PART FIRST.
"WHAT are you, where did you come from, and
whither are you bound?"—the question which
from Homer's days has been put to the wayfarer in
strange lands—is likewise the all-absorbing question
which man is ever asking of the universe of which he
is himself so tiny yet so wondrous a part. From the
earliest times the ultimate purpose of all scientific
research has been to elicit fragmentary or partial responses
to this question, and philosophy has ever busied itself
in piecing together these several bits of information
according to the best methods at its disposal, in order to
make up something like a satisfactory answer. In old
times the best methods which philosophy had at its
disposal for this purpose were such as now seem very
crude, and accordingly ancient philosophers bungled
considerably in their task, though now and then they came
surprisingly near what would to-day be called the truth.
It was natural that their methods should be crude, for
scientific inquiry had as yet supplied but scanty materials
for them to work with, and it was only after a
very long course of speculation and criticism that men
could find out what ways of going to work are likely to
prove successful and what are not. The earliest thinkers,
indeed, were further hindered from accomplishing
much by the imperfections of the language by the aid
of which their thinking was done; for science and philosophy
have had to make a serviceable terminology by
dint of long and arduous trial and practice, and linguistic
processes fit for expressing general or abstract notions
accurately grew up only through numberless failures
and at the expense of much inaccurate thinking and
loose talking. As in most of nature's processes, there
was a great waste of energy before a good result could
be secured. Accordingly primitive men were very wide
of the mark in their views of nature. To them the
world was a sort of enchanted ground, peopled with
sprites and goblins; the quaint notions with which we
now amuse our children in fairy tales represent a style
of thinking which once was current among grown men
and women, and which is still current wherever men
remain in a savage condition. The theories of the world
wrought out by early priest-philosophers were in great
part made up of such grotesque notions; and having
become variously implicated with ethical opinions as
to the nature and consequences of right and wrong behaviour,
they acquired a kind of sanctity, so that any
thinker who in the light of a wider experience ventured
to alter or amend the primitive theory was likely to
be vituperated as an irreligious man or atheist. This
sort of inference has not yet been wholly abandoned,
even in civilized communities. Even to-day books are
written about "the conflict between religion and science,"
and other books are written with intent to reconcile
the two presumed antagonists. But when we look
beneath the surface of things, we see that in reality there
has never been any conflict between religion and science,
nor is any reconciliation called for where harmony has
always existed. The real historical conflict, which has
been thus curiously misnamed, has been the conflict between
the more-crude opinions belonging to the science
of an earlier age and the less-crude opinions belonging
to the science of a later age. In the course of this contest
the more-crude opinions have usually been defended
in the name of religion, and the less-crude opinions have
invariably won the victory; but religion itself, which
is not concerned with opinion, but with the aspiration
which leads us to strive after a purer and holier life, has
seldom or never been attacked. On the contrary, the
scientific men who have conducted the battle on behalf
of the less-crude opinions have generally been influenced
by this religious aspiration quite as strongly as the apologists
of the more-crude opinions, and so far from religious
feeling having been weakened by their perennial
series of victories, it has apparently been growing deeper
and stronger all the time. The religious sense is as yet
too feebly developed in most of us; but certainly in no
preceding age have men taken up the work of life with
more earnestness or with more real faith in the unseen
than at the present day, when so much of what was once
deemed all-important knowledge has been consigned to
the limbo of mythology.
The more-crude theories of early times are to be chiefly
distinguished from the less-crude theories of to-day as
being largely the products of random guesswork. Hypothesis,
or guesswork, indeed, lies at the foundation of
all scientific knowledge. The riddle of the universe, like
less important riddles, is unravelled only by approximative
trials, and the most brilliant discoverers have usually
been the bravest guessers. Kepler's laws were the result
of indefatigable guessing, and so, in a somewhat different
sense, was the wave-theory of light. But the guesswork
of scientific inquirers is very different now from
what it was in older times. In the first place, we have
slowly learned that a guess must be verified before it
can be accepted as a sound theory; and, secondly, so
many truths have been established beyond contravention,
that the latitude for hypothesis is much less than
it once was. Nine tenths of the guesses which might
have occurred to a mediæval philosopher would now be
ruled out as inadmissible, because they would not harmonize
with the knowledge which has been acquired since
the Middle Ages. There is one direction especially in
which this continuous limitation of guesswork by ever-accumulating experience has manifested itself. From
first to last, all our speculative successes and failures
have agreed in teaching us that the most general principles
of action which prevail to-day, and in our own corner
of the universe, have always prevailed throughout as
much of the universe as is accessible to our research.
They have taught us that for the deciphering of the
past and the predicting of the future, no hypotheses are
admissible which are not based upon the actual behaviour
of things in the present. Once there was unlimited
facility for guessing as to how the solar system might
have come into existence; now the origin of the sun and
planets is adequately explained when we have unfolded
all that is implied in the processes which are still going
on in the solar system. Formerly appeals were made to
all manner of violent agencies to account for the changes
which the earth's surface has undergone since our planet
began its independent career; now it is seen that the
same slow working of rain and tide, of wind and wave
and frost, of secular contraction and of earthquake pulse,
which is visible to-day, will account for the whole.
It is not long since it was supposed that a species of
animals or plants could be swept away only by some
unusual catastrophe, while for the origination of new
species something called an act of "special creation" was
necessary; and as to the nature of such extraordinary
events there was endless room for guesswork; but the
discovery of natural selection was the discovery of a
process, going on perpetually under our very eyes, which
must inevitably of itself extinguish some species and
bring new ones into being. In these and countless other
ways we have learned that all the rich variety of nature
is pervaded by unity of action, such as we might expect
to find if nature is the manifestation of an infinite God
who is without variableness or shadow of turning, but
quite incompatible with the fitful behaviour of the
anthropomorphic deities of the old mythologies. By thus
abstaining from all appeal to agencies that are extra-cosmic,
or not involved in the orderly system of events that
we see occurring around us, we have at last succeeded in
eliminating from philosophic speculation the character
of random guesswork which at first of necessity belonged
to it. Modern scientific hypothesis is so far from being
a haphazard mental proceeding that it is perhaps hardly
fair to classify it with guesses. It is lifted out of the
plane of guesswork, in so far as it has acquired the character
of inevitable inference from that which now is to
that which has been or will be. Instead of the innumerable
particular assumptions which were once admitted
into cosmic philosophy, we are now reduced to the one
universal assumption which has been variously described
as the "principle of continuity," the "uniformity of nature,"
the "persistence of force," or the "law of causation,"
and which has been variously explained as a necessary
datum for scientific thinking or as a net result of
all induction. I am not unwilling, however, to adopt the
language of a book which has furnished the occasion for
the present discussion, and to say that this grand assumption
is a supreme act of faith, the definite expression
of a trust that the infinite Sustainer of the universe
"will not put us to permanent intellectual confusion."
For in this mode of statement the harmony between the
scientific and the religious points of view is well brought
out. It is as affording the only outlet from permanent
intellectual confusion that inquirers have been driven
to appeal to the principle of continuity; and it is by
unswerving reliance upon this principle that we have
obtained such insight into the past, present, and future
of the world as we now possess.
The work just mentioned[1]
is especially interesting
as an attempt to bring the probable destiny of the
human soul into connection with the modern theories
which explain the past and future career of the physical
universe in accordance with the principle of continuity.
Its authorship is as yet unknown, but it is believed to be
the joint production of two of the most eminent physicists
in Great Britain, and certainly the accurate knowledge
and the ingenuity and subtlety of thought displayed
in it are such as to lend great probability to this
conjecture. Some account of the argument it contains
may well precede the suggestions presently to be set
forth concerning the Unseen World; and we shall find
it most convenient to begin, like our authors, with a
brief statement of what the principle of continuity
teaches as to the proximate beginning and end of the
visible universe. I shall in the main set down only
results, having elsewhere
[2]
given a simple exposition of
the arguments upon which these results are founded.
The first great cosmological speculation which has
been raised quite above the plane of guesswork by
making no other assumption than that of the uniformity
of nature, is the well-known Nebular Hypothesis.
Every astronomer knows that the earth, like all other
cosmical bodies which are flattened at the poles, was
formerly a mass of fluid, and consequently filled a
much larger space than at present. It is further agreed,
on all hands, that the sun is a contracting body, since
there is no other possible way of accounting for the
enormous quantity of heat which he generates. The
so-called primeval nebula follows as a necessary inference
from these facts. There was once a time when the
earth was distended on all sides away out to the moon
and beyond it, so that the matter now contained in the
moon was then a part of our equatorial zone. And at
a still remoter date in the past, the mass of the sun was
diffused in every direction beyond the orbit of Neptune,
and no planet had an individual existence, for all were
indistinguishable parts of the solar mass. When the
great mass of the sun, increased by the relatively small
mass of all the planets put together, was spread out in
this way, it was a rare vapour or gas. At the period
where the question is taken up in Laplace's treatment
of the nebular theory, the shape of this mass is regarded
as spheroidal; but at an earlier period its shape may
well have been as irregular as that of any of the nebuæ
which we now see in distant parts of the heavens, for,
whatever its primitive shape, the equalization of its
rotation would in time make it spheroidal. That the
quantity of rotation was the same then as now is
unquestionable; for no system of particles, great or small,
can acquire or lose rotation by any action going on
within itself, any more than a man could pick himself
up by his waistband and lift himself over a stone wale
So that the primitive rotating spheroidal solar nebula is
not a matter of assumption, but is just what must once
have existed, provided there has been no breach of
continuity in nature's operations. Now proceeding to
reason back from the past to the present, it has been
shown that the abandonment of successive equatorial
belts by the contracting solar mass must have ensued
in accordance with known mechanical laws; and in
similar wise, under ordinary circumstances. each belt
must have parted into fragments, and the fragments
chasing each other around the same orbit, must have at
last coalesced into a spheroidal planet. Not only this,
but it has also been shown that as the result of such a
process the relative sizes of the planets would be likely
to take the order which they now follow; that the ring
immediately succeeding that of Jupiter would be likely
to abort and produce a great number of tiny planets
instead of one good-sized one; that the outer planets
would be likely to have many moons, and that Saturn,
besides having the greatest number of moons, would be
likely to retain some of his inner rings unbroken; that
the earth would be likely to have a long day and Jupiter
a short one; that the extreme outer planets would
be not unlikely to rotate in a retrograde direction; and
so on, through a long list of interesting and striking
details. Not only, therefore, are we driven to the inference
that our solar system was once a vaporous nebula,
but we find that the mere contraction of such a nebula,
under the influence of the enormous mutual gravitation
of its particles, carries with it the explanation of both
the more general and the more particular features of the
present system. So that we may fairly regard this stupendous
process as veritable matter of history, while we
proceed to study it under some further aspects and to
consider what consequences are likely to follow.
Our attention should first be directed to the enormous
waste of energy which has accompanied this contraction
of the solar nebula. The first result of such a contraction
is the generation of a great quantity of heat, and
when the heat thus generated has been lost by radiation
into surrounding space it becomes possible for
the contraction to continue. Thus, as concentration
goes on, heat is incessantly generated and incessantly
dissipated. How long this process is to endure depends
chiefly on the size of the contracting mass, as
small bodies radiate heat much faster than large ones.
The moon seems to be already thoroughly refrigerated,
while Jupiter and Saturn are very much hotter than
the earth, as is shown by the tremendous atmospheric
phenomena which occur on their surfaces. The sun,
again, generates heat so rapidly, owing to his great
energy of contraction, and loses it so slowly, owing to
his great size, that his surface is always kept in a state
of incandescence. His surface-temperature is estimated
at some three million degrees of Fahrenheit, and a
diminution of his diameter far too small to be detected
by the finest existing instruments would suffice to maintain
the present supply of heat for more than fifty centuries.
These facts point to a very long future during
which the sun will continue to warm the earth and its
companion planets, but at the same time they carry on
their face the story of inevitable ultimate doom. If
things continue to go on as they have all along gone on,
the sun must by and by grow black and cold, and all
life whatever throughout the solar system must come to
an end. Long before this consummation, however, life
will probably have become extinct through the refrigeration
of each of the planets into a state like the present
state of the moon, in which the atmosphere and oceans
have disappeared from the surface. No doubt the sun
will continue to give out heat a long time after heat has
ceased to be needed for the support of living organisms.
For the final refrigeration of the sun will long be postponed
by the fate of the planets themselves. The separation
of the planets from their parent solar mass seems
to be after all but a temporary separation. So nicely
balanced are they now in their orbits that they may
well seem capable of rolling on in their present courses
forever. But this is not the case. Two sets of circumstances
are all the while striving, the one to drive the
planets farther away from the sun, the other to draw
them all into it. On the one hand, every body in our
system which contains fluid matter has tides raised
upon its surface by the attraction of neighbouring bodies.
All the planets raise tides upon the surface of the sun
and the periodicity of sun-spots (or solar cyclones) depends
upon this fact. These tidal waves act as a drag
or brake upon the rotation of the sun, somewhat diminishing
its rapidity. But, in conformity with a principle
of mechanics well known to astronomers, though not
familiar to the general reader, all the motion of rotation
thus lost by the sun is added to the planets in the shape
of annual motion of revolution, and thus their orbits all
tend to enlarge,—they all tend to recede somewhat
from the sun. But this state of things, though long-enduring
enough, is after all only temporary, and will
at any rate come to an end when the sun and planets
have become solid. Meanwhile another set of circumstances
is all the time tending to bring the planets
nearer to the sun, and in the long run must gain the
mastery. The space through which the planets move is
filled with a kind of matter which serves as a medium
for the transmission of heat and light, and this kind of
matter, though different in some respects from ordinary
ponderable matter, is yet like it in exerting friction.
This friction is almost infinitely little, yet it has a
wellnigh infinite length of time to work in, and during all
this wellnigh infinite length of time it is slowly eating
up the momentum of the planets and diminishing their
ability to maintain their distances from the sun. Hence
in course of time the planets will all fall into the sun,
one after another, so that the solar system will end, as
it began, by consisting of a single mass of matter.
But this is by no means the end of the story. When
two bodies rush together, each parts with some of its energy
of motion, and this lost energy of motion reappears
as heat. In the concussion of two cosmical bodies, like
the sun and the earth, an enormous quantity of motion
is thus converted into heat. Now heat, when not
allowed to radiate, or when generated faster than it can
be radiated, is transformed into motion of expansion.
Hence the shock of sun and planet would at once result
in the vaporization of both bodies; and there can be no
doubt that by the time the sun has absorbed the outermost
of his attendant planets, he will have resumed
something like his original nebulous condition. He will
have been dilated into a huge mass of vapour, and will
have become fit for a new process of contraction and for
a new production of life-bearing planets.
We are now, however, confronted by an interesting
but difficult question. Throughout all this grand past
and future career of the solar system which we have
just briefly traced, we have been witnessing a most
prodigal dissipation of energy in the shape of radiant
heat. At the outset we had an enormous quantity of
what is called "energy of position," that is, the outer
parts of our primitive nebula had a very long distance
through which to travel towards one another in the
slow process of concentration; and this distance was
the measure of the quantity of work possible to our
system. As the particles of our nebula drew nearer
and nearer together, the energy of position continually
lost reappeared continually as heat, of which the greater
part was radiated off, but of which a certain amount was
retained. All the gigantic amount of work achieved in
the geologic development of our earth and its companion
planets, and in the development of life wherever life
may exist in our system, has been the product of this
retained heat. At the present day the same wasteful
process is going on. Each moment the sun's particles
are losing energy of position as they draw closer and
closer together, and the heat into which this lost energy
is metamorphosed is poured out most prodigally in
every direction. Let us consider for a moment how
little of it gets used in our system. The earth's orbit
is a nearly circular figure more than five hundred million
miles in circumference, while only eight thousand
miles of this path are at any one time occupied by the
earth's mass. Through these eight thousand miles the
sun's radiated energy is doing work, but through the
remainder of the five hundred million it is idle and
wasted. But the case is far more striking when we
reflect that it is not in the plane of the earth's orbit
only that the sun's radiance is being poured out. It
is not an affair of a circle, but of a sphere. In order to
utilize all the solar rays, we should need to have an
immense number of earths arranged so as to touch each
other, forming a hollow sphere around the sun, with
the present radius of the earth's orbit. We may well
believe Professor Tyndall, therefore, when he tells us
that all the solar radiance we receive is less than a two-billionth part of what is sent flying through the desert
regions of space. Some of the immense residue of
course hits other planets stationed in the way of it, and
is utilized upon their surfaces; but the planets, all put
together, stop so little of the total quantity that our
startling illustration is not materially altered by taking
them into the account. Now this two-billionth part of
the solar radiance poured out from moment to moment
suffices to blow every wind, to raise every cloud, to
drive every engine, to build up the tissue of every
plant, to sustain the activity of every animal, including
man, upon the surface of our vast and stately globe.
Considering the wondrous richness and variety of the
terrestrial life wrought out by the few sunbeams which
we catch in our career through space, we may well
pause overwhelmed and stupefied at the thought of the
incalculable possibilities of existence which are thrown
away with the potent actinism that darts unceasingly
into the unfathomed abysms of immensity. Where it
goes to or what becomes of it, no one of us can surmise.
Now when, in the remote future, our sun is reduced
to vapour by the impact of the several planets upon his
surface, the resulting nebulous mass must be a very
insignificant affair compared with the nebulous mass
with which we started. In order to make a second
nebula equal in size and potential energy to the first
one, all the energy of position at first existing should
have been retained in some form or other. But nearly
all of it has been lost, and only an insignificant fraction
remains with which to endow a new system. In order
to reproduce, in future ages, anything like that cosmical
development which is now going on in the solar
system, aid must be sought from without. We must
endeavour to frame some valid hypothesis as to the
relation of our solar system to other systems.
Thus far our view has been confined to the career of
a single star,—our sun,—with the tiny, easily-cooling
balls which it has cast off in the course of its development.
Thus far, too, our inferences have been very
secure, for we have been dealing with a circumscribed
group of phenomena, the beginning and end of which
have been brought pretty well within the compass of
our imagination. It is quite another thing to deal with
the actual or probable career of the stars in general,
inasmuch as we do not even know how many stars there
are, which form parts of a common system, or what. are
their precise dynamic relations to one another. Nevertheless
we have knowledge of a few facts which may
support some cautious inferences. All the stars which
we can see are undoubtedly bound together by relations
of gravitation. No doubt our sun attracts all the other
stars within our ken, and is reciprocally attracted by
them. The stars, too, lie mostly in or around one great
plane, as is the case with the members of the solar system.
Moreover, the stars are shown by the spectroscope
to consist of chemical elements identical with those
which are found in the solar system. Such facts as
these make it probable that the career of other stars,
when adequately inquired into, would be found to
be like that of our own sun. Observation daily enhances
this probability, for our study of the sidereal
universe is continually showing us stars in all stages
of development. We find irregular nebuæ, for example;
we find spiral and spheroidal nebulæ; we find
stars which have got beyond the nebulous stage, but
are still at a whiter heat than our sun; and we also
find many stars which yield the same sort of spectrum
as our sun. The inference seems forced upon us that
the same process of concentration which has gone on in
the case of our solar nebula has been going on in the
case of other nebulæ. The history of the sun is but
a type of the history of stars in general. And when
we consider that all other visible stars and nebulæ are
cooling and contracting bodies, like our sun, to what
other conclusion could we very well come? When we
look at Sirius, for instance, we do not see him surrounded
by planets, for at such a distance no planet
could be visible, even Sirius himself, though fourteen
times larger than our sun, appearing only as a "twinkling
little star." But a comparative survey of the heavens
assures us that Sirius can hardly have arrived at
his present stage of concentration without detaching,
planet-forming rings, for there is no reason for supposing
that mechanical laws out there are at all different
from what they are in our own system. And the same
kind of inference must apply to all the matured stars
which we see in the heavens.
When we duly take all these things into the account,
the case of our solar system will appear as only one of a
thousand cases of evolution and dissolution with which
the heavens furnish us. Other stars, like our sun, have
undoubtedly started as vaporous masses, and have thrown
off planets in contracting. The inference may seem a
bold one, but it after all involves no other assumption
than that of the continuity of natural phenomena. It is
not likely, therefore, that the solar system will forever
be left to itself. Stars which strongly gravitate toward
each other, while moving through a perennially resisting
medium, must in time be drawn together. The collision
of our extinct sun with one of the Pleiades, after this
manner, would very likely suffice to generate even a
grander nebula than the one with which we started.
Possibly the entire galactic system may, in an inconceivably
remote future, remodel itself in this way; and
possibly the nebula from which our own group of planets
has been formed may have owed its origin to the
disintegration of systems which had accomplished their
career in the depths of the bygone eternity.
When the problem is extended to these huge dimensions,
the prospect of an ultimate cessation of cosmical
work is indefinitely postponed, but at the same time it
becomes impossible for us to deal very securely with the
questions we have raised. The magnitudes and periods
we have introduced are so nearly infinite as to baffle
speculation itself: One point, however, we seem dimly
to discern. Supposing the stellar universe not to be
absolutely infinite in extent, we may hold that the day of
doom, so often postponed, must come at last. The
concentration of matter and dissipation of energy, so often
checked, must in the end prevail, so that, as the final
outcome of things, the entire universe will be reduced to
a single enormous ball, dead and frozen, solid and black,
its potential energy of motion having been all transformed
into heat and radiated away. Such a conclusion
has been suggested by Sir William Thomson, and it is
quite forcibly stated by the authors of "The Unseen
Universe." They remind us that "if there be any one
form of energy less readily or less completely transformable
than the others, and if transformations constantly
go on, more and more of the whole energy of the universe
will inevitably sink into this lower grade as time
advances." Now radiant heat, as we have seen, is such
a lower grade of energy. "At each transformation of
heat-energy into work, a large portion is degraded, while
only a small portion is transformed into work. So that
while it is very easy to change all of our mechanical or
useful energy into heat, it is only possible to transform
a portion of this heat-energy back again into work.
After each change, too, the heat becomes more and more
dissipated or degraded, and less and less available for
any future transformation. In other words," our authors
continue, "the tendency of heat is towards equalization;
heat is
par excellence the communist of our universe, and
it will no doubt ultimately bring the system to an end.
.... It is absolutely certain that life, so far as it is
physical, depends essentially upon transformations of
energy; it is also absolutely certain that age after age
the possibility of such transformations is becoming less
and less; and, so far as we yet know, the final state of
the present universe must be an aggregation (into one
mass) of all the matter it contains,
i. e. the potential
energy gone, and a practically useless state of kinetic
energy,
i. e. uniform temperature throughout that mass."
Thus our authors conclude that the visible universe
began in time and will in time come to an end; and
they add that under the physical conditions of such a
universe "immortality is impossible."
Concerning the latter inference we shall by and by
have something to say. Meanwhile this whole speculation
as to the final cessation of cosmical work seems to
me—as it does to my friend, Professor Clifford
[3]—by
no means trustworthy. The conditions of the problem
so far transcend our grasp that any such speculation
must remain an unverifiable guess. I do not go with
Professor Clifford in doubting whether the laws of mechanics
are absolutely the same throughout eternity; I
cannot quite reconcile such a doubt with faith in the
principle of continuity. But it does seem to me needful,
before we conclude that radiated energy is absolutely
and forever wasted, that we should find out what becomes
of it. What we call radiant heat is simply transverse
wave-motion, propagated with enormous velocity
through an ocean of subtle ethereal matter which bathes
the atoms of all visible or palpable bodies and fills the
whole of space, extending beyond the remotest star
which the telescope can reach. Whether there are any
bounds at all to this ethereal ocean, or whether it is as
infinite as space itself, we cannot surmise. If it be
limited, the possible dispersion of radiant energy is limited
by its extent. Heat and light cannot travel through
emptiness. If the ether is bounded by surrounding
emptiness, then a ray of heat, on arriving at this limiting
emptiness, would be reflected back as surely as a ball
is sent back when thrown against a solid wall. If this
be the case, it will not affect our conclusions concerning
such a tiny region of space as is occupied by the solar
system, but it will seriously modify Sir William Thomson's
suggestion as to the fate of the universe as a whole.
The radiance thrown away by the sun is indeed lost so
far as the future of our system is concerned, but not a
single unit of it is lost from the universe. Sooner or
later, reflected back in all directions, it must do work in
one quarter or another, so that ultimate stagnation be
comes impossible. It is true that no such return of
radiant energy has been detected in our corner of the
world; but we have not yet so far disentangled all the
force-relations of the universe that we are entitled to
regard such a return as impossible. This is one way
of escape from the consummation of things depicted by
our authors. Another way of escape is equally available,
if we suppose that while the ether is without bounds the
stellar universe also extends to infinity. For in this case
the reproduction of nebulous masses fit for generating
new systems of worlds must go on through space that is
endless, and consequently the process can never come to
an end and can never have had a beginning. We have,
therefore, three alternatives: either the visible universe
is finite, while the ether is infinite; or both are finite;
or both are infinite. Only on the first supposition, I
think, do we get a universe which began in time and
must end in time. Between such stupendous alternatives
we have no grounds for choosing. But it would
seem that the third, whether strictly true or not, best
represents the state of the case relatively to our feeble
capacity of comprehension. Whether absolutely infinite
or not, the dimensions of the universe must be taken as
practically infinite, so far as human thought is concerned.
They immeasurably transcend the capabilities
of any gauge we can bring to bear on them. Accordingly
all that we are really entitled to hold, as the outcome
of sound speculation, is the conception of innumerable
systems of worlds concentrating out of nebulous
masses, and then rushing together and dissolving into
similar masses, as bubbles unite and break up—now
here, now there—in their play on the surface of a pool,
and to this tremendous series of events we can assign
neither a beginning nor an end.
We must now make some more explicit mention of
the ether which carries through space the rays of heat
and light. In closest connection with the visible stellar
universe, the vicissitudes of which we have briefly traced,
the all-pervading ether constitutes a sort of unseen world
remarkable enough from any point of view, but to which
the theory of our authors ascribes capacities hitherto
unsuspected by science. The very existence of an ocean
of ether enveloping the molecules of material bodies has
been doubted or denied by many eminent physicists,
though of course none have called in question the necessity
for some interstellar medium for the transmission of
thermal and luminous vibrations. This scepticism has
been, I think, partially justified by the many difficulties
encompassing the conception, into which, however, we
need not here enter. That light and heat cannot be conveyed
by any of the ordinary sensible forms of matter is
unquestionable. None of the forms of sensible matter
can be imagined sufficiently elastic to propagate wave-motion at the rate of one hundred and eighty-eight
thousand miles per second. Yet a ray of light is a
series of waves, and implies some substance in which
the waves occur. The substance required is one which
seems to possess strangely contradictory properties. It
is commonly regarded as an "ether" or infinitely rare
substance; but, as Professor Jevons observes, we might
as well regard it as an infinitely solid "adamant." "Sir
John Herschel has calculated the amount of force
which may be supposed, according to the undulatory
theory of light, to be exerted at each point in space, and
finds it to be 1,148,000,000,000 times the elastic force
of ordinary air at the earth's surface, so that the pressure
of the ether upon a square inch of surface must be about
17,000,000,000,000, or seventeen billions of pounds."
[4]
Yet at the same time the resistance offered by the ether
to the planetary motions is too minute to be appreciable.
"All our ordinary notions," says Professor Jevons,
"must be laid aside in contemplating such an hypothesis;
yet [it is] no more than the observed phenomena
of light and heat force us to accept. We cannot
deny even the strange suggestion of Dr. Young, that
there may be independent worlds, some possibly existing
in different parts of space, but others perhaps pervading
each other, unseen and unknown, in the same
space. For if we are bound to admit the conception of
this adamantine firmament, it is equally easy to admit a
plurality of such."
The ether, therefore, is unlike any of the forms of matter
which we can weigh and measure. In some respects
it resembles a fluid, in some respects a solid. It is both
hard and elastic to an almost inconceivable degree. It
fills all material bodies like a sea in which the atoms of
the material bodies are as islands, and it occupies the
whole of what we call empty space. It is so sensitive
that a disturbance in any part of it causes a "tremour
which is felt on the surface of countless worlds." Our
old experiences of matter give us no account of any
substance like this; yet the undulatory theory of light
obliges us to admit such a substance, and that theory is
as well established as the theory of gravitation. Obviously
we have here an enlargement of our experience of
matter. The analysis of the phenomena of light and
radiant heat has brought us into mental relations with
matter in a different state from any in which we previously
knew it. For the supposition that the ether may
be something essentially different from matter is contradicted
by all the terms we have used in describing it.
Strange and contradictory as its properties may seem,
are they any more strange than the properties of a gas
would seem if we were for the first time to discover
a gas after heretofore knowing nothing but solids and
liquids? I think not; and the conclusion implied by
our authors seems to me eminently probable, that in the
so-called ether we have simply a state of matter more
primitive than what we know as the gaseous state. Indeed,
the conceptions of matter now current, and inherited
from barbarous ages, are likely enough to be crude
in the extreme. It is not strange that the study of such
subtle agencies as heat and light should oblige us to
modify them; and it will not be strange if the study
of electricity should entail still further revision of our
ideas.
We are now brought to one of the profoundest speculations
of modern times, the vortex-atom theory of
Helmholtz and Thomson, in which the evolution of
ordinary matter from ether is plainly indicated. The
reader first needs to know what vortex-motion is; and
this has been so beautifully explained by Professor
Clifford, that I quote his description entire: "Imagine
a ring of india-rubber, made by joining together the
ends of a cylindrical piece (like a lead-pencil before
it is cut), to be put upon a round stick which it will
just fit with a little stretching. Let the stick be now
pulled through the ring while the latter is kept in its
place by being pulled the other way on the outside.
The india-rubber has then what is called vortex-motion.
Before the ends were joined together, while it was
straight, it might have been made to turn around without
changing position, by rolling it between the hands.
Just the same motion of rotation it has on the stick,
only that the ends are now joined together. All the inside
surface of the ring is going one way, namely, the
way the stick is pulled; and all the outside is going
the other way. Such a vortex-ring is made by the
smoker who purses his lips into a round hole and sends
out a puff of smoke. The outside of the ring is kept
back by the friction of his lips while the inside is going
forwards; thus a rotation is set up all round the smoke-ring as it travels out into the air." In these cases, and
in others as we commonly find it, vortex-motion owes
its origin to friction and is after a while brought to an
end by friction. But in 1858 the equations of motion
of an incompressible frictionless fluid were first successfully
solved by Helmholtz, and among other things he
proved that, though vortex-motion could not be originated
in such a fluid, yet supposing it once to exist, it
would exist to all eternity and could not be diminished
by any mechanical action whatever. A vortex-ring, for
example, in such a fluid, would forever preserve its own
rotation, and would thus forever retain its peculiar
individuality, being, as it were, marked off from its
neighbour vortex-rings. Upon this mechanical truth Sir
William Thomson based his wonderfully suggestive theory
of the constitution of matter. That which is permanent
or indestructible in matter is the ultimate homogeneous
atom; and this is probably all that is permanent, since
chemists now almost unanimously hold that so-called
elementary molecules are not really simple, but owe
their sensible differences to the various groupings of an
ultimate atom which is alike for all. Relatively to our
powers of comprehension the atom endures eternally;
that is, it retains forever unalterable its definite mass
and its definite rate of vibration. Now this is just
what a vortex-ring would do in an incompressible frictionless
fluid. Thus the startling question is suggested,
Why may not the ultimate atoms of matter be vortex-
rings forever existing in such a frictionless fluid filling
the whole of space? Such a hypothesis is not less
brilliant than Huyghens's conjectural identification of
light with undulatory motion; and it is moreover a
legitimate hypothesis, since it can be brought to the test
of verification. Sir William Thomson has shown that
it explains a great many of the physical properties of
matter: it remains to be seen whether it can explain
them all.
Of course the ether which conveys thermal and luminous
undulations is not the frictionless fluid postulated
by Sir William Thomson. The most conspicuous property
of the ether is its enormous elasticity, a property
which we should not find in a frictionless fluid. "To
account for such elasticity," says Professor Clifford
(whose exposition of the subject is still more lucid than
that of our authors), "it has to be supposed that even
where there are no material molecules the universal
fluid is full of vortex-motion, but that the vortices are
smaller and more closely packed than those of [ordinary]
matter, forming altogether a more finely grained
structure. So that the difference between matter and
ether is reduced to a mere difference in the size and
arrangement of the component vortex-rings. Now,
whatever may turn out to be the ultimate nature of the
ether and of molecules, we know that to some extent at
least they obey the same dynamic laws, and that they
act upon one another in accordance with these laws.
Until, therefore, it is absolutely disproved, it must
remain the simplest and most probable assumption
that they are finally made of the same stuff, that the
material molecule is some kind of knot or coagulation
of ether."[5]
Another interesting consequence of Sir William
Thomson's pregnant hypothesis is that the absolute
hardness which has been attributed to material atoms
from the time of Lucretius downward may be dispensed
with. Somewhat in the same way that a loosely suspended
chain becomes rigid with rapid rotation, the
hardness and elasticity of the vortex-atom are explained
as due to the swift rotary motion of a soft and yielding
fluid. So that the vortex-atom is really indivisible, not
by reason of its hardness or solidity, but by reason of
the indestructibleness of its motion.
Supposing, now, that we adopt provisionally the vortex
theory,—the great power of which is well shown
by the consideration just mentioned,—we must not
forget that it is absolutely essential to the indestructibleness
of the material atom that the universal fluid
in which it has an existence as a vortex-ring should be
entirely destitute of friction. Once admit even the
most infinitesimal amount of friction, while retaining
the conception of vortex-motion in a universal fluid,
and the whole case is so far altered that the material
atom can no longer be regarded as absolutely indestructible,
but only as indefinitely enduring. It may have
been generated, in bygone eternity, by a natural process
of evolution, and in future eternity may come to
an end. Relatively to our powers of comprehension
the practical difference is perhaps not great. Scientifically
speaking, Helmholtz and Thomson are as well
entitled to reason upon the assumption of a perfectly
frictionless fluid as geometers in general are entitled
to assume perfect lines without breadth and perfect
surfaces without thickness. Perfect lines and surfaces
do not exist within the region of our experience; yet
the conclusions of geometry are none the less true
ideally, though in any particular concrete instance
they are only approximately realized. Just so with the
conception of a frictionless fluid. So far as experience
goes, such a thing has no more real existence than a
line without breadth; and hence an atomic theory based
upon such an assumption may be as true ideally as any
of the theorems of Euclid, but it can give only an
approximatively true account of the actual universe.
These considerations do not at all affect the scientific
value of the theory; but they will modify the tenour of
such transcendental inferences as may be drawn from it
regarding, the probable origin and destiny of the universe.
The conclusions reached in the first part of this paper,
while we were dealing only with gross visible matter,
may have seemed bold enough; but they are far surpassed
by the inference which our authors draw from
the vortex theory as they interpret it. Our authors exhibit
various reasons, more or less sound, for attributing
to the primordial fluid some slight amount of friction;
and in support of this view they adduce Le Sage's
explanation of gravitation as a differential result of
pressure, and Struve's theory of the partial absorption
of light-rays by the ether,—questions with which our
present purpose does not require us to meddle. Apart
from such questions it is every way probable that the
primary assumption of Helmholtz and Thomson is only
an approximation to the truth. But if we accredit the
primordial fluid with even an infinitesimal amount of
friction, then we are required to conceive of the visible
universe as developed from the invisible and as destined
to return into the invisible. The vortex-atom, produced
by infinitesimal friction operating through wellnigh infinite
time, is to be ultimately abolished by the agency
which produced it. In the words of our authors, "If
the visible universe be developed from an invisible
which is not a perfect fluid, then the argument deduced
by Sir William Thomson in favour of the eternity of
ordinary matter disappears, since this eternity depends
upon the perfect fluidity of the invisible. In fine, if
we suppose the material universe to be composed of a
series of vortex-rings developed from an invisible universe
which is not a perfect fluid, it will be ephemeral,
just as the smoke-ring which we develop from air, or
that which we develop from water, is ephemeral, the only
difference being in duration, these lasting only for a few
seconds, and the others it may be for billions of years."
Thus, as our authors suppose that "the available energy
of the visible universe will ultimately be appropriated
by the invisible," they go on to imagine, "at least as a
possibility, that the separate existence of the visible
universe will share the same fate, so that we shall have
no huge, useless, inert mass existing in after ages to remind
the passer-by of a form of energy and a species of
matter that is long since out of date and functionally
effete. Why should not the universe bury its dead out
of sight?"
In one respect perhaps no more stupendous subject
of contemplation than this has ever been offered to the
mind of man. In comparison with the length of time
thus required to efface the tiny individual atom, the
entire cosmical career of our solar system, or even that
of the whole starry galaxy, shrinks into utter nothingness.
Whether we shall adopt the conclusion suggested
must depend on the extent of our speculative audacity.
We have seen wherein its probability consists, but in
reasoning upon such a scale we may fitly be cautious
and modest in accepting inferences, and our authors,
we may be sure, would be the first to recommend such
modesty and caution. Even at the dimensions to which
our theorizing has here grown, we may for instance discern
the possible alternative of a simultaneous or rhythmically
successive generation and destruction of vortex-atoms which would go far to modify the conclusion just
suggested. But here we must pause for a moment, reserving
for a second paper the weightier thoughts as to
futurity which our authors have sought to enwrap in
these sublime physical speculations.