facts from another part of Captain Ericsson's monograph, where he
says: "Engineers of great experience in the application of heat
for the production of motive power and other purposes deny that
the temperature of a body can be increased by the application of
heat of a lower degree than that of the body whose temperature we
desire to augment." The soundness of their reasoning is apparently
incontrovertible, yet the temperature of the mercury in the instrument
just described raised to 600°F. by means of the parabolic reflector,
increases at once when solar heat is admitted through the circular
apertures, although the sun's radiant intensity at the time may not
reach one-tenth of the stated temperature. It should be mentioned that
the trial of this new pyrheliometer has not been concluded, owing to
very unfavourable atmospheric conditions since its completion. For
our present purpose the great fact established by the illustrated
instrument is sufficient, namely, that the previous temperature of a
body exposed to the sun's radiant heat is immaterial. The augmentation
of temperature resulting from exposure to the sun, the pyrheliometer
shows, depends upon the intensity of the sun's rays.
A little study shows us that the steam engineers are perfectly right
in their doctrine. The heat of steam can only be called a variety of
the temperature of water. At 300 lb. pressure per square inch the heat
of steam is 417·5°F., while at 20 lb. pressure it is only 228·0°F.,
and therefore the steam engineer has good reason to say that steam at
the lower pressure--or derived from heat that can only produce that
pressure--can add no heat to the higher; on the contrary, the only
possible means of applying the heat of the lower to that of the other
would be by mixing them, and we know what the result of that would
be. This brings before us the fact that the steam engineer's heat is
very limited, and can only be communicated in certain ways, while the
sun's heat is comparatively unlimited, and can only be communicated
to anything through the medium of the ether. But it probably teaches
more than that. Were the engineer's heat unlimited in quantity at
low pressure it can easily be believed that it could be transmitted
to another body at any temperature by radiation, the same as it is
radiated from the sun to a hot box; but it is not, and we thus seem
to find that radiation is a mode, possessed by the ether alone, of
conveying heat from one body to another. It has nothing whatever to do
with mixing, conduction, convection, or anything, except in so far as
the ether is mixed in a more or less limited quantity with all matter.
In support of this idea we can refer to Professor Tait's treatise
on heat, where we find it stated that "heat does pass (though on an
infinitesimal scale) from colder to hotter bodies"; and we can easily
understand that the infinitesimal quantity so passed is due to the
comparatively infinitesimal quantity of ether there is in either of the
two bodies to perform the work of transference. Professor Tait has not
told us how heat is carried from a cold to a hot body, but there can
be no doubt about its being a function of the ether which can only be
found out by a careful and analytical study of that agent. Such a study
we propose to undertake presently without much expectation of being
successful, but still with the hope of helping in some measure to find
out how the ether operates. Meanwhile we shall return to what we had
begun to say about the sun being a hollow sphere, and to our proposal
to treat of the nebula contracted from 58 million miles to its present
diameter, as if it were a model representing a _résumé_ of all the
effects produced on the nebula by that amount of condensation.
We know from all our work that the sun must be a gasiform body, which
means that all the cosmic matter contained in it must be in the form
of vapour, even although its consistence should outrival a London
fog--notwithstanding that some physicists have supposed that it may be
solid at the centre through extreme pressure--and it is not altogether
correct to compare its construction to that of a solid body such as the
earth; but as we have no other we shall begin to make a comparison with
it, which, it will be found, can lead us into no appreciable error.
Considering then the sun to be 867,000 miles in diameter, with mean
density of 1·413 that of water, the hollow part being still completely
empty, and applying to it the same proportion we have deduced for the
earth, we find that the region of greatest density would be at 0·7937
of the radius of the sphere--a proportion really derived from the
line of division into two equal parts of the volume of a sphere--from
the centre, or 89,431 miles from the surface; and the inner surface
of the shell at 0·548--a proportion derived from our calculations for
the earth--of the radius of 433,500 miles, or 237,558 miles from the
centre; which in turn makes the shell to be 195,942 miles thick, and
the hollow centre to be 475,116 miles in diameter. On the other hand,
still following the proportions derived from the earth, we find that
the density at the surface might be one-third of the mean density or
0·471; that it might be one-fifth greater than the mean, or 1·7 at the
region of greatest density and one-half, or 0·71 at the inner surface
of the shell--all of these three densities being in terms of water.
Now, the hollow centre of 475,116 miles in diameter would have a
volume of one-sixth of the whole volume of the sun, which, filled
with gases, would diminish all these densities just in proportion to
what may be considered the degree of compression and condensation
the gases might be subjected to. That there should be gases in the
interior hardly requires to be more than stated, as there can be no
doubt that the degree of heat to which the shell had arrived by the
time it came to have the dimensions above mentioned, would be amply
sufficient to excite chemical action among the elements of which the
sun is composed; and the gases or vapours produced by that action would
flow as naturally towards the interior of the hollow centre as towards
the space beyond the outer surface of the shell, until they were
stopped by increase of pressure, which of course would mean increase
of density in this case. We see then that if the hollow centre has a
volume of one-sixth of the whole volume of the sun and we multiply this
volume by 6, we have a mass equal to the whole mass of the sun, were
its mean density only the same as that of water. Consequently, if we
multiply the said volume by 6 and by 1·413, that is by 8·478, we get
a mass equal to the whole mass of the sun at its known mean density.
Again, were we to suppose the hollow centre to be filled with gases
of the same specific gravity of air, condensed to a pressure of 6560
atmospheres--which would correspond in density to 8·478 times the
density of water--we should have in the hollow centre alone a mass
equal to another sun, in addition to the one made up by the dimensions
and densities stated above. We see then that if we fill the hollow
centre with gases at the pressure, and with the density just stated,
we have a sun of twice the mass it should be. But if we leave the
specified gases in the hollow with one-half of the above density, and
deduct the equivalent mass of the other half density of the gases from
the shell, as estimated for the hollow centre, we should have a sun of
the mass required by astronomy. In this way we should have the three
specified densities reduced from 0·471, 1·70 and 0·71 to 0·236, 0·85
and 0·355, for the outer surface, the region of greatest density, and
the inner surface of the shell, respectively; and the pressure and
density of the gases in the hollow centre reduced to 3280 atmospheres.
Thus, from what has just been shown, which at first sight may be
thought very irrelevant matter, we discover that it is not necessary
that there should be any matter in the sun even so dense as water. And
still we have to think of what an insignificant pressure three or four
thousand atmospheres would be in the centre of the sun.
No one will pretend to allege that no gases can be produced in the
shell of the sun, or to say anything against those formed in the
inner half of it finding their way to the hollow centre, and going on
increasing there till they were able to force their way out through
the shell; that is, until their pressure was equal to the resistance
offered by the gaseous body of the sun, or against their temperature
increasing until it came to correspond to their density and most
probably rising to a much higher degree. Such, then, must even now be
the construction of the sun, as reduced to its present diameter and
density. That is, a hollow sphere consisting of cosmic matter combined
with gases and having a hollow centre filled with chemically formed
gases or vapours.
Here it may be argued that the sun ceases to be a hollow sphere, but
that is not so. The most that can be said about it is that it is a
hollow sphere with the empty part filled up. It would only be in much
the same condition as a hollow globe of iron filled with melted
antimony or bismuth. Its construction would be in no way changed by
the empty hollow being filled up, so long as its condition remained
gaseous--not changed to liquid or solid. The only difference in our
sphere would be that its density would virtually be the same from what
we have called the region of greatest density to the centre, which
would not only involve a greater distance of that region from the
surface of the sphere, but another reduction of the above mentioned
densities of the sun; for we cannot in any way imagine that the
pressure in its interior can be less than many thousands of atmospheres.
Whatever may be the relative densities of the shell and the gases in
the hollow, they will have no necessary effect upon the temperature
of the latter, because, let the densities be what they may, the gases
might be cooled down to absolute zero of temperature, or raised to
any imaginary degree without any change being made in their weight as
long as their volume was maintained the same. This has been proved by
laboratory experiments almost as far as possible. Gases at very high
degrees of pressure and consequent densities have been cooled down
to not far from the absolute zero of temperature, while others under
very low pressures have been heated up to nearly as great heat as the
enclosing vessel would bear, without their weight being altered in
either case; but in the sun there is a larger laboratory in which we
can place no limit to pressure or temperature. We know, however, that
pressures are required sufficiently great to blow out jet prominences
with velocities of 100,000 miles per second or more, to heights 200,000
and even 350,000 miles above the photosphere; and if we knew what these
pressures are we might be able to learn something about the minimum
temperatures of the gases. To obtain these pressures we have--in the
construction we are advocating--a real containing receptacle with sides
195,942 miles thick, in the outer half of which we have the compressing
force, due to the gravitation of the whole mass of the sun acting at
the centre, and over and above, both in it and the inner half, we have
the cohesive force of the matter of which it is composed. In fact we
have a sun whose construction we can understand, in which we have
gases shut up without their expansive forces being impaired in any
way, ready to be exerted with full energy whenever they are relieved
from compression by any commotions in any part of the whole body, and
taking their part in keeping the whole of the matter composing it in
constant motion. How these commotions are produced it is not difficult
to explain to a very considerable extent at least, but this we must
leave over until we have reconstructed the original nebula, and shown
how the solar system could be elaborated from it, almost exactly in the
way conceived by Laplace in his nebular hypothesis. We shall then also
be able to extend our exposition of what is to be learnt from our mode
of construction, and to still further reduce our estimate of the mean
density of the sun.
Meanwhile we have to go into another long digression, with the view of
trying to find out something about what the nature of the ether is or
may be, which we think to be quite necessary before we go any farther.
CHAPTER XIII.
PAGE
226 The ether. Its nature considered. Behaves like a gas.
227 Can be pumped out of a receiver.
228 Light and heat do not pass through a tube _in vacuo_.
Laboratory experiments examined.
229 Light and darkness in a partial vacuum, though high.
230 Electricity not a carrying agent.
232 Why there are light and dark strata in a high vacuum.
233 The real carrying agent through a high vacuum is the residue
of ether left in it. Digression to consider the aurora.
234 How air may be carried to extraordinary heights. Zones of air
carried up are made luminous by electricity.
236 Comparison of this method with experiments quoted.
237 Experiment suggested to prove whether light passes freely
through a vacuum tube.
238 The ether does not pervade all bodies freely.
239 It must be renounced altogether or acknowledged to be a material
body, subject to expansion, condensation, heating or cooling.
239 How light and heat pass through glass.
240 Temperature of the ether variable. Zodiacal light, cause of.
THE ETHER A MATERIAL SUBSTANCE, PROVED BY ITS BEHAVIOUR.
We have said in a former part of this work, pages 153 and following,
that if the ether is capable of performing all the functions that
are attributed to it, it must have some consistence or substance
of some kind; that it must be matter of some kind in some form,
and consequently must have density in some degree however low; and
we might, for the same reasons, suppose that it must have some
temperature; but as long as we believe that without motion there can
be no heat, we cannot conceive it to have any temperature. No doubt we
might suppose it to be in a constant state of vibration, and to have
the temperature corresponding to that state, whatever that may be; but
this, in addition to leaving us just where we were, would only entail
upon us the task of supplying temperature as well as density to a body
of whose existence no positive proof has hitherto been given, whatever
we may believe about it. At the same time, the evident necessity of
taking its temperature into consideration, seems to supply another
reason for concluding that it is a material substance, over and above
those we have cited now and before.
The general belief regarding the ether has been, ever since it was
invented, that it is a substance of some kind (imponderable and
impalpable?) which fills and pervades all space and matter; but
a little consideration will show that this belief requires to be
modified. The ether is supposed to be the connecting link of the
universe, and the agent for carrying light, heat, electricity, and
magnetism from the sun to the earth and planets, and all over space;
but it has been found that electricity will not pass through a vacuum,
such as has been produced by experimenters, unless it be with a very
powerful current. This, of course, would seem to prove that there must
be almost no ether in such a vacuum; because if there was ether in
it, of the same density as there is in space, electricity would pass
through it with the same ease as it does from one body to another
on the earth or in space; it would seem, also, to justify us in
inferring that electricity would not pass through an absolute vacuum
at all, however powerful the current might be, because there would
be absolutely no ether to carry it; and, likewise, that the quantity
of ether remaining in the experimenter's receiver had as much to do
with the passing of a very powerful current of electricity through
it--perhaps a great deal more--as the small quantity of air, or gas,
or dust not altogether exhausted from it, to which the experimenters
attribute its passage. Moreover, it would appear that when air or any
gas is pumped out of a receiver, the ether mixed with it is pumped out
along with it; consequently it must be a material, tangible substance,
possessing density in some degree, however low it may be. Here, then,
we have, it would appear, proof positive that there is such a carrying
substance as the ether has been supposed to be. It is a thing which we
have not to conceive of, fabricate, or build up in our minds. It is a
thing we can pump out of a tube, and is as much a material substance,
in that respect, as air or any other gas that is as invisible as
itself--yet nevertheless in the tube until it is pumped out.
Against this idea of the nature of the ether, and what may be done with
it, it may be argued that light and heat pass freely through a tube or
receiver _in vacuo_, when electricity refuses to pass; but are we sure
that they do pass? It would be a much more difficult matter to prove
that they do, than to prove that electricity does not, because our
eyesight gives us evidence in the latter case. Besides, there are facts
which, when thoroughly looked into, induce us to believe that light
actually does disappear gradually from a vacuum as it is being formed.
In an article on "The Northern Lights," in "Science for All," Vol.
II., reference is made to a well-known laboratory experiment in the
following words: "We take a glass cylinder, covered at the ends with
brass caps, one of which is fitted with a stop-cock, which we can
screw to the plate of an air-pump. To the brass caps we now attach
the terminals of a powerful induction coil, but as yet we perceive no
result. We now begin to exhaust the air from the cylinder, and as the
exhaustion goes on we soon see a soft tremulous light beginning to play
about the ends of the cylinder; and this, when the air is sufficiently
rarefied, gradually extends right through the cylinder. As we continue
the exhaustion these phenomena will be reversed, the light gradually
dying away as the exhaustion increases. We shall at once perceive how
very much this resembles an aurora on a small scale, and so we have
electricity suggested to us as the agent which produces the aurora."
Farther on in the same article we find that: "Aurora displays usually
take place at a great height--sometimes so high as 300 miles--while
their average height is over 100 miles. At such heights the air must
be extremely rarefied, and we should be disposed to expect that the
electric discharge could not take place through it."
Now, at the beginning of this experiment, it must be granted that light
was passing freely through the glass cylinder from side to side, and
also that, when the electric current was turned on, the electricity
was passing freely through the air in the cylinder though it was not
visible. It could not pass through the glass on account of its being
a non-conductor. Then, when the air had been partially exhausted from
the cylinder, and the "soft tremulous light" began to appear about its
ends, it is clear that some interference with, or change in, the free
passage of light through it must have been produced, both transversely
and longitudinally, which occasioned the difference in the appearance
of the light and caused its tremulous motion. And as change in the
appearance of the light extended through the length of the cylinder
as the exhaustion increased, and finally died away--light, change and
all--when it approached more nearly that of an absolute vacuum, we
cannot help concluding that the light disappeared because there was no
medium left in the cylinder, of sufficient density at least, through
which it could pass; which, of course, means that light cannot pass
through a vacuum any more than electricity can.
The experiment we have cited above may be considered antiquated, but
similar results are presented to us in Professor Balfour Stewart's
"Elementary Physics," where he says at page 399 of the Reprint of 1891:
"Another peculiarity of the current is the stratification of the light
which is given out when it traverses a gas or vapour of very small
pressure. We have a series of zones alternately light and dark, which
occasionally present a display of colours. These stratifications have
been much studied by Gassiot and others, and are found to depend upon
the nature of the substance in the tube." [The ether?] "If, however,
the vacuum be a perfect one, Gassiot has found that the most powerful
current is unable to pass through any considerable length of such a
tube."
[In passing, we take the opportunity to assert, with confidence, that
there can be no perfect vacuum on the earth.]
Here we see the gas or vapour in the tube divided into zones
alternately light and dark, which occasionally present a display of
colours, and are led to infer, from the colours depending upon the
nature of the substance in the tube, that they disappear altogether
when the exhaustion is sufficiently great; and are finally told that
the most powerful current is unable to pass through such a tube of
any considerable length. In this case also, we can say with perfect
confidence that there can be no ether left in the tube, in sufficient
quantity, or else it would be able to carry the electricity through it
much more easily than from the sun to the earth, or from one part of
the earth to another. If we refuse to acknowledge that the ether has
been removed from the tube or cylinder, we are forced to conclude that
it is not the carrying agent, for which alone it has been called into
existence by the imagination of scientists; and we have to invent new
theories, new methods for explaining what we have been accustomed to
think we thoroughly understood. We have to look for a new dog to carry
and fetch. Furthermore, all that has been said about electricity is
equally applicable to light, whether we can prove it or not. If light
could pass freely through the experimental cylinder from side to side,
as it was certainly doing before the exhaustion was begun, we cannot
understand why there should be, first tremulous light which finally
disappeared, and why dark strata were displayed in it by the forced
passage of electricity; unless it was that the carrier of the light was
removed, and then we naturally think of why there should be dark strata
in the tube. We can understand electricity lighting up darkness, but
not its darkening light--it lightens up midday--and we must conclude
that both the one and the other were driven through the cylinder, or
similarly conducted through it, by the same force, or were left behind.
Following up the quotations we have already made from "Science for
All," Vol. II., we now add another for further illustration of what we
have been saying, to wit: "Let us now return to the laboratory, and
see whether we can make any experiment which will throw light upon
this difficulty. If we send the electric discharge through one of the
so-called vacuum tubes--choosing one which consists, through part of
its length, of tube which is much narrower than the main portion--we
find that when the discharge is passing the pressure is greater in the
narrow part of the tube, showing that in some way gas is being carried
along by means of the current, and Professor A. S. Herschel suggests
that in some similar way air may be electrically carried up to these
great heights." This quotation, of course, refers to the Northern
Lights, but it serves to illustrate what we are seeking to show with
respect to the ether.
In this experiment, the explanation of the pressure being greater in
the narrow part of the tube, is exactly the same as that for water
passing through a conduit which is narrower at one place than another.
The same quantity of water has to pass through the narrow as through
the wide part, consequently the velocity and pressure (head) have to
be greater than in the wide part--the water arranges that for itself;
and the seeming difficulty of explanation arose from the idea "that in
some way gas is (was) being carried along by the current," when it was
only the gas that was being lighted up more vividly by the electricity
passing through it, because the same amount of electricity had to be
carried through the narrow part as the wide one. No portion of the
gas could be carried along with the electricity, else it would very
soon have been all accumulated at one end of the tube, or a reverse
current must have been set up to restore the balance, which would
speedily have shown itself. Had the said tube been filled with copper
instead of gas, the experimenter must have known that the electricity,
in passing through it, would have spread itself all through the wide
part, and contracted itself to pass through the narrow part, spreading
itself out again through the other wide part, thus giving rise to
differences of pressures and velocities at the different widths of the
tube; but, of course, he would not have been able to see this, because
the electricity could hardly be in sufficient quantity to light up the
copper, or to impart to it sufficient heat to make it visible. Neither
would the electricity carry with it part, or the whole, of the copper
when passing through the narrow part. It would be the gas lighted up
more vividly, not set in motion, by the electricity that the operator
saw in the experiment under discussion, and, no doubt, if the tube had
been sufficiently exhausted of gas, the light would have disappeared
the same as in the first quoted experiment, and the electricity would
have ceased to pass because there was nothing, in sufficient quantity
at least, to carry it along, not even the universally commissioned
monopolist the ether. Let us ask here: Does not all this seem to prove
that electricity is a carried, not a carrying, agent?
In the quotation made, at page 229, from "Elementary Physics," we are
told that when electricity passes through a gas or vapour of very small
pressure, "We have a series of zones alternately light and dark." Now
we ask, Why should part of these zones be dark? and the only answer
to be given is--simply because there is no light in them, nothing in
them to carry or hold light. Otherwise, we cannot understand why they
should appear to be dark. We cannot imagine a glass tube with light
and dark zones in it longitudinally--we have understood the zone to
be longitudinal; transverse sections would not be zones--at the same
time that light is passing freely through it transversely, i.e. from
side to side, unless it is that in the dark zones there is nothing, not
even the all-pervading ether, to carry or hold light in; therefore, we
conclude again that there is no light where there is no ether.
For an explanation of the existence of light and dark zones in the
almost exhausted cylinder or tube, we refer to Professor Tait's
treatise on "Heat," where he says, in section 358, "What happens at
exceedingly small pressures is not certainly known. In fact, if the
kinetic gas theory be true, a gas whose volume is immensely increased,
cannot in any strict sense be said to have one definite pressure
throughout. At any instant there would be here and there isolated
impacts on widely different portions of the walls of the containing
vessel, instead of that close and continuous bombardment which (to our
coarse senses) appears as uniform and constant pressure." Admitting
the truth of the kinetic theory of gases, we can see that in a vacuum
so rare that only electricity at a very high pressure could be forced
(carried?) through it, we have the prescribed conditions in which
there cannot be "one definite pressure throughout" the whole tube; in
other words, we shall have some places in a vacuum tube where there
is no gas at all, or perhaps even ether, and others where the gas is
so rare that it takes a powerful stream of electricity to light it
up in passing through, whether the lighted-up zones be composed of
gas, or of ether, or part of both. If it did not pass, there would be
no light-streak even. And further, we have to notice that the light
and dark streaks would be changing places constantly, owing to the
collisions of the small number of atoms or molecules of the gas, still
not exhausted from the tube, driving each other from place to place.
All this makes us think of what is the real carrier of electricity
through a partial vacuum, through a gas, or through a substance of any
kind whatever, and we can only imagine it to be the ether. In that
case the conductivity of any substance would depend upon the quantity
of ether contained in it, and we can give no other reason for there
being conductors and non-conductors of electricity. All matter has been
thought to be pervaded by the ether, but we have said before that this
must be the case in a limited sense only. It can be shown that glass
is permeable to ether, and is therefore not an absolute non-conductor.
Metals are supposed to consist of atoms bombarding and revolving around
each other under the control of ether. Intermediate conductors may have
the quantity in them of ether corresponding to their conductivity;
and the compressibility of water, or any liquid, may depend upon the
quantity of the ether mixed with its ultimate atoms.
Although we consider it to be going rather beyond the course we had
laid out for ourselves, we cannot help returning to the article on the
"Northern Lights" in "Science for All," quoted above in connection with
electricity in the presence of a vacuum; because it helps to illustrate
the subject we are dealing with.
In the regions where these Lights are seen, we know that there can be
no want of ether, because it is supposed to pervade all space; but we
know that there must be a very great want of air, or vapour of any
kind, due to the height above the earth at which they are seen. Here,
then, we have a great field for differences of pressures being caused
all through it, by the collisions among themselves of the molecules
or atoms of the extremely attenuated air; we have the higher or lower
pressed zones of the laboratory experiment spread out before us, and
if we suppose currents of electricity to be passed through them, we
have an aurora in the high heavens, a counterpart of what was seen in
the vacuum tube. The bombardment of the molecules continually shifting
their positions and creating zones of different pressures, when lighted
up by electricity, would easily account for the flashes, coruscations,
and changes of the aurora; but, how does the air get up so high as is
stated in the quotation at page 228?
We cannot accept the supposition of Professor A. S. Herschel that
the air is carried up to the height of from 100 to 300 miles by
electricity. We must believe, till evidence is given to the contrary,
that electricity is a carried, not a carrying, power. Conductors of
sound are all material substances; sound is not. It seems logical,
therefore, to conclude that the ether is a material substance, because
it conducts light, heat, etc. etc., which are not material substances.
Proof is therefore required that electricity is a material substance,
before it can be called a carrier. That air does somehow get up so high
there can be little doubt, as is satisfactorily proved by the burning
of meteorites when they come into our atmosphere at heights said to be
more than 300 miles. How it does mount up so high is not so wonderful
as it seems, when we take into consideration the causes of the trade
winds, which are: The upward currents of the air created by the heat of
the sun; the centrifugal force inherent in it at the time of leaving
the earth; and its angular motion, which may be, at a guess, from 10 to
16 miles per minute, seeing that the equator has an angular velocity
of over 1000 miles per hour. Then, from the time it leaves the earth,
the air must begin to lose its angular velocity, the impelling power
being cut off, and form a bank higher up, opposing the motion forward
of all the air following it, so that immediately above the tropics
there must be forward motion and obstruction, producing whirlwinds
of which we can see or know really nothing, though they must exist,
and which may carry air or vapours up to very great heights, carrying
with them densities far beyond what would correspond to the simple
attraction of the earth. At these heights this attraction would be very
much diminished, and almost the only way in which the density of the
whirlwinds could be diminished would be by expansion, which would not
be very active in bodies already very considerably attenuated, as the
whirlwinds would naturally be. Their movement towards the poles would
be the same as that of the trade winds has always been supposed to be;
and we can now see how there can be air at great heights in the aurora
regions, not carried up by electricity. In fact, the air may, or rather
must, have carried the electricity up with it, as we shall, we believe,
presently see.
We have not supposed that all the air, raised from the earth by the
heat of the sun, is carried up to such altitudes and to its polar
regions, but only a very small part of it; and we have to add that
there is perhaps not always electricity present in sufficient quantity
to illuminate the air when it is carried up, which would, from the
nature of its ascent, be undoubtedly divided into zones, streams, or
belts at different degrees of tenuity. We do not doubt, or rather we
believe, that electricity is always present in the atmosphere; but we
are not sure that it is always so in sufficient force to make itself
manifest. A very homely example of this is: Stroke a cat's back in
ordinary circumstances, and it will only arch it up in recognition of
the caress; but stroke it on a frosty night and it will emit sparks of
electricity. The cat's hair does not shine--perhaps fortunately for the
cat--because the electricity in it is not present in sufficient force,
and only shows itself when the hand acting like a brush collects it
into sparks. This shows not only that electricity is more abundant in
the air at one time than at another, but that it is more so in cold and
dry than in warm and moist air. It also shows one of the reasons why
auroras of great brilliancy and extent are not continually in play in
their own special regions, which is the want of a sufficient supply of
electricity; another reason being, the absence of the requisite zones,
or masses of air in cyclonic motion at different pressure and in
sufficient quantity. We understand from what we have read that the glow
of the aurora is seldom awanting in clear weather in the far north, and
can imagine that there is always a sufficient supply of electricity
and attenuated air to maintain the glow constantly; and also that the
brilliant displays are only made when there is a sufficient influx of
whirlwinds of air at low and varying pressures, and of electricity in
sufficient force to light them up. We should suppose that the bright
flashes would take place where the pressure was greatest, and the
illuminated darkness, so to speak, where it was least. Electricity does
not carry up air to these heights, neither does magnetism bring it down
from the sun; still a magnetic storm produces brilliant auroras.
Confronting these reflections with the laboratory experiment we have
cited at page 228, we see that they are very fully confirmed by it;
perhaps it would be more true to say that they were originated by
it. When the current of electricity was first turned into the glass
cylinder, no result was perceived. This must undoubtedly be construed
into showing that the light in the cylinder, passing through it
from side to side, was more powerful than the diffused light of the
electricity passing through it from end to end; which was the reason
why there was no result. By diffused, we mean that the electricity,
turned into the cylinder through a thin wire, would immediately spread
out over the whole of its width (or cross section) and thus very much
weaken its light-giving power. When exhaustion had proceeded to a
sufficient extent to produce the soft tremulous light, we can only
conceive that the transverse light had decreased so far that the
diffused light of the electricity, passing longitudinally, had begun
to balance it, which caused the tremulous appearance on account of the
one beginning to disappear and the other to take its place. And when
the light extended through the whole length of the cylinder and the
phenomena were reversed; and when the light died away altogether, when
the vacuum became sufficiently pronounced; we can only believe that
there was no light at all in it; neither natural light passing through
it transversely, nor light of electricity passing longitudinally.
Should any one object to this demonstration, as we may call it, we
refer him to the quotation, made at page 229, from Professor Balfour
Stewart's "Elementary Physics," and ask him, How could there be dark
zones in a tube, through which light ought to pass freely from side
to side? The thing appears to be tremendously absurd. There were dark
streaks in the tube and other streaks of gas, or vapour of some kind
at very low pressures (see also quotation from Professor Tait at page
232) that were lighted up to some extent by the current of electricity,
but even these died away. We do not pretend to impugn the idea that the
stratification of light and dark zones depended upon the nature of the
substances in the tube, we only want to insist that the substances left
in it were so extremely rare that electricity could not pass freely
through it longitudinally, nor daylight transversely, else there could
have been no dark zones in it; and that even the ether was in such
small force that it could not perform the carrying duties assigned to
it.
We have often wondered whether any experiments have ever been made
to ascertain whether any changes, as far as the presence of light is
concerned alone, have been brought about by producing a vacuum in a
tube. The gradual dying away of light, and its final disappearance,
are certainly suggestive of changes, and may have excited curiosity to
know what actually happens. That there are changes cannot be denied,
and it would be satisfactory to know what they are. It appears to us
that one simple and easily made experiment would give a good deal of
information on the subject. Let a glass tube of cylindrical form--one
of those prepared for vacuum experiments--be placed in a slit in the
window-shutter of a dark room, so that absolutely no light can pass
into the room except through the hollow part of the tube; which might
be effectually managed by burying two opposite sixth parts of its
circumference in the wood of the shutter, and there would still be left
one-third of its diameter for the free passage of light from side to
side. When so arranged, and when still full of air, let a spectrum be
taken of sunlight passing through it, to serve for comparison. Then
let a high vacuum be produced in the tube, and another spectrum taken
and compared with the first. This will at once show whether any change
has been produced or not. Should the difference we expect be found,
the experiment might be extended by spectra being taken at different
degrees of exhaustion, from which some useful information might be
derived.
We have said, at page 129, that the ether does not pervade all
bodies of all classes, and such must be the case in some measure at
least, otherwise there would be no non-conductors of electricity, no
insulators for our electric telegraphs and deep sea cables. Were glass,
for instance, pervaded freely by the ether, and the ether is in reality
the carrier of electricity, then electricity could pass freely through
glass, but it does not; therefore, there can be no, or at all events
very little, ether in glass or any other insulator. We can see, then,
the possibility of the ether being removed from a glass tube, provided
it is a material substance, by shutting up one end of it with a stopper
of glass and passing a perfectly-fitting glass piston through it to
the other end. Suppose this done, it would be quite safe to say that
electricity could not pass through the tube, because there would be
nothing--absolutely nothing--to carry it, not even the piston-rod, for
we could have that not only made of glass but on the outside of the
piston. In this case the result would be exactly the same as when the
contents of the tube were pumped out of it, and the residue left, if
any, would be the same, that is, an immeasurably small quantity of the
ether which had filtered through the glass. It may be argued that it
would be impossible to make such an experiment as we have proposed,
but that does not damage in the slightest degree the correctness of
the consequences deduced from it; any more than the impossibility of
constructing a perfect heat engine destroys the deductions drawn by
Sadi Carnot, from the study of such an ideal machine. We can grant that
glass being not an absolute non-conductor, the ether might, in course
of time, ooze through it and fill the tube again, while gas, air, or
dust could not so ooze through it, and thus re-establish the current
of electricity that was stopped for want of it; but we cannot grant
that there was any very perceptible quantity of ether in the tube, when
the electric current could not pass through it without dismissing the
ether altogether, and dropping back into the difficulties out of which
it has in many cases lifted us.
The evident fact that the ether cannot pass through glass freely,
and therefore cannot carry electricity with it, may be disputed by
referring to the free passage of light, and also of heat, through glass
and other substances, in virtue of transparency and diathermancy, two
terms that have the same meaning, at least, as nearly as that light
and heat mean the same thing; but we believe that this free passage,
instead of invalidating our reasoning, only tends to prove that the
ether is a material substance; because, if it is not, it might pass
through transparent bodies just as easily as light and heat do. Of
course, this belief obliges us to show how light and heat do pass
through a transparent body such as glass, and the mode is exactly the
same as of heat passing through any other body that is a conductor
of heat. Glass is a substance that is known to be a bad conductor,
but it is also known that it is not an absolute non-conductor of
heat; therefore, there is no difficulty in supposing that it, and
its companion light, can be conducted through glass with velocity
proportioned to its thickness. We know that in the case of a pane of
glass in a window it is practically instantaneous, but that does not
mean that it is absolutely so. We know also, that in passing through,
both are refracted, and that comparatively little heat is imparted to
the glass, even under bright sunshine, which may be very well accounted
for by the ether on the other side of the window pane carrying them
(light and heat) off, in the same direction they were going, quite
as fast as they could be conducted through the glass. But, supposing
there was no ether in the room to which the window gave light, or gas,
or elementary matter of any kind--a condition which could be obtained
by making the room of glass and pumping out its contents as was done
with the vacuum tube--What would be the result? There would be no wave
motion to carry on light and heat into the room, and it would be
in the same state as the exhausted tube, except that there would be
no electricity in the room--no current being passed through it--nor
anything in sufficient quantity to be lighted up if there was; the
light would be stopped and reflected back from the glass, and nothing
inside the room could be seen; not even that it was dark, because there
would be no electricity to make dark zones visible. The window, or
rather the whole room, would become a many-sided mirror, for reasons
almost identical with those that account for a sheet of glass being
made into a mirror.
We confess that all these deductions have startled us, but we can see
no flaw in the reasonings which have led to them. If it is not for
want of ether--in sufficient quantity at least--and the admission of
variable quantity is to admit that it is a material substance, that
electricity will not pass through a highly exhausted tube, we cannot
imagine what can be the reason why it does not; simply accepting it as
a fact is by no means satisfactory. In the dilemma between renouncing
the ether altogether or acknowledging its disappearance--effective at
least--it occurred to us that it might be for want of heat, and that
in terms of the inter-dependency of temperature and pressure in a gas,
heat disappeared in proportion to the decrease of pressure in the air
or gas that was being exhausted from the tube, or from cold being
applied to it from without; but that notion has already been disposed
of by our own work, when we have seen that a gas in a close vessel can
be heated or cooled to any degree, altogether independently of pressure.
When, acknowledging that the ether ought to have some temperature as
well as density, we have said that it might have the temperature of
vibration whatever that might be, thereby admitting that we could not
pretend to determine what it is; nevertheless, we may take a look at it
from a distance, and at least see what it cannot be, anywhere within
the limits of our system. We have shown, at page 220, that when the
original nebula was about 29,000,000 miles in diameter, its density
must have been 0·179 that of air at atmospheric pressure, and its
temperature -225°, and that these could be neither the density nor
temperature of space. With this temperature, then, it is evident that
there was still heat enough and to spare in the ether--considering it
to be a material substance--to cause it to vibrate and perform its
assigned offices; and, therefore, it could not be for want of heat that
neither it, nor light, nor electricity could be carried through the
vacuum tube, but for want of the ether in due quantity; consequently,
the temperature of vibration cannot be so great as -225°. Turning
back now to page 129, we find the density of the ether estimated at
1/5,264,800th of an atmosphere, which corresponds to an absolute
temperature of 0·000052° or -273·999948°; but on the following page we
expressed our opinion--well founded, we believe--that the estimate was
too high, i.e. too dense, and that it might be 2, 3, or 4 times, or
more, too great. Be this as it may, we can see that if the ether alone
occupies space--beyond a comparatively very limited distance from any
body belonging to the solar system--it must be almost absolutely free
from temperature of any degree, for the difference between -273·999948°
and -274° is virtually nothing; or it must have a special temperature
derived from the collisions of its own atoms, or from the sun. We have
said more than once that the temperature of space cannot be so high
as _minus_ 225°, and now we cannot believe that it can be so low as
absolute zero, because the ether in it is credited with the motion of
vibration, which must be either the cause or effect of heat. What then
shall we say? We can only speculate.
We can suppose that when the chemical elements were created, or evolved
by some process, and began to attract each other, they had the ether
to carry them into collision and produce heat; and that it, being also
a material substance, became heated to the same degree as the other
matter, always increasing in proportion to its state of condensation,
the ether mixed with the other matter being also, of course, condensed.
Then, following up this supposition, we can see that when the sun came
to be condensed to its present state, the ether must have had the same
degree of heat as itself at its surface, and be of the same density as
it would in our air at the earth's surface condensed to the pressure
of nearly 28 atmospheres; knowing as we do that the attraction of the
sun at the surface of its photosphere is almost 28 times greater than
that of the earth at its surface. Under this supposition, therefore,
the ether might emit light just as surely as any other matter that may
exist, or can be seen, in the corona or atmosphere of the sun, and
might be the cause of the Zodiacal Light, probably more naturally than
any other cause that has been imagined for it.
Mr. Proctor, in his "Sun," has given us a most elaborate description of
how the Zodiacal Light could be produced by the swarms of meteorites
and meteors, that are generally supposed to be floating around the sun
and continually showering in upon it, and we confess that his reasoning
is very plausible; but it, along with other similar hypotheses, has one
very serious defect which it is hard to get over, under our existing
ideas about matter and its origin. If there is a constant rain of
meteorites and meteors falling into the sun now, and the same has
been going on during the multitude of millions of years that it is
supposed to have existed, we have to acknowledge that it must either
come to an end some day, or that there is going on a constant creation
or evolution of matter to keep up the supply. It will not suffice to
accept the hypothesis that the supply comes from other suns, or any
idea of that kind, because each one of them would finally find itself
alone with its planets, etc., if it has any, in its domains the same
as our sun. Neither would it suit the ideas of those who consider that
matter has existed from all eternity and has _made itself_ into all
sorts of bodies or systems to suit them. Without continued creation,
or evolution, matter must end in condensation into one mass. There can
be no self-evolution to keep up the supply of matter. It would require
another and exactly opposite power to unmake the final mass, and
another change to original matter to start anew on the old course.
But we are speculating too soon. It may be said that if the Zodiacal
Light is caused by the ether, and if the ether is a material substance,
it must be exhausted sooner or later, just the same as all other
matter and the whole universe to one mass the same as before; and also
that we have no authority for supposing that the ether can be heated
and cooled or condensed and expanded. But we think that with what we
have done in this chapter, and what we will be able to show in the
following one, we shall be able to get over all these difficulties,
and also show how the universe might be dissolved and renewed by the
ordained process of evolution.
CHAPTER XIV.
PAGE
244 The ether considered and its nature explained. Further proofs
given by Dr. Crookes's work, of its material substance.
246 Highest vacuum yet produced. Absorbents cannot absorb the ether.
247 Dr. Crookes's definition of a gas. Not satisfactory. Why.
248 A fluid required to pump matter out of a vessel.
249 Gas as described by Dr. Crookes would not suit.
250 The ether the only elastic fluid we have.
The only real gas, if it is a gas.
250 A possible measure of the density of the ether.
251 Causes of dark and light zones in high vacua.
252 The real conductor of light in a high vacuum.
254 How a vacuum tube glows, when electricity passes through it.
255 Conclusions arrived at through foregoing discussions.
256 Some exhibitions of light explained.
257 Gases can be put in motion, but cannot move even themselves.
258 The ether shown to be attraction. And primitive matter also.
259 All chemical elements evolved from it. Its nature stated.
259 Action at a distance explained by the ether and attraction
being one and the same.
The idea that the ether can be pumped out of a tube of any kind,
along with the air or gas that has been shut up with it therein, will
very probably be declared to be absurd, by reference to Dr. Crookes's
experiments with his Radiometer, and investigations into the nature
of radiant matter; but when duly considered his work seems to confirm
it, and our reasonings in support of it, in a very convincing manner.
Radiant heat, or light, is shown, no doubt, to penetrate into an
exhausted bulb and to cause a radiometer to revolve, but we have to
consider what is the state of exhaustion at which its force is shown to
be greatest, and why that force decreases rapidly when the exhaustion
is progressively increased beyond a certain point; for a certain amount
of exhaustion is required first of all to diminish the resistance of
the air or gas to the vanes of the radiometer, before the radiant heat
gathers force enough to make them revolve at all. Its greatest power
to produce revolution is shown to be when the exhaustion is at from
30 to 60 millionths of an atmosphere, according to the gas or medium
in the bulb--see "Engineering," Vol. XXV., page 155--and decreases
from that point, often rapidly, as the exhaustion is increased, till
at last it ceases altogether. Everybody who has taken any interest
in the subject, knows that Dr. Crookes has exhausted radiometers to
such a degree that they could not be influenced by the radiation of
a candle placed a few inches from the bulb. We are not told at what
degree of exhaustion this took place, nor at what degree repulsion,
by radiation of heat, is supposed to have ceased altogether, but that
does not matter, even though it should only cease when the vacuum
comes to be absolute--most probably a stage to which it is impossible
to attain. What concerns us is the fact that repulsion by radiation
does reach a maximum at a certain degree of exhaustion, and then falls
off as the exhaustion is increased; and what we have got to consider
is what is the cause of the falling off. We are told it is caused by
the attenuation of the matter, gaseous or material, contained in the
bulb, and we are satisfied with the explanation. But in order to be
thoroughly so, we must insist on believing that it is part of the whole
of the matter that has been operated on; not only of the gas and other
matter to the exclusion of the ether, but of the whole, ether and
all. If the ether is left behind intact, it must perform the offices
it was created for by the imagination of man, or man must discard it
altogether. If it ceases to carry light and heat through a vacuum, it
is of no more use than we found it to be in the case of electricity,
and man is bound to dismiss it as a useless operative, who will strike
work for no reason whatever. Some people have supposed the ether to
be an absolute non-conductor of electricity, because it does not
convey that agent through a vacuum. Will they also declare it to be a
non-conductor of light and heat? If they will not, then they--and we
presume everyone else--must admit that it can be pumped out of a bulb,
in the same way as a gas or any other fluid matter.
Here we are led into another consideration, viz., whether the ether
is exhausted from a receiver by pumping alone, or by the help of
absorption. In his lecture, "On Radiant Matter," delivered at the
British Association, at Sheffield, August 22, 1879, Dr. Crookes said:
"By introducing into the tubes appropriate absorbents of residual
gas, I can see that the chemical attraction goes on long after the
attenuation has reached the best stage for showing the phenomena now
under illustration, and I am able by this means to carry the exhaustion
to much higher degrees than I get by mere pumping;" and that when
working with absorbents: "The highest vacuum I have succeeded in
obtaining has been 1/20,000,000th of an atmosphere, a degree which
may be better understood if I say that it corresponds to about the
hundredth of an inch in a barometer column three miles high." (We quote
from "Engineering," Vol. XXVIII., page 188.)
Now, what are we to think? Are we to suppose that the ether was in
part removed by the absorbents? We think we are justified in saying
that the absorbents had not anything to do with the exhaustion of the
ether, because Dr. Crookes used different kinds of absorbents for the
different kinds of gases he dealt with, and it is hard to believe
that all the _media_ he used were equally effective in absorbing the
ether as they were with the gases. On the other hand, if we consider
that the pumping was the only agent in removing the ether, we ought to
acknowledge that it must have been more effective with regard to it
than to the gases before absorption was resorted to with them; or that
a stage had been reached at which the pump could not extract any more
ether from the bulb. We shall have more to say of this presently. It
is a difficult matter to determine, but there is one thing we can see
clearly; when the exhaustion of the bulb was raised to 1/20,000,000th
of an atmosphere, the density of the ether--of itself--must have been
at a lower degree than that. Consequently if we assume its normal
density to be 1/5,264,800th of an atmosphere, in terms of the estimate
we quoted from "Engineering," it must have been diminished to less than
one-fourth of that when the above high vacuum was obtained; because it
must have been the density of the residual gas, or matter, and of the
ether, added together which amounted to 1/20,000,000th; the same as we
have argued with regard to the solar nebula when at 6,600,000,000 and
29,000,000 miles in diameter.
One thing leads to another, and we have again to repeat our
question--What is a gas? And all the answers we have been able to get
to it hitherto have been far from satisfactory.
A little earlier in the same lecture, referred to a few pages back,
Dr. Crookes, after telling us, very elaborately, what would have been
the definition of a gas at the beginning of this century, goes on to
say: "Modern research, however, has greatly enlarged and modified
our views on the construction of these elastic fluids. Gases are
now considered to be composed of an almost infinite number of small
particles or molecules, which are constantly moving in every direction
with velocities of all conceivable magnitudes. As these molecules are
exceedingly numerous, it follows that no molecule can move far in any
direction without coming in contact with some other molecule. But if
we exhaust the air or gas contained in a close vessel, the number of
molecules becomes diminished, and the distance through which any one of
them can move without coming in contact with another is increased, the
length of the mean free path being inversely proportional to the number
of molecules present. The farther this process is carried, the longer
becomes the average distance a molecule can travel before entering into
collision; or, in other words, the longer its mean free path, the more
the physical properties of the gas or air are modified."
Of course, what we have looked upon as Dr. Crookes's definition of
a gas, ends with the second sentence of the above quotation, and
is far from being sufficiently complete to be satisfactory; but we
have continued to quote from the lecture, because it contains matter
which demands consideration, and helps very powerfully to support the
conclusions we have been arriving at.
Why the definition is not satisfactory, is that it does not tell us
what there is in the spaces between the molecules of what is called the
gas. If there is room for them to move in every direction there must
be spaces between them, and these spaces must either be absolutely
empty, or filled with something. If they are supposed to be empty, then
the molecules being actually small pellets, like diminutive marbles,
or snipe-shot, we immediately begin to think why gravitation does not
make them, being ponderable bodies, fall down to the bottom of the
bulb; and seeing that, by the definition, they are evidently considered
not to do so, we think of what can keep them from falling, and of how
they can be pumped out of a bulb or any sort of vessel. If we fill
a vessel with marbles, snipe-shot, wheat flour, or dust, and set a
pump to work on it, we shall find that we make very little progress
in pumping them out of it. At first we might extract a puff or two of
flour or dust--marbles or snipe-shot by no means--carried into the
pump by any air there might be mixed with them, but that would very
soon come to an end; besides, there would be air, gas, something, in
the interstices--if any--of the flour or dust to drive them into the
pump when a vacuum was formed in it, and the puffs would cease when the
air, which would be in exceedingly small quantity, was all extracted.
But independently of all this, we have supposed the spaces between the
gas pellets or molecules to be absolutely empty, and there would be
nothing to push them into the vacuum created in the pump. There is no
possibility of pumping marbles, sand, flour, or dust out of a vessel
without the assistance of a fluid agent of some kind, water, gas, or
air; and even then it would be done with much difficulty.
Let us, then, suppose there is some such agent filling the spaces
between the atoms of the gas and think of what it must be. Were we to
ask the question we have a strong suspicion the first impulse of many
people would be to reply--With gas of course. But this reply could
not satisfy us. We should immediately be led to think of that gas
also consisting of atoms with vacant spaces between them filled with
something--some more gas; and were we to follow up that thought through
a sufficient number of stages, it is easy to see that in the end the
whole space occupied by any gas would come to be filled up with its own
solid atoms, without any empty spaces between them through which they
could move; and so rendered quite incapable of pushing each other into
a vacuum formed by any pump that might be applied to extract them from
any vessel of any kind; or we must suppose that each particle would
fly of its own good will into the vacuum made by the pump--as it were
on the wings of the morning. But we recall to memory that the wings of
the morning do not always carry us to rest, and we see that filling the
spaces with gas would only end in choking up the vessel altogether. It
might be said: Nobody imagines that the molecules of the gas in the
spaces would be sufficient to fill them up altogether; and then we
have only to ask, What then would there be in the spaces between the
molecules of these successive gases to prevent the whole of them from
gravitating to the bottom of the vessel? And to add that there would
still be empty spaces left, absolutely empty, that would have nothing
in them to help in any way to force the molecules or atoms of any gas
or vapour into a vacuum anywhere. It is clear then that a gas, such as
Dr. Crookes has described a gas to be, could only end in filling the
spaces left between its molecules or atoms. It would be an obstruction
to their collisions and bombardments which form an essential part of
the description or definition.
We must, therefore, have recourse to something else for filling up the
spaces between the molecules of a gas, and the only thing we can lay
hold of is our _limited liability_ agent the ether, which we allow to
do all we want it to do and nothing more. Vapours of solid or liquid
matter would be of no use, for they would only condense into solid
or liquid matter; unless always maintained at their temperatures of
evaporation or ebullition, and that would at the best be only another
form of a gas--nobody would use a liquid to assist in pumping air out
of a vessel--and, besides, we should still have to show what keeps
their particles apart, what fills the spaces between them, which would
force us to appeal to the ether as the only source, just as before. If
there are no spaces between the particles there can be no vapours.
If by pumping air out of a close vessel the number of its particles is
diminished, and we acknowledge that the ether pervades all space and
matter, in a greater or smaller degree, then we must either recognise
that a pump is able to separate the particles of the air from the ether
which pervades it in the vessel, and extract them alone; or we must
acknowledge that along with the particles of the air, the pump extracts
a corresponding portion of the ether. Which of these two consequences
of the pumping we have to choose cannot for a moment be doubtful. It
would be as reasonable to suppose that we could pump the colouring
matter out of a pond of muddy water, or the mud itself, and leave the
clear water behind, as to suppose that the molecules of air, or of a
gas, could be extracted from a close vessel, by a pump, and the ether
left behind in it.
We have called attention two or three pages back to the fact that a
fluid agent of some kind is required, in order to be able to pump
matter of any description out of any kind of vessel. For solid matter
a non-elastic fluid will suit, but for gaseous or vaporous bodies
an elastic fluid is required; but we have just seen that what have
hitherto been considered to be elastic fluids, that is, gases and
vapours, have no elasticity whatever of their own, but are undoubtedly
and in reality solid matter; and that in order to become elastic fluids
they have to be mixed with the ether, or something that has yet to
be discovered, invented, or imagined. If, then, until such a body is
found we take the ether as a substitute, we have to acknowledge that it
must be not only an elastic fluid but a material substance, capable of
being compressed and expanded, and heated and cooled; for nobody could
conceive clearly the existence of an elastic fluid that is not subject
to these conditions. He could not understand how the molecules of a gas
could be contracted, expanded, heated and cooled in a vessel, while the
elastic fluid which gave them liberty to move or to be moved, remained
constantly at one density and temperature. Furthermore, until such a
substitute is found, we have to acknowledge that it is the only thing
we have any idea of corresponding to a gas as described by Dr. Crookes;
that is, a multitude of molecules colliding with and bombarding each
other or their prison walls. But even beyond this we can uphold it to
be the only real, independent gas there is; because, being an elastic
fluid, there is no necessity for there being empty spaces between its
molecules, or even having molecules in the common acceptation of the
term. We have no reason to think that there are empty spaces between
the molecules or particles of indiarubber; and if there are, the ether
is the only substance we can properly conceive them to be filled with.
The law of Avogadro is, that "Equal volumes of gases and vapours
contain the same numbers of molecules, and consequently that the
relative weights of these molecules are proportioned to the densities."
Therefore we must always bear in mind that it is the _weights_, not
the _volumes_, which are equal, and that the volumes may be very
different. On this earth of ours, then, we may say with certainty that
an atmosphere of gas is composed of a definite number of its special
kind of molecules, mixed with a definite quantity of the ether, in
such proportion that the sum of their densities shall be equal to the
density of the air, at atmospheric pressure at sea level, and at 0°
of temperature. Holding this belief, we can see that each molecule,
or rather atom, of each gas must have its own amount of displacement
to enable it to float in the ether with which it is mixed. This would
account in the most satisfactory manner for the diffusion of gases,
whereby any molecule, or atom, may float wherever it is driven by
collisions with its neighbours, be it above, or below, or on a level
with, a molecule of a lighter or heavier gas. Therefore, were it
possible to determine with sufficient accuracy the dimensions of the
atoms of all gases, perhaps even of a limited number of them, it would
be possible to calculate the real density, or specific gravity, of the
ether.
We have not forgotten that when, by pumping, the ether was reduced to
at least one-fourth of its normal density, its buoyant power would be
reduced in the same proportion, nor that, when in a state of rest, the
displacement of a molecule, which enabled it to float in the ether,
would not be sufficient to make it float at one-fourth of that density;
but it might be supposed that when so far relieved from pressure, the
molecule could expand in proportion to the relief, especially if its
form were that of a vortex ring, or of a hollow sphere. However, should
this supposition not be admissible, we shall see presently that it is
not necessary. We know that as long as any degree of heat remains in
a gas collisions of its molecules will continue, dependent on their
attraction for each other, which may drive them to any part of the
containing vessel; and that it can only be when they are cooled down
to the absolute zero of temperature that they can come to be at rest.
But as we believe that the ether can never be reduced to this absolute
absence of temperature, nor completely extracted from any vessel, we
cannot acknowledge that the molecules of any gas, left along with it in
the vessel, could ever come to be absolutely at rest, even although the
molecules did not increase in volume with the diminution of pressure.
And we think this conclusion will agree with the opinion of Professor
Tait, expressed in the quotation, made at page 232, from his work on
"Heat," where he says: "In fact, if the kinetic gas theory be true, a
gas whose volume is immensely increased, cannot in any strict sense be
said to have one definite pressure throughout." This, of course, is
tantamount to saying that the diffusion of gases cannot continue to be
always exactly regular at extremely low pressures, and must vary as the
vacuum is increased; so that the volumes of the atoms and consequent
displacements may continue always the same under all pressures. We see,
then, from this quotation, that in all probability the molecules of a
gas are not always equally buoyed up by the ether in a high vacuum;
which very likely is the reason why there are dark streaks in it;
streaks without any visible molecules of gas in them, because the ether
was not dense enough to keep them afloat.
We have still something to add in support of what we said, at page 238,
of glass not being pervaded by the ether, in the common acceptation of
the word, and of our acknowledging that the ether might, in the course
of time, ooze through it and fill up the bulb again, while air, gas
and dust could not so ooze through it--nor even the larger particles
of the ether; should we be forced to acknowledge that it consists of
particles.
In one of a series of articles in "Engineering," Vol. XXV., on
Repulsion from Radiation, we find, at page 155, what follows: "With
the same apparatus, Mr. Crookes conducted a long series of experiments
for determining the conductivity of the residual gas to a spark from
the induction coil. In air he found, at a pressure of 40 millionths
(1/25,000th) of an atmosphere, which will be seen from the diagram,
is the pressure at which the force of repulsion is at a maximum,
that a spark whose striking distance at the normal pressure of the
atmosphere is half an inch will illuminate a tube whose terminals are
3 millimetres apart. By pushing the exhaustion farther, the half-inch
spark ceases to pass, but a one-inch spark will illuminate the tube,
and as a vacuum is approached more electromotive-force is required to
force the spark to cross the space separating the terminals within
the tube, until at still higher exhaustion a coil capable of giving a
6-inch spark in air at the pressure of the atmosphere is required to
show any indication of conductivity in the residual air. It was found,
however, in experimenting with so powerful a spark that occasionally
the glass was perforated by the discharge taking place through the
bulb; but it is a remarkable fact that the perforation in such cases
was so excessively small that several days were occupied before
equilibrium of pressure was established between the inside and outside
of the bulb."
Here we notice first--and it was the reason why we have made the first
and longest part of the quotation--that the spark whose striking
distance was half an inch at the normal pressure of the atmosphere,
fell to under one-fourth of its power in a vacuum of only 1/25,000th of
that pressure; that when a one-inch spark was required to illuminate
the tube, it must have decreased to one-eighth in a vacuum of
1/50,000th; and, if it be admissible to follow the same proportion,
the 6-inch spark must have been exhibited in a vacuum of 1/250,000th
an atmosphere at least. Perhaps all this experiment was carried on
in _vacua_ produced by pumping alone, and the final vacuum may have
reached a greater height than that which we have just mentioned; but
the most interesting part of it is the perforation of the bulb by the
6-inch spark. In it we have to consider what was the conveyer which
carried the electric spark through the glass of the bulb, instead of
to the other terminal of the coil so close at hand, and it is a very
difficult problem to solve. We naturally recur for some solution to the
stratification of light given out when an electric current traverses
a gas at very low pressure and gives rise to zones alternately light
and dark as noted in the reference we made, at page 229, to Professor
Balfour Stewart's experiments. We cannot think it unreasonable to
suppose that the dark zones contained no matter at all that could be
lighted up, and that it was the lighted zones alone which contained
carrying matter for the electricity. If so, we can easily imagine
one of these zones or strata carrying the perforating spark from the
induction terminal to the nearest part of the glass of the bulb, for it
was as possible for it to lie in that direction as in the direction of
the other terminal, and the difference of distance between the first
terminal and the glass, and between the two terminals, would not be
so great as it appears to be on simply reading the accounts of the
experiments; but we have still to think of how it managed to force
itself through the glass of the bulb.
To get over this difficulty, we can refer to what we have said, that
is, that glass may be thoroughly pervaded by the ether in an almost
infinitesimal degree, and suppose that the electricity may have
discovered, or rather been led to, the ether contained in the glass
tube or bulb, and so found its way to one of the oozing holes we have
said might exist in the glass; even the oozing hole may not have passed
quite through the glass, and there might remain a very thin film to be
burst open before perforation was complete. Also we may note that the
zone which performed the office of carrier to the side of the bulb was
much more probably composed of residual ether than residual air or gas,
or at the least formed a preponderating part of the carrying element.
The fact of the hole being so minute "that several days were occupied
before equilibrium of pressure was established between the inside and
outside of the bulb" on such occasions, goes far to prove that the
carrying agent through the glass must have been the natural carrier
of electricity, light, and heat. We cannot conceive that an eruptive
force could open such a small passage through the glass of the bulb,
but we can conceive that it should be able to force itself through
a very minute passage already open, and even join two or more such
passages into one. This conception makes us think of the many oozing
passages there may be through a glass bulb; passages so minute that
the ether might pass through them, but nothing so gross as any of our
known gases; in fine, so minute that glass, for all the compact look
it presents to us, may be only as a very fine sponge in respect to the
ether. However, that the perforations related in the above quotation
were large enough for air to pass through them there can be no doubt,
otherwise the equilibrium between the pressures on the inside and
outside of the bulb could not have been re-established even after many
days; for there still remains the idea that the oozing holes might be
so small that nothing but the ether could pass through them.
Should the glass of a vacuum tube or bulb be pervaded by the ether in
the manner we have supposed it to be, and we believe there can be no
doubt that it is so, it is obvious that its glowing when a current of
electricity is passed through it must be caused by the electricity and
consequently of its light, being carried into the body of the glass by
means of the ether imbedded in, and forming a constituent part of, it.
In connection with this we have to remember that the air in the tube
does not glow when it is at full atmospheric pressure, but only when
a certain degree of vacuum has been produced in it; and therefore it
is equally obvious that it is only when the ether enclosed in the tube
is reduced to the same degree of tenuity as that imbedded in the glass
forming the tube, that the light of the electricity can be carried by
it into the glass and make it glow. But to show this more clearly, it
is necessary to refer to the steps by which we believe we have made
very plain what must undoubtedly be the nature of the ether.
(1) First of all we have shown that, if there be such a thing as the
ether, it can be pumped out of a close vessel of any kind; which
proves that it must be a material substance, and in consequence can be
expanded, or rarefied, and compressed the same as any other material
substance; and that if there is no such thing, something else, having
these qualities, has to be invented to take its place. (2) In showing
this it has been made abundantly clear by the example of the hair
of a cat in variable weather, to which we may add the exhibition of
lightning in daylight, that it cannot make electricity visible, or
illuminate any matter, unless the quantity of electricity it has to
carry bears some certain proportion to the density of the ether in the
matter that is illuminated. (3) In proof of this we have shown how,
through its carrying power it can convey electricity of adequate force
up to very great heights, so as to illuminate very rarefied air and
cause auroras; the conveying being done either directly from the earth
or by means of the ether mixed with the air carried up by whirlwinds to
those great heights; and (4) how electricity is carried into the body
of a tube of glass and makes it glow.
With these examples we can extend our ideas to other exhibitions
of light, which, otherwise, we could hardly avoid looking upon as
mysterious. We can see how marsh gas, rising up from boggy ground,
becomes mixed with common air till it reaches a certain density, and
forms the Will-o'-the-wisp when there is sufficient electricity in the
air to make the diffused marsh gas visible, through the medium of the
ether always mixed with it; or, perhaps, rather when the density of
the diffused gas corresponds to the density of the ether. Then we have
the phenomena of films of matter on the surfaces of certain liquids
glowing with appropriate colours; which films must be pervaded by the
ether in proportion to their conducting powers, the same as we have
seen must be the case with all kinds of matter, the light given off
corresponding as is natural to the composition of the films; and of
course this same reasoning, or exposition, applies to the films formed
on, or near, the surface of the sea which produce what sailors call
"fire-on-the-wave." Lastly, and akin to the glowing caused in a vacuum
tube, we cite the case of the glow-worm, the radiation from which must
of necessity contain a certain amount of the ether in it, and may
either glow constantly or intermittently according to its capacity for
carrying electricity or light of any kind, constant or inconstant. Or
if there is no radiation from it, its skin may possess the properties
of a film on the surface of a liquid. We have seen in the "Times" of
September 21, 1896, in its report for that day of the Meeting of the
British Association at Liverpool, that in experimenting with glow-worms
Dr. Dawson Turner had found some difficulty in getting them to glow
when he wanted, but found they gave off the radiation whether glowing
or not. Perhaps his interference with them destroyed the balance of
force between the electricity present and the density of the ether in
it without stopping the radiation.
Hitherto the light given out by a nebula, and any light of the kind
not easily accounted for, has been attributed to incandescent gas not
burning or being consumed, but only glowing. Now it is time to look
upon it as belonging, at least in part, to the ether, and to look upon
the bright line in the spectrum of a nebula as the _Ether Line_. We
shall have to return to this later on.
We said, at page 248, that a fluid of some kind, elastic or not
elastic, is necessary to enable us to pump solid matter out of a
vessel of any kind, and went on to show that a gas as described by
Dr. Crookes, or that can be described, in its own independent state
of existence, by anybody, could not supply the want; because it
consists of particles, molecules, atoms--any name that can be given
to them--which have no power in themselves to move or to give motion
to anything; they can be moved but cannot impart motion to anything,
even to one another, until they are first set in motion by attraction.
This in its turn led us to see that the only elastic fluid we have is
the ether, and our work since then has taught us that we were wrong
in saying at page 250 that a non-elastic fluid would suit for pumping
solid matter out of a vessel; for we now see that what we have been
in the habit of looking upon as non-elastic fluids, must owe their
fluidity, such as it is, to the ether, which, in proportionate degree,
pervades them the same as it does all other matter. In this way we are
run down to the only conclusion we can come to, namely, that the ether
is the only connecting medium and carrying agent of matter that we
have, or even initiator of motion, except attraction; and being matter
of the nature of an elastic fluid, there is no reason why we should not
at once consider it to be attraction itself. It has been looked upon,
for no one can exactly tell how long, as the connecting mechanism of
the universe, thus having, in reality, assigned to it the attributes of
the law of attraction, and all that we have to do is to put it in its
right place. We are, in a manner, taught to look with suspicion on two
agents being required to do one kind of work, or even two kinds of work
that are so closely allied that we cannot separate them in a way that
satisfies us; and this is precisely a case in which we can have one
agent that can connect matter, and at the same time carry immaterial
elements from one place to another.
Having got this length we have still to go one step farther. We
cannot now doubt that the ether is a material substance, and if it
is, there is nothing to prevent us from considering it to be the
primitive matter; in fact it would be absurd to look upon it in any
other light. We cannot conceive of anything having been created before
the ether, or ordained before the law of attraction, and thus we have
the two coeval and one. It is long years since physicists, chemists
especially perhaps, began to think that the great number of chemical
elements cannot all have existed from the beginning of things, and
that it is far more probable that they have all been evolved from
one primitive substance, and this idea must now be gathering more
strength from day to day in view of the new elements that are being
constantly discovered; the unknown is being made known, and the air we
breathe instead of being one in four elements, as in former times it
was considered to be, is now not far from double that number in one.
Adopting this notion, then, the ether is much more likely to have been
the primitive element than any other material substance that can be
thought of. If it has never been thought of in this light, it has come
to be very remarkably near it, as may be seen by referring to the long
quotation we made in Chapter VII., beginning at page 129, where the
idea of the ether being the connecting _medium_ of matter is made use
of to compute its density. Little thought we of this when we made the
quotation, but there was the idea whether the author saw or not all
that was implied in it.
Having broached the notion of the ether being the primitive element
of the universe, or at all events, of the solar system, we might be
expected to show how all the other elements were formed from it; but
that has been done for us in a very much more able manner than we could
have done it. Anyone who chooses to refer to "Nature" of September
2, 1886, will find--in Dr. Crookes's opening address, on Chemical
Science in Section B, at the meeting of the British Association for
that year--a very detailed explanation of how all the chemical elements
might have been elaborated from one that he called Protyle; in which
explanation he will only have to change this word into Ether to
comprehend the process much more easily than by any exposition we could
pretend to draw up. To quote the whole address would be altogether out
of place, and besides, our notes of it are only fragmentary. But for
present satisfaction of those who cannot immediately refer to "Nature,"
we may say that in the same report it is clearly stated that Sir George
B. Airy was of opinion that all bodies may not be subject to the law of
gravitation; and have no cause to think it strange we do not see that,
were the ether and attraction one and the same, the whole universe
would be finally collected into one mass, itself included. They will
have better authority than ours for believing that the ether may
connect matter evolved from itself, without being materially confounded
with it. At the same time we acknowledge the necessity for expressing
our idea of what we consider to be its nature, and in compliance with
this obligation we say we have conceived it to be of the nature of
indiarubber, not an elastic fluid as we have called it before, but
rather an elastic substance like a jelly, as some people have conceived
it to be; not a gas, because it does not require any medium to connect
its particles.
Looking upon it in this light, action at a distance can be accounted
for in a very natural manner. When a stretched indiarubber band is
relieved from strain, the relief must be felt instantly throughout
every part of its length; for, although the band may take time to
contract, no time is required for the relief from strain being felt. In
like manner an alteration in strain between the sun and the earth--and
these alterations of strain are taking place every instant--connected
by an indiarubber ether will be felt instantly in both bodies;
and should anyone stand out for time being required to convey the
attraction, let him remember that the difference of its power would be
felt first at the two ends of the connecting medium, for the very good
reason that even attraction itself could not prefer one extreme to the
other. And that is all that is meant by action at a distance.
Here are some other things that could be explained more easily than
they can be at present, through the ether and attraction being
considered to be one and the same, than under any other conception
we can form; but although we have a dim vision of such explanations
in some cases, our knowledge of the sciences involved in them is not
sufficient to warrant us in letting our dim conceptions see the light.
Therefore all that remains for us to add is, that some things we have
said of the ether may have to be so far modified now, but as they have
had their part in leading us to the conclusions we have arrived at,
they cannot be altogether suppressed.
CHAPTER XV.
PAGE
261 Construction of the solar system. Matter out of which
it was formed.
262 Domains of the sun out of which the matter was collected.
263 Stars nearest to the sun. Table VII. showing distances.
265 Remarks on Binary Stars. Table VIII. showing spheres of
attraction between the sun and a very few.
266 Sirius actually our nearest neighbour. Form of the sun's
domains of a very jagged nature.
267 Creation of matter for the nebulæ, out of which the whole
universe was elaborated. Beginning of construction.
267 The law of attraction begins to operate through the agency
of evolution.
268 Form of the primitive solar nebula. The jagged peaks probably
soon left behind in contraction.
269 How the nebula contracted. Two views of the form it might take.
Comparison of the two forms, solid or hollow.
272 The hollow centre form adopted. The jagged peaks left behind.
273 The nebula assuming a spherical form. Shreds, masses, crescents
separated from one side.
274 Probable form of interior of nebula. Compared with envelopes
in heads of some comets.
275 Reflections on the nebula being hollow. Opinions of others quoted.
276 The matter of a sphere solid to the centre must be inert there.
277 Further proofs of the nebula being hollow.
278 How rotary motion was instituted.
279 Such a nebula might take one of two forms.
280 The form depending on the class of nebula. Planetary in the case
of the solar system. A similar conception of how rotary motion
could be instituted.
In this chapter we proceed to consider how the original nebula was
formed, and whether the solar system could be evolved therefrom in the
manner shown in the analysis of Chapter V.
The usual way of treating the solar system has been to suppose it
to have been formed out of a nebula extending far beyond the planet
Neptune, generally in a vague way; although some writers have specified
a limit to the distance, in order to give some definite idea of what
must have been the density of the nebula at some particular period
of its existence. In the first part of our work we have adopted the
same plan and we mean to follow it out, because it gives us a greater
degree of facility for expressing our ideas, and making them more
intelligible, than by adopting a new method. But we shall previously
endeavour to show where the nebula itself came from and how it was
formed, which seems to us to be as necessary as to show how it was
transformed into the solar system.
We understand Laplace to have supposed the nebula to have been formed
out of cosmic matter in its simplest condition, and in its most
primitive atomic state, collected from enormously distant regions
of space by the power or law of attraction. In this we shall follow
him, because we do not see the necessity for matter having to be
created in the form of meteorites or meteors, or any other form, to
be afterwards dissociated and reduced to the atomic state, by heat
produced by collisions amongst the dissociated atoms. Surely it would
show more prescience, more simplicity of work, and economy of labour,
to create matter in this primitive state, than in one which required
it to be passed through a mill of some kind, as it were, before it
was manufactured into nebulous matter; in fact, to make brickbats in
order that they should be afterwards ground down--dissociated--into
impalpable powder, to render them fit to be worked up into bricks. But
our first effort will be to attempt to define the collecting grounds
of this cosmic matter, somewhat more particularly than has been done
hitherto, as we believe that even a superficial study of them will
assist us greatly in forming a more comprehensive idea of the whole
solar system than anything we have met with in any of the books which
we have had the opportunity of applying to for information.
The collecting grounds, then, are clearly the whole region of space
to which the attractive power of the sun extends, or what astronomers
would call within the sphere of his attraction. These domains, like
those of any other proprietor, are limited by the domains of his
neighbours. At first sight, it would seem that his neighbours are
infinite in number, but a little thought will show that the number
may be very limited indeed. On this small earth of ours, it is a very
common thing for a landed proprietor to be able to look over the
domains of his neighbours, and see those of proprietors more remote;
even to look over the domains of his neighbours' neighbours, and see
properties so remote that he does not even know to whom they belong nor
how they are named. With much more reason, the same must be the case
with the sun, more especially as he, from his own mansion-house, sees
nothing of the domains, but only the mansion-houses of others, there
being no landmarks, hills, fences or woods to cut off his view, as
there are upon the earth; the only interruption possible to his view
being that another mansion-house should come to be exactly between
his and that of a farther-off neighbour. For our purposes, we will
assume that his nearest neighbours are those the distances of whose
mansion-houses have been measured, and will adopt the following list
of them, taken from Mr. George Chambers's "Hand-Book of Astronomy,"
part 3, page 10, 5th edition, 1889, and forming Table VII. All that we
can learn from this table is that the boundary between the sun and any
one of the stars mentioned in it must be somewhere on a straight line
connecting the two, but that does not furnish us with any information
as to the extent of the sun's domains, although it does help to give
us some idea of their form. For some knowledge of their extent, we
require to know how far the lordship of each one of the proprietors
extends from his mansion-house; which, very much the same as it does
upon the earth, depends upon the power he has to take and keep it; it
depends on the mass of each neighbour who actually marches with the sun
when compared with his own mass. The list referred to does not help us
in any way to determine this, as we have just said, but we have found
in Professor Charles A. Young's "Lessons in Astronomy," of 1891, page
270, the masses of six binary stars whose distances, calculated from
the parallaxes given in it, furnish us with data from which we can
calculate the distance from the sun of the boundary between him and any
one of them. The number is very small, but still from them we can gain
some notion of what was the form of the domains from which the original
nebula was collected; that is, always under the supposition that the
sun and his system were evolved from a nebula. From these data, Table
VIII. has been drawn up, which shows the distances of the six stars
from the sun, and the limits of his sphere of attraction in relation
to them expressed in terms of radii of the earth's orbit, and also in
radii of Neptune's orbit, which gives numbers more easily comprehended
by us.
TABLE VII.--LIST OF STARS WHOSE DISTANCES FROM THE SUN
HAVE BEEN MEASURED, AND WHICH ARE ASSUMED
TO BE HIS NEAREST NEIGHBOURS.
--------------------+-----+------+----+------------------+-----------+
| M | P | | Distance. | |
| a | r | P |---------+--------| |
Star. | g | o | a | Sun's |Time of | Observers |
| n | p M | r |Distance | its | |
| i | e o | a | = 1. | Light | |
| t | r t | l | |reaching| |
| u | i | l | | Earth. | |
| d | o | a | | | |
| e | n | x | | | |
| | (") | (")| |(years) | |
--------------------+-----+------+----+---------+--------+-----------+
[Greek: a] Centauri | 1 | 3·67 |0·75| 275,000| 4·34 |Gill. |
| | | | | | |
61 Cygni | 6 | 5·14 |0·50| 412,500| 6·51 |O. Struve. |
| | | | | | |
21185 Lalande |7-1/4| 4·75 |0·50| 412,500| 6·51 |Winnecke. |
| | | | | | |
Sirius | 1 | 1·24 |0·38| 543,000| 8·57 |Gill. |
| | | | | | |
[Greek: m] Cassiopeiæ| | |0·34| 606,000| 9·57 |O. Struve. |
| | | | | | |
34 Groombridge | 8 | 2·81 |0·29| 711,000| 11·23 |Auwers. |
| | | | | | |
9352 Lacaille |7-1/2| 6·95 |0·28| 737,000| 11·62 |Gill. |
| | | | | | |
21258 Lalande |8-1/2| 4·40 |0·26| 793,000| 12·52 |Krüger. |
| | | | | | |
Ö Arg. 17415 | 9 | 1·27 |0·25| 825,000| 13·02 |Krüger. |
| | | | | | |
[Greek: s] Draconis | 5 | 1·87 |0·25| 825,000| 13·02 |Brunnow. |
| | | | | | |
[Greek: e] Indi |5-1/4| 4·68 |0·22| 938,000| 14·80 |Gill. |
| | | | | | |
[Greek: a] Lyræ | 1 | 0·31 |0·20|1,031,000| 16·27 | |
| | | | | | |
O^2 Eridani |4-1/2| 4·10 |0·17|1,213,000| 19·15 |Gill. |
| | | | | | |
[Greek: r] Ophiuchi |4-1/2| 1·00 |0·17|1,213,000| 19·15 |Krüger. |
| | | | | | |
[Greek: e] Eridani |4-1/2| 3·03 |0·14|1,473,000| 23·24 |Elkin. |
| | | | | | |
[Greek: i] Ursæ Majoris 3 | 0·52 |0·13|1,586,000| 25·04 |C.A.F. |
| | | | | | Peters.|
[Greek: a] Boötis | 1 | 2·43 |0·13|1,586,000| 25·04 |C.A.F. |
| | | | | | Peters.|
[Greek: g] Draconis | 2 | 0·06 |0·09|2,292,000| 36·17 | |
| | | | | | |
1830 Groombridge | 7 | 7·705|0·09|2,292,000| 36·17 |Brunnow. |
| | | | | | |
Polaris | 2 | |0·07|2,947,000| 46·50 |C.A.F. |
| | | | | | Peters.|
3077 Bradley | 6 | 2·09 |0·07|2,947,000| 46·00 |Brunnow. |
| | | | | | |
[Greek: s] Foucani | 6 | 2·05 |0·06|3,438,000| 54·25 |Elkin. |
| | | | | | |
85 Pegasi | 6 | 1·38 |0·05|4,125,000| 65·10 |Brunnow. |
| | | | | | |
[Greek: a] Aurigæ | 1 | 0·43 |0·04|5,157,000| 81·37 |C.A.F. |
| | | | | | Peters.|
Canopus | 1 | |0·03|6,875,000|108·50 |Elkin. |
--------------------+-----+------+----+---------+--------+-----------+
TABLE VIII.--MASSES OF A FEW BINARY STARS SHOWING THE LIMIT OF
THE SUN'S SPHERE OF ATTRACTION WITH RESPECT TO THEM,
IN RADII OF THE EARTH'S ORBIT, AND DISTANCES OF THEIR
BOUNDARIES WITH THE SUN IN THE SAME MEASURE,
AND ALSO IN NEPTUNE DISTANCES.
-----------+-----+------+-------------+------------+---------------+
| P | |Distance of |Distance of | |
| a | Mass |Star from Sun| Limit of | Distance of |
| r | |in radii of |Sun's Sphere|Limit in radii |
Name of | a |Sun's |the Earth's |of Attract'n| of Neptune's |
Star. | l | Mass | Orbit |in radii of | Orbit |
| l | = 1. | | Earth's | |
| a | |(93,000,000 | Miles. | |
| x | | Miles.) | |= 2,794,000,000|
| (") | | | Orbit = 1. | |
-----------+-----+------+-------------+------------+---------------+
[Greek: a] | | | | | |
Centauri | 0·75| 2·14 | 275,000 | 128,505 | 4,277 |
| | | | | |
61 Cygni | 0·43| 0·23 | 479,686 | 369,358 | 12,294 |
| | | | | |
Sirius | 0·38| 4·26 | 543,000 | 127,465 | 4,243 |
| | | | | |
[Greek: a] | | | | | |
Geminorum | 0·20| 0·30 | 1,031,325 | 721,927 | 24,030 |
| | | | | |
70 Ophiuchi | 0·16| 5·00 | 1,289,150 | 257,830 | 8,582 |
| | | | | |
[Greek: ê] | | | | | |
Cassiopeiæ | 0·15| 3·00 | 1,375,100 | 458,366 | 15,257 |
------------+-----+------+-------------+------------+---------------+
But there is still something to be said with respect to the Binary
Stars of Table VIII., and any others whose masses may be met with later
on. If those forming a pair revolve around each other, or a common
centre, in orbits, it must happen that they will be sometimes more or
less in conjunction, opposition, and quadrature with regard to the sun;
also the angles of the planes of their orbits to direct lines between
them and the sun, whatever these angles may be, will cause variations
in the separate and combined forces of attraction they exercise in
the domains of the sun, at different periods of their revolutions;
so that these powers of attraction will be constantly increasing and
diminishing, and causing the boundaries of their domains to approach
and recede from the sun; thus introducing between their domains and
those of the sun a debatable land, which will reduce celestial to be
very much like terrestrial affairs, where each proprietor, or power,
takes the pull when an opportunity presents itself. No doubt all such
invasions, or claims, between proprietors will be settled by the law of
attraction, without lawsuit, arbitration or conflict; but as law gives
right, and might is right--most emphatically in this case--we come back
to the old seesaw of earthly matters. Well, therefore, many astronomers
teach that the whole universe is formed out of the same kind of
materials, and governed by the same laws that we are having good reason
to know something about on this earth of ours.
Accustomed to look upon [Greek: a] Centauri as the star nearest to
us, on account of its light-distance being so much smaller than any
other noted in our text-books, we were not prepared to find that, when
measured by his sphere-of-attraction distance, Sirius is actually a
rather nearer neighbour to the sun than it; nor that his, apparently,
next nearest neighbour, when measured in the same way, is twice as far
away as either of them; and thus we have the conviction thrust upon us
that they must have made deep hollows in the solar nebula when it was
being formed. On the other hand, when we think of three of the other
stars mentioned in the list of six, being practically from three to
six times farther off than either of them, we come to the conclusion
that the form of the nebula, when in its most primitive state, must
have been of a very jagged character; a conclusion which is very
considerably strengthened when we look at Table VII., and see that the
stars noted in it run up to from twice to not far from thirty times
more distant from the sun than [Greek: a] Centauri. And now, having
got a somewhat definite idea of the form of the sun's domains, we may
attempt the construction in them, first of a nebula and afterwards of a
solar system, such as our text-books describe to us; introducing into
the construction, as a matter of course, the variations from existing
theories which, we believe, we have demonstrated to be necessary.
Perhaps we ought to confine our operations to these domains, and so
we will almost exclusively; but the sun has been so long considered
as one of many millions of stars, and as part of what is now looked
upon as our universe, that we cannot help looking upon the whole as
having been the result of one act of creation; more especially as we
have no reason whatever for supposing it to have been built up piece
by piece; and whatever ideas we may form of our own little part of it,
we are bound to apply them to the whole. We may, therefore, lay the
foundations of our undertaking in the following manner. By creation we
mean only creation of nebulæ.
We shall suppose all space--if we can comprehend what that means--to
have been filled with the ether, and the law of attraction to have
been in force previous to the time when our operations are supposed to
have commenced. These we may consider to have been the first acts of
creation, or to have existed from all eternity. Then, in that part of
space occupied by our universe--even though it should extend infinitely
beyond the reach of our most powerful telescopes--we shall suppose the
work of creation to have begun by filling the whole of that space with
what are known as the chemical elements, reduced to their atomic state.
We do not want to have molecules or particles of matter, or meteorites
or meteors; because they involve the idea of previous manipulation or
agglomeration, but matter in its very simplest form, if there is any
more simple than the atomic. At this stage the most natural idea is to
suppose that the whole of this matter was at rest, without motion of
any kind, because we cannot understand how motion could be an object
of creation, but can very easily see how it might be of evolution; and
because, under the law of attraction, matter had the elements of motion
in itself. Under that law it is quite possible for us to comprehend
that all the suns of our universe could have been formed just as they
are, with all their movements of rotation, revolution in the cases of
multiple stars, and translation or what is called proper motion. And it
is within the bounds of possibility that future astronomers may be able
to show how these movements have been brought about, should it ever be
possible for them to find out and define with sufficient accuracy what
the translatory, or proper, motions are. Then, as for the temperature
of this newly created matter, we have no resource left but to suppose
that it must have been that of space, whatever that may have been then,
even as we have been obliged to say before.
Once created, the atoms of the cosmic matter would immediately begin
to attract each other in all directions, and form themselves into
groups. At first thought it might be supposed that these groups, and
suns formed from them, ought to have been all of the same size, being
formed from the same material under the same conditions, but nature,
or evolution, seems never to be disposed to produce the same results
in its manipulations of matter, whatever they may be. When the water
is drawn off from a pond, and the mud left in the bottom of it allowed
to dry in the sun, it breaks up into cakes of very various shapes and
sizes. No doubt there are physical causes for this being the case,
but, though perhaps not altogether impossible, it would be a hard task
to find them out. Much more so would it be with originally created
matter, and we have only to accept the fact. Moreover, there can be
little doubt but that the universe was formed, evolved, according to
some design--not at hap-hazard--and that the cosmic matter was created
with the distribution necessary to carry out the plan. That the stars
differ from each other in magnitude is the best proof of design; for no
one can believe that inert matter could determine into what shapes and
sizes it could arrange itself. But we have now nothing more to do with
the universe, and will confine our operations to the domains of the sun.
Notwithstanding the vagueness and dimness of the description we have
been able to give of the part of space to which our work is now to
be confined, we can conceive it to resemble in some degree--not a
comparatively flat but--a round starfish, with arms more unequal in
length, and irregular in position than the kind we are accustomed to
see. In such an allotment of space we can easily conceive that the work
of attraction and condensation, of the newly created cosmic matter, in
forming itself into a nebula, would be most active in the main body;
that in the arms, or projecting peaks as they may be called, it would
go on more slowly in the direction towards the centre, the quantity
being smaller; and that on account of the greater distance in each from
the centre of attraction, and of its being more under the influence of
the still existing counter-attraction of the matter in the domains of
the sun's neighbours, they might become almost, or rather altogether,
detached from the more rapidly contracting main body.
We shall, then, suppose that all this has taken place in our incipient
nebula. The centre of attraction would at first be the centre of
gravity of the whole region occupied by the cosmic matter, which would
be ruled in due measure by the projecting peaks, and the indentations
or hollows produced in it by the attractive force of the most powerful
neighbours; which hollows would gradually disappear as the process of
condensation went on, and the main mass would assume the figure of a
nebula of some shape. From this stage we may reasonably conclude that,
as it was contracting towards the common centre of gravity of all its
parts, it would gradually assume a somewhat globular form, and we may
now suppose it to have contracted to, say three times the diameter of
the orbit of Neptune. Here, then, we may take into consideration what
was the interior construction of the main mass which we may now look
upon as a nebula; and we have only two states in which we can conceive
it to have been. Either that the whole was condensing to the common
centre of gravity, in which case its greatest density would be at the
centre; or that it was condensing towards the region of greatest mass,
in which case its greatest density would be at that region, and its
least density at the exterior of the nebula, and also at, or at some
distance from, its centre; that is, that the nebula was hollow and
without any cosmic matter at all at its centre.
In the first case we must recognise that, from that period of time
at least, the cosmic matter that was at, or even near, the centre of
gravity then, must be there still all but inert, and being gradually
compressed to a greater and greater degree of density. There would, no
doubt, be attraction and collisions going on amongst the particles,
with condensation towards the centre and production of heat--as long
as the particles retained the gasiform condition--which might be
increased in activity by the pressure, or superincumbent weight, of the
whole exterior mass, but there would be no tendency in them to move
outwards--provided their gravitation was always towards the centre; and
any motion amongst them would be of the same kind as the vibration of
the particles of air shut up in a cylinder and gradually compressed by
a piston forced in upon them, and not allowed to escape owing to the
sides of the cylinder exerting upon them a pressure increasing exactly
in the same proportion as the pressure on the piston was increased.
And if this was the case with the matter at or near the centre, it
would be the same with that of the whole mass, with the exception,
perhaps, of the outer layer, which might act the part of the piston in
the cylinder. There could be no motions among the particles, except
those of collisions and of falling down towards the centre. The outward
impacts of collisions would be less strong than those inwards, on
account of gravitation acting against them, and the general tendency
of all matter would be to move towards the centre. Even were we to
assume that the whole mass was endowed with a rotary motion, the result
would be much the same, that is, increasing stagnation of the matter
as it approached to the centre. The areolar law teaches us, however,
that the increase of condensation at the centre would increase the
rotation there; but in that case we have to acknowledge that this
increase of rotation would have to be propagated from near the centre
to the circumference, which would be by far the most difficult mode of
propagation, and we are forced to think of what would be the rate of
rotation at the centre, of a nebulous globe, of some sixteen thousand
million miles in diameter, required to produce a rotation at the
circumference of even once in four or five hundred years; and from that
to think of what must be the speed of rotation at the centre of the
sun, at the present day, to produce one rotation at the circumference
of twenty-five to twenty-seven days. We should also have to think
seriously of how the rotary motion was instituted, and we could only
appeal either to simple assumption, or to the impact theory, which,
applied to a mass of the dimensions of the one we are dealing with,
would require more explanation than the whole formation of the nebula
itself.
In the second case, that is, looking upon the nebula as a hollow
sphere--when it was of the dimensions we have just supposed it to
be--we get rid of all the difficulties, and we may add impossibilities,
that we encountered in the first case. In such a formation there
could be no particle of matter in a state approaching to inertness,
not one that could not work its way, through force of attraction and
collisions, from the outer to the inner surface of the hollow shell,
or _vice versâ_, or all through and round it and from pole to pole--if
it had poles then; it might increase or decrease in density, according
to the density of the particles with which it came into collision, as
it moved from one place to another, but it would find no spot where
it could stand still or be imprisoned. Even arrived at the region of
greatest density, it could change places with its neighbours and move
all over that region, if it were condemned to remain with one density
once it had acquired it; if not, by acquiring or loosing a little
density--_i.e._ by being compressed or allowed to expand a little--it
could work its way outwards or inwards, as we have just said, and be as
free as the law of attraction would admit of, and as active as that law
would oblige it to be. It must be borne in mind that gravitation would
act in two opposite directions depending on whether it was acting on
the outside or inside of the region of greatest density. We do not go
the length of supposing that it could escape altogether from the nebula
were its progress outwards; because, as it approached the border, it
would meet with plenty of other particles coming in, which would reduce
its velocity and prevent its escape. Besides, the law of attraction
would take good care to prevent it from passing over to a neighbour
nebula or sun.
It may be argued that in the first case--_i.e._ condensation to the
centre--the particles would have the same facilities for changing
place, in so far as moving all round the interior of the nebula, or
across it, on their way to quasi stagnation, as their densities and
the superincumbent weight concentrated and increased; but there could
be no motion outwards because the _attraction of gravitation_ would not
permit it; nothing could _fall upwards_, all must _gravitate_ to the
centre. Thus the power of motion in the particles would be limited to
very much less than half what they would have in the case of the hollow
sphere.
It will not do to argue that the increasing heat at the centre would
create an upward current. It might create repulsion and prevent the
farther-out particles from so soon reaching their final resting or
vibrating place, but it could not create an upward convection current
of any magnitude; because the colder particles falling down to replace
those rising up--that is, if the warmer ones did rise up--being greater
in number because occupying greater space, would soon cool down the
centre and put an end to the upward current, that is, if it ever came
to be set in motion. The greater weight of the greater number would be
sure to keep the lesser number in their prison. If any one should say
that those nearest the centre would be the heaviest, let him remember
that the heaviest liquid or fluid does not rise to the surface. There
could be no furnace at the centre to heat the cold particles as they
came down to replace those that had just risen up; and if there was, it
would be gradually cooled and extinguished. In fact, the centre region
would become colder than that immediately outside of it, and so on
until the greatest heat would be at the surface of the nebula. Should
it be argued that the vastly greater number of particles in the outer
regions would help those at the centre to rise up, we agree; but it
would be because the attraction would be greater outwards than inwards,
as we have shown all along, and not because the pressure forced them
out--against itself. But, it must be added, this means that if there
was still a plenum at the centre the particles that had once left the
centre could never come back again, nor any others to replace them, and
that no convection current could ever be formed for carrying heat or
matter from the centre, or its immediate neighbourhood, outwards.
In view of the above comparison of the two cases--added as a complement
to what we believe we have demonstrated in a former part of our
work--we shall adopt the second as being most in harmony with the
laws of attraction, and of nature in general, and shall endeavour to
describe in some detail, the construction of the nebula out of the
matter belonging to the domains of the sun, as we have marked them out.
We have already said that on account of being at the greatest distance
from the main body, and at the same time nearer than all other parts
of it, to the attractive force in the domains of the neighbouring
stars or nebulæ--which attraction continues to be exerted upon the
solar system up to the present day--the matter in the high peaks which
we have shown would form part of the sun's domains, would come to be
completely separated from the rest of the nebulous matter. We shall
now assume this to have come about, the detached pieces, somewhat in
the shape of cones, occupying positions distant from the main body, in
some sort of proportion to their altitudes and masses. This separation
would naturally make some alteration on the centre of gravity of the
remaining mass. It would come to be nearer to the deep hollows, made
in the mass by the attraction of the most powerful of the nearest
neighbouring stars; and as we have seen that the hollows made by Sirius
and [Greek: a] Centauri would be the deepest, and also for greater
simplicity in description, we shall suppose that the centre of gravity
would come to be nearer to these hollows than it had been before. Then,
as the condensation and contraction proceeded, the tendency would be
to fill up these hollows, and, as a consequence, the matter at the
opposite side of the nebula would at the same time tend to lag behind
in approaching the centre--for the same reasons we have given in the
case of the peaks--and might easily come to be detached from the main
body altogether, first in the form of shreds, then in larger masses,
and afterwards in concave segments of hollow spheres, as contraction
advanced; and the whole seen from a sufficient distance, would have
the appearance of a nebula with crescents, perhaps almost rings, of
nebulous matter and detached masses on one side of it; all very much
like what we know to be the figures presented by some nebulæ.
When contraction had continued till the hollows caused by Sirius
and [Greek: a] Centauri were filled up, we might suppose that the
nebula had come to be somewhat of a spherical form, although far from
being very pronounced, and we have now to consider what its internal
structure might be and most probably was.
In describing the construction of the earth-nebula we showed that
particles of matter placed at different parts of its interior, even not
very far from the surface, would be drawn out, in the first place by
the greater number coming in from a greater distance from the centre,
and that when they met they would all be drawn in towards the centre by
the conjoint attraction of the whole mass; and now we can apply this
fact to the larger solar nebula, and consider what might be the result.
Let us fix upon a certain number of equidistant zones in a sphere of
cosmic matter, extending from the centre at _a_ to _b_, _c_, _d_ and
_e_, at the surface. We know that, according to our former reasoning on
particles, and the law of attraction, part of the matter of the zone at
_a_ will be drawn outwards by that at _b_, while part of that at _b_
will be drawn inwards by that at _a_, and that the same will take place
with all the other zones out to the surface at _e_; and thus there
might come to be congested layers between these equidistant places,
and there might even be formed hollow spheres within hollow spheres,
independent of each other, all through the nebula from near the centre
to the surface. This idea is by no means fanciful, as is witnessed
by the accounts given in Chambers's "Handbook of Astronomy," already
referred to, Vol. I., and the Figs. 215, 222 and 223, showing the form
and appearance of the remarkable comets of 1874 and 1882. If different,
almost concentric, zones or layers of cosmic matter can be constituted
in the hemisphere forming the head of a comet, there is no reason why
concentric layers of the same matter should not be formed in a nearly
spherical nebula. In fact, we can appeal to what is seen in the heads
of the two comets cited, Donati's also represented in the same work,
Figs. 199-203, as convincing proof of the correctness of our contention
and demonstration that all satellites, planets, suns, and stars are
hollow bodies. Even the tails of comets, at least of the larger ones,
are acknowledged to be hollow bodies.
When steadily looked into we find the notion that all fluid bodies
are hollow to be much more common than is perhaps generally believed.
Beginning with the smallest, we find what follows in the Rev. Dr.
Samuel Kinn's work, entitled "Moses and Geology," Edition 1889, page
86: "A mist, whether in the form of a cloud or fog, is composed of
small bodies of water obeying the laws of universal gravitation by
forming themselves into spherules, which Halley and other eminent
philosophers thought to be hollow. As water is heavier than air,
scientists were for a long time seeking for a good reason to account
for clouds floating. It may be that Kratzenstein has somewhat solved
the problem. He was examining in the sunshine some of the vesicles of
steam through a magnifying glass when he observed upon their surface
coloured rings like those of soap-bubbles, and some of the rays of
light were reflected by the outside surface, others penetrated through
and were reflected by the inner surface; he concluded, therefore, that
the envelope of the sphere must be excessively thin to admit of this
taking place. We may, therefore, suppose that these vesicles are filled
in some way with rarefied air, and are so many little balloons whose
height in the atmosphere varies in proportion to the density of the
air they contain. How this enclosed air should become rarefied on the
formation of the tiny globule is a problem still to be solved."
Dr. Kinn says nothing of _how_ the spherules of cloud or fog were
formed by the laws of universal gravitation, nor _why_ Halley and the
other eminent philosophers thought them to be hollow, and only states
the fact that Kratzenstein found the vesicles of steam to be hollow;
and only one cause can be assigned for such being the case, namely, the
manner in which we have shown how hollow spheres can alone be formed.
That the vesicles of steam examined in the sunshine were hollow it
would seem there can be no doubt; and if so, there can be as little
that Halley and the others were right in thinking the spherules of
clouds to be hollow. The steam vesicles could not come into existence
at once in the air, in form large enough to be examined through a
magnifying glass, but must have been built up out of a multitude of the
very smallest atoms of water turned into vapour; and would follow the
same law as the atoms of cosmic matter and so form the little balloons.
In their formation the hollow space would be filled with air, which
would expand when heated and contract when cooled, and so regulate
their height in the atmosphere. And thus the problem of the last
sentence of the quotation is solved.
We shall now go to the opposite extreme of matter, and see what Mr.
Proctor says when treating of the formation of a Stellar System; but
we must state that it is not very clear to us, whether he is exposing
Mädler's ideas or his own, although we think they are his own or, at
least, adopted. He says in "The Universe of Stars" at page 112: "He
(Mädler) argues that if a galaxy has a centre within the range of the
visible stars, a certain peculiarity must mark the motions of the
stars which lie nearer to the centre than our sun does. As has already
been mentioned, the neighbourhood of the centre of a stellar system is
a scene of comparative rest. In the solar system we see the planets
travelling faster and faster, the nearer they are to the great ruling
centre of the scheme; and the reason is obvious. _a._ The nearer a body
is to a great centre of attraction like the sun, the greater is the
attraction to which it is subject, and the more rapid must its motion
be to enable it to maintain itself, so to speak, against the increased
attraction; but in a vast scheme of stars tolerably uniform in
magnitude and distribution, _the outside of the scheme is the region of
greatest attraction, for there the mass of all the stars is operative
in one general direction_. (The italics are ours.) As we leave the
outskirts of the scheme, the attraction towards the centre becomes
counterbalanced by the attractions towards the circumference; and at
the centre there is a perfect balance of force, so that a body placed
there would remain in absolute rest. It is clear, then, that the
nearer a body is to the centre, the more slowly will it move." (Compare
this last sentence with the one beginning at _a_ above.)
Here we have recognised, the principle that in a star system the
immensely greater number of stars at the outside of the scheme would
produce a perfect balance of force, and that a body placed at the
centre would remain in absolute rest. This agrees wonderfully well with
what we have been arguing, a few pages back, with respect to a sun
solid to the centre. Matter at the centre would be at absolute rest,
_dead_, that nearest to it would be nearest to dead, and so on through
a sun or planet, gradually coming to life as it came nearer to the
surface; exactly as we have shown it would be, having in it little more
than rotary motion. When once acknowledging the immense superiority
of attractive force of the stars at the outskirts of the system, over
the very few there could be at its centre, Mr. Proctor seems to have
stopped short with the idea and to have contented himself with one body
at the centre in absolute rest. Had he gone one step further he must
have seen that one, or even a very few, could not maintain themselves
near the centre with such an immense number pulling them away in every
direction. There could be no perfect balance of force. And had he
applied the same idea to the earth, and followed it out to the end, he
could not have written as he has done, in "The Poetry of Astronomy," at
page 354, "that the frame of the earth is demonstrably not the hollow
shell formerly imagined, but even denser at its core than near the
surface." He would have found some difficulty in fixing his first dead
particle at the centre, when there were such infinite hosts of near and
far-off neighbours endeavouring to annex it. He would have found that
the absolute rest was neither more nor less than absolute vacuum. It
is utterly impossible to show how any body could be built up out of a
nebula of cosmic matter, or even meteorites, from a solid centre, under
the law of attraction. We repeat that any foundation laid there would
be in a state of unstable equilibrium, and would be hauled away out of
its place never to return; unless the cosmic matter around it were so
perfectly arranged on all sides that its attraction on the foundation
would be absolutely equal in all directions; a condition which cannot
be imagined by any one who takes the trouble to think of it. And we
think we may add, that no body could be established at the centre of a
system of any kind unless it were of sufficient magnitude to control
the whole matter within range of it, exactly as we see in the solar
system; and that the central body could be no other than a hollow
sphere. Thus we have either to look upon the sun with his planets and
their satellites as hollow bodies or to conclude that the solar system
was not formed out of a nebula.
Coming back to our nebula after the hollows in it, caused by the
attraction of Sirius and [Greek: a] Centauri, were filled up, and
when we showed that it might have had the interior form of a series
of hollow spheres one within the other, and also might be accompanied
by crescents and shreds of cosmic matter on the opposite side to the
hollows--a supposition we put forward more in explanation of what is
to be seen in some nebulæ and comets, than as in any way necessary for
our purposes--then, even although it had been separated interiorly
into different layers or concentric shells of spheres, these layers
continuing to attract each other, would finally come to form one hollow
sphere with its greatest density at the region where the inwards and
outwards attractions came to balance each other. Long previous to this
stage--even from the very beginning--the atoms gradually coalescing
into larger bodies, would be attracting, colliding with, repelling
and revolving around each other, sometimes increasing in dimensions,
at others knocking each other to atoms again; but there would be a
tendency in them to combine into larger masses as they approached the
region of greater density, where the attraction was greatest.