COSMOGONY IN THE TWENTIETH CENTURY
Prospective and retrospective inquiries into physical conditions stand
very much on the same footing. The same degree of uncertainty attaches
to results of both kinds; the same qualifications need to be applied
to them; a similar reserve is understood to accompany our admission of
them. The reserve grows more marked as science unfolds to our surprised
apprehension the multiplex possibilities of Nature. The time has gone
by when 'men of light and leading' could draw cheques for unlimited
amounts on the bank of public credulity. Not that the balance has
diminished, but that it is reserved for other uses. Most of us in these
days, have learnt to 'look before and after' for ourselves, and we
instinctively mix the proverbial grain of salt with what is told to
us, even on the highest authority. Ideas are on the move; dim vistas
are opening out; much that lies beyond the verge of actual experience
is seen to be possible, and sedate reasoning may at any moment suffer
outrage by fantastic discovery. Hence, finality of assertion is out of
date.
The secular parallax affecting men's views of the universe is nowhere
more strongly apparent than in the trend taken by speculations as to
its origin. They have become more subtle, more far-reaching, yet less
confident. They have ramified in unexpected directions, but rather
tentatively, than with the full assurance of attaining absolute truth.
Laplace considered only the solar system, from which he arbitrarily
excluded comets. On the vast sidereal world he bestowed barely casual
attention. Sir William Herschel, on the other hand, occupied himself
exclusively with the growth-processes of nebulæ, relegating the details
of planetary evolution to a position of secondary importance. Later,
the spectroscope having become available for discriminating generic
differences among the suns in space, their relative ages, the order
of their succession, their mutual affinities, claimed predominant
attention. Just now, however, the flood of speculation is too high to
be restrained within separate channels; cosmogonists look far afield;
they aim at obtaining a general survey of relations bewildering in
their complexity. To some extent they have succeeded; parts are
beginning to find their places in a great whole; links are seen to
connect phenomena at first sight seemingly isolated; on all sides
analogies are springing into view. The unwearied circling of the moon
and its imperturbable face remind us how a sun may have been born;
the flash of every meteor suggests the mode by which suns die. The
filmy traceries of comets intimate the nature of the force acting in
nebulæ; the great cosmic law of spirality is remotely hinted at by the
antipodal disturbances of the sun. Thus, one set of facts dovetails
into the next; none can be properly considered apart from the rest.
The limitations of the human mind impose, nevertheless, restrictions
of treatment. Individual efforts cannot grapple with the whole of
the known and the knowable, and the larger part of both is included
in the scope of modern cosmogony. It deals with all that the skies
hold, visibly or invisibly; draws unstintingly on time past and time
to come; concerns itself equally with gradual transformations and
sudden catastrophes, with the dissipation and concentration of energy,
with the subtle interplay of matter and force, with physical and
ultra-physical, chemical and electrical modes of action. But let us
consider a little more particularly how things actually stand, so as to
collect some definite ideas regarding the lines of advance practicable
and promising for the immediate future.
To begin with our domestic circle. The insecure state to which
Laplace's scheme has been reduced by the assaults of numerous objectors
has found compensation in the development of the tidal theory. Much
light has thereby been thrown upon planetary pre-history. The relations
of planets to the sun, and of satellites to planets, have been rendered
comparatively intelligible. Noticeable above all is the discovery
thence ensuing of the earth's suggestive position, just outside the
boundary of the region where planetary rotation was destroyed by
sun-raised tides, and with it the prospects of planetary vitality.
Moreover, the dubious state of the inchoate terrestrial spheroid,
consequent upon its intermediate situation, accounts for the peculiar
mode of birth of the moon, and the distinctively binary character
of the earth-moon system; while the variety perceptible in the
circumstances of the different planets precludes the employment
of any single recipe for their development from a primal vortex.
The forces concerned, we can now see, acted in a far more complex
manner than could formerly have been supposed, and their balance was
proportionately more delicate. To which side it would have inclined in
a given case must then often be incalculable, or calculable only with
the guidance of the known result. The strict bonds of reasoning have
thus become somewhat relaxed, and difficulties that looked formidable
have, in the long run, proved not to be insuperable. But conviction has
also grown faint. The old, imposing façade of theory remains erect;
the building behind it has been, for the most part, pulled to pieces,
and the architect has yet to be found who can reconstruct it to our
satisfaction.
On one point we have, nevertheless, acquired certainty. It is now known
that comets with their dependent trains of meteors are aboriginal in
the solar system. They are no unlicensed intruders, but collateral
relations of the planetary family. Possibly they represent waste scraps
of world-stuff which escaped the action of the formative machinery;
and if so, they exemplify its primitive texture. Not that their
composition need be, on this supposition, identical with that of the
planets. A sifting of elements would have been likely to accompany the
processes of cooling and contraction. Comets were, perhaps, made (to
speak illustratively) of the white of the nebulous egg, planets of
its yolk. But in any case we may safely regard the glimmering fabrics
of acetylene and cyanogen that occasionally illuminate our skies as
shearings from a wide-spreading, fleecy haze, flung aside before
'the starry tides' had as yet begun to 'set towards the centre.' In
one respect the quality of these relics is a surprise. They show no
chemical affinity with nebulæ. Their spectra are radically different
from nebular spectra, gaseous or continuous. They accordingly lend no
countenance, although not fatally adverse to the view that the sun was
once, in the distinctive sense, a nebulous star.
The grand topic of sidereal succession is no longer abandoned to
fruitless surmises. Broad lines have been laid down, along which,
so far as we can at present see, progress must inevitably have been
conducted. And one fact of overwhelming significance in this connection
is entirely of recent discovery. The multitudinous existence of obscure
bodies in space had, indeed, been foreseen as a logical necessity long
before Bessel founded the 'Astronomy of the Invisible'; but its strong
substantiation is almost wholly due to the use of modern spectrographic
methods. Decrepit or dusky suns are assuredly no imaginary product,
but a potent reality, though it would be too much to assert that all
have sunk to extinction by the same road. Nor is it absolutely certain
that their present state is uniformly the outcome of prolonged decay.
Circumstances connected with many of them suggest rather a congenital
incapacity for shining.
We stand, too, on firmer ground than our predecessors in respect to the
history of stellar systems. That its course is mainly prescribed by
the influence of tidal friction has been ably demonstrated by Dr. See.
Telescopic double stars can be led back by the aid of this clue to an
initial stage, when they revolved close together, very much like the
earth and moon in Professor Darwin's theory; and it was owing to their
voluminousness and the unequal attractions it engendered that their
orbits became enlarged and elongated to the degree generally observed.
This theoretical inference has been confirmed with singular aptness by
the discovery of spectroscopic binaries. Pairs circling in orbits too
narrow for visual discernment are the natural complement of pairs just
divisible with the telescope; the first class represent the unseen,
early stages of the second. The two together form an unbroken sequence
of stellar systems, for spectroscopic binaries include couples fully
separated, and still separating, as well as others barely divided, and
revolving almost in contact. Nay, they include specimens, we are led
to believe, of globes conjoined into the apioidal figure theoretically
investigated by Darwin and Poincaré, which may be regarded as
preparatory to the development by fission of two mutually revolving
stars from one primitive rotating mass. Some of these supposed
dumb-bell systems are variable in light; and if the eclipse-rationale
of their obscurations be confirmed by the spectroscope, there is no
gainsaying the inference that each flickering object is composed of two
stars actually contiguous, if not confluent.
Now, compound stars are by no means of exceptional occurrence. Their
relative abundance has been found to augment rapidly with every advance
in our knowledge of the heavens. From the measures of stellar radial
velocity lately carried out at the Yerkes Observatory by Professors
Frost and Adams, it appears that the proportion of binary to single
stars considerably exceeds Professor Campbell's earlier estimate.
If those giving helium-spectra are alone considered, there are most
probably as many of one kind as of the other. But why the distinction?
it may be asked. The answer is not far to seek. Helium stars are the
most primitive, and form the closest and most readily apparent systems.
The companions of more fully developed stars would be likely to give
less striking spectroscopic signs of their presence. A physically
double star must always remain such. There is no law of divorce by
which it can put away its companion, although their relations must
alter with time. But their alteration tends continually to enhance the
difficulty of their detection. For as the members of a pair are pushed
asunder by tidal friction their velocity slackens, and the tell-tale
swing of their spectral lines diminishes in amplitude, and finally, by
its minuteness, evades observation.
And since the majority of spectroscopic satellite-stars are very
imperfectly luminous, their eventual telescopic discovery, when far
enough away from their primaries to be optically separable from them,
would rarely ensue. It must then be concluded that half the stars in
the heavens (let us say) broke up into two or more bodies as they
condensed. What follows? Well, this. Half the stars in the heavens
were, from the first, incapacitated from becoming the centres of
planetary systems. To our apprehension, at least, it appears obvious
that a binary condition must have inhibited the operations of planetary
growth. These innumerable systems are doubtless organized on a totally
different principle from that regulating the family of the sun. The
nebular hypothesis, even in its most improved form, has no application
to them; the meteoritic hypothesis still less. Mathematical theories
of fluid equilibrium, combined with a long series of changes due to
tidal friction, afford some degree of insight into the mode of their
origin and the course of their development. Yet the analogy with the
earth-moon couple, which irresistibly suggests itself, is imperfect,
and may be misleading, owing to the wide difference in state between
plastic globes approaching solidification, and sunlike bodies radiating
intensely and probably gaseous to the core.[50]
The world of nebulæ confronts us with entire cycles of evolutionary
problems, which can no longer be treated in the offhand manner perforce
adopted by Herschel. The objects in question are of bewildering
variety; yet we can trace, amid their fantastic irregularities, the
underlying uniformity of one constructive thought. Nearly all show,
more or less markedly, a spiral conformation, and a spiral conformation
intimates the action of known or discoverable laws. Their investigation
must, indeed, be slow and toilsome; its progress may long be impeded by
the interposition of novel questions, both in physics and mechanics;
nevertheless, the lines prescribed for it seem definite enough to
give hope of its leading finally to a clear issue. And when at last
something has been fairly well ascertained regarding the past and
future of nebulous spirals, no contemptible inroad will have been made
on the stupendous enigma of sidereal relationships.
Its aspect, if we venture to look at it in its entirety, is vast
and formidable. Not now, as in former times, with a mere fragment
of creation--a single star and its puny client-globes, one of which
happens to be the temporary abode of the human race--but with the
undivided, abysmal cosmos, the science of origin and destiny concerns
itself. The obscure and immeasurable uncertainties of galactic history
invite or compel attention. We know just enough to whet our desire to
know a great deal more. The distribution of stars and nebulæ is easily
seen to be the outcome of design. By what means, we cannot but ask
ourselves, was the design executed? How were things ordered when those
means began to be employed? How will they be ordered when all is done?
For an ultimate condition has, presumably, not yet been reached. And
if not, agencies must be at work for the perfecting of the supreme
purpose, which are not, perhaps, too subtle for our apprehension.
Meanwhile, facts bearing on sidereal construction are being diligently
collected and sifted, and we shall do well to suspend speculation until
their larger import is made known.
The inquisitions of science do not cease here. They strive to penetrate
a deeper mystery than that of the scattering in space of stars and
nebulæ. What are they made of? is the further question that presents
itself. What is the nature of the primal world-stuff? Whence did
it obtain heat? By what means was motion imparted to it? If it be
urged that such-like topics elude the grasp of finite intelligence
and belong to the secrets of creative power, we may reply that we are
not entitled, nor are we able, to draw an arbitrary line, not to be
transgressed by our vagrant thoughts. The world has been, by express
decree, thrown wide to their excursions, and it is not for us to
restrict their freedom. We need not fear getting too near the heart of
the mystery; there is no terminus in the unknown to which we can travel
by express; in a sense, we are always starting, and never get nearer to
our destination. But that is because it retreats before us. We do, in
truth, advance; and as we advance the mists clear, and we see glimpses
beyond of imperishable order, of impenetrable splendour. Our inquiries
need not then be abandoned in despair at the far-reaching character
they have spontaneously assumed.
From the earliest times there has been a tendency to regard varieties
of matter as derivative. They have been supposed to be procured by
supramundane agency, or by the operation of inherent law, from some
universal undifferentiated substance. We moderns call that substance
'protyle,'[51] and believe ourselves to be in experimental touch
with it. The implications of this view we shall consider in the next
chapter.
FOOTNOTES:
[Footnote 50: _Cf._ Jeans, _Astrophysical Journal_, vol. xxii., p. 93.]
[Footnote 51: A term signifying 'first matter,' constructed from
corresponding Greek words by Roger Bacon, and revived by Sir William
Crookes.]