature and extent of the stellar
universe, by a careful study of the materials obtained
by the old methods, and by the application of the
doctrine of probabilities to the observed facts. In
this way alone some very striking results have been
reached, and these have been supported and strength-
ened by the newer methods, and also by the use of
new instruments in the measurement of stellar dis-
tances. Some of these results bear so closely and
directly upon the special subject of the present
volume, that our next chapter must be devoted to a
consideration of them.
CHAPTER IV
THE DISTRIBUTION OF THE STARS
IF we look at the heavens on a clear, moonless night
in winter, and from a position embracing the entire
horizon, the scene is an inexpressibly grand one.
The intense sparkling brilliancy of Sirius, Capella,
Vega, and other stars of the first magnitude; their
striking arrangement in constellations or groups, of
which Orion, the Great Bear, Cassiopeia, and the
Pleiades, are familiar exam pIes; and the filling up
between these by less and less brilliant points down
to the limit of vision, so as to cover the whole sky
with a scintillating tracery of minute points of light,
convey together an idea of such confused scattering
and such enormous numbers, that it seems impossible
to count them or to reduce them to systematic order.
Yet this was done for all except the faintest stars by
Hipparchus, 134 B.C., who catalogued and fixed the
positions of more than 1000 stars, and this is about
the number, down to the fifth magnitude, visible in
the latitude of Greece. A recent enumeration of all
the stars visible to the naked eye, under the most
favourable conditions and by the best eyesight, has
been made by the American astronomer, Pickering.
His numbers are-for the Northern Hemisphere
25 0 9, and for the Southern Hemisphere 2824, thus
47
48 MAN'S PLACE IN THE UNIVERSE [CHAP.
sho\ving a somewhat greater richness in the southern
celestial hemisphere. But as this difference is due
entirely to a preponderance of stars between mag-
nitudes s! and 6, that is, just on the limits of vision,
while those down to magnitude st are more numerous
by 85 in the Northern Hemisphere, Professor New-
comb is of opinion that there is no real superiority of
numbers of visible stars in one hemisphere over the
other. Again, the total number of the visible stars
by the above enumeration is 5333. But this includes
stars down to 6'2 magnitude, while it is generally
considered that magnitude 6 marks the limit of
visibility. On a re-examination of all the materials,
the I talian astronomer Schiaparelli concludes that
the total number of stars down to the sixth magnitude
is 4303; and they seem to be about equally divided
bet\veen the northern and southern skies.
THE l\HLKY WAY
But besides the stars themselves, a most con-
spicuous object both in the northern and southern
hemisphere is that wonderful irregular belt of faintly
diffused light termed the Milky Way or Galaxy.
This forms a magnificent arch across the sky, best
seen in the autumn months in our latitude. This
arch, while following the general course of a great
circle round the heavens, is extremely irregular in
detail, sometimes being single, sometimes double,
sending off occasional branches or offshoots, and
also containing in its very midst dark rifts, spots,
or patches, where the black background of almost
starless sky can be seen through it. When examined
IV.] THE DISTRIBUTION OF THE STARS 49
through an opera-glass or small telescope quantities
of stars are seen on the luminous background, and
with every increase in the size and power of the
telescope more and more stars becon1e visible, till
with the largest and best modern instruments the
whole of the Galaxy seems densely packed with them,
though still full of irregularities, ,yavy stredms of
stars, and dark rifts and patches, but always showing
a faint nebulous background as if there remained
other myriads of stars which a still higher optical
power would reveal.
The relations of this great belt of telescopic stars
to the rest of the star-system have long interested
astronomers, and many have attempted its solution.
By a system of gauging, that is counting all the stars
that passed over the field of his telescope in a certain
time, Sir \Villiam Herschel ,vas the first who made
a systematic effort to determine the shape of the
stellar universe. From the fact that the number of
stars increased rapidly as the Milky Way was ap-
proached from whatever direction, while in the
Galaxy itself the numbers visible were at once more
than doubled, he formed the idea that the shape of
the entire system must be that of a highly compressed
very broad mass or ring rather less dense towards the
centre where our sun was situated. Roughly speak-
ing, the form was likened to a flat disc or grindstone,
but of irregular thickness, and split in two on one
side ,vhere it appears to be double. The immense
quantity of the stars which formed it was supposed
to be due to the fact that ,ve looked at it edgewise
through an immense depth of stars; while at right
angles to its direction when looking towards what is
D
50 MAN'S PLACE IN THE UNIVERSE [CHAP.
termed the pole of the Galaxy, and also in a less
degree when looking obliquely, we see out into
space through a much thinner stratum of stars, which
thus seem on the average to be very much farther
a part.
But, in the latter part of his life, Sir \Villiam
Herschel realised that this was not the true explana-
tion of the features presented by the Galaxy. The
brilliant spots and patches in it, the dark rifts and
openings, the narrow streams of light often bounded
by equally narrow streams or rifts of darkness, render
it quite impossible to conceive that this complex
luminous ring has the form of a compressed disc
extending in the direction in \vhich we see it to a
distance many times greater than its thickness. In
one very luminous cluster Herschel thought that
his telescope had penetrated to regions twenty times
as far off as the more brilliant stars forming the
nearer portions of the same object. N ow, in the case
of the Magellanic clouds, which are two roundish
nebular patches of large size some distance from the
Milky Way in the Southern Hemisphere and looking
like detached portions of it, Sir John Herschel him-
self has shown that any such interpretation of its
form is impossible; because it requires us to suppose
that in both these cases we see, not rounded masses of
a roughly globular shape, but immensely long cones or
cylinders, placed in such a direction that we see only
the ends of them. He remarks that one such object
so situated would be an extraordinary coincidence,
but that there should be two or many such is alto-
gether out of the question. But in the Milky Way
there are hunàreds or even thousands of such spots
IV.] THE DISTRIBUTION OF THE STARS 51
or masses of exceptional brilliancy or exceptional
darkness; and, if the forn1 of the Galaxy is that of a
disc many times broader than thick, and which we
see edgewise, then everyone of these patches and
clusters, and all the narrow winding streams of bright
light or intense blackness, must be really excessively
long cylinders, or tunnels, or deep curving laminæ,
or narrow fissures. And everyone of these, which
are to be found in every part of this vast circle of
luminosity, must be so arranged as to be exactly
turned to\vards our sun. The weight of this argu-
ment, which has been most forcibly and clearly set
forth by the late Mr. R. A. Proctor, in his very
instructive volume Our Place anlong Infinities, is
now generally admitted by astronomers, and the
natural conclusion is that the form of the l\'iilky
Way is that of a vast irregular ring, of which the
section at any part is, roughly speaking, circular;
while the many narrow rifts or lanes or openings
where we seem to be able to see completely through
it to the darkness of outer space beyond, render it
probable that in those directions its thickness is less
instead of greater than its apparent width, that is,
that we see the broader side rather than the narrow
edge of it.
Before entering on the consideration of the rela-
tions which the bulk of the stars we see scattered
over the entire vault of heaven bear to this great
belt of telescopic stars, it will be advisable to give
a somewhat full description of the Galaxy itself, both
because it is not often delineated on star-maps with
sufficient accuracy
or so as to show its wonderful
intricacies of structure, and also because it constitutes
52 MAN'S PLACE IN THE UNIVERSE [CHAP.
the fundamental phenomenon upon which the argu-
ment set forth in this volume primarily rests. For
this purpose I shall use the description of it given by
Sir John Herschel in his Outlines of Astrononzy,
both because he, of all the astronomers of the last
century, had studied it most thoroughly, in the
northern and in the southern hemispheres, by eye-
observation and with the aid of telescopes of great
power and admirable quality; and also because, amid
the throng of modern works and the exciting novel-
ties of the last thirty years, his instructive volume is,
comparatively speaking, very little known. This
precise and careful description will also be ,of service
to any of my readers who may wish to form a closer
personal acquaintance with this magnificent and in-
tensely interesting object, by examining its peculi-
arities of form and beauties of structure either with
the naked eye, or with the aid of a good opera-glass,
or with a small telescope of good defining power.
A DESCRIPTION OF THE MILKY WAY
Sir John Herschel's description is as fol1o\vs:-
'The course of the Milky Way as traced through the
heavens by the unaided eye, neglecting occasional
deviations and following the line of its greatest
brightness as well as its varying breadth and inten-
sity \vill permit, conforms, as nearly as the indefinite-
ness of its boundary will allow it to be fixed, to that of
a great circle inclined at an angle of about 63 0 to the
equinoctial, and cutting that circle in Right Ascen-
sion 6h. 47ffi. and .18h. 47m., so that its northern and
southern poles respectively are situated in Right
IV.] TI-II
DISTRIBlTTION OF TIlE ST.L\RS 53
Ascension 12h. 47m., North Polar Distance 63 0 , and
R.A. oh. 47m., N PD. 1 17 0 . Throughout the region
where it is so remarkably subdivided, this great circle
holds an intermediate situation between the two great
streams; with a nearer approximation however to the
brighter and continuous stream than to the fainter
and interrupted one. If \ve trace its course in order
of right ascension, \ve find it traversing the constella-
tion Cassiopeia, its brightest part passing about two
degrees to the north of the star Delta of that con-
stellation. Passing thence bet\\"een Gamma and
Epsilon Cassiopeiæ, it sends off a branch to the
south-preceding side, towards Alpha Persei, very con-
spicuous as far as that star, prolonged faintly to\vards
Eta of the sanle constellation, and possibly traceable
towards the Hyades and Pleiades as remote outliers.
The main stream, however (which is here very faint),
passes on through Auriga, over the three remarkable
stars, Epsilon, Zeta, Eta, of that constellation called
the Hædi, preceding Capella, bet\veen the feet of
Gemini and the horns of the Bull (where it intersects
the ecliptic nearly in the Solstitial Colure) and thence
over the club of Orion to the neck of Monoceros,
intersecting the equinoctial in R.A. 6h. 54m. Up to
this point, from the offset in Perseus, its light is feeble
and indefinite, but thenceforward it receives a gradual
accession of brightness, and where it passes through
the shoulder of l\lonoceros and over the head of
Canis lVlajor it presents a broad, moderately bright,
very uniform, and to the naked eye, starless stream
up to the point where it enters the prow of the ship
Argo, nearly on the southern tropic. Here it again
subdivides (about the star nz. Puppis), sending off a
54 MAN'S PLACE IN THE UNIVERSE [CHAP.
narrow and winding branch on the preceding side as
far as Gamma Argûs, where it terminates abruptly.
The main stream pursues its southward course to
the I23rd parallel of N PD., where it diffuses itself
broadly and again subdivides, opening out into a wide
fan-like expanse, nearly 20 0 in breadth, formed of
interlacing branches, which all terminate abruptly,
in a line drawn nearly through Lambda and Gamma
Argûs.
'At this place the continuity of the Milky Way is
interrupted by a wide gap, and where it recommences
on the opposite side it is by a somewhat similar fan-
shaped assemblage of branches which converge upon
the bright star Eta Argûs. Thence it crosses the
hind feet of the Centaur, forming a curious and
sharply-defined semicircular concavity of small radius,
and enters the Cross by a very bright neck or isthmus
of not more than three or four degrees in breadth,
being the narrowest portion of the Milky Way. After
this it immediately expands into a broad and bright
mass, enclosing the stars Alpha and Beta Crucis and
Beta Centauri, and extending almost up to Alpha of
the latter constellation. I n the midst of this bright
mass, surrounded by it on all sides, and occupying
about half its breadth, occurs a singular dark pear-
shaped vacancy, so conspicuous and remarkable as
to attract the notice of the most superficial gazer
and to have acquired among the early southern
navigators the uncouth but expressive appellation
of the coal-sack. In this vacancy, which is about
go in length and 50 broad, only one very small star
visible to the naked eye occurs, though it is far
from devoid of telescopic stars, so that its striking
IV.] THE DISTRIBUTION OF THE STARS 55
blackness is simply due to the effect of contrast with
the bril1iant ground with \vhich it is on all sides sur-
rounded. This is the place of nearest approach of
the 1\1ilky \Vay to the South Pole. Throughout all
this region its brightness is very striking, and \vhen
compared with that of its more northern course
already traced, conveys strongly the impression of
greater proximity, and would almost lead to a belief
that our situation as spectators is separated on all
sides by a considerable interval from the dense body
of stars composing the Galaxy, which in this view of
the subject would come to be considered as a flat ring
or some other re-entering form of immense and irre-
gular breadth and thickness, within which \ve are
excentricalIy situated, nearer to the southern than to
the northern part of its circuit.
'At Alpha Centauri the Milky vVay again sub-
divides, sending off a great branch of nearly half its
breadth, but \vhich thins off rapidly, at an angle of
about 20 0 \vith its general direction to Eta and d Lupit
beyond which it loses itself in a narro\v and faint
streamlet. The main stream passes on increasing in
breadth to Gamma N ormæ, where it makes an
abrupt elbow and again subdivides into one principal
and continuous stream of very irregular breadth and
brightness, and a complicated system of interlaced
streaks and masses, which covers the tail of Scorpio,
and terminates in a vast and faint effusion over the
whole extensive region occupied by the preceding
leg of Ophiuchus, extending northward to the
parallel of 1030 NPD., beyond which it cannot be
traced; a wide interval of 14 0 , free from all appear-
ance of nebulous light, separating it from the great
56 MAN'S PLACE I
THE UNIVERSE [CHAP.
branch on the north side of the equinoctial of which
it is usually represented as a continuation.
, Returning to the point of separation of this great
branch from the main stream, let us no\v pursue the
course of the latter. 1\1aking an abrupt bend to the
following side, it passes over the stars Iota Aræ,
Theta and Iota Scorpii, and Gamma Tubi to
Gamma Sagittarii, where it suddenly collects into
a vivid oval mass about 6 0 in length and 4 0 in
breadth, so excessively rich in stars that a very
moderate calculation makes their number exceed
100,000. Northward of this mass, this stream
crosses the ecliptic in longitude about 2760, and
proceeding along the bow of Sagittarius into
Antinous has its course rippled by three deep con-
cavities, separated from each other by remarkable
protuberances, of \vhich the larger and .brighter forms
the most conspicuous patch in the southern portion
of the Milky Way visible in our latitudes.
'Crossing the equinoctial at the 19th hour of
R.A., it next runs in an irregular, patchy, and \\rind-
ing stream through Aquila, Sagitta, and Vulpecula
up to Cygnus; at Epsilon of which constellation its
continuity is interrupted, and a very confused and
irregular region commences, marked by a broad dark
vacuity, not unlike the southern "coal-sack," occupy-
ing the space between Epsilon, Alpha, and Gamma
Cygni, which serves as a kind of centre for the
divergence of three great streams; one, which we
have already traced; a second, the continuation of
the first (across the interval) from Alpha northward,
between Lacerta and the head of Cepheus to the
point in Cassiopeia whence we set out, and a third
IV.] THE DISTRIBUTION O}"' THE STARS 57
branching off from Gamma Cygni, very vivid and
conspicuous, running off in a southern direction
through Beta Cygni, and s Aquilæ almost to the
equinoctial, where it loses itself in a region thinly
sprinkled with stars, where in some maps the modern
constellation Taurus Poniatowski is placed. This is
the branch which, if continued across the equinoctial,
inight be supposed to unite with the great southern
effusion in Ophiuchus already noticed. A consider-
able offset, or protuberant appendage, is also thrown
off by the northern stream from the head of Cepheus
directly towards the pole, occupying the greater part
of the quartile formed by Alpha, Beta, Iota, and
Delta of that constelIa
ion.'
To conlplete this careful, detailed description of
the l\Iilky \Vay, it will be well to add a few passages
from the same \vork as to its telescopic appearance
and structure.
'\\Then exanlined with powerful telescopes, the
constitution of this wonderful zone is found to be no
less various than its aspect to the naked eye is
irregular. I n some regions the stars of which it is
composed are scattered \vith remarkable uniformity
over immense tracts, while in others the irregularity
of their distribution is quite as striking, exhibiting a
rapid succession of closely clustering rich patches
separated by comparatively poor intervals, and in-
deed in some instances by spaces absolutely dark
and c077Zpletely vozd of any sta1', even of the smallest
telescopic magnitude. I n some places not more than
4 0 or 50 stars on an average occur in a gauge-field
of 15', while in others a similar average gives a
result of 400 or 500. N or is less variety observable
58 MAN'S PLACE IN THE UNIVERSE [CHAP.
in the character of its different regions in respect of
the magnitudes of the stars they exhibit, and the
proportional numbers of the larger and smaller
magnitudes associated together, than in respect of
their aggregate numbers. In some, for instance,
extremely minute stars occur in numbers so moderate
as to lead us irresistibly to the conclusion that in
these regions we see fairly through the starry
stratum, since it is impossible otherwise that the
numbers of the smaller magnitudes should not go on
continually increasing ad infinitum. In such cases,
moreover, the ground of the heavens is for the most
part perfectly dark, which again would not be the
case if innumerable multitudes of stars, too minute
to be individually discernible, existed beyond. In
other regions we are presented with the phænomenon
of an almost uniform degree of brightness of the
individual stars, accompanied with a very even dis-
tribution of them over the ground of the heavens,
both the larger and smaller magnitudes being
strikingly deficient. In such cases it is equal1y
impossible not to perceive that we are looking
through a sheet of stars nearly of a size, and of
no great thickness compared with the distance which
separates them from us. Were it otherwise we
should be driven to suppose the more distant stars
uniformly the larger, so as to compensate by their
greater intrinsic brightness for their greater distance,
a supposition contrary to all probability. . . .
'Throughout by far the larger portion of the
extent of the Milky Way in both hemispheres, the
general blackness of the ground of the heavens on
which its stars are projected, and the absence of that
IV.] THE DISTRIBUTION OF THE STARS 59
innumerable multitude and excessive crowding of the
smallest visible magnitudes, and of glare produced by
the aggregate light of multitudes too small to affect
the eye singly, must, we think t be considered un-
equivocal indications that its dimensions in directions
'ii/here these cOlldilions obtain are not only not infinite,
but that the space-penetrating power of our telescopes
suffices fairly to pierce through and beyond it.'
In the above-quoted passages the italics are those
of Sir John Herschel himself, and we see that he
drew the very same conclusions from the facts he
describes, and for much the same reasons, as J\tlr.
Proctor has drawn from the observations of Sir
\Villiam Herschel; and, as ,ve shall see, the best
astronomers to-day have arrived at a similar result,
from the additional facts at their disposal, and in
some cases from fresh lines of argument.
THE STARS IN RELATION TO THE MILKY WAY
Sir John Herschel was so impressed with the
form, structure, and immensity of the Galactic Circle,
as he sometimes terms it, that he says (in a footnote
p. 575, 10th ed.), 'This circle is to sidereal what
the invariable ecliptic is to planetary astronomy-a
plane of ultimate reference, the ground -plane of the
sidereal system.' We have now to consider what are
the relations of the whole body of the stars to this
Galactic Circle-this plane of ultimate reference for
the \vhole stellar universe.
If ,ve look at the heavens on a starry night, the
whole vault appears to be thickly strewn \vith stars
of various degrees of brightness, so that we could
60 MAN'S PLACE IN THE UNIVERSE [CHAP.
hardly say that any extensive region-the north,
east, south, or west, or the portion vertically above
us-is very conspicuously deficient or superior in
numbers. In every part there are to be found a fair
proportion of stars of the first two or three magni-
tudes, while where these may seem deficient a crowd
of smaller stars takes their place.
But an accurate survey of the visible stars shows
that there is a large amount of irregularity in their
distribution, and that all magnitudes are really more
numerous in or near the Milky Way, than at a dis-
tance from it, though not in so large a degree as to
be very conspicuous to the naked eye. The area
of the whole of the Milky Way cannot be estimated
at more than one-seventh of the whole sphere, while
some astronomers reckon it at only one-tenth. If
stars of any particular size were uniformly distributed,
at most one-seventh of the whole number should be
found within its limits. But lVlr. Gore finds that of
32 stars brighter than the second magnitude 12 lie
upon the Milky vVay, or considerably more than
twice as many as there should be if they were
uniformly distributed. And in the case of the 99
stars which are brighter than the third magnitude 33
lie upon the IVlilky Way, or one-third instead of one-
seven tho Mr. Gore also counted all the stars in H eis's
Atlas which lie upon the Milky Way, and finds there
are 1186 out of a total of 5356, a proportion of
between a fourth and a fifth instead of a seventh.
The late Mr. Proctor in 1871 laid down on a chart
two feet diameter all the stars down to magnitude
9-l given in Agrelander's forty large charts of the
stars visible in the northern hemisphere. They were
IV.] THE DISTRIBUTION OF THE STARS 61
324, 198 in number, and they distinctly sho,ved by
their greater density not only the whole course of the
Milky Way but also its more luminous portions and
many of the curious dark rifts and vacuities, \vhich
latter are almost ,vholly avoided by these stars.
Later on Professor Seeliger of Munich made an
investigation of the relation of more than 135,000
stars down to the ninth magnitude to the Milky Way,
by dividing the whole of the heavens into nine
regions, one and nine being circles of 20 0 wide (equal
to 400 diameter) at the two poles of the Galaxy; the
middle region, five, is a zone 20 0 wide including the
11ilky \\' ay itself, and the other six intermediate
zones are each 20 0 ,vide. The following table shows
the results as given by Professor Newcomb, \vho has
made some alterations in the last column of ' Density
of Stars' in order to correct differences in the estimate
of magnitudes by the different authorities.
Regions. Area in Degrees. !\umber of Stars. Density.
I. 1,39 8 '7 4, 2 7 7 2'7 8
II. 3, I 4 6 '9 10, 185 3'03
III. 5, I 26"6 19,4 88 3'54
IV. 4,5 8 9'8 24,49 2 5'3 2
V. 4, 5 I 9" 5 33, 26 7 8'17
VI. 3,97 1 '5 23,5 80 6'07
VII. 2,954 '4 I 1,790 3'7 1
VIII. 1,79 6 "6 6,375 3"2 I
IX. 4 68 "2 1,644 3'14
N.B.- The inequality of the N. and S" areas is because the
enumeration of the stars only went as far as 24 0 S. Dec!., and there-
fore included only a part of Regions VII., VIII., and IX.
Upon this table of densities Professor Newcomb
remarks as follows :-' The star-density in the several
regions increases continuously from each pole (regions
62 MAN'S PLACE IN THE UNIVERSE [CHAP.
I. and IX.) to the Galaxy itself (region v.). If the
]atter were a simple ring of stars surrounding a
DIAGRA1\I OF STAR-DENSITY
.r. n m IY V W l7f J7.DI..Ir
7
From Herschel's Gauges (as given by Professor Newcomb, p. 251).
spherical system of stars, the star-density would be
about the same in regions I., II., and 111., and also
in VII., VIII., and IX., but would suddenly increase
in IV. and VI. as the boundary of the ring was
approached. I nstead of such being the case, the
numbers 2.78, 3'03, and 3'54 in the north, and 3'14,
3 '21, and 3'7 I in the south, show a progressive
increase from the galactic pole to the Galaxy itself.
IV.] THE DISTRIBUTION OF THE STARS 63
The conclusion to be drawn is a fundamental one.
The universe, or at least the denser portion of it, is
really flattened between the galactic poles, as supposed
by Herschel and S tru ve.'
But looking at the series of figures in the table, and
again as quoted by Professor Newcomb, they seem
to me to show in some measure what he says they
<10 not show. I therefore drew out the above diagram
from the figures in the table, and it certainly shows
that the density in regions I., II., and III., and in
regions VII., VIII., and IX., maybe said to be
"about the same,' that is, they increase very slo\vly,
and that they do 'suddenly increase' in IV. and VI.
as the boundary of the Galaxy is approached. This
may be eXplained either by a flattening towards the
poles of the Galaxy, or by the thinning out of stars
in that direction.
In order to show the enormous difference of star-
density in the Galaxy and at the galactic poles,
Professor Newcomb gives the following table of the
Herschelian gauges, on which he only remarks that
they show an enormously increased density in the
galactic region due to the Herschels having counted
so many more stars there than any other observers.
Region, I. II. III. IV. V. I r IX.
. VI. VII. VI II.
Density, . 10 7 154 281 5 60 2, 01 9 67 2 261 154 III
I
But an important characteristic of these figures is,
that the Herschels alone surveyed the whole of the
heavens from the north to the south pole, that they
did this with instruments of the same size and quality,
64 MAN'S PLACE IN THE UNIVERSE [CHAP.
and that from almost life-long experience in this
particular work they were unrivalled in their po,ver
of counting rapidly and accurately the stars that
passed over each field of view of their telescopes.
DIAGRAM OF STAR-DENSITY
.I .H:or.IV" V 1!T VU FBI
".
From a table in The Stars (p. 249).
Their results, therefore, must be held to have a com-
parative value far above those of any other observer
or combination of observers. I have therefore thought
it advisable to draw a diagram from their figures,
and it will be seen how strikingly it agrees ,vith the
former diagram in the very slow increase of star-
richness in the first three regions north and south,
the sudden increase in regions IV. and VI. as we
approach the Galaxy, while the only marked differ-
ence is in the enormously greater richness of the
IV.] THE DISTRIBUTION OF THE STARS 65
Galaxy itself, which is an undoubtedly real pheno-
menon, and is brought out here by the unrivalled
observing po\ver of the two greatest astronomers in
this special department that have ever lived.
We shall find later on that Professor Newcomb
himself, as the result of a quite different inquiry
arrives at a result in accordance with these diagrams
which will then be again referred to. As this is a
very interesting subject, it will be well to give another
diagram from two tables of star-density in Sir John
Herschel's volume already quoted. The tables are
as follows :-
Zones of Galactic
North Polar Distance.
0 0 to 15 0
15 0 to 300
300 to 45 0
45 0 to 60 0
60 0 to 75 0
75 0 to 900
Average number of Stars
per Field of 15'.
4"3 2
5'4 2
8'2 I
I 3 "6 I
24'09
53"43
Zones of Galactic
South Polar Distance.
0 0 to 15 0
o 0
15 to 3 0
300 to 45 0
45 0 to 60 0
60 0 to 75 0
o 0
75 to 9 0
Average number of Stars
per Field of IS'.
6"05
6'62
9'08
13'49
26'29
59'06
In these tables the Milky Way itself is taken as
occupying two zones of I SO each, instead of one of
20 0 as in Professor N e\vcomb's tables, so that the
excess in the number of stars over the other zones is
not so large. They show also a slight preponderance
in all the zones of the southern hemisphere, but this
E
66 MAN'S PLACE IN THE UNIVERSE [CHAP
is not great, and may probably be due to the clearer
atmosphere of the Cape of Good Hope as compared
with that of England.
DIAGRAM OF STAR-DENSITY.
s. ole
ç
lax
From Table in Sir J. Herschel's Outlines of Astronomy
(loth ed., pp. 577-578).
I t need only be noted here that this diagram shows
the same general features às those already given, of
a continuous increase of star-density from the poles
of the Galaxy, but more rapidly as the Galaxy itself
IV.] THE DISTRIBUTION OF THE STARS 67
is more nearly approached. This fact must, there-
fore, be accepted as indisputable.
CLUSTERS AND NEBULÆ IN RELATION TO THE GALAXY
An important factor in the structure of the heavens
is afforded by the distribution of the two classes of
objects known as clusters and nebulæ. Although we
can form an almost continuous series from double stars
which revolve round their common centre of gravity,
through triple and quadruple stars, to groups and
aggregations of indefinite extent-of which the
Pleiades form a good example, since the six stars
visible to the naked eye are increased to hundreds
by high telescopic po,vers, while photographs with
three hours' exposure show more than 2000 stars-
yet none of these correspond to the large class known
as clusters, whether globular or irregular, \vhich
are very numerous, about 600 having been re-
corded by Sir John Herschel n10re than fifty years
ago. l\Iany of these are among the most beautiful
and striking objects in the heavens even \vith a very
small telescope or good opera-glass. Such is the
luminous spot called Praesepe, or the Beehive in
the constellation Cancer, and another in the s\vord-
handle of Perseus.
I n the southern hemisPhere there is a hazy star
of about the fourth magnitude, Omega Centauri,
which \vith a good telescope is seen to be really a
magnificent cluster nearly two-thirds the diameter of
the moon, and described by Sir John Herschel as very
gradually increasing in brightness to the centre, and
composed of innumerable stars of the thirteenth and
68 MAN'S PLACE IN THE UNIVERSE [CHAP.
fifteenth magnitudes, forming the richest and largest
object of the kind in the heavens. He describes it
as having rings like lace-work formed of the larger
stars. By actual count, on a good photograph,
there are more than 6000 stars, while other
observers consider that there are at least 10,000.
In the northern hemisphere one of the finest is that
in the constellation Hercules, known as 13M essier.
I t is just visible to the naked eye or \vith an opera-
glass as a hazy star of the sixth magnitude, but a
good telescope shows it to be a globular cluster, and
the great Lick telescope resolves even the densest
central portion into distinct stars, of which Sir John
Herschel considered there were many thousands.
These two fine clusters are figured in many of the
modern popular works on astronomy, and they afford
an excellent idea of these beautiful and remarkable
objects, which, when more thoroughly studied, win
probably aid in elucidating some of the obscure
problems connected with the constitution and de-
velopment of the stellar universe.
But for the purpose of the present work the most
interesting fact connected with star-clusters is their
remarkable distribution in the heavens. Their special
abundance in and near the Milky Way had often
been noted, but the full importance of the fact could
not be appreciated till Mr. Proctor and, later, Mr.
Sidney Waters marked down, on maps of the two
hemispheres, all the star-clusters and nebulæ in the
best catalogues. The result is most interesting. The
clusters are seen to be thickly strewn over the entire
course of the Milky \Vay, and along its margins,
wh 
