Return to the peaks abandoned by the original nebula.
An idea of their number 319
Example of their dimensions. What was made out of them 320
What could be made from one of them 321
How it could be divided into comets and meteor swarms 322
An example given. How a comet may rotate on its axis.
And what might be explained thereby. Orbits and
periods of revolution 323
Not ejected from planets. Their true origin 324
Study of the velocities in orbit of comets, and
results thereof 326
How far comets may wander from the sun and return again 327
No reason why comets should wander from one sun to another.
Confirmatory of the description, in Chapter XV. of the
sun's domains 328
Of the eternal evolution and involution of matter.
The atmosphere and corona of the sun 329
Partial analogy between it and the earth's atmosphere 331
The density of it near the sun's surface cannot be normally
less than 28 atmospheres, but might be so partially
and accidentally 332
Probable causes of the enormous height of its atmosphere 332
The mass taken into account, but cannot be valued 334
Most probably no matter in the sun exceeds half the density
of water. The unknown line in the spectrum of the
corona belongs to the ether 335
NEW THEORIES IN ASTRONOMY.
INTRODUCTION.
That a little knowledge is a dangerous thing to the possessor, has
been pointed out often enough, probably with the idea of keeping him
quiet, but it is very certain that the warning has not always had the
desired effect; and in some respects it is perhaps much better that it
has not, for it is sometimes the case that a little knowledge exhibited
on an inappropriate occasion, or even wrongly applied, throws light
upon some subject that was previously not very well understood. It
sometimes happens that unconscious error leads to the discovery of what
is right. The fact is, all knowledge is at first little, so that if
the first possessor of it is kept quiet there is little chance of its
ever increasing. On the other hand, much knowledge seems to be quite
as ready to become dangerous on occasion, for it has sometimes led its
possessor to fall into errors that can be easily pointed out, even by
the possessor of little, if it is combined with ordinary intelligence.
The possessor of much knowledge is apt to forget, in his keen desire
to acquire more, that he has not examined with sufficient care all the
steps by which he has attained to what he has got, and that by placing
reliance on one false step he has erected for himself a structure that
cannot stand; or, what is worse perhaps, has prevented those who have
followed him in implicit dependence on his attainments and fame from
finding out the truth. If, then, both of these classes are liable to
fall into error, there appears to be no good reason why one belonging
to the first mentioned of them should absolutely refrain from making
his ideas known, especially as he may thus induce someone of the
second to re-examine the foundations on which he has built up his
knowledge.
These reflections are in greater or lesser degree applicable to all
knowledge and science of all kinds, even theological, in all their
individual branches, and can be very easily shown to be both reasonable
and true. And it may be added, or rather it is necessary to add, that
every one of all the branches of all of them has a very manifest
tendency towards despotism; to impose its sway and way of thinking upon
the whole world.
At various intervals during the present century speculation has been
indulged in, and more or less lively discussion has taken place about
the great benefit it would confer on universal humanity, were all the
weights and measures of the whole earth arranged on the same standard.
The universal standard proposed has been, of course, the metrical
system, which had been elaborated by French _savants_ who most probably
thought they had arrived at such a state of knowledge that they were
able to establish the foundations of all science of all kinds and
for all time, upon the most sure and most durable principles. These
periods of metrical fever, so to speak, seem to come on without any
apparent immediately exciting cause, and some people succumb to the
disease, others do not, just the same as in the cases of cholera,
influenza, plague, etc. Whether some species of inoculation for it may
be discovered, or whether it will be found that an unlimited attack is
really perfect health, will most probably be found out in the course of
time, although it may be some centuries hence. What is of interest to
understand at the present time is, what are the benefits to be derived
from the proposed universal standard of weights and measures, and how
they are to be attained.
The principal and most imposing reason for its adoption is that it
would be of immense service to scientific men all over the world,
who would thus be able to understand the discourses, writings,
discoveries, etc. of each other without the necessity of having to
enter into calculations of any kind in order to be able to comprehend
the arithmetical part of what they have listened to or read. Another
argument brought forward in favour is, that it would greatly facilitate
commercial transactions with foreign countries; and it has been lately
advanced that great loss is suffered by one country selling its goods,
manufactured according to its own measures, in countries where the
metrical system has been adopted. Yet another advantage held out is
the convenience it would be to travellers in money matters; but as
this argument cannot be admitted without taking into consideration
the necessity for one universal language all over the world, it has
practically no place in any discussion on the subject, until the evil
caused by the building of the Tower of Babel has been remedied.
Not long after one of the periodical attacks of metric fever we came
upon an essay written by J. J. Jeans on "England's Supremacy," and
published in New York by Harper and Brothers, in 1886, in which we
found the following:--
Numerical relation of occupations in England and Wales in 1881:
Professional 2·5 per cent.
Domestic 7·0 "
Agricultural 5·3 "
Commercial 3·7 "
Industrial 24·5 "
In all 43·0 "
This statement shows that 43 per cent. of the whole population are
occupied in some business or work of some kind, and leads us reasonably
to suppose that the remaining 57 per cent. consist of women, children,
and people who--to put it short--are non-producers; the whole of whom
can hardly be considered as much interested in the making of any
alterations in the weights and measures of their country, rather the
contrary, for they cannot expect to be much benefited by any change.
The professional class naturally comprehends Theology, Law, Medicine,
and Science generally, so that the 2·5 per cent. ascribed to it would
be seriously reduced, if the advantage derived from the desired change
were reckoned by the number really benefited by it. A similar reduction
would have to be made on the 3·7 per cent. stated to be occupied in
Commerce, as it is not to be supposed that the whole of the number
are engaged in foreign trade. Thus the number of people in these two
classes who might really reap some advantage from the change, may
be reduced by at least one half; and if we consider that one person
in ten of those occupied in the Agricultural and Industrial classes
is a scientist--we may pardon the Domestic class--a very liberal
allowance indeed, we arrive at the conclusion that 6 per cent. of the
whole population might find, some more, some less, interest in the
introduction into our country of the French metric system.
The above statement refers only to England and Wales, but if Scotland
and Ireland are added to them, the 6 per cent. proportion could not
be very greatly altered: perhaps it would be less favourable to the
change. Thus 94 per cent., or something like 37 millions, of the whole
population of the United Kingdom would be called upon to change their
whole system of weights and measures, in order that 6 per cent.,
or somewhere between 2 and 2-1/2 millions, should find some little
alleviation in a part of their labours; and surely 2 to 2-1/2 millions
of scientists and merchants engaged in foreign trade is a very liberal
allowance for the population of our country. If this does not show a
tendency towards despotism, it would be hard to tell what it does show.
Of course, it would not be fair to assume that the whole of the 6 per
cent. would desire to see the proposed change carried into effect. In
all likelihood, a very considerable portion of the number would be
disposed to count the cost of erecting such a structure before actually
laying its foundations, and would refrain from beginning the work on
considering by what means it was to be brought to a conclusion; even
without going so far as to find out that 94 per cent. of it at least
would have to be done by forced labour. They might even go the length
of speculating on how long it would take to coerce the 94 per cent.
into furnishing the forced labour, and on the hopelessness of the task.
On the other hand, they might think it more natural to lay hold of the
alternative of adopting a special system of weights and measures for
the use of Science and Foreign Commerce alone, and leave the 94 per
cent. to follow their own national and natural customs, which they
would be very likely to do whatever might be determined, if we may
judge by the progress made in France a century after the system was
thought to be established. Very little opposition could be made to
such a course, and if the best possible system were not adopted, the
scientists would be the only parties put to inconvenience. They could
improve and reform it, should they find it not to be perfect, without
the necessity of coercing the 94 per cent. into furnishing another
contingent of forced labour. But little is to be gained by saying any
more about it. Should the metrical system be adopted some day by Act
of Parliament, Science will have obtained what it has so long coveted,
will be quite satisfied, and will trouble itself very little about how
it affects the rest of the population. It will perhaps never even think
of how India will be brought to buy and sell through the medium of the
French Metrical System.
And now we have only one step to take on this subject. We may say
that the project of establishing one standard of weights and measures
for the whole world has a most unpleasant resemblance to the object
proposed by the builders of the Tower of Babel; the only thing that
can be said in its favour being that it points towards an endeavour to
do away with the bad results produced by that enterprise and to bring
matters back to the state the world was in before the foundations of
that celebrated edifice were laid.
The foregoing is only one instance of the many that could be cited
where science has schemed projects for universal progress without due
thought, and has come to the conclusion that they could be easily
carried out. There are as many examples of this jumping at conclusions
as would fill many books, which of course it is not our purpose to
do; but there is one that it is necessary to have brought forward for
examination, because of its having, through a most incomprehensible
want of thought, a tendency to establish Natural Religion on the very
bases upon which the Christian Religion is established.
The one referred to is that by which some of the most eminent
scientists of the present century, following up what was done in former
times, have been able by deep study and experiment, unfortunately
coupled with unaccountable blindness or preconceived erroneous ideas,
to formulate processes by which the whole universe may have elaborated
itself from protyle and protoplasm, or some such substances which,
without any foundation to build upon, they suppose to have existed
from all eternity. This advance in science has been called the Theory
of Evolution, and has been very generally considered to be new, or of
comparatively very recent conception; but it is only a piece of the
evidence of a very general propensity in those who come to acquire a
little more knowledge, to flatter themselves that they have power to
seize hold of the Unknown.
The theory may be _new_, but evolution most assuredly is not, as any
one may convince himself who will take the trouble to read the first
chapter of the Book of Genesis _and to think_. There he will find it
stated that the earth and all things in it and on it were created and
made in six days, or periods of time, showing him distinctly, if he
does not shut his eyes wilfully, that two operations were employed in
the process, one of creation and the other of making, which last can
mean nothing but _evolution_. It does not matter a straw whether the
latter operation was carried on personally by the Creator and Maker,
or under the power of laws ordained by Him for the purpose; it was
evolution all the same, and just the kind of evolution the scientists
above alluded to would have us believe to be new, not far from 3500
years after the account of the creation and making of the world was
written by Moses.
It will do no harm to take special notice of the work that was done
in each of the six periods, as it will help to fix attention on the
subject during examination and judgment; and may even tend to open the
eyes of any one who had made up his mind to keep them shut.
In the first period the heavens and the earth were created, but the
earth was without form and void, _inanis et vacuus_, according to _The
Vulgate_--(does that mean empty and hollow?)--and darkness was upon the
face of the deep; but light was _let_ shine upon the earth to alternate
with darkness, and between the two to establish day and night. It
is therefore evident that after the earth was created it had to be
reduced to something like its present form, a globe of some kind, and
to rotate on an axis, otherwise there could have been no alternations
of light and darkness, of day and night. Where did the light come from?
Some people seem to think that Moses should have included a treatise
on the creation and evolution of the universe, in his account of the
work done in the first period of creation. For all that can be truly
said to the contrary, he seems to have been quite as able to do so
as any scientist of the present day; but it is evident he thought it
best to limit himself to writing only of the earth, as being of most
interest to its inhabitants, and enough for them as a first lesson.
The literature of science, however, of the present day, will tell them
that long ages after the earth was _evolved_ into a globe, it must have
been in a molten, liquid state, surrounded by an atmosphere of vapours
of some of the chemical elements so dense that no light from without
could shine through it, and could only be penetrated by light after
the cooling of the earth had dispelled a sufficient portion of that
dense atmosphere. With this explanation, which they had at hand for the
looking for, they might have been so far satisfied, and have left Moses
to tell his story in his own way.
In passing, it may not be out of place to say that, after the cooling
of the earth had proceeded so far that the vapours of matter had
been condensed and precipitated on its surface, all boiling of water
whether in the seas or on its surface must soon have ceased, so that
no inconceivably enormous volumes of steam could be thrown upwards
to maintain an atmosphere impenetrable to light; and that when dense
volumes of steam ceased to be thrown up, the condensation of what was
already in the atmosphere would be so rapid, and its density so soon
reduced sufficiently to admit of the passage of light through it, that
one can almost fancy himself present on the occasion and appreciate the
sublimity of the language. "And God said, Let there be light, and there
was light"; more especially if he had ever stood by the side of the
cylinder of a large steam engine, and understood what he heard when the
steam rushed from it into the condenser, and noted how instantaneous it
seemed to be. Any one who has watched a pot of water boiling on the
fire and emitting clouds of steam, will have noticed how immediately
the boiling ceased whenever the pot was removed from the fire; but
he will also have noticed that the water still continued to emit a
considerable quantity of vapour, and will be able to understand how it
was that the cloudy atmosphere of the earth, at the time we are dealing
with, could allow light to pass through it but still keep the source of
light from being visible. He experiences daily how thin a cloud will
hide the sun from his sight. But there is more to be said about this
when the time comes for taking note of the actual appearance on the
scene of the sun, moon, and stars.
To obtain some rude idea of the time to be disposed of for evolution
during the first period, let it be supposed that the whole of the time
consumed in the creation and development of the earth was 300 million
years, as demanded by some geologists, the first period of the six
would naturally be somewhere about 50 millions of years, a period which
would allow, probably, very liberal time for evolution, but could never
have been consumed in creation, seeing that creation has always been
looked upon as an almost instantaneous act. And if anyone is still
capable of exacting that the period was a day of twenty-four hours, he
has to acknowledge that at least twenty-three of them were dedicated to
the work of evolution.
The second period was evidently one solely of evolution, as all that
was done during it was confined to _making_ the firmament which
divides the waters from the waters; an operation which could never be
confounded with creation, being probably brought about solely by the
cooling of the earth, which was the only means by which a separation
between the waters covering the earth, and those held in suspension
above it by the atmosphere, could be brought about, and must have been
purely the work of evolution.
The third period was begun by collecting the waters under the firmament
into one place and letting the dry land appear; which, it may be well
to note, gives it to be understood that the surface of the solid
part of the earth had come to be uneven either by the elevation or
depression, perhaps both, of some parts of it, and next the earth was
_let_ bring forth grass and trees, and in general vegetation of all
kinds. These cannot be considered otherwise than as operations of
evolution: there was no creation going on beyond what may have been
necessary to help evolution, and of that not a word is said. Here it is
well to notice that until the waters were gathered together into one
place and the dry land appeared there could be no alluvial deposits
made in the sea, and that till well on into this third period, that is
well on for 150 million years from the beginning, there could be no
geological strata deposited in it containing vegetable matter, for the
very good reason that although rains and rivers may have swept earthy
matter into the sea, the rivers could not carry along in their flow any
vegetable matter until it had time to grow.
Should evolutionists think they have discovered something new in
spontaneous generation, we refer them to the 11th verse of the chapter,
where they will see--"And God said, Let the earth bring forth grass,
the herb yielding seed, and the fruit-tree yielding fruit after his
kind, whose seed is in itself, upon the earth." The conclusion of this
passage asserts plainly that the seed was already in the earth, somehow
or other, ready to germinate and sprout when the necessary accompanying
conditions were prepared. The words are very few, and they can have no
other meaning.
In the first period "God made two great lights: the greater light to
rule the day and the lesser light to rule the night; he made the stars
also." This passage has been "a stumbling block and rock of offence"
to some people possessed of much knowledge and to some possessed of
little; the one party professing to disbelieve all because the sun was
_made_ four days after there was light, and the other party, supposing
that there might have been light proceeding from some other source
during the first four days. Both parties seem to have forgotten that
the earth was created without form and void, and that being so the same
would naturally be the case with the sun and the moon; all of them had
to be made into form after their creation. By what means? By evolution,
of course, or whatever else anyone chooses to call it; that will make
no difference.
As far as it can penetrate into the mysteries of creation, Physical
Astronomy has endeavoured to show how the solar system may have been
formed out of a mass of nebulous matter. Furthermore, as has already
been adduced in evidence, that at one time the earth must have been
a molten, liquid globe surrounded by vapours of metals, metalloids,
gases, and finally by water; and even goes the length of supposing
that the planets were evolved to something approaching their present
state, long before the sun attained its present form. Following up this
hypothesis, it is more than probable that the sun had not attained that
form when this fourth period began, and, although capable of emitting
light early in the first period, still required a vast amount of
evolution to reduce it to the brilliant globe now seen in the heavens.
Everybody knows that plants grow without sunshine, and it is generally
believed that the primary forests of the earth grew most rapidly in
a moist, stifling atmosphere, which neither admitted of animal life,
nor could be penetrated by sunshine. Thus Physical Astronomy cannot
say that the sun could not have been made into its present state until
near the end of this fourth period. It _may_ have been as bright as it
is now, though very probably not, as we shall see in due time; but it
could not _shine_ upon the earth, neither could the earth, nor anything
thereon, see it. It is not necessary to say anything about the moon, as
it only reflects sunlight, and the reflection could not reach the earth
if the light could not.
In the fifth period the waters were _let_ "bring forth the moving
creature that hath life, and fowl that may fly above the earth in the
open firmament of heaven." Here again spontaneous generation may have
been provided for beforehand, the same as in the case of vegetation.
Also it is said "God created great whales," and it is to be observed
that this is only the second time that creation has been mentioned in
the book, and would seem to teach that _making_, or evolution, was the
most active agent at work in the construction of the earth--and, we may
add, of the universe.
The sixth period was one almost exclusively of evolution, unless it
should be considered that spontaneous generation is a different, and
newly discovered process. In it God _made_ the beast of the earth,
cattle, and everything that creepeth upon the earth, after his kind.
Last of all: "God said, let us make man in our image, after our
likeness." Thus it appears that the only work of creation done in this
period was that of creating man, and even that _after_ some length of
time and work had been expended in _making_ or _evolution_, which may
have extended over a very considerable portion of the fifty millions of
years corresponding to it.
We have supposed the work of creation to have extended over three
hundred million years to satisfy some geologists, but our arguments
would not be affected in any way by the time being reduced to the limit
given by Lord Kelvin to the heat-giving power of the sun in the past,
which he has made out to be between fifteen and twenty million years.
That would only limit our periods of evolution to two and a half or
three million years each; each of them quite long enough to be totally
inconsistent with our ideas of creation, which conceive of this as an
instantaneous act. But although Lord Kelvin has in rather strong terms
placed this limit, he at the same time says that it could by no means
exceed four hundred million years, which is one-third more than we have
calculated upon. Neither can our arguments be affected in any serious
way by our dividing the periods into fifty million years each; these
may have varied much in length, but whatever was taken from one would
have to be added to the others.
Furthermore, we may be allowed to say that fifteen to twenty millions
of years of the sun's heat at the rate it is now being expended, can be
no reliable measure of the time required for the operations of geology,
for the reason that its heat must have been emitted in proportion to
the quantity it possessed at any time. When it was created without form
and void as no doubt it was, the same as the earth, it would have no
heat to emit, but that does not mean that it possessed no heat until
it was formed into the brilliant globe that we cannot now bear to turn
our eyes upon. Even when it became hot enough to show light sufficient
to penetrate the "darkness that was upon the face of the deep," it
may still have been an almost shapeless mass, and have continued more
or less so until it was formed into the body of the fourth period,
which may even then have been very different from what it is now. Thus
geology would have not far from one hundred and fifty million years
in which a very small fractional part of the sun's emission of heat
would suffice for its operations. But we shall have more to say on this
subject when the time comes.
It being, therefore, a matter beyond all question--to people possessed
of the faculty of thinking, and of candour to confess that they
cannot help seeing what has been set plainly before their sight and
understanding--that the opening chapter of the book of Genesis plainly
teaches that making--evolution--had a very large and active part to
perform in the creation of the universe and--much more within our
grasp--of the earth; we can come to the conclusion that the theory
of evolution, instead of being new and wonderful, comes to be almost
infinitely older than the everlasting hills, without losing any of its
power of inspiring inexpressible wonder.
Looking back over the examination into the first chapter of the book of
Genesis we have just concluded, we cannot conceive how it could ever
have entered into the thoughts of man, that the state of vegetable and
animal life on the earth, at the present day, must have been brought
about by continual and unceasing acts of creation, when creation
has been mentioned only on three occasions during the whole process
described in the chapter we have analysed, that is, 3 out of 31 verses;
and while the other processes which we have brought forward--making and
spontaneous generation--have never been alluded to, perhaps not even
thought of.
We have no desire, neither are we qualified, to follow up this subject
any further, but we have still one or two things to bring into
remembrance.
One of the most illustrious of the founders of the Theory of Evolution
has based his dissertations on the Descent of Man, on the Variation
of Animals and Plants under Domestication, and on their _wonderful
plasticity under the care of man_. Here there is an explicit
acknowledgment of the necessity for the direction of an intelligent
guiding power to produce such variations; these never having any useful
or progressive results except under such care. If, then, there is a
necessity of such directing and guiding power in the case of variations
of such inferior importance, the superintendence of some similar power
must have assuredly been much more necessary for the creation and
evolution of matter, of life, and of man himself. This is what, one
would think, common sense and reason would point, and what the Theory
of Evolution seems to think--evidently without studying the subject
far enough; but all that it has been able to do has been to substitute
Nature for the Creator to whom Moses has ascribed not only _Creation_
but the _Making--Evolution_--of the universe.
This naturally leads us to speculate on what Evolutionists consider
Nature to be, and as none of them--nor anyone else--as far as we know,
has ever thought it necessary to define Nature, we have to endeavour
to draw from their writings what, in some measure and some way, they
would like us to believe it to be. We find, then, that the base of
their operations seems to be Natural Selection, which can hardly be
interpreted in any other way than by calling it the Selection of
Nature. Thus, then, they apparently want us to look upon Nature as
the _First Cause_. But, if Nature can select, it must be a being, an
entity, a something, that can distinguish one particle of matter from
another, and be able to choose such pieces of it, be they protyle or
protoplasm, and to make them unite, so as to form some special body,
organic or inorganic. It is plain, also, that Selection can only be
performed by such a being, or something, such as just so far described,
that can distinguish, choose, and arrange the particles of matter
destined to form the very smallest body or the universe. Thus we see
that in whatever way the basis of the Theory of Evolution is looked
upon--_even for its own evolution_--there is required a being of some
kind that has knowledge and power to evolve or make all things that
are "in heaven above, or in the earth beneath, or in the waters under
the earth." So we see that, if the theory of evolution dethrones the
Creator and Evolver of the first chapter of Genesis, it has to enthrone
another god which it calls Nature; and has to get rid of that god, and
any number of others, before it can be what it pretends to be.
We are all very voluble in talking of Nature, and enthusiastic in
admiring its beauties, wonders, and wisdom, but it seldom occurs to
us that we are really doing so without thinking of whence come the
beauty, wonders, and wisdom. We must, therefore, not be too hard on
evolutionists, as they have only done what we all do every day of
our lives; but if the theory of evolution is to be looked upon as a
branch of science, we would recommend its students to open their eyes
and think of it as a process which has been in existence from the
beginning of things at least, and not as one of their invention or
discovery. They may be able some day, through more accurate study and
more convincing argumentation than they generally use, to lay claim to
having discovered, as far as it is possible for man to do, the _modus
operandi_ of evolution, but that is all, and we would also warn some
of them to think that, when we see them in their highest flights of
science, genius, and self-sufficiency, we can
"Conceive the bard the hero of the story."
We have read a good deal of what has been called the War of Science,
without having been able to see that there ever was any cause for such
a war, with the exception of ignorance.
If Theology had been able, or rather had taken the trouble, to study
thoroughly the first chapter of Genesis, and thus to comprehend that,
if the earth was created without form and void, a great deal of
work had to be done, after creation, in forming it into its present
condition, there was no call upon it to find fault with Copernicus or
persecute Galileus, because they said the earth revolved round the
sun; more especially as they do not appear to have ever said anything
against religion or revelation. Neither was there any necessity for
opposing the so-called new science of evolution, because it (Theology)
ought to have seen that the work expended in reducing the earth into
form could hardly be conceived of otherwise than as a process of
evolution; and would thus have been in a position to tell the authors
of the _new_ science that they had only discovered what had existed
before the beginning of time.
On the other hand, there was no occasion for Science to take up the
war. If it, in its turn, had taken the trouble to study and understand
the first chapter of Genesis, it could have shown Theology that _it_
did not comprehend, and could not give a true account of what religion
and revelation are; whereas it (Science) seems to have had a strong
tendency to demonstrate that religion and revelation are altogether
false, and that the great work it has to perform is to dethrone
Theology, and set itself up it in its stead.
It is not worth while even to think of who or which was the aggressor,
seeing that the war originated from ignorance caused by want of thought
and study on both sides. All that has to be said on the subject reduces
itself to the fact that both Religion and Science have been coming,
and are at present going, through the process of evolution. Can anyone
say that Science has been truly scientific, without ever incurring in
error, from the beginning of history up to the present day? Will any
one venture to maintain that there has been no evolution, no progress,
no softening of the spirit of Religion, from the institution of
Christianity up to the end of the nineteenth century? If such there be,
let the one look back to the time of Aristotle, and the other to the
establishment of the Church under Constantine.
There has been for long an opinion, which goes on increasing in
strength, that Science will ultimately reform Theology and put Religion
in its right place; but if such is to be the case, Science has to
begin by reforming itself and putting an end to error it has been, in
many cases, teaching for generations; and by ceasing to formulate new
theories, or bases of progress, which can be in many cases exploded
by suppressing some of the error just alluded to. Little advance is
made in science by forming hypotheses and theories, however brilliant
they may appear, unless they are carefully studied and thought out to
the very uttermost; because, if published abroad on the authority of
some celebrated or even well-known name, they have a tendency to stop
further investigation, and prevent students from exercising their own
judgment and perhaps discovering what they might possibly find out
were they to study them to the very end for their own satisfaction.
This is in some measure the case even with respect to the solar
system. We believe it can be shown that a more complete knowledge and
comprehension of it, and even of the universe, has been kept back by
the unquestioning acceptation by successive astronomers of the ideas
and conceptions of their predecessors.
We have to acknowledge, at the same time, that Astronomy could not
start into perfection at once, any more than any other science, and it
is not to be wondered at that in times past ideas relating to it should
have been formed without being properly thought out; even ideas that
could not be properly thought out to the end for want of the requisite
knowledge. But it is much to be regretted that such ideas should
continue to be published at the present day as trustworthy instruction
for readers who may look upon it as strictly correct. Among those who
read text-books even on Astronomy, there must be a very considerable
number who are rather surprised when they see statements made which do
not agree with what they were taught at school, or with what they have
practised in other sciences in their own professions or trades. It may
be said that any person of ordinary intelligence will easily be able to
correct such errors, but the evil does not stop here. If he can really
correct them he will most probably find as well, that his instructors
have been led into more serious errors, perhaps in more important
matters, founded on the ideas which they had not fully studied out
before giving them a place in their books. He may also find sometimes,
in his reading, such ideas brought forward to substantiate some theory,
just as far as they are required and then dropped, while a step or two
further forward in the examination of these same ideas, would have
exploded the theory altogether; because, although founded to a certain
extent on one law of nature, they are in contradiction with what is
laid down in some other law.
The above will be looked upon as an unwarrantably bold assertion; but a
careful study of, or attention to, what is taught in the most advanced
works on the solar system, even in science generally, will show it to
be perfectly true. It is not only true, but the consequences of its
being true have been much more serious than will be readily believed.
In our own endeavours to understand what we had been reading, we have
seen that some of the notions presented to us were only half formed,
and that they have led to theories being founded which could never
have been entertained at all had they been thoroughly studied out.
More than that, they have prevented the truth from being arrived at in
the fundamental conceptions of the construction of the earth, and, as
a natural consequence, of the whole solar system, perhaps even of the
whole universe.
There are probably many, even a great many, people who have arrived
at the same conclusions as we have, but as far as it has been in our
power to search into the matter, we have met with no attempt from any
quarter to put an end to this defect in the literature of science;
perhaps because the work has the appearance of being too great to be
readily undertaken, and also because it may be thought that there is
little to be gained by it--as all is sure to be set right through time.
But, as we believe that it will be beneficial immediately, in the case
of the earth and solar system at least, we shall first attempt to show
what are some of the defects alluded to, and then what knowledge may be
acquired through their removal.
CHAPTER I.
PAGE
18 The bases of modern astronomy. Their late formation
19 Instruments and measures used by ancient astronomers
20 Weights and measures sought out by modern astronomers
20 Means employed to discover the density of the earth.
Measuring by means of plummets not sufficiently exact
21 Measurements with torsion and chemical balances more accurate
22 Sir George B. Airy's theory,
and experiments at the Harton colliery
23 Results of experiments not reliable.
Theory contrary to the Law of Attraction
24 Proof by arithmetical calculation of its error
26 Difficulties in comparing beats of pendulums at top
and bottom of a mine
27 The theory upheld by text-books without proper examination
28 Of a particle of matter within the shell of a hollow sphere.
Not exempt from the law of Attraction
29 A particle so situated confronted with the law of the
inverse square ofdistance from an attracting body.
Remarks thereon
31 It is not true that the attraction of a spherical shell
is "zero" for a particle of matter within it
Before astronomers could begin to determine the relative distances
from each other, and the relative dimensions and masses of the
various members of the solar system, they had to establish scales of
measurements appropriate to their undertaking. This entailed upon
them, of course, the necessity of determining the form, the different
circumferences and diameters, and the weight of the whole earth, as any
other scales derived from the only available source, the earth, would
have been too small to give even an approximate value of the measures
and masses to be sought for.
History tells us that at least one attempt had been made, over two
thousand years ago, to find the circumference and necessarily the
diameter of the earth, but it says nothing of any to ascertain its
weight. There may have been many to determine both diameter and mass,
but we know nothing of them; and when we think seriously about this,
we cannot help feeling somewhat surprised that no attempt had been
made to find out the density and mass till more than a century after
Sir Isaac Newton's discovery of the law of Attraction, or Gravitation,
as it is more usually called. But perhaps this is an idea that could
only occur to one who has been _spoilt_ by witnessing, in great
measure, the immense strides in advance that have been made during the
nineteenth century in science of all kinds, and does not duly take
into account the immense labour, and the incessant meeting with almost
insurmountable difficulties, that astronomers have had to encounter
and overcome between the birth of modern astronomy and the end of the
eighteenth century. Indeed, the difficulties can hardly be looked upon
as altogether overcome even yet, as efforts are still being made to
find out the exact distance of the sun, and it is not impossible that
some small difference may be found, plus or minus, in the density at
present adopted for the earth of 5·66 times the weight of water.
The geometer who, more than two thousand years ago, set himself the
task of measuring the circumference of the earth, is supposed to have
made use of very much the same kind of implements as those employed
by modern astronomers. He must have had a very fair instrument for
measuring angles, and have known very well how to use it, seeing he
was able to determine a value for the obliquity of the ecliptic which
agrees so well with that established by modern science, its variations
being, for what we know, taken into account; and for length or distance
he would doubtless have some implement analogous to the metre, chain,
foot-rule, or something called by other name that would, in those days,
present facilities for selling a yard of calico. His operations would
probably be as plain and simple as those applied to the measuring of a
village green--for we are not told that he had any idea of there being
any difference between the length of a degree of the meridian at the
equator and one nearer either of the poles--and involved no hypotheses
or theories, any more than modern operations have done.
When the time came for making efforts to ascertain the density of the
earth, science seems to have employed the very simplest means it had
at its disposal for attaining its object, and to have gone on refining
its implements and operations in conformity with the lessons it went
on learning while pursuing its self-imposed task. Every one who, even
for recreation, has read a fair amount of the multitude of works and
writings that have been published on Popular Astronomy--not to speak of
text-books--knows that the first attempts were made by measuring the
attraction of steep, or precipitous, mountains for plummets suspended
in appropriate positions in their neighbourhood; then--evidently from
knowledge acquired during these operations--by the attraction for each
other of large and small leaden balls suspended on frames and torsion
balances, which go under the name of the Cavendish Experiment; and
afterwards by a refinement on this in using the Chemical Balance,
where only one large and one small ball of metal are required. All
these operations and their results are to be found described in works
of various kinds, and are generally reduced to something like the
following tubular form, which we reproduce in order to make more
intelligible what we have just said, and that we may make a few remarks
upon them.
There is no hypothesis, no theory, connected with any of the
operations, unless it was the supposition that a plummet--which was
naturally believed to point to the centre of the earth--should be
pulled to one side by the attraction for it of a mountain in its
neighbourhood, and that was found to be a fact.
METHODS EMPLOYED FOR FINDING THE DENSITY OF THE EARTH,
AND THEIR RESULTS.
(1) _Deviation of Plummet by the Attraction of Mountains_:--
Experiments made. By whom, and Date. Mean Density found.
At Schiehallien Maskelyne 1772 4·713
At Arthur's Seat Sir H. James 1855 5·316
(2) _Torsion Balance Experiments_:--
Cavendish 1798 5·448
At Freyberg, Saxony Reich 1837 5·438
At Manchester Francis Baily 1838-1842 5·675
(3) _Chemical Balance Experiments_:--
J. H. Pointing 1878 5·690
In the case of the plummet deviating from its absolutely straight
direction towards the centre of the earth, caused by their attraction,
not only the mountains themselves had to be measured and virtually
weighed as far as they were measurable, but the weight of the wedge or
pyramid between that measurable point, in each case, and the centre
of the earth had to be estimated in some way; then the centre of
gravity of the whole of this mass had to be ascertained, as well as
the respective distances from the centre of the earth of this centre
of gravity and that of the plummet, and only after all this and a deep
study of the mutual attractions of this mass and the plummet could
an estimate be formed of the mass of the earth. It will thus be seen
that such measurements and estimates could never be looked upon as
very exact and reliable; and nevertheless they have come very near the
density of 5·66 finally adopted for the earth.
In the case of the Torsion Balance experiments a very considerable
advance was made in consequence, most undoubtedly, of the knowledge
acquired from what had been done by Maskelyne. When it was found that
the attraction of Schiehallien for the plummets was such a measurable
quantity, Cavendish evidently saw that the attraction of manageable
leaden balls for each other would be measurable also, and that as no
calculations of any kind whatever were necessary to find the masses
of the balls, the mutual attraction of large and small balls would
furnish a more exact means of measuring the density of the earth, than
the roundabout way of having to calculate the weight of a mountain as
a beginning; and with the requisite ingenuity, invention, and labour,
he found the means of applying the torsion balance, to make the
experiments.
After these experiments were revised by Reich and Baily--and the
density of 5·66 adopted, we believe--still another set were undertaken
by J. H. Pointing, with the Chemical Balance, in which only two metal
balls, one large and one small were required, which gave a density of
5·690 as shown opposite, and from its extreme simplicity may perhaps
have been the most exact of all.
We have said, we think with truth, that there is no hypothesis or
theory involved in any of these experiments, but only the simplest
form of--we might almost say--arithmetical calculation. But there is
a theory built up on hypothesis which has no foundation whatever, and
about which most people, who take the trouble to study it out to the
very end, will come to the conclusion that "the less said the better."
This, at all events, is our opinion, and we would not have taken any
notice whatever of it had it not been that up to the present day, it
is published in many works on Popular Astronomy, and even in some
text-books, and is looked upon in them, apparently, as an example of
the transcendent height to which human science can reach.
We allude, of course, to the theory that the deeper we go down into the
earth--at least to an undefined and undefinable depth--the greater is
its attraction for the bob of a pendulum at that depth, and the greater
the number of vibrations the pendulum is caused to make in a given
time. The explanation of the theory is, that were the earth homogeneous
throughout its whole volume, the pendulum ought to make the fewer
vibrations, the deeper down in the earth it is placed; but as the earth
is not homogeneous, it actually makes a greater number of vibrations in
a given time, because the attractive force of the earth increases--up
to the undefined and undefinable depth--on account of the denser matter
beneath the pendulum bob more than overbalancing the loss of attraction
from the lighter matter left above it. The author of the theory was the
late Astronomer Royal, Sir George B. Airy, who from it endeavoured to
calculate the mean density of the earth, and with that view made two
experiments which are thus described by Professor C. Piazzi Smythe in
his work on the Great Pyramid:--
"Another species of experiment... was tried in 1826 by Mr. (now Sir)
George B. Airy, Astronomer Royal, Dr. Whewell, and the Rev. Richard
Sheepshanks, by means of pendulum observations at the top and bottom
of a deep mine in Cornwall; but the proceedings at that time failed.
Subsequently, in 1855, the case was taken up again by Sir George B.
Airy and his Greenwich assistants, in a mine near Newcastle. They were
reinforced by the new invention of sympathetic electric control between
clocks at the top and bottom of a mine, and had much better, though
still unexpectedly large results--the mean density of the earth coming
out, for them, 6·565."
From other sources we have also found that the pit, or mine, was at the
Harton Colliery and 1260 feet deep, that the pendulum at the bottom of
it gained 2-1/4 seconds on the similar one at the top, in 24 hours; and
that the surrounding country had to be extensively surveyed, the strata
had to be studied, and their specific gravities ascertained.
A little unbiassed thought bestowed on this theory will at once show
that it begins by violating the law of attraction discovered by Newton,
when he showed _that the mutually attractive forces of several bodies
are the same as if they were resident in the centres of gravity of
the bodies_. In the case in point this means, that the attraction of
the earth for the bob of the pendulum at the top of the mine was the
same as if all its force was collected at its (the earth's) centre.
In that position the force of the earth's attraction comprehended,
most undeniably, the whole of its attractive power, including whatever
might be imagined to be derived from the non-homogeneity of the earth,
due to its density increasing towards the centre; and we are called
upon to believe that when, virtually, the same pendulum was removed to
the bottom of the mine, and a segment 1260 feet thick, at the centre
as good as cut off from the earth and--as far as the pendulum was
concerned--hung up on a peg in a laboratory, the diminished quantity
of its matter had a greater attractive force, a very little beyond the
centre--non-homogeneity again included--than the whole when the sphere
was intact. This we cannot do, because all that we can see in the
placing of the pendulum at the bottom of the mine, is that the position
of the bob has divided the earth into two sections, one of which has a
tendency to pull it up towards the surface, and the other to pull it
down towards its centre of gravity; and because the mass of the smaller
segment is so insignificant that its entire removal to the laboratory
peg, not only could not produce the reverse action, on which the theory
is based, but could not be measured by any stretch of human invention
or ingenuity; it is far beyond the reach of mathematics and human
comprehension of quantity.
The difficulty of belief is increased when we reflect that, were
the pendulum taken down towards the centre of the earth, the number
of its vibrations in a given time ought gradually to decrease as it
approached the centre, and would cease altogether when that point was
reached. And we feel confident that no mathematician could calculate
where the theoretical acceleration of the vibrations would cease, and
the inevitable retardation commence; where the theory would come to
an end and the law of attraction begin to assert its rights, simply
because he does not know how the non-homogeneity is distributed in the
earth. No man can tell, even yet, how the mean density of 5·66 is made
up throughout the earth, and without that any theory founded on its
non-homogeneity is out of place.
But to follow up our assertion of non-commensurability. Taking the
diameter of the earth at 8000 miles, and its mean specific gravity at
5·66, its mass would be represented by 1,517,391,000,000 cubic miles
of water. On the other hand, supposing the earth to be a true sphere,
the volume of a segment of it cut off from one side, at one quarter
of a mile deep--not 1260, but 1320 feet--would be 785·35 cubic miles
in volume, and if we suppose its specific gravity to be 2·5--greater
most probably than the average of all the strata in the neighbourhood
of the Harton Colliery--its mass would be represented by 1963·38 cubic
miles of water. Then, if we divide the mass of the section below the
pendulum, that is, 1,517,391,000,000 minus the mass of the one above
it, 1963·38, viz. 1,517,390,998,036·62 by the mass of 1963·38 just
mentioned, we find that the proportion they bear to each other is as 1
to 772,846,315. This being so, we are asked to believe that by removing
1/772,846,315th part of the mass of the earth from one side of it,
its force of attraction at the centre will not only not be decreased,
but will be so increased that it will cause a pendulum, suspended at
the centre of the flat left by the removal of the segment, to vibrate
86,402·25 times in twenty-four hours instead of 86,400 times as it did
when suspended at the surface before the segment was removed; that is,
that the vibrations will be increased by 1/38,400th part. Again we
cannot do so. Had we been asked to believe that the removal of so small
a fraction as 1/772,846,315th had decreased the earth's attraction at
its centre, so much as to produce a diminution of 1/38,400th part in
the number of vibrations of the pendulum, we could not have done so;
how much less then can we believe that the central attractive force had
increased so much as to produce an augmentation of the vibrations in
the same proportions? But more in this strain presently.
We have no doubt whatever that Sir George B. Airy and his assistants
satisfied themselves that the pendulum at the bottom of the mine gained
2-1/4 seconds in twenty-four hours over the one at the top, but they
may have been deceived by their over-enthusiastic adoption of what
seemed to be a very grandly scientific theory, or by some unperceived
changes in the temperature in the pendulums, caused by varying
ventilation in the mine or the varying weather outside of it, or by the
insidious manifestations of the "sympathetic electric control between
clocks at the top and bottom of a mine," called in to assist at the
experiments. An error of 1/38,400th part of the time the sympathetic
electricity would take to travel from the top to the bottom of the
shaft would be sufficient to make the experiments of no value whatever;
not to speak of the small errors that may have been made in surveying
the surrounding country, calculating the specific gravities of the
strata--for we are told that all this had to be done-and applying the
elements thus obtained to the solution of the problem they had in hand.
We have read of the difficulties met with by Mr. Francis Baily when he
began to revise the Cavendish Experiment--some twelve or fifteen years
before the final Harton Colliery experiments were made, and suppose it
possible that they met with similar difficulties without being aware
of it. And 1/38,400th part is such a very small fractional difference
in the vibrations in twenty-four hours, of the pendulums of the two
separate clocks, that--taking into consideration the circumstances
under which it was found--it would hardly be looked upon as reliable
at the present day, when the clocks of astronomical observatories are
placed in the deepest cellars or even caves available, so as to free
them as much as possible from variations of temperature.
Having referred to the difficulties met with by Mr. Baily, we believe
it worth while to transcribe Professor C. Piazzi Smythe's account of
them, given in his work already referred to at page 22; because it not
only has a very direct bearing on what we have been saying of changes
of temperature, but is exceedingly interesting, and probably very
rarely to be met with in other works. It is as follows:--
"Nearly forty years after Cavendish's great work, his experiment was
repeated by Professor Reich of Freyberg, in Saxony, with a result of
5·44; and then came the grander repetition of the late Mr. Francis
Baily, representing therein the Royal Astronomical Society, and, in
fact, the British Government and the British Nation.
"With exquisite care did that well-versed and methodical observer
proceed to his task, and yet his observations did not prosper.
"Week after week, and month after month, unceasing measures were
recorded; but only to show that some disturbing element was at work,
overpowering the attraction of the larger on the smaller balls.
"What could it be?
"Professor Reich was applied to, and requested to state how he had
continued to get the much greater degree of accordance with each other,
that his published observations showed.
"'Ah!' he explained, 'he had to reject all his earlier observations
until he had guarded against variations of _temperature_ by putting the
whole apparatus into a cellar, and only looking at it with a telescope
through a small hole in the door.'
"Then it was remembered that a very similar plan had been adopted
by Cavendish, who had furthermore left this note behind him for his
successor's attention--'that even still or after all the precautions
which he did take, minute variations and small changes of _temperature_
between the large and small balls were the chief obstacles to full
accuracy.'
"Mr. Baily therefore adopted yet further, and very peculiar, means to
prevent sudden changes of temperature in his observing room, and then
only did the anomalies vanish and the real observations begin.
"The full history of them, and all the particulars of every numerical
entry, and the whole of the steps of calculation, are to be found in
the Memoirs of the Royal Astronomical Society, and constitute one of
the most interesting volumes (the Fourteenth) of that important series;
and its final result for the earth's mean density was announced as
5·675, probable error ± 0·0038."
After reading this story of Baily's experiments with care, one cannot
help feeling something stronger than want of confidence in those made
at the Harton Colliery, especially after what has been shown of the
smallness of the fraction of the earth that was dealt with, and due
consideration is given to the insignificant difference of effect that
the non-homogeneity of the earth could produce on the remainder after
the supposed removal of such a small fraction; and here we might let
the theory drop. Perhaps it may be thought that now there is nothing
to be gained by spending time and work in showing it to be more truly
erroneous than we have yet made it out to be; but if there is error,
it cannot be too clearly exposed, and the sooner it is put an end to,
the better; more especially as it has been accepted as true by some
authors of text-books, and by some competent astronomers who, in trying
to explain the anomaly of the increase instead of decrease in the force
of attraction at the bottom of a mine compared with the top, have used
arguments which are not consistent with the law of gravitation, or
rather attraction.
Messrs. Newcomb and Holden in their work, entitled "Astronomy for High
Schools and Colleges," sixth edition, 1889, apparently accept the
theory, and proceed to explain and support it by showing what would be
the action of a hollow spherical shell of any substance on a particle
of it, say the bob of a pendulum, placed on the outside and also on the
inside of the shell; and give us two theorems which are supposed to
comprehend both cases. These are:--
(1) "If the particle be outside of the shell, it will be attracted as
if the whole mass of the shell were concentrated at its centre."
(2) "If it be inside the shell, the opposite attractions in every
direction will neutralise each other, no matter whereabouts in the
interior the particles may be, and the resultant attraction of the
shell will therefore be zero."
To the first theorem no objection can be made: The particle on the
outside of the shell will undoubtedly be attracted by every particle in
the shell, with the same force as if the attractive power of all the
particles composing it were concentrated in the centre. Not so with
the second theorem: for it can be objected that it altogether ignores
the Law of Attraction laid down by Sir Isaac Newton, where it asserts
that the resultant attraction of the shell for the particle will be
zero, when it is placed anywhere on the inside. In fact the theorem
supposes a case impossible for the Harton Colliery experiments, in
order to demonstrate their accuracy; for it makes use of the bob of
the pendulum--a particle of matter--as if it were transferable to any
part of the interior of the earth instead of being confined within
the bounds of its swing. That the attraction of the shell--1260 feet
thick all round the earth--on the pendulum bob inside of it continues
in all its force, and is only divided into two opposing parts, is made
plain by Fig. 1. Supposing O to represent the bob of the pendulum at
the bottom of the mine, and the space between the two circles the
shell of the earth. Then the line B C will show where the attraction
of the shell for the bob is divided into two parts acting in opposite
directions. Supposing these two parts to be separated from each other,
only far enough to admit the bob--a particle to all intents and
purposes--between them; the part B A C will attract the bob as if its
whole attractive force were collected at its centre of gravity, and
the part B D C as if the whole of its attractive force were collected,
not at the centre B of the shell, but at its centre of gravity, a
very little distance from B in the direction towards D. This is an
incontrovertible fact, because it is in strict accordance with Newton's
Law of Attraction, which is: _Every particle of matter in the universe
attracts every other particle with a force directly as their masses,
and inversely as the square of the distance which separates them._
[Illustration: FIG. 1.]
If we now suppose the interior of the shell to be filled up solid,
that will make no difference, because the mass of the part B D C will
only be increased vastly thereby, while the mass of A B C will remain
the same; the two parts only increasing their proportion to each
other, and thus coming to be for the earth--in the Harton Colliery
experiments--what we represented them to be at page 24; and we can now
proceed to find the attractive force of each of the two masses for the
bob of the pendulum which is as the inverse square of their distances
from it. These distances may be taken, without any very great stretch
of conscience, as one-tenth of a mile and 3999·75 miles; because the
centre of gravity of the segment A B C will be about that distance from
O, and that of B D C cannot be adequately represented by a greater
sum than 3999·75, always supposing the diameter of the earth to be
8000 miles. Thus the squares of these two distances will be 0·01 and
15,898,000 miles respectively, and the relative force of attraction
for the pendulum of the two segments A B C and B D C will be as 1 ×
0·01 and 772,846,315, and 772,846,315 × 15,898,000; that is as 1 is
to 1,228,671,000,000,000,000. Here then we get confirmed the unbelief
in the theory we expressed at pages 23 and 24. Surely no one will be
bold enough to assert that by decreasing the total attractive force
of the earth by a little less than a 1-1/4 trillionth part cut off
from one side of it, the want of homogeneity in what remains will not
only not decrease its attractive force at the centre, but increase it
so as to make a pendulum be lessened by 1/38,400th part of its time
in beating one second. This fraction of time is quite small enough to
inspire doubt of any theory founded upon it; and if there ever is a
quantity in mathematics that can be called negligible, the fraction of
attractive force found above ought to be included in the same category.
We may therefore assert that no human measurements could find a true
difference between the beats of a seconds pendulum at the top and
bottom of the pit at the Harton Colliery. If all the people who have
puzzled themselves with this theory had spent an hour or two in making
the above calculations before they began them, there would have been
no experiments made, and the theory would have died almost ere it was
born. Those who believed in it may have looked upon a particle as a
negligible quantity, but as the whole earth is made up of particles a
little thought would have put an end to such a notion. What puzzles
us is how such a theory could be formed by people who knew nothing
whatever of the nature of the interior of the earth at a depth of even
one mile, and how they could speculate on its want of homogeneity
without knowing anything of how the density of 5·66 is made up in it?
To suppose that the earth is made up of strata of different densities,
and that each is in some degree elliptical--the ellipticity of one
stratum being different from another, as the French mathematician
Clairaut did--is all very allowable; but to build up any theory on any
such suppositions is to build upon shifting sands without examining the
foundations. For anything that is known up to the present time, the
density of the earth may go on increasing gradually from the surface to
the centre, or it may attain nearly its greatest density at a few miles
from the surface, and continue homogeneous or nearly so from there to
the centre.
To go further now: it is not true that the attraction of a hollow
shell of a sphere for any particle within it, is the same "no matter
whereabouts in the interior the particle may be." The only place where
the attraction will be the same is when the particle is at the centre.
In that position a particle would be in a state of very unstable
equilibrium, and a little greater thickness of the shell on one side
than the others, would pull it a little, perhaps a great, distance from
the centre towards that side; and if we extend our ideas to a plurality
of particles within the shell of a sphere, we are led to speculate on
how they would be distributed, and to see the possibility of there not
being any at all at the centre. This is a point which has never been
mooted, as far as we have been able to learn, and we shall have to
return to it when the proper time comes.
It is difficult to understand how any man could conceive the notion
that a shell of a sphere, such as that shown at Fig. 1, could have no
attraction for each separate one of all the particles which make up the
mass of the whole solid sphere within it; for that is the truth of the
matter if properly looked into, when it is asserted, as has been done
by Messrs. Newcomb and Holden, that "the resultant attraction of the
shell will therefore be zero." If such a notion could be carried out in
a supposed formation of the earth, an infinity of particles would carry
off the whole of the interior, and leave the earth as only a shell of
1260 feet thick, as per the Hartley Colliery experiment; only we are
told, or left to understand, that that process could not go on for
ever, but would have to come to an end somehow and somewhere; and then
we are left to speculate on how the unattracted particles could come
back to take part in the composition of the earth. Left to ourselves
we can only liken the process to that followed by a man who peels off
the outer layer of an onion, eats the interior part, and when he is
satisfied throws down the outer layer and thinks no more of it; not
even that he might be asked what had become of the interior part.
Curiously enough, there is a way of explaining how, or rather why, the
notion was formed--not unlike the one just given--to be found in the
third of Sir George B. Airy's lectures on Popular Astronomy, delivered
at Ipswich several years before the final experiments were made at
the Harton Colliery. In that lecture, while describing how the Greek
Astronomers accounted for the motions of the sun and planets round the
stationary earth, he says, "It does appear strange that any reasonable
man could entertain such a theory as this. It is, however, certain that
they did entertain such a notion; and there is one thing which seems to
me to give something of a clue to it. In speaking to-day and yesterday
of the faults of education, I said that we take things for granted
without evidence; mankind in general adopts things instilled into them
in early youth as truths, without sufficient examination; and I now
add that philosophers are much influenced by the common belief of the
common people."
We can agree with Sir George B. Airy in his ideas about education, and
now conclude by saying that he has given us a very clear and notable
example of a theory being accepted very generally, without being
thoroughly examined to the very end, and of how easy it is for such
theories to be handed down to future generations for their admiration.
CHAPTER II.
PAGE
33 The moon cannot have even an imaginary rotation on its axis, but
is generally believed to have. Quotations to prove this.
35 Proofs that there can be no rotation. The most confused assertion
that there is rotation shown to be without foundations.
37 A gin horse does not rotate on its axis in its revolution.
38 A gin horse, or a substitute, driven instead of being a driver.
38 Results of the wooden horse being driven by the mill.
39 The same results produced by the revolution of the moon.
Centrifugal force sufficient to drive air and water away
from our side of the moon.
40 That force not sufficient to drive them away from its other side.
41 No one seems ever to have thought of centrifugal force in
connection with air and water on the moon.
41 Near approach made by Hansen to this notion.
42 Far-fetched reasons given for the non-appearance of air and water.
44 The moon must have both on the far-off hemisphere.
44 Proofs of this deduced from its appearance at change.
45 Where the evidences of this may be seen if looked for at the right
place. The centrifugal force shown to be insufficient to drive
off even air, and less water, altogether from the moon.
47 The moon must have rotated on its axis at one period of
its existence.
48 The want of polar compression no proof to the contrary.
48 Want of proper study gives rise to extravagant conceptions,
jumping at conclusions, and formation of "curious theories."
A good deal of theorising has been expended in accounting for the
absence of all but traces of an atmosphere and water on the moon, which
might have been avoided had astronomers not caught up the notion, and
stuck to it, that it rotates on its axis once for every revolution
that it makes round the earth. It might be difficult to find out with
whom the notion originated; but perhaps it was first conceived to
be the case by some celebrated astronomer, and has been accepted by
almost all his successors without being properly looked into. Any one
who chose to take the trouble to study the matter thoroughly, would
have easily discovered that the moon can have no rotation of any kind
on its axis, and immediately afterwards have found out the reason why
nothing beyond traces of air and water were to be seen on the side
of it constantly turned towards the earth. This is another example
we can give of erroneous ideas leading to erroneous and impossible
conclusions, and preventing the truth from being discovered. That the
rotation of the moon on its axis is stated to be a fact, by recognised
and celebrated astronomers, will be seen from the following quotations.
(1) Sir John Herschel, in his "Treatise on Astronomy," new edition of
1835, says at page 230: "The lunar summer and winter arise, in fact,
from the rotation of the moon on its own axis, the period of which
rotation is exactly equal to its sidereal revolution about the earth,
and is performed in a plane 1° 31´ 11´´ inclined to the ecliptic, and
therefore nearly coincident with her own orbit. This is the cause why
we always see the same face of the moon, and have no knowledge of the
other side."
(2) In his "Poetry of Astronomy," page 187, Mr. Proctor says: "For
my own part, though I cannot doubt that the substance of the moon
once formed a ring around the earth, I think there is good reason for
believing that when the earth's vaporous mass, receding, left the
moon's mass behind, this mass must have been already gathered up into
a single vaporous globe. My chief reason for thinking this is, that I
cannot on any other supposition find a sufficient explanation of one
of the most singular characteristics of our satellite--her revolution
on her axis in the same mean time, exactly, as she circuits around the
earth."
(3) Professor Newcomb, in his "Popular Astronomy," 5th edition, 1884,
at page 313, has what follows: "The most remarkable feature in the
motion of the moon is, that she makes one revolution on her axis
in the same time that she revolves around the earth, and so always
presents the same face to us. In consequence, the other side of the
moon must remain for ever invisible to human eyes. The reason for this
peculiarity is to be found in the ellipticity of her globe." Then he
enlarges upon and confirms the fact of her rotation.
(4) Mr. George F. Chambers, in his "Handbook of Astronomy," 4th
edition, 1889, says at page 119, Vol. I.: "In order that the same
hemisphere should be continually turned towards us, it would be
necessary not only that the time of the moon's rotation on its axis
should be precisely equal to the time of the revolution in its orbit,
but that the angular velocity in its orbit should, in every part of its
course, exactly equal its angular velocity on its axis."
It may be necessary, to avoid misconception, to note that angular
velocity on its axis confirms rotation; and what is more extraordinary,
that Chambers must have thought that its angular velocity on its axis
must have increased and diminished in order to agree with its increased
and diminished velocities in its elliptic orbit at its perigee, apogee,
and quadratures. A rather strange notion in mechanics where there is no
provision made for acceleration or retardation of rotation.
(5) Dr. Samuel Kinns, in "Moses and Geology," twelfth thousand, 1889,
says at page 208, "the same side of its (the moon's) sphere is always
towards us. This could only happen by its having an axial rotation
equal in period to its orbital revolution, which is 27d. 7h. 43m. 11s."
(6) In the "Story of the Heavens," Sir Robert S. Ball informs us, in
the fifteenth thousand, 1890, page 530, "That the moon should bend
the same face to the earth depends immediately on the condition that
the moon should rotate on its axis in precisely the same period as
that which it requires to revolve around the earth. The tides are a
regulating power of the most unremitting efficiency to ensure that this
condition should be observed."
(7) And finally we have what follows from Messrs. Newcomb and Holden,
at page 164 of their work already referred to at page 27, "The moon
rotates on her axis in the same time and in the same direction in
which she moves around the earth. In consequence, she always presents
very nearly the same face to the earth." And in a footnote to this
consequence, add: "This conclusion is often a _pons asinorum_ to some
who conceive that, if the same face of the moon is always presented
to the earth, she cannot rotate at all. The difficulty arises from a
misunderstanding of the difference between a relative and an absolute
rotation. It is true that she does not rotate relatively to a line
drawn from the earth to her centre, but she must rotate relative to a
fixed line, or a line drawn to a fixed star."
In six of the above cases it is distinctly maintained that the moon
rotates once on its axis in the same time that it makes one revolution
round the earth, and that it is in consequence of this rotation that
it always presents the same side to the earth. Thus we feel authorised
to conclude that their authors did either believe that it does so
rotate, or that they entertained some confused idea on the subject,
which they did not take the trouble to examine properly, but accepted
as a dogma, because some predecessor, with a great name, had stated
that such rotation was necessary in order that its same side should
be always turned towards the earth. In the seventh case the authors,
while actually making the same assertion, try to persuade those who
they acknowledge can see that the moon does not rotate on its axis in
any sense, that their difficulty in comprehending what is meant by
rotation, arises from the misunderstanding of the difference between
an absolute rotation and one relative to a line drawn to a fixed star.
But they do not attempt to show how this relative rotation has anything
to do with or has any effect in causing the moon to present always the
same side to the earth; and leave the story in the same confused state,
out of which nobody can draw any satisfactory conclusion. Also, though
they distinctly recognise that it does not rotate relatively to a line
drawn from the surface of the earth to its centre, they do not include
in their general description of the moon anything in any way connected
with what would be the consequences of its not really rotating on its
axis relatively to the earth. So they leave us the problem in much the
same state as they found it, and it is still necessary to show that
there can be no actual rotation of any kind on its axis; and the worst
of it is that it is a thing that will have to be done in such very
plain language that it will compel people to think of the absurdity of
the idea so generally accepted.
To begin, it is very difficult to comprehend what the authors, above
alluded to, meant by saying that the moon "must rotate relative to a
fixed line, or a line drawn to a fixed star." It may mean relative to
the line itself or to the star to which it is drawn. If it is to the
line itself we cannot form any notion of what direction the rotation
will have, direct, retrograde, or otherwise; and if it is relative
to the star itself, then we can see that the relative rotation must
depend on what is the position of the star. Should it be placed in the
"milky way," we can understand how the moon could show every side it
has--almost, not quite--to the star during every revolution it makes
round the earth, and how they may look upon it as a relative rotation.
But if we draw the line to the pole star we cannot see how the moon
can show every side it has to it in every revolution round the earth,
so there can be no relative rotation in that case--and the "almost,
not quite," applies to every star between the pole and the ecliptic.
The moon shows only the northern hemisphere, or a little more due to
libration of its own kind, to that star, and would have to remove
its poles to the equator, and make a new departure, in order to show
the whole of its surface to that star in every revolution round the
earth. Thus it is clear that the explanation given us of the relative
rotation, is evidently one of the kind not properly thought out to the
end.
No one has ever said, or perhaps even thought, that a gin-horse makes
one rotation on his vertical axis, in the same time as he makes a
circuit round his ring, but, all the same, he keeps his same side
always towards the gin, or mill, he is giving motion to. The proof
that he does not make any such rotation is easy--no proof is really
required. But, suppose he is giving motion to a whim for raising ores
from a mine, and that his motion is what is called direct. When the
cage containing the ore is brought to bank, is emptied, and has to be
lowered into the mine again, the horse has then to reverse his motion
to retrograde, in doing which he has to make a half rotation on his
vertical axis, and turn his other side to the whim. When again the
cage has to be raised to bank, he has to resume his direct motion, for
which he has to make another half rotation on his vertical axis, but
it is this time in the opposite direction. Thus it is shown that he
can only make half rotations, under any circumstances, on his axis,
and these in opposite directions, when he changes his motion from
direct to retrograde, or _vice versâ_; and that, when he moves in only
one direction he cannot make even one rotation on his vertical axis,
however long he may travel round the mill. In the same manner the
moon which never turns back in its orbit can never make even one half
rotation on its axis, which is all that we have had to prove. It is
hardly necessary to observe that its axis is nearly parallel to the
earth's, just the same as the horse's is to that of the whim. Neither
could any one say that the relative rotation of the horse to a star, or
tower, or, say, a bridge, outside of his ring, could have any effect on
his revolution round the mill, or his always keeping his same side to
it, there being no mechanical connection between them, nor any law of
attraction; and the same is the case between the moon and a fixed star.
Now, we may begin to consider what effects must be produced by the moon
not rotating on its axis, and we can do so most easily by continuing to
work with our gin horse, or some equivalent substitute. It would not
cost a great deal of ingenuity to plant a steam engine in the centre of
the mill he is supposed to be driving, and to drive with it not only
the mill but the horse also at the end of his lever. There might be
some dissipation--Professor Tate would call it degradation--of energy
in such an experiment, but we could get over that by making _divina
Palladis arte_ a wooden horse. We might arrange the steam-engine so as
to cause the mill to make 27-1/3 revolutions for one made by our wooden
horse, and so have a sort of a model of the earth and moon performing
their most important relative motions. Then, having got our model ready
for action, instead of filling it _armato milite_ we might fill it half
full of water. We fill it only half full, because the armed soldiers
could not lie on the top of each other in the _other_ horse, and there
would be a vacant space above them for air, thus making the resemblance
between the two the more similar; and also because it suits our purpose
better, as will soon be seen. We have still to propose that a lot of
holes should be supposed to be made in the sides of _our_ horse all
round, just a little higher than between wind and water. _Pallas_
did not order any holes to be made in _hers_ as far as we know, even
for ventilation, though we think it would have been an advantage; but
that will not spoil the experiment we are now prepared for. Let the
steam-engine be started now and we shall soon see what will happen to
the water. As the speed increases it will not be long till it begins to
be thrown out, not from the side turned towards the mill but from the
one furthest from it; and if it is increased sufficiently the whole of
it will be very soon thrown out. If we could now close up the holes on
the side of the horse turned towards the mill, it would so happen that
a good deal of the air would be expelled also; and if the speed of the
horse were brought up so as to equal that of the moon in its orbit,
there would be nothing more, at the most, than traces of air left even
in it. The expelling agent in this experiment would, of course, be
centrifugal force, and we do not need to exercise our mental faculties
very greatly, to comprehend that it is the same force that has driven
both air and water away from the side of the moon always turned towards
the earth. All the difficulty we have to contend with will be to make
sure that the orbital velocity of the moon is sufficient to produce
the force required. That the force is exceedingly greater than what is
required is proved by the fact, that the velocity with which the moon
travels in its orbit is a little more than 38 miles per minute, whereas
the velocity of the circumference of a centrifugal machine, used for
clarifying sugar, drying clothes, or any other similar industrial
purpose, does not require a greater velocity than about _one_ mile per
minute, in order to throw everything in the form of water out of the
material to be dried, and out of the centrifugal machine itself; and
we know that air would be expelled more easily than water, were none
re-admitted to supply the place of what was expelled.
Here the idea very naturally occurs to any one, that so great a
velocity would drive both air and water away, even from the far off
side of the moon, into space, but in order to do so the velocity would
have to be 120, not 38, miles per minute. Our authority for this
statement will be found in "The Nineteenth Century," for August 1896,
in an article written by Prince Kropotkin, in which he says: "But
it appears from Dr. Johnstone Stoney's investigations that even if
the moon was surrounded at some time of its existence with a gaseous
envelope consisting of oxygen, nitrogen and water vapour, it would not
have retained much of it. The gases, as is known, consist of molecules
rushing in all directions at immense speeds; and the moment that
the speed of a molecule which moves near the outer boundary of the
atmosphere exceeds a certain limit (which would be about 10,600 feet
in a second for the moon) it can escape from the sphere of attraction
of the planet. Molecule by molecule the gas must wander off into
interplanetary space; and the smaller the mass of the molecule of a
given gas, the feebler the planet's attraction, and this is why no free
hydrogen could be retained in the earth's atmosphere, and why the moon
could retain no air or water vapour."
A velocity of 10,600 feet per second is as near 120 miles per minute as
there is any use for, which is more than three times as great as the
velocity of the moon in its orbit, so there is no possibility whatever
of air and water having been swept away from the far off side of it
by centrifugal force; more especially as it ought to be well known
that that force is always counteracted by the attractive force of the
satellite for these or any other elements.
We do not want to discuss the point of whether the mutual collisions
of the molecules of a gas could get up such a velocity as would enable
them to free themselves from the attraction of the moon, for it looks
to us too much like one of those notions that are got up to account for
something that does not exist; but we do want to state our dissent to
the conclusion--evidently jumped at--that because there are hardly any
signs of there being air or water on our side of the moon, there can
be none on the other. No astronomer, physicist, scientist of any kind,
can prove that there is none, simply because he has never been round
there to see or make experiments to prove it; and if there is any one
bold enough to make such an assertion, it is only an example of how
stupendous a jump to a conclusion can be made.
When we first read, many years ago, some of the reasons given for there
being no water visible on the side of the moon constantly turned to
the earth, one of which was that if there ever had been any it must
have been absorbed into its body during the process of cooling and
consolidation; and when we had convinced ourselves, by placing two
oranges on two ends of a wire and revolving the one round the other,
that the moon did not rotate on its axis in any sense whatever, we
came to the conclusion that both water and air could be removed to the
far off hemisphere by centrifugal force. We thought this so simple,
so self-evident, and so indisputable an explanation, that every one
who had read what we had read must have come to the same conclusion;
so that we were not a little surprised when we saw it stated by "The
Times" of September 15, 1893, in its first report of the meeting of the
British Association for that year, that Sir Robert Ball had suggested,
some time previously, that the "absence of any atmosphere investing the
moon is a simple and necessary consequence of the kinetic theory of
gases." This at once made us suspect that the theory--our theory--must
have been new, but we could not altogether believe it. It seemed to us
passing strange that it should not have occurred to astronomers, from
the moment they discovered that they could not find any, or hardly any,
traces of air or water on the only hemisphere they could examine; but
it would appear from Sir Robert Ball's suggestion, being even discussed
at that meeting, that the notion of their having been removed simply by
centrifugal force to the unseen hemisphere, had never been entertained
by, to say the least, any one who was present at that discussion.
Not satisfied with this conclusion, we proceeded to examine all the
books, journals, magazines, and _papers_ we could get hold of, to
see whether we could find any indication of such a conception having
been published previously, and the nearest approach to anything of
the kind having been conceived of by anyone, we found in Chambers's
work--already referred to--at page 134, Vol. I., where we read,
"Professor Hansen has recently started a curious theory from which
he concludes that the hemisphere of the moon which is turned away
from the earth may possess an atmosphere. Having discovered certain
irregularities in the moon's motion, which he was unable to reconcile
with theory, he was led to suspect that they might arise from the
centre of gravity of the moon not coinciding with the centre of
figure. Pursuing this idea, he found upon actual investigation that
the irregularities could be almost wholly accounted for by supposing
the centre of gravity to be at a distance of 33-1/2 miles _beyond_
the centre of figure. Assuming this hypothesis to be well founded,
Professor Hansen remarks that the hemisphere of the moon, which is
turned towards the earth, is in the condition of a high mountain, and
that consequently we need not be surprised that (little or) no trace of
an atmosphere exists; but that on the opposite hemisphere, the surface
of which is situated _beneath_ the mean level, we have no reason
to suppose that there may not exist an atmosphere and consequently
both animal and vegetable life. Professor Newcomb has disputed these
conclusions of Hansen, which it is obvious must be very difficult of
either proof or disproof."
What Professor Newcomb's objections to the conclusions of Hansen were
we do not know, but we do know that Mr. Proctor also objected to the
"curious theory," as it is called by Mr. Chambers. In his "Poetry on
Astronomy," he discusses pretty fully the withdrawal of water from the
surface of the moon during the process of cooling and condensation,
ascribing the conception of it to four independent authors, namely,
Seeman, a German geologist, Frankland in England, Stanislas Mennier in
France, and Sterry Hunt in America; and in a footnote, at page 163,
says of Hansen's theory: "The idea was that the moon, though nearly
spherical, is sometimes egg-shaped, the smaller end of the egg-shaped
figure being directed towards the earth. Now, while it is perfectly
clear that on this supposition the greater part of the moon's visible
half would be of the nature of a gigantic elevation above the mean
level, and would, therefore, be denuded (or might be denuded) of its
seas and denser parts of the air covering it, yet it is equally clear
that all around the base of this monstrous lunar elevation, the seas
would be gathered together, and the air would be at its densest. But
it is precisely round the base of this part of the moon or, in other
words, round the border of the lunar hemisphere, that we should have
the best chance of perceiving the effects of air and seas, if any
really existed; and it is because of the absolute absence of all
evidence of the kind, that astronomers regard the moon as having no
seas and very little air."
Had the idea of centrifugal force ever occurred to Mr. Proctor, he
could not have written this last sentence; for he could not have
failed to see that "the border of the visible lunar hemisphere" would
be the very place, from which it could most easily remove air and
water, after they had got so far down the monstrous elevation; because
there it--the centrifugal force--would be acting at right angles to
the moon's attraction, instead of having to contend against it, as it
would have to do in a constantly increasing degree until it arrived at
its maximum, just in proportion to the distance the air and water got
down to the similar monstrous _depression_ on the other hemisphere,
down which the gradient would start off under the most favourable
circumstances possible.
From what has been said, it is very evident that neither Hansen,
Chambers, Proctor, nor any of those whose names have been mentioned
by the last, in connexion with the withdrawal of water into the body
of the moon by absorption, while cooling and condensing, had ever
thought of the possibility of air and water having been removed by
centrifugal force from the side of the moon turned towards the earth.
That it should not have occurred to Hansen seems passing strange,
seeing that he had conceived the idea of their possible existence on
the hemisphere turned away from the earth, which could hardly fail to
make him think of how they got there, and could exist only there; and
the only explanation of his not having perceived the true cause seems
to be, that his thoughts were hampered by a sort of confused notion
that the moon actually rotates on its axis once for every revolution
it makes around the earth, that being, as it were, one of the dogmas
of astronomic belief, handed down from some great authority of times
past, and never properly inquired into.
We do not want to question the suggestion, that the absence of any
atmosphere investing the moon is a simple and necessary consequence of
the kinetic theory of gases--though we see that a good deal could be
argued against it--as we do not consider it to be necessary--neither
the questioning nor the theory. We have demonstrated clearly, how both
air and water could be removed from the side of the moon constantly
shown to us, and that is sufficient for our purpose both now and later
on; besides it would appear that the moon really has some sort of an
atmosphere somewhere.
Following up the quotation, made at page 39, from Prince Kropotkin's
article in the "Nineteenth Century" as being the latest information we
have on the subject, we are told that "a feeble twilight is seen on our
satellite, and twilight is due, as is known, to the reflection of light
within the gaseous envelope; besides it has been remarked long since
at Greenwich that the stars which are covered by the moon during its
movements in its orbit remain visible for a couple of seconds longer
than they ought to be visible if their rays were not slightly broken as
they pass near the moon's surface. Consequently it was concluded that
the moon must have an atmosphere" ... and:
"The observations made at Lick, Paris, and Arequipa, fully confirm
this view. A twilight is decidedly visible at the cusps of the
crescent-moon, especially near the first and last quarters. It prolongs
the cusps as a faint glow over the dark shadowed part, for a distance
of about 70 miles (60"), and this indicates the existence of an
atmosphere having on the surface of the moon the same density as our
atmosphere has at a height of about forty miles."
What is of interest for us to know is where that "feeble twilight," or,
"reflection of light within the gaseous envelope," is seen. Whether
it is at what Mr. Proctor calls "the border of the visible lunar
hemisphere," on this side of it, or beyond it. It cannot be a difficult
matter to decide. It must be beyond it, for the following reasons: If
the atmosphere has been driven away to the far-off hemisphere of the
moon by centrifugal force, its natural tendency would be to spread
out immediately after it had passed the visible border where we have
said the centrifugal force would be acting most effectively. Also, if
all the air at one time belonging to our side of the moon has been
driven away to the other, that side must have a double allowance of
atmosphere, which, though it does not increase its density at the
surface, on account of the centrifugal force, will double its volume,
and enable it to extend to a greater proportionate distance in all
directions from the border and from the far-off hemisphere. In this
way there must be a considerable wedge of atmosphere illuminated by
the sun, and visible past the edge of the moon's disc, to reflect a
feeble twilight--perhaps something stronger--towards the earth, and to
intercept the light of a star before its edge and that of the moon come
into actual apparent contact. But before the wedge becomes thick enough
to reflect that light, the reflecting part must be far beyond the edge
of the moon's disc. Perhaps the feeble light might be seen more clearly
when looked for in the proper place; quite possibly hundreds of miles
beyond the disc.
In order to make more clear the truth of what we have said about water
and air--and more especially the latter--being thrown away to the
far-off side of the moon by centrifugal force, we may add the following
details: If the force of gravity at its surface is one-sixth part of
what it is at the surface of the earth, the pressure of an atmosphere
there would be 2·5 lb. per square inch, if it rotated on its axis;
but as it does not so rotate and is subjected to centrifugal force,
the pressure of an atmosphere will vary according to the part of it
over which it exists. On the nearest part of the side turned towards
the earth, gravity, which we have just seen must be equal to 2·5 lb.,
would be acting in the same direction as centrifugal force, which in
its turn is equal to 0·7 lb. or thereby, and the whole would be 3·2
lb. per square inch tending to drive off air and water to the far-off
hemisphere. But from that place, gravity would gradually diminish its
aid till it came to be nil at the disc separating the two hemispheres,
where it would have no effect whatever as it would be acting at right
angles to centrifugal force, and this would be reduced to 0·7 lb. per
square inch. Then, from the edges of the disc forward, on the far-off
hemisphere, gravity would begin to act against centrifugal force, or
rather _vice versâ_, until it, gravity, got reduced to 1·8 lb. per
square inch. Also, as that hemisphere must have a double portion of
air or atmosphere on it, and as its pressure on any part of it cannot
be greater than the 1·8 lb. just mentioned, we can imagine that the
double quantity will hang closer to the surface than if there was
only one portion. Such being the case the atmosphere would spread out
much more rapidly than would be represented by the extension of a
triangle starting from the earth and reaching beyond the moon's disc
to the farthest limit of the atmosphere; and thus the wedge, which we
have supposed to be visible beyond the edges of the disc may come to
have a very considerable thickness. What that thickness may be, and
up to what distance beyond the disc the density of the wedge would be
sufficient to reflect the light of the sun, it would be very difficult
to calculate, but we think it might possibly extend even as far as
one-fourth of the radius of the moon--because at that point the force
of gravity pulling it towards the centre, or the axis, would be very
small, and its distance from the axis would be little less than the
radius, not over 33 miles--and cause it to project over the edges as
far, to appearance, as the 70 miles (60") that have been observed at
Greenwich. This reflected light must be all round the moon--not at the
cusps only of the crescent-moon--and it has occurred to us that it may,
most probably does, account for the appearance of what we call "the old
moon in the young moon's arms." We know what effect the "earth-shine"
has upon the moon at its change, and the brighter _ring-shine_ just
outside of it, may very well be caused by the sunlight reflected from
the atmosphere far beyond the visible limit of the hemisphere turned to
us.
In support of this suggestion we may refer to Professor C. A. Young's
description, in his "Sun," p. 213, of one particular feature observed
at the time of a total eclipse of the sun. He says:--"On such an
occasion, if the sky is clear, the moon appears of almost inky
darkness, with just a sufficient illumination at the edge of the disc
to bring out its rotundity in a striking manner. It looks not like a
flat screen, but like a huge black ball, as it really is. From behind
it stream out on all sides radiant filaments, beams, and sheets of
pearly light, which reach to a distance sometimes of several degrees
from the solar surface, forming an irregular stellate halo, with the
black globe of the moon in its apparent centre."
There can be little doubt, we think, from what is said here, that
Professor Young looks upon this "illumination of the edge of the
disc" as pertaining to the moon, and upon the "radiant filaments,
beams," etc. behind it as belonging to the sun. And in that case the
illumination can only be caused by the light of the sun, refracted by
the atmosphere belonging to the hemisphere of the moon that is never
seen from the earth.
We have taken it for granted in what we have been doing, that the
moon has really rotated on its axis, and to some purpose, at some
former period of its existence. Some people think otherwise, or that
there is at least a doubt about it; we cannot see even the shadow of
a doubt. All that we need to say in support of our opinion is, that
there is no other conceivable way of accounting for its perfectly
circular form. All the planets are circular, or spheroidal--to speak
more correctly--in form, admittedly in consequence of rotation on their
axes; and if one or two of Jupiter's satellites are not completely
circular or spheroidal, it does not stretch our conscience very much
to suppose that it is because they have not yet been rotated into
form. Saturn apparently has satellites still in the form of rings, and
there can be nothing out of the way in supposing that all of Jupiter's
are not yet licked into shape. The fact that there is no appearance
of compression on the moon makes us think of why there is none, and
the only explanation that occurs to us is, that, as its rotation
must have come to an end gradually, the compression it must have had
when rotating must have disappeared gradually also, by reason of the
differences of force in the equatorial and polar attractions, drawing
in the bulged out, and thus forcing out the compressed parts. This is
a notion that will be scoffed at by those who have always thought,
and maintained, that the earth acquired its present form when in a
liquid state; but they have not thought this supposition--for it is
nothing else--out to the very end. Several reasons could easily be
given against their opinion, among others the variations in rate of
rotation we so frequently see used in favour of other notions; but we
shall content ourselves with the best one of all, which is this: The
pressures in the interior of the earth must be so enormous that they
are quite sufficient to compress steel, or adamant if that is supposed
to be more resistant, into any shape whatever, almost as if it were
dough, and there can be no doubt--mathematics notwithstanding--that
the earth has the form, to-day, due to its present rate of rotation.
We shall have to return to this subject some time hence, if we live to
complete what we have taken in hand.
How many things there are, in what is considered to be astronomical
science, that have not been properly thought out to the end, and to
what strange notions they have given rise! This one of the rotation of
the moon which we have been discussing, has evidently given occasion
for the conception of the theory that the absence of atmosphere and
seas from the moon is the natural consequence of the kinetic theory of
gases; and the author of the theory, and its supporters, have never,
apparently, taken the trouble to think whether their absence from the
near hemisphere is a satisfactory and convincing proof of there not
being any air or water on the far-off one. In what we have proposed to
write many similar examples of want of study will be met with, but we
do not intend to call special attention to them, unless it be in cases
where we consider it to be of some importance to do so. In fact we have
already been working on that plan.
CHAPTER III.
PAGE
49 Remarks on some of the principal cosmogonies. Ancient notions.
50 The Nebular hypothesis of Laplace. Early opinions on it. Received
into favour. Again condemned as erroneous.
51 Defects attributed to it as fatal. New cosmogonies advanced.
53 Dr. Croll's collision, or impact, theory discussed.
59 Dr. Braun's cosmogony examined.
61 M. Faye's "Origine du Monde" defined.
65 Shown to be without proper foundation, confused, and in some parts
contradictory.
70 Reference to other hypotheses not noticed. All more or less only
variations on the nebular hypothesis.
71 Necessity for more particular examination into it.
We have thought it worth while to dedicate this chapter to some remarks
on cosmogonies in general, and examination into a very few conceived by
eminent men; these forming in our opinion the most attractive matter
for those readers who do not pretend to make a study of astronomy,
but are very desirous to have some knowledge of the most plausible
ideas which have been conceived by astronomers, of how the universe,
and more particularly the solar system, were brought into existence;
while, at the same time, they are the subjects on which more crude
conceptions, more limited study, and more fanciful unexamined thought
have been expended, than any others we have met with. Some readers
will, no doubt, be able to reject what is erroneous, to speak mildly,
but there will be, equally surely, some who cannot do so; and it
must be confessed there are a good many to whom the most complicated
conceptions, and the most difficult of comprehension, are the most
attractive.
A great many centuries ago, astronomers and philosophers had already
conceived the idea that the sun and stars had been formed into
spherical bodies by the condensation of celestial vapours; but when
the telescope was invented, and the nature of nebulæ in some measure
understood, it was not long till it came to be thought that the matter,
out of which the sun and stars were formed, must have been much more
substantial in its nature than celestial vapours. Being visible,
they were naturally considered to be self-luminous, and consequently
endowed with great heat, because the self-luminous sun was felt to
be so endowed, though perhaps not with the same degree. Accordingly,
astronomers began to form theories, or hypotheses, on the construction
of the solar system out of a nebula, which, like everything else,
went on each one improving on its predecessor as, through continued
observation and study, more knowledge was acquired of the nature of
nebulæ. The most notable of these cosmogonists were Descartes, Newton,
Kant, and Laplace, each of whom contributed valuable contingents to the
general work; which may be said to have culminated about a century ago
in the Nebular Hypothesis of the last-named; for the many attempts that
have been made to improve upon it, or to supplant it altogether, have
been very far from successful.
The hypothesis is about a century old, as we have said, and there may
still be many people who can remember having heard it denounced as a
profane, impious, atheistic speculation, for it is not over half a
century since the ban begun to be taken off it. Sir David Brewster,
in his "Life of Newton," said of it, "That the nebular hypothesis,
that dull and dangerous heresy of the age, is incompatible with the
established laws of the material universe, and that an omnipotent arm
was required to give the planets their positions and motions in space,
and a presiding intelligence to assign to them the different functions
they had to perform." With others, its chief defect was that the time
required to form even the earth in the manner prescribed by it, must
have been infinitely greater than six days of twenty-four hours each.
In the meantime, geologists had also discovered that, for the formation
of the strata of the earth, which they had been examining and studying,
the time required for their being deposited must have been, not days
of twenty-four hours, but periods of many millions of years each; and
the evidence adduced by them that such must have been the case was so
overwhelming, that Theology had to acknowledge its force, and gradually
to recognise that the days must have been periods of undefinable
length. Thus relieved from the charge of heresy, the hypothesis rose
rapidly into favour, and came to be generally accepted by the most
eminent astronomers, subject always to certain modifications, which
modifications have never been clearly defined, if at all. It was not,
however, allowed to enjoy long the exalted station to which it had
attained.
Astronomers had begun to consider from whence the sun had acquired the
enormous quantity of heat it had been expending ever since the world
began, and, after long discussion, had come to the conclusion that
by far the greatest source must have been the condensation from the
nebulous state of the matter of which it is composed. Having settled
this point, it was calculated that the amount of heat derived from that
and all other sources could not have kept up its expenditure, at the
present rate of consumption, for more than twenty million years, and
could not maintain it for more than from six to eight million years in
the time to come. Owing in good part to this great difference between
the calculations of astronomers and geologists about the age of the
earth, the hypothesis began again to suffer in repute, and then all its
faults and shortcomings were sought out and arrayed against it.
The chief defects attributed to it were: The retrograde motion of
rotation of Uranus and Neptune and revolution of their satellites--that
fault in the former having been noted by Sir John Herschel, in his
Treatise on Astronomy already cited; the discovery of the satellites
of Mars which exposed the facts, that the inner one revolves round
the planet in less than one-third of the time that it ought to, and
that the outer one is too small to have been thrown off by Mars,
in accordance with the terms of the hypothesis; the exclusion from
it of comets, some of which at least have been proved, in the most
irrefutable manner, to form part of the solar system; and what can only
be called _speculations_, on the formation of a lens-shaped nebula
brought about by the acceleration of rotation--caused by condensation
according to the areolar theory--which it is supposed would be
enormously in excess of the actual revolution of the inner planets, and
of the rotation of the sun. Here we must protest against retrograde
motion of rotation in any of the members of the solar system being
considered as militating against the theory, because Laplace states
distinctly, while explaining his hypothesis, that the rotation of the
earth might just as well have been retrograde as direct: a fact that
some eminent astronomers have not noticed, simply because they have
not paid proper attention to what they were reading. We shall have to
return to this statement again, and to present the proof of its being
true.
An idea of how far the hypothesis had fallen into disrepute may be
formed from the following extract, from "Nature" of August 4, 1887, of
a Review of a "New Cosmogony," by A. M. Clerke, in which it is said:
"But now the reiterated blows of objectors may fairly be said to have
shattered the symmetrical mould in which Laplace cast his ideas. What
remains of it is summed up in the statement that the solar system did
originate somehow, by the condensation of a primitive nebula. The rest
is irrecoverably gone, and the field is open for ingenious theorising.
It has not been wanting.... The newer cosmogonists are divided into
two schools by the more or less radical tendencies of the reforms
they propose. Some seek wholly to abolish, others merely to renovate
the Kant Laplace scheme. The first class is best represented by M.
Faye, the second by Mr. Wolfe and Dr. Braun"--the author of the "New
Cosmogony."
We cannot pass this quotation without remarking "How glibly some people
can write!" More we do not want to say about it, except that it gave us
the notion to examine closely some of the new cosmogonies, _which have
not been wanting_, to see whether they are better than Laplace's.
We have not had the opportunity of knowing what are Mr. Wolfe's
amendments, but the Review, just cited, gives us a pretty good notion
of those of Dr. Braun, and we have been able to study carefully M.
Faye's "Origine du Monde," in which he considers the solar system to
have been evolved from cosmic matter partially endowed with motion
in the form of eddies, whirlwinds, vortices, or _tourbillons_, which
last may comprehend all of them, and even more. We have also studied,
with some surprise, in "Climate and Cosmology" Dr. Croll's Impact, or
Collision, Theory, and will confine our examination to the three of
which we know something, beginning with Dr. Croll's, which we believe
to be the oldest of the three.
We understand that Dr. Croll accepts the nebular hypothesis in all its
main features, including the intense heat in which the original nebula
is supposed to have existed from the beginning; and has only invented
the collision theory in order to increase its quantity, to suit the
demands of geologists for unlimited time, by showing how an unlimited
supply of both heat and time may be obtained. But he has incurred
an oversight in not taking into consideration the kind of matter in
which that unlimited supply of heat was to be stored up--whether it
would hold it. He wrote in times when something was really known about
heat, and we cannot suppose him to have believed that heat could exist
independent of matter, or that a gas or vapour could be heated to
a high temperature except under corresponding pressure; but he has
evidently overlooked this point, his thoughts recurring to old notions;
and he has fallen, probably for the same reason, into other oversights
equally as grave.
When showing how a supply of fifty millions of years of sun-heat
could be produced from the collision of two half-suns colliding with
velocities of 476 miles per second, Dr. Croll says in his "Discussions
on Climate and Cosmology," of 1885, at page 301: "The whole mass would
be converted into an incandescent gas" (the handmaid of the period),
"with a temperature of which we can have no adequate conception. If we
assume the specific heat of the gaseous mass to be equal to that of air
(viz. 0·2374), the mass would have a temperature of about 300,000,000°
C., or more than 140,000 times that of the voltaic arc."
Now, let us suppose the whole mass of the whole solar system to be
converted into a gas, or vapour, at the pressure of our atmosphere,
and temperature of 0° C., its volume would be equal to that of a sphere
of not quite 9,000,000 miles in diameter. Suppose, then, this volume to
be heated to 300,000,000° C. in a close vessel, as would necessarily
have to be the case, the pressure corresponding to that temperature
would be 1,094,480 atmospheres, according to the theory on which the
absolute zero of temperature is founded. Without stopping to consider
whether air or any gas could be heated to the temperature mentioned;
or the strength of the vessel 9,000,000 miles in diameter required
to retain it at the equivalent pressure; if we increase the diameter
of the containing sphere to a little more than that of the orbit of
Neptune, or, say 6,000,000,000 miles, and allow the air or gas or
vapour to expand into it; then, as the volume of the new sphere will
be greater than the former one in the proportion of 9,000,000 cubed to
6,000,000,000 cubed, or as 1 is to 296,296,296, the pressure of the gas
will be reduced to 296,296,296 divided by 1,094,980, that is just over
the 270th part of an atmosphere; which, in its turn would correspond to
a temperature of a very little more than -273°, or what is considered
to be[A] 273° C. above absolute zero of temperature; or, at all events,
to the temperature of space, whatever that may be.
[A] This temperature is altogether erroneous, as we shall show in
due time; at present our proof would not be accepted without a
demonstration, for which we have not sufficient data.
Dr. Croll goes on to say at page 302: "It may be objected that enormous
as would be such a temperature, it would nevertheless be insufficient
to expand the mass against gravity so as to occupy the entire space
included within the orbit of Neptune. To this objection it might be
replied, that if the temperature in question were not sufficient to
produce the required expansion, it might readily have been so if the
two bodies before encounter be assumed to possess a higher velocity,
which of course might have been the case. But without making any such
assumption, the necessary expansion of the mass can be accounted for on
very simple principles. It follows in fact from the theory, that the
expansion of the gaseous mass must have been far greater than could
have resulted simply from the temperature produced by the concussion.
This will be obvious by considering what must take place immediately
after the encounter of the two bodies, and before the mass has had
sufficient time to pass completely into the gaseous condition. The
two bodies coming into collision with such enormous velocities would
not rebound like two elastic balls, neither would they instantly be
converted into vapour by the encounter. The first effect of the blow
would be to shiver them into fragments, small indeed as compared with
the size of the bodies themselves, but still into what might be called
in ordinary language immense blocks. Before the motion of the two
bodies could be stopped, they would undoubtedly interpenetrate each
other; and this of course would break them up into fragments. But this
would only be the work of a few minutes. Here then we should have all
the energy of the lost motion existing in the blocks as heat (molecular
motion), while they were still in the solid state; for as yet they
would not have had time to assume the gaseous condition. It is obvious,
however, that the greater part of the heat would exist on the surface
of the blocks (the place receiving the greatest concussion), and would
continue there while the blocks retained their solid condition. It
is difficult in imagination to realize what the temperature of the
surfaces would be at this moment. For supposing the heat were uniformly
distributed through the entire mass, each pound, as we have already
seen, would possess 100,000,000,000 foot-pounds of heat. But, as the
greater part of the heat would at this instant be concentrated on the
outer layers of the blocks, these layers would be at once transformed
into the gaseous condition, thus enveloping the blocks and filling up
the interstices. The temperature of the incandescent gas, owing to this
enormous concentration of heat, would be excessive, and its expansive
force inconceivably great. As a consequence the blocks would be
separated from each other, and driven in all directions with a velocity
far more than sufficient to carry them to an infinite distance against
the force of gravity were no opposing obstacle in the way. The blocks,
by their mutual impact, would be shivered into small fragments, each
of which would consequently become enveloped in incandescent gas. These
smaller fragments would in a similar manner break up into smaller
pieces, and so on until the whole came to assume the gaseous state. The
general effect of the explosion would be to disperse the blocks in all
directions, radiating from the centre of the mass. Those towards the
circumference of the mass, meeting with little or no obstruction to
their outward progress, would pass outwards into space to indefinite
distances, leaving in this manner a free path for the layers of blocks
behind them to follow in their track. Thus eventually a space, perhaps
twice or even thrice that included within the orbit of Neptune, might
be filled with fragments by the time the whole had assumed the gaseous
condition.
"It would be the suddenness and almost instantaneity with which the
mass would receive the entire store of energy before it had time even
to assume the molten, far less the gaseous condition, which would lead
to such fearful explosions and dispersion of the materials. If the
heat had been gradually applied, no explosions, and consequently no
dispersion of the materials would have taken place. There would first
have been a gradual melting; and then the mass would pass by slow
degrees in vapour, after which the vapour would rise in temperature as
the heat continued, until it became possessed of the entire amount.
But the space thus occupied by the gaseous mass would necessarily be
very much smaller than in the case we have been considering, where the
shattered materials were first dispersed in space before the gaseous
condition could be assumed."
We have made this very long quotation; first, because we have not
been able to condense it without running the risk of not placing
sufficiently clearly the whole of the argumentations employed in it;
secondly, because the purport of the whole explanation set forth is
evidently to demonstrate that, by means of the explosions of gases
produced by the collision, the matter of the whole mass would be more
extensively distributed into space--bearing heat along with it--than
were it gradually melted and converted into vapour; and thirdly,
because every argument advanced in favour of the theory of explosions,
if carefully looked into, brings along with it its testimony that it
has not been studied thoroughly out to the end. Thus the quotation in a
great measure saves us that labour.
Dr. Croll seems sometimes to demand more from the laws of nature than
they can give. He says, at p. 42 of the work cited, that the expansion
of the gaseous mass, produced by the collision of the two bodies,
must have been far greater than could have resulted simply from the
temperature produced by the concussion; and goes on to show how it--the
expansion--might be caused by explosions of gases blowing out blocks
of matter in all directions to indefinite distances. But he forgets
that these explosions of gases would consume a great part of the heat
they contained, that is, turn it into motion of the blocks, and so
diminish the quantity produced by the collision, just in proportion
to the velocities given to the masses of all the blocks blown out; so
that what was gained in expansion would be lost in heat, and the object
aimed at--of producing heat for the expenditure of the sun--so far
lost. Also, that, were the thing feasible, the blocks could not carry
with them any of the heat of the exploded gases that might not be used
up, and that the heat contained in them derived from the concussion
would have time in their flight--about two hours at 476 miles per
second--to melt the matter composing them and turn it into vapour, long
before even the orbit of Neptune was reached. The heat produced by the
explosion of powder in a cannon gives the projectile all the impulse it
can, and disappears; it is converted into motion. It does not cluster
round the projectile, nor follow it up in its flight, nor push it
through an armour plate when it pierces one. We cannot admit--for this
reason--the possibility of a block of matter flying off into space,
with a mass of heat clustering round it, like bees when swarming round
a branch of a tree. Thermodynamics does not teach us anything about a
mass of heat sticking to the surface of a block of matter of any kind.