Myths and Marvels of Astronomy
may float with the Nereids upon the deep, or mount upon wings as eagles,
or rise upon the pinions of the dove, that he may flee away and be at
rest,' with much more in the same fanciful vein. We now know that there
can be no cavities more than a few miles below the crust of a planet,
simply because, under the enormous pressures which would exist, the most
solid matter would be perfectly plastic. But while Whewell's general
objection to the theory that Jupiter or Saturn is in the same condition
as our earth thus acquires new force, the particular explanation which
he gave of the planet's small density is open to precisely the same
general objection. For he assumes that, because the planet's mean
density is little greater than that of water, the planet is probably a
world of water and ice with a cindery nucleus, or in fact just such a
world as would be formed if a sufficient quantity of water in the same
condition as the water of our seas were placed at Jupiter's greater
distance from the sun, around a nucleus of earthy or cindery matter
large enough to make the density of the entire planet thus formed equal
to that of Jupiter, or about one-third greater than the density of
water. In this argument there are in reality two assumptions, of
precisely the same nature as those which Whewell set himself to combat.
It is first assumed that some material existing on a large scale in our
earth, and nearly of the same density as Jupiter, must constitute the
chief bulk of that planet, and secondly that the temperature of
Jupiter's globe must be that which a globe of such material would have
if placed where Jupiter is. The possibility that Jupiter may be in an
entirely different stage of planetary life--or, in other words, that the
youth, middle life, and old age of that planet may belong to quite
different eras from the corresponding periods of our earth's life--is
entirely overlooked. Rather, indeed, it may be said that the extreme
probability of this, on any hypothesis respecting the origin of the
solar system, and its absolute certainty on the hypothesis of the
development of that system, are entirely overlooked.
A fair illustration of the erroneous nature of the arguments which have
been used, not only in advocating rival theories respecting the
plurality of worlds, but also in dealing with subordinate points, may be
presented as follows:
Imagine a wide extent of country covered with scattered trees of various
size, and with plants and shrubs, flowers and herbs, down to the
minutest known. Let us suppose a race of tiny creatures to subsist on
one of the fruits of a tree of moderate size, their existence as a race
depending entirely on the existence of the fruit on which they subsist,
while the existence of the individuals of their race lasts but for a few
minutes. Furthermore, let there be no regular fruit season either on
their tree or in their region of vegetable life, but fruits forming,
growing, and decaying all the time.
Let us next conceive these creatures to be possessed of a power of
reasoning respecting themselves, their fruit world, the tree on which it
hangs, and to some degree even respecting such other trees, plants,
flowers, and so forth, as the limited range of their vision might be
supposed to include. It would be a natural thought with them, when first
they began to exercise this power of reasoning, that their fruit home
was the most important object in existence, and themselves the chief and
noblest of living beings. It would also be very natural that they should
suppose the formation of their world to correspond with the beginning of
time, and the formation of their race to have followed the formation of
their world by but a few seconds. They would conclude that a Supreme
Being had fashioned their world and themselves by special creative acts,
and that what they saw outside their fruit world had been also specially
created, doubtless to subserve their wants.
Let us now imagine that gradually, by becoming more closely observant
than they had been, by combining together to make more complete
observations, and above all by preserving the records of observations
made by successive generations, these creatures began to obtain clearer
ideas respecting their world and the surrounding regions of space. They
would find evidence that the fruit on which they lived had not been
formed precisely as they knew it, but had undergone processes of
development. The distressing discovery would be made that this
development could not possibly have taken place in a few seconds, but
must have required many hours, nay, even several of those enormous
periods called by us days.
This, however, would only be the beginning of their troubles. Gradually
the more advanced thinkers and the closest observers would perceive that
not only had their world undergone processes of development, but that
its entire mass had been formed by such processes--that in fact it had
not been created at all, in the sense in which they had understood the
word, but had _grown_. This would be very dreadful to these creatures,
because they would not readily be able to dispossess their minds of the
notion that they were the most important beings in the universe, their
domain of space coextensive with the universe, the duration of their
world coextensive with time.
But passing over the difficulties thus arising, and the persecution and
abuse to which those would be subjected who maintained the dangerous
doctrine that their fruit home had been developed, not created, let us
consider how these creatures would regard the question of other worlds
than their own. At first they would naturally be unwilling to admit the
possibility that other worlds as important as their own could exist. But
if after a time they found reason to believe that their world was only
one of several belonging to a certain tree system, the idea would occur
to them, and would gradually come to be regarded as something more than
probable, that those other fruit worlds, like their own, might be the
abode of living creatures. And probably at first, while as yet the
development of their own world was little understood, they would
conceive the notion that all the fruits, large or small, upon their tree
system were in the same condition as their own, and either inhabited by
similar races or at least in the same full vigour of life-bearing
existence. But so soon as they recognised the law of development of
their own world, and the relation between such development and their own
requirements, they would form a different opinion, if they found that
only during certain stages of their world's existence life could exist
upon it. If, for instance, they perceived that their fruit world must
once have been so bitter and harsh in texture that no creatures in the
least degree like themselves could have lived upon it, and that it was
passing slowly but surely through processes by which it would become one
day dry and shrivelled and unable to support living creatures, they
would be apt, if their reasoning powers were fairly developed, to
inquire whether other fruits which they saw around them on their tree
system were either in the former or in the latter condition. If they
found reason to believe certain fruits were in one or other of these
stages, they would regard such fruits as not yet the abode of life or as
past the life-supporting era. It seems probable even that another idea
would suggest itself to some among their bolder thinkers. Recognising in
their own world in several instances what to their ideas resembled
absolute waste of material or of force, it might appear to them quite
possible that some, perhaps even a large proportion, of the fruits upon
their tree were not only not supporting life at the particular epoch of
observation, but never had supported life and never would--that, through
some cause or other, life would never appear upon such fruits even when
they were excellently fitted for the support of life. They might even
conceive that some among the fruits of their tree had failed or would
fail to come to the full perfection of fruit life.
Looking beyond their own tree--that is, the tree to which their own
fruit world belonged--they would perceive other trees, though their
visual powers might not enable them to know whether such trees bore
fruit, whether they were in other respects like their own, whether those
which seemed larger or smaller were really so, or owed their apparent
largeness to nearness, or their apparent smallness to great distance.
They would be apt perhaps to generalise a little too daringly respecting
these remote tree systems, concluding too confidently that a shrub or a
flower was a tree system like their own, or that a great tree, every
branch of which was far larger than their entire tree system, belonged
to the same order and bore similar fruit. They might mistake, also, in
forgetting the probable fact that as every fruit in their own tree
system had its own period of life, very brief compared with the entire
existence of the fruit, so every tree might have its own fruit-bearing
season. Thus, contemplating a tree which they supposed to be like their
own in its nature, they might say, 'Yonder is a tree system crowded with
fruits, each the abode of many myriads of creatures like ourselves:'
whereas in reality the tree might be utterly unlike their own, might not
yet have reached or might long since have passed the fruit-bearing
stage, might when in that stage bear fruit utterly unlike any they could
even imagine, and each such fruit during its brief life-bearing
condition might be inhabited by living beings utterly unlike any
creatures they could conceive.
Yet again, we can very well imagine that the inhabitants of our fruit
world, though they might daringly overleap the narrow limits of space
and time within which their actual life or the life of their race was
cast, though they might learn to recognise the development of their own
world and of others like it, even from the very blossom, would be
utterly unable to conceive the possibility that the tree itself to which
their world belonged had developed by slow processes of growth from a
time when it was less even than their own relatively minute home.
Still less would it seem credible to them, or even conceivable, that the
whole forest region to which they belonged, containing many orders of
trees differing altogether from their own tree system, besides plants
and shrubs, and flowers and herbs (forms of vegetation of whose use they
could form no just conception whatever), had itself grown; that once the
entire forest domain had been under vast masses of water--the substance
which occasionally visited their world in the form of small drops; that
such changes were but minute local phenomena of a world infinitely
higher in order than their own; that that world in turn was but one of
the least of the worlds forming a yet higher system; and so on _ad
infinitum_. Such ideas would seem to them not merely inconceivable, but
many degrees beyond the widest conceptions of space and time which they
could regard as admissible.
Our position differs only in degree, not in kind, from that of these
imagined creatures, and the reasoning which we perceive (though they
could not) to be just for such creatures is just for us also. It was
perfectly natural that before men recognised the evidences of
development in the structure of our earth they should regard the earth
and all things upon the earth and visible from the earth as formed by
special creative acts precisely as we see them now. But so soon as they
perceived that the earth is undergoing processes of development and has
undergone such processes in the past, it was reasonable, though at