MATTER AND ETHER.
‘Felix qui potuit rerum cognoscere causas,
atque metus omnis et inexorabile fatum
subjecit pedibus, strepitumque Acherontis avari.’
VERGIL.
‘Who shall tempt with wandering feet
The dark, unbottomed, infinite abyss,
And through the palpable obscure find out
His uncouth way; or spread his airy flight
Over the vast abrupt, ere he arrive
The happy isle?’—MILTON, _Paradise Lost_.
117. The next portion of the preliminary inquiry necessary to our
concluding argument is that which relates to the intimate nature of
matter; and more especially of that very wonderful form of matter
which is the vehicle of all the energy we receive from the sun, as it
is that of all the information we obtain about the position, motion,
nature, mass, condition, and properties of the almost infinitely more
distant bodies, which are scattered through cosmical space. In other
words, we have hitherto spoken only of the laws of working of the
machine called the physical universe; let us now endeavour to study
the structure of the materials of which it is composed.
118. Various hypotheses have been proposed as to the ultimate nature
of matter. To give even a general account of all the less absurd of
these would require a large volume, so we content ourselves with a
few of the more reasonable or historically more important.
(1.) The foremost place must of course be taken by the old Greek
notion of the _Atom_. The outlines of the atomic theory were laid
down very precisely by Democritus and Leukippus (_circa_ 400 B.C.),
who taught that the whole universe is made up of empty space and
eternal atoms, differing only in form (as =Α= and =Ν=), order (as
=ΑΝ= and =ΝΑ=), and posture (as =Ζ= and =Ν=). The atoms are endued
with a primitive motion in virtue of their weight, and, clashing
together, produce vortices from which the world is formed. The
gradual progress of this whirl of atoms brings similar elements
together, as in the sifting of grain, and so the atoms are sorted
into homogeneous groups.
The great weakness of this theory lay in the very false ideas then
held as to the nature of motion by weight, which was supposed to
be necessarily in parallel lines, and with a velocity greater for
heavy than for light bodies. The difficulty which arose from this
notion led Epicurus to give to the atoms a perfectly arbitrary and
capricious side movement, as well as the rectilineal motion due to
their weight, and thus, in his school, the theory became really a
metaphysical one, reducing the order of the universe to pure chance.
It is such a medley of physical speculations, with metaphysical
notions, that we find in the greatest exponent of the system, the
‘poet philosopher’ Lucretius. With the help of Munro’s splendid
edition of the text of Lucretius, and his very valuable translation
and notes, it is now a comparatively easy matter to give a concise
summary of the principal points of this most remarkable early
physical speculation. In attempting to do so we will endeavour, so
far as we can, to bear in mind the awful but too often disregarded
warning given by the poet himself:—
‘Omnia enim stolidi magis admirantur amantque,
inversis quæ sub verbis latitantia cernunt,
veraque constituunt quæ belle tangere possunt
auris et lepido quæ sunt fucata sonore.’[44]
119. As the purpose of the poem of Lucretius is the establishment
of the very opposite of our present theme, we must consider a good
deal more of his work than the mere properties of atoms. Lucretius
tells us that his object is to dispel the fear of the gods, which he
supposes to arise simply from the fact that there are so many things
which men do not yet understand, and therefore imagine to be effected
by divine power.
Religion, which crushes human life prostrate upon earth, is, he says,
now put under foot; and the great victory achieved by his Greek
instructor over the immeasurable universe (in finding what can and
what cannot come into being) brings us level with heaven.
His followers are not to fancy that there is any sin in this; on the
contrary, religion has perpetually been the cause of sinful deeds.
There is, however, danger of their relapse, for the terror-speaking
seers may once more overcome them. But if men could only be convinced
that the soul is born and perishes with us, then they would be able
to take their ease, and withstand alike religious scruples and
threatenings of the seers. For this purpose we must find out what
mind and soul consist of, and how everything on earth proceeds; and
if we can do this, we may, of course, dispense with the gods.
120. FIRST, then, _nothing comes from nothing_, which seems to be
meant in the sense that there is a physical cause for everything; at
least all the examples which are adduced in proof of the statement
are mere instances of what might be conceived to happen if there were
no fixed determining physical law or cause. But the author is obscure
on this point, for he sometimes makes us inclined to think that he is
virtually only asserting the eternal, unchangeable, existence of the
atom,—the ‘first beginning of things.’
As a corollary to this, of course, _nature does not annihilate
things_, but dissolves them back into their first bodies. The same
negative proof is here attempted. Nothing is lost, but nature can
beget nothing till she is recruited by the death of something else.
Then, to reconcile the reader to the invisibility of these first
bodies, he is shown how nature works by invisible things, as wind
and moisture; how marriage-rings and paving-stones, ploughshares and
statues, are worn away without the loss of any visible particles.
Nature, therefore, works by unseen bodies. Smell, heat, cold, etc.,
must consist of a bodily nature, because they affect the senses; for
nothing but body can touch and be touched.
121. But, SECONDLY, _there is also void in things_, else they would
be jammed together, and unable to move. It is false to say that
things may move in a _plenum_: as, when a fish presses on, it leaves
room behind it, into which the water may stream; for on what side
can the scaly creature move forwards unless the waters have first
made room; and on what side can the waters give place so long as the
fish cannot move? (This of course is metaphysics, and is altogether
absurd. It is the old story of the immovable body receiving the
irresistible blow.) Hence there cannot be motion unless there be void
to allow of a start. Dripping of water in caves, the passage of food
throughout the whole of the body of an animal, the fact that buds
and fruit of trees are nourished from the root, voices heard through
walls, cold penetrating the very bones, all are proofs that there is
void as well as body. Also when one thing is as large as another, but
yet lighter, there must be more void in it.
122. THIRD. _There can be no third thing besides body and void._ For
if it be to the smallest extent tangible, it is body; if not, it is
void.
123. FOURTH. _Bodies are either first beginnings of things_ (atoms),
_or a union of such_. Any thing which can be broken or crushed, or
which can transmit heat or electricity, is partly body and partly
void. Hence body cannot be crushed, and ‘therefore first beginnings
are of solid singleness, and in no other way can they have been
preserved through ages during infinite time past, in order to
reproduce things.’
124. FIFTH. If there be no limit to breakage, nothing could be
reproduced; for reproduction is slower than decay, and therefore the
breaking of infinite past ages would have produced a state of things
incompatible with the reproduction of anything within finite time.
_Hence there exists a least in things._ This cannot be soft, else it
would consist partly of void, and be therefore breakable.
_First beginnings, then, are strong in solid singleness._ Hence the
unreason of those who held fire to be the matter of things, for what
surer test can we have than the senses whereby to note truth and
falsehood!
The doctrine called that of Homœomeria by Anaxagoras is folly,—his
notion, to wit, that everything is made up of little parts the same
as itself—bones of little bones, flesh of little fleshes, etc. For
thus corn and other food, which go to nourish our blood, must be in
part composed of blood, and must therefore bleed when crushed by the
formidable force of the millstone!
125. SIXTH. _Are the atoms infinite in number, and is the void in
which they move unlimited?_ Both questions are answered in the
affirmative, but the proof given is metaphysical and altogether
ridiculous, though it contains a fragmentary passage of real merit,
hinting at Le Sage’s explanation (presently to be given) of the cause
of gravity. One illustration of it must suffice:—‘Nature keeps the
sum of things from setting any limit to itself, since she compels
body to be ended by void, and void in turn by body;’ so that either
by the alternation of the two, or by the infinite extension of one
if the other do not bound it, immeasurable space must be filled. If,
for instance, body were finite, and void infinite, matter would in a
very short time be scattered and borne along in the mighty void; or,
rather, could never have been brought together.
This agrees with an idea which is propounded in the second book, as
to the velocity which the atoms have given them (he does not say how
or whence), and which enables them to cohere for a time and then to
break up again, as everything wanes. Those whose close-tangled shapes
hold them fast together form enduring stone and unyielding iron,
others spring far off and rebound, leaving great spaces between;
‘these furnish us with thin air and bright sunlight.’ Shortly
afterwards, we are told that the velocity of the first beginnings
when passing through empty void must be greater than that of sunlight!
We need not trouble ourselves here with Lucretius’s speculations
as to the formation of tangible bodies from a vertical downpour of
atoms, which, unlike drops of rain, now and then swerve from their
courses so as to clash together, save to mention that he affirms
that, even if he did not know what atoms are, he could be sure, from
its defects, that the world was not made for us by divine power.
126. SEVENTH. This, one of the most important points of the whole
theory, is entirely ignored by some good commentators, and by others
who have more or less closely followed them:—_The first beginnings of
things have different shapes, but the number of shapes is finite_.
127. EIGHTH. _The first beginnings which have a like shape, one with
another, are infinite in number._
That is, there is a finite number of kinds of atoms, but an infinite
number of each kind.
128. NINTH. _Nothing whose nature is apparent to sense consists of
one kind of first beginnings_ (only).
129. We need not trouble ourselves with his notion of the smallness,
smoothness, and roundness of the atoms which make up the mind,
qualities which he arrives at from the rapidity with which the
mind originates and works out a suggestion, contrasting here the
mobility of water with the viscosity of honey. Nor his proof (by the
non-diminution of the weight and dimensions of the body at death),
that the whole mass of the mind must be exceedingly small. But we
may quote, in two of its many forms, his constant reiteration of the
unreasonableness of the fear of death, and his philosophic mode of
overcoming it:—
‘Some wear themselves to death for the sake of statues and a name.
And often to such a degree, through dread of death, does hate of life
and of the sight of daylight seize upon mortals, that they consider
self-murder with a sorrowing heart, quite forgetting that this fear
is the source of their cares (this fear which urges men to every
sin), prompts this one to put all shame to rout, another to burst
asunder the bonds of friendship; and, in fine, to overturn duty from
its very base, since often ere now men have betrayed country and
dear parents in seeking to shun the Acherusian quarters. For, even
as children are flurried and dread all things in the thick darkness,
thus we in the daylight fear at times things not a whit more to be
dreaded than what children shudder at in the dark, and fancy sure to
be. This terror, therefore, and darkness of mind must be dispelled,
not by the rays of the sun and glittering shafts of day, but by the
aspect and law of nature.’ Book III. 78.
‘Now no more shall thy house admit thee with glad welcome, nor a
most virtuous wife and sweet children run to be the first to snatch
kisses, and touch thy heart with silent joy. No more mayest thou be
prosperous in thy doings, a safeguard to thine own. One disastrous
day has taken from thee, luckless man, in luckless wise, all the
many prizes of life. This do men say; but add not thereto: “And now
no longer does any craving for these things beset thee withal.” For
if they could rightly perceive this in thought, and follow up the
thought in words, they would release themselves from great distress
and apprehension of mind. Thou, even as now thou art, sunk in the
sleep of death, shalt continue so to be in all time to come, freed
from all distressing pains; but we, with a sorrow that would not be
sated, wept for thee, when close by thou didst turn to an ashen hue
on thy appalling funeral pile, and no length of days shall pluck from
our hearts our ever-enduring grief. This question, therefore, should
be asked of this speaker, what there is in it so passing bitter, if
it come in the end to sleep and rest, that any one should pine in
never-ending sorrow.’ Book III. 894.
130. To conclude, there is a great deal in Lucretius (whether his
own or derived from others does not matter to us) which is of
considerable value, even from a modern scientific point of view,
though, of course, of far greater value from the point of view of the
student of development. But his attempted proofs are for the most
part absurd, based, as they generally are, upon mere metaphysical
speculations and altogether preposterous analogies.
131. (2.) Boscovich and others endeavoured to dispense with the
atom altogether, substituting in its place the conception (which
mathematicians often find useful) of a mere geometrical point, which
is a _centre of force_, as it is called. Here we get rid of the idea
of _substance_ entirely, but we preserve (all but inertia) those
external relations by which alone the atom is capable of making
known its presence. Even so great an experimental philosopher as
Faraday may be quoted as, to some extent at least, agreeing with this
notion. It seems to us, however, that this is the embodiment of an
over-refinement of speculation, surrounded on almost all sides by
the gravest difficulties. It may suffice merely to mention again the
property of mass, or inertia, which Faraday himself seemed to look
upon as the _one_ essential characteristic of matter, and which we
can hardly bring ourselves to associate with the absence of what we
understand by substance.
132. (3.) Another speculation leads us to imagine matter as not
ultimately atomic—as, in fact, infinitely divisible. But, if it
be so, it must (in order that various elementary physical facts
may be capable of explanation) be practically continuous but
intensely heterogeneous. That solid or liquid matter has a grained
structure of not infinitely small dimensions is proved by many
simple and generally known facts; among others by the separation
of white light into its constituent colours when refracted through
a prism, by the phenomena of capillarity, and by those of contact
electricity. If such heterogeneity were only pronounced enough, it
appears that the law of gravitation would be capable of accounting
for at least the greater number of effects at present attributed
to the so-called molecular forces and the force of chemical
affinity. Here, however, we are met by the grand difficulty, that of
accounting for gravitation. And the only attempt at explanation of
gravitation-attraction, which can be called even plausible, can only,
with very great straining, be made compatible with this idea of the
nature of matter.
133. (4.) The fourth and most recent speculation revives the atom (in
the literal sense of the word), but not ‘strong in solid singleness’
like those contemplated by Lucretius,—much rather yielding to the
least external force, and thus escaping from the knife or wriggling
round it, so that it cannot be cut,—not, however, on account of its
hardness, but on account of its mobility, which makes it impossible
for the knife to get at it.
This is the vortex-atom theory of Sir W. Thomson, dimly foreshadowed
in the writings of Hobbes, Malebranche, and others, but only made
distinctly conceivable in very recent times by the hydrokinetic
researches of Helmholtz. Helmholtz, in 1858, first successfully
attacked the equations of motion of an incompressible frictionless
fluid, without introducing the great simplification which had been
adopted by his predecessors, and which consisted in supposing the
motion to be non-rotational. He proved, among other valuable results,
that those portions of the fluid which at any time possess rotation
preserve it for ever, and are thus as it were marked off from the
others; also that these portions must be arranged in filaments
whose direction is at each point the axis of rotation, and that the
filaments are either endless, _i.e._ form closed curves (whether
knotted or not), or terminate in the free surface of the fluid.
Hence Sir William Thomson’s idea that what we call matter may consist
of the rotating portions of a perfect fluid, which continuously fills
space. This definition involves the necessity of a creative act for
the production or destruction of the smallest portion of matter,
because rotation can only be produced or destroyed by us in a fluid
in virtue of its viscosity (or internal friction), and in a perfect
fluid there is nothing of the kind.
134. Of course it may be objected to this theory that it merely
shifts the difficulty one step further back,—after all, explaining
what we call matter by certain motions of something which, as it
must have inertia, it would appear we are bound to call matter
also. We have been careful to mention this (latest) speculation as
to the nature of matter for three reasons: 1st, because we shall
have to make considerable use of it in the course of our argument,
for purposes of illustration; 2d, because it shows one way of at
once thoroughly accounting for the conservation of tangible matter;
3d, because it shows the possibility of forming an idea of a true
atom which shall not require, even for perfect elasticity, the
inconceivable quality of perfect hardness necessary to the atom of
Lucretius. In fact, the few words which we have given above about
Helmholtz’s investigations show that, to cut a vortex-atom, it would
be necessary to give a free surface to the perfect fluid which on
this theory is supposed to fill space, _i.e._ virtually to sever
space itself! This suggestion of Thomson’s promises to be very
valuable from one point of view at least, viz., the extension and
improvement of mathematical methods; for in the treatment of its
very elements it requires the application of the most powerful of
hitherto invented processes, and even with their aid, the mutual
action of two ring-vortices (the simplest possible space-form) has
not yet been investigated except in the special cases of symmetrical
disposition about an axis. Hence we are at present altogether unable
to decide or even to guess whether this idea will or will not pass
with credit some of the most elementary examinations to which a
theory of the ultimate nature of matter must of course be subjected.
135. Take them for what they are worth. The four forms of speculation
we have just sketched represent the most plausible guesses yet
propounded as to the ultimate nature of matter, the second being
probably because the most artificial and the most arbitrary, the most
completely developed. For in it the representation is self-contained
as it were; it does not base itself upon extraneous postulates, as
of ultimate hard particles (of what?), nor upon vortex motion (of
what? again), nor, finally, upon mere intense heterogeneity (of what?
once more), as do the other three. But we naturally object to it as
refining away altogether the idea of _stuff_ or _substance_ which the
mind seems to require as something underlying the notion of anything
which is found to be directly capable of affecting our senses.
136. The reader who has followed us so far, must now see that our
notions of the nature of matter are, at best, but hazy. We know, it
is true, a great many of its properties very exactly, so much so
indeed, as to be able to deduce from them mathematically an immense
variety of consequences which subsequent experiment shows to be
correct, at least within the limits of accuracy of our methods of
observation and measurement. But as to _what it is_ we know no more
than Democritus or Lucretius did, though as to what it may be or may
not be we are perhaps considerably better prepared with an opinion
than they could possibly be.
137. We have seen in the preceding chapter that energy is never found
separate from matter, so that we might, with perfect propriety,
define matter as the seat or vehicle of energy—that which is
essential to the existence of the known forms of energy, without
which, therefore, there could be no transformations of energy, and
therefore no _life_ such as we now know it.
138. The transformability of a given amount of energy, or, at
least, the mode of its transformation, often depends in a very
curious manner upon the relative quantity of matter with which it
is associated. We have already seen this in the case of heat. For,
when a given quantity of heat is associated with a small quantity of
matter, it is at a high temperature, and has great availability, but
its temperature, and therefore its availability, become lower as the
quantity of matter with which it is associated is increased. It is
possible that radiant heat and light owe their high availability to
the very small density of the luminiferous ether.
But it is not of heat alone that this statement is true. The same
thing holds with regard to other forms of energy, even the very
simplest forms of visible kinetic energy for instance. A pillow or
bolster (stuffed with eider-down, let us say) of 30 lbs. weight,
and moving at 10 feet per second—_i.e._ as if it had fallen from a
height of considerably _less than two feet_,—has nearly the same
energy as a pellet of No. 1 shot when it leaves the muzzle of a
fowling-piece. How different the quality of these equal quantities
even of energy of the same kind! For, delivered horizontally, the
one would correspond to a staggering push which few men could resist
if it came unexpectedly; while the other would scarcely affect one’s
equilibrium, though it might easily kill by penetrating a vital
organ. [In the brutal pastimes of the last generation, as we now
in our advanced humanitarianism call them, this was well known as
the difference between the effects of a slow knock-down blow by a
heavy-weight, and a ‘punishing facer’ from a feather-weight. Alas for
the good old times! for our comparison, apt as it is, is too probably
thrown away on the degenerate inhabitants of (once) merry England,
erewhile the home of the ‘Miller,’ with his honest quarterstaff, of
jolly and chivalrous wrestlers, boxers, and bowmen, now the hell of
running-kicks, garrotting, gouging,[45] and stabbing.
Aetas parentum, pejor avis, tulit
nos nequiores, mox daturos
progeniem vitiosiorem.
The dissipation of energy is a great fact in a moral as well as
in a physical sense. In those good old times _men_ fought with
_men_,—irrepressible energy, rather than any sordid passion or
uncontrolled vice, constantly pulling the trigger! _Now_ creatures
in the likeness of men vent their despicable passions in murderous
assaults upon women and children. But science hints at an effectual
cure. It is probable that before many years have passed, electricity,
which by some mysterious means enables our nerves to call our muscles
into play, will be called upon by an enlightened legislature to solve
this desperate social problem. Imprisonment has been tried in vain,
and, besides, it involves great and needless expense. The ‘cat,’
though thoroughly appropriate, is objected to as tending to brutalise
(!) the patient, and render murder not unlikely. No such objections
can be urged against the use of electricity in any of its many forms.
For it can easily be applied so as to produce for the requisite time,
_and for that only_, and under the direction of skilled physicists
and physiologists, absolutely indescribable torture (unaccompanied by
wound or even bruise), thrilling through every fibre of the frame of
such miscreants.]
139. After inertia, which is not accounted for by any of the
hypotheses as to the ultimate nature of matter which we have just
given, the most general property of matter which we recognise is that
of universal gravitation, in virtue of which portions of matter, if
situated at a distance from one another, are possessed of potential
energy. We are apt to hold exaggerated notions of the immense power
of gravity; but a little consideration will show us that it is in
reality one of the most trivial of the forces to which matter is
directly or indirectly subject.
Think for a moment of the fundamental experiments in electricity and
magnetism, known to men for far more than 2000 years,—the lifting of
light bodies in general by rubbed amber, and of iron filings by a
loadstone. To produce the same effects by gravitation-attraction,—at
least if the attracting body had the moderate dimensions of a
hand-specimen of amber or loadstone,—we should require it to be of so
dense a material as to weigh at the very least 1,000,000,000 lbs.,
instead of (as usual) a mere fraction of a pound. Hence it is at once
obvious that the imposing nature of the force of gravity, as usually
compared with other attractive forces, is due not to its superior
qualitative magnitude, but to the enormous masses of the bodies which
exercise it.
In fact, the excessively delicate Torsion-balance of Michell was
absolutely requisite to demonstrate, much more to measure, the mutual
attraction between a large and a small leaden sphere. And (unless
the third of the hypotheses as to the nature of matter above given
be correct, in which case the _form_ of our statement would require
modification) small or even moderately large pieces of matter are
held together entirely by cohesion, gravitation being absolutely
insensible; though in a huge mass like the earth, the force exerted
by one hemisphere on the other (_i.e._ the force which would be
called into play to prevent its being split in two) depends mainly
upon gravitation, in comparison with whose enormous amount even a
cohesive force of 500 lbs. weight per square inch over a circular
surface of 4000 miles radius sinks into utter insignificance![46]
140. One only of the many hypotheses which have been advanced to
explain the cause of gravitation has succeeded in passing the first
preliminary tests. Of course, the assumption of action at a distance
may be made to account for anything; but it is impossible (as Newton
long ago pointed out in his celebrated letters to Bentley) for
any one ‘who has in philosophical matters a competent faculty of
thinking’ for a moment to admit the possibility of such action.
Hence we have but two ways of accounting for gravitation:—either it
is due to differences of pressure in a substance continuously filling
all space, except where matter displaces it (?), or it is due to
impacts, in some respects analogous to those of the particles of a
gas which have been found to be capable of accounting for gaseous
pressure.
Now, all attempts as yet made to connect it with the luminiferous
ether, or the medium required to explain electric and magnetic
distance-action, have completely failed; so that we are apparently
driven to the impact theory as the only tenable one.
141. To this theory Le Sage of Geneva devoted a singularly acute mind
during the whole of his exceptionally long life; but, for all that,
his posthumous tract on the subject is but little in advance of the
results he had arrived at in his eighteenth year.
He assumes the existence of ultra-mundane corpuscles; in infinite
numbers, even compared with those of the particles of matter; of
dimensions excessively small, but flying about in all directions
with velocities enormously great. Portions of gross matter virtually
screen one another to a certain extent from the pressure due to this
perpetual rain of corpuscles; but only on the sides turned towards
one another. Hence a lone body would be equally battered on all
sides; but the introduction of a second mass interferes with this
arrangement, and diminishes the pressure on the side next it. It is
easy to show that the amount of this diminution, for _given small
masses_, is inversely as the square of their relative distance. But
when larger masses are taken account of, this diminution of pressure
will not be (as gravity is) directly as the quantities of matter
present, unless the further assumption is made that matter, whether
by the great distance between its particles, or by the cage-like form
of these particles, is almost perfectly permeable to the corpuscles;
so that, practically, the corpuscles rain upon each of the interior
particles of a mass as freely as if it had been alone in space.
Some of the postulates of this theory are hard to grant, and there is
additional difficulty as to the mode in which the supply of energy
of the corpuscles is to be kept up. To enter into details on this
subject is not in accordance with our plan. We therefore refer the
reader to Sir W. Thomson’s account of Le Sage’s theory (Proc. R.S.E.,
1871), and his suggestions for its improvement, based upon his theory
of vortex-atoms.[47]
142. But we must make one remark. If Le Sage’s theory, or anything
of a similar nature, be at all a representation of the mechanism of
gravitation, a fatal blow is dealt to the notion of the tranquil
form of power we have called _potential_ energy. Not that there will
cease to be a profound difference in kind between it and ordinary
_kinetic_ energy; but that BOTH must come henceforth to be regarded
as kinetic. What we now call kinetic energy is that of visible
motions, also of motions of the smaller parts of bodies, and of the
luminiferous ether, etc., each of these being more refined, as it
were, than the preceding. But if Le Sage’s theory be true, potential
energy of gravitation is a kinetic form still further refined than
any of these. And the conservation of energy may perhaps once
more be completely and accurately expressed as the conservation
of _vis viva_, though the term will of course have then a meaning
incomparably more extensive than its original one.
143. But, in speculations like these, we have soared far beyond that
which may be called the first refinement on ordinary gross matter;
_i.e._ the luminiferous, probably also the electric and magnetic,
medium, provisionally the _Ether_.
To the consideration of its principal properties we now turn our
attention.
These are, at first sight at least, of an apparently incongruous
character; for, from one point of view, the ether appears as a
fluid, from another as an elastic solid. Nothing is more certainly
established in physical astronomy than the excessive minuteness
of the resistance offered by the ether to the planetary motions,
if, indeed, there be such a resistance at all appretiable, even
when the velocity is, as in the case of the earth, somewhere about
100,000 feet per second! On the other hand, we learn from physical
optics that light, transmitted with a velocity of 188,000 miles per
second, depends upon transverse disturbances of some kind or other;
while several optical phenomena indicate that a disturbance of the
nature of compression (if such be possible) would be transmitted
with velocity almost infinitely great, in comparison even with this
enormous velocity.
144. Stokes, however, has given a very ingenious illustration
which enables us to see that such an extraordinary combination of
apparently irreconcilable properties is by no means without analogy,
even in common matter. He takes the case of a solution of glue, or
isinglass, or jelly, in different relative amounts of water. When
the quantity of water is small, we have the elastic solid; when
large, a liquid little different from water. And Stokes shows that
it is excessively improbable that there is any definite intermediate
stage which we could assign as that at which the transition from the
solid to the liquid takes place. Of course, any such analogy must
necessarily be excessively imperfect; but a great deal is gained by
our being able to trace even a very imperfect analogy in a case like
this.
145. The ether, in fact, must be distorted as well as displaced by
matter passing through it; but any distortion of the nature of a
shear, such as would give rise in water to vortex-motion accompanied
by friction (the whole energy being thus ultimately frittered down
into heat), would in the ether be handed on at once, as vibratory
motion, with the velocity of light. Thus vortex-motion of the ether
may be conceived to be impossible, simply in consequence of the
minuteness of its density in comparison with the great tangential
force called into play by a shear; and a body moving in it with a
velocity not so great as that of light would thus not have eddies in
its wake, as in an ordinary fluid, but, on the contrary, would be a
source of radiation, even although there may have been no heating
either of the body or of the medium it is displacing, paradoxical as
this result may appear. In this connection it is hardly possible to
avoid quoting Milton—though there may be a suspicion of something
analogous to a pun:—
‘The grinding sword with discontinuous wound
Passed through him—but the ethereal substance closed
Not long divisible.’
146. Sir William Thomson has endeavoured to obtain at least an
inferior limit to the density of the ether in planetary space. His
method is based upon the measurements by Pouillet and Herschel
of the whole amount of radiant energy received from the sun by a
given amount of terrestrial surface in a given time, and upon an
assumption that the extreme amplitude of distortion of the ether
in any radiation is small compared with the length of a wave. In
this way he finds that, as a cubic mile of the ether near the earth
contains about 12,000 foot-pounds of radiant solar energy, the mass
of the ether in that cubic mile must be at least 1/1,000,000,000 of
a pound.[48] To show that this is not by any means a surprisingly
small quantity he compares it with the mass of a cubic mile of air at
a distance of only a few radii from the earth’s surface (supposing
that the atmosphere extends so far; which, by the way, the recent
calculations of the velocities of the particles of a gas render
exceedingly improbable). This, he finds, will be probably represented
by a fraction of a pound having unit for a numerator and 329 places
of figures in the denominator!!!
147. In a very remarkable paper by Struve,[49] an attempt was made to
settle the question, _Is the ether perfectly transparent?_ or, as we
may now put it, Is any radiant energy absorbed by the ether, whether
to produce other forms of energy, or to be dissipated by radiation
in all directions? Long ago it had been pointed out by Olbers and
others, that if the stars be infinite in number, and be distributed
with anything roughly approximating to an average density through
infinite space, the sky ought, night and day, to be all over of a
brightness of the same order as that of the sun. Is the number of
stars, then, finite; or does the ether absorb their light? Now, it
need not in the least surprise us to find that the number of stars is
_finite_, even though matter be infinite in quantity, and distributed
with something like uniformity through infinite space. For only a
finite portion of it may yet have fallen together so as to produce
incandescent bodies; or, the other extreme, only a finite portion of
it may be left incandescent. Either of these altogether different
hypotheses is perfectly reasonable and scientifically justifiable;
so that, from this point of view, we are not at present likely to
obtain any information. Struve’s reasoning, which, by the way, is
not accepted by Sir J. Herschel, introduces another consideration,
viz., _the number of stars of each visible magnitude_. To apply
this: suppose for a moment we make the assumption (actually measured
values of annual parallax show it is certainly at best a very rough
one) that the brighter stars are the nearer, and that a set of
stars, on the average one-fourth as bright as another set, are on
the average twice as far off, etc. A great deal of what we know to
be certainly false is here assumed as true, but it is possible that
the general accuracy of the results of the reasoning from it may
not be thereby much affected. On the supposition of a sort of rough
uniformity of distribution through space, we can easily calculate
approximately what ought to be the relative numbers of the stars,
classed by astronomers as of the various different magnitudes,
once we have obtained (as it is not difficult to do) an estimate
of the relative brightness of typical stars of these (arbitrary)
magnitudes. From their brightness we calculate at once their relative
distances, and thence (according to our hypothesis of approximately
uniform distribution) what ought to be _the relative numbers of each
magnitude_. When this is done, it appears that there is a great
excess of the calculated over the observed numbers, at least for
telescopic stars, and the greater the smaller the magnitude. This is
the gist of Struve’s method, and he arrives at the result that the
light of stars of the sixth magnitude (the smallest visible to an
ordinary unaided eye, and whose average distance from us is supposed
to be somewhere about ninefold that of stars of the first magnitude)
loses about eight per cent. in its passage to the earth. Thus the
light of stars of the first magnitude does not lose so much as one
per cent.; but, on the other hand, stars of the ninth magnitude are
enfeebled to the extent of about 30 per cent. Struve shows that, if
his result is to be accepted, W. Herschel’s idea that his 40-foot
telescope would show him stars seven times farther off than those
visible with the 10-foot, was erroneous. He would, in fact, have been
able to see little more than _twice_ as far.
It will be obvious now that an enormous increase of the so-called
_space-penetrating_ power of a telescope gives it in reality but
a very feeble additional advantage, in fact, that, if there be
absorption by the ether, we have already instruments capable of
showing us, at the very least, half of the whole number of stars
which any conceivable improvement of telescopes would enable us to
see.
148. It would be out of place here to speculate on what becomes
of the light thus supposed to be absorbed, for we have as yet no
experimental bases on which to reason. We have not the least idea,
for instance, what is the effect of change of temperature in the
luminiferous ether. That it is practically incompressible we know; it
is quite probable that it may not be sensibly compressed (if it be
subject to gravity, of which we have no proof) even by the attraction
of the mass of the whole earth—though, so great is the intensity of
molecular or cohesive attraction, we may easily conceive that in
the interior of bodies the ether may be considerably compressed.
And it is not improbable that the ether, as a whole, may have, in
virtue of its internal forces, a property (akin, as it were, to a
liquid film) such that the gravitation action, which appears to be
between particles of matter, may merely be the visible result of a
tendency to a minimum of some affection of the fluid in which they
are immersed.
Regard the ether as we please, there can be no doubt that its
properties are of a much higher order in the arcana of nature than
those of tangible matter. And as even the high-priests of science
still find the latter far beyond their comprehension, except in
numerous but minute and often isolated particulars, it would not
become us to speculate further. It is sufficient for our purpose to
know from what the ether certainly does that it is capable of vastly
more than any one has yet ventured to guess.
149. If we review the attempts recorded in this chapter we see how
the scientific mind is led from the visible and tangible to the
invisible and intangible.
In the first place, we know that one body, such as the sun, can
part with its radiant energy to another body, such as the earth,
and observation and experiment alike lead us to acknowledge a stage
in which the energy has left the one body and has not yet arrived
at the other. But we have already seen that energy is always found
associated with matter, never by itself. In fact we have spoken of
matter as the ‘vehicle of energy.’ Hence it necessarily follows
that there is something between the sun and earth capable of moving
and transmitting energy, and therefore, from the very conception of
energy, possessing mass—this something we agree to call the ethereal
medium.
Again, we know that different masses of visible matter attract one
another apparently at a distance. Our first attempt to analyse the
nature of this force leads to the question:—Does it proceed from
the surfaces of the attracting bodies, or does it penetrate their
entire mass? This question was answered by Newton, who came to
the conclusion that every particle of matter attracts every other
particle with a force proportional to the product of their masses,
and inversely proportional to the square of their distances.
But this drives the mystery of gravitation only from the mass to the
particle, and here the same sort of questions again occur. A particle
as truly as a mass occupies space, and we wish to know whether
gravitation force proceeds from the surface of the particle or from
its interior.
150. We likewise wish to know how this force is communicated between
one particle and another? Before we can solve these questions we
must have some definite conception of the nature of a particle and
of the constitution of the surrounding medium. Sir W. Thomson, as we
have seen, has attempted to advance towards the nature of an atom or
particle in his supposition that atoms are vortex-rings generated out
of a perfect fluid filling all space. While, however, this conception
accounts for some of the properties of an atom it does not at all
directly account for anything like gravitation, and hence he adopts
in addition the hypothesis of ultra-mundane corpuscles, which he
supposes to be only a finer form of vortices.
151. There is, however, one objection to the precise form of
vortex-ring hypothesis introduced by Thomson which from our point
of view is very strong. The act by which the atom was produced must
surely on this hypothesis have been an act of creation in time
(Art. 133), that is to say, an act impressed upon the universe from
without, and it must therefore have denoted a breach of continuity
(Art. 85); for if the antecedent of the visible universe be nothing
but a perfect fluid, can we imagine it capable of originating such a
development in virtue of its own inherent properties, and without
some external act implying a breach of continuity?—we think most
assuredly not. In the production of the vortex-atom from a perfect
fluid we are driven at once to the unconditioned—to the Great First
Cause; it is, in fine, an act of creation and not of development.
But from our point of view (Art. 86) creation belongs to eternity
and development to time, and we are therefore induced at least to
modify the hypothesis so as to make it consistent with this view. We
cannot, in fact, if we agree to hold at the same time the principle
of unbroken continuity and the vortex-ring theory of formation of
the visible universe, regard the material whose rotating parts are
ordinary matter as an absolutely perfect fluid.
152. This way of regarding this supposed material is strengthened
by the fact that the hypothesis which seems most likely to account
for gravitation presumes the existence of ultra-mundane corpuscles:
and the observations of Struve upon the extinction of starlight
tend (whatever they are worth) towards the same conclusion, since
the absorption of light is more compatible with a corpuscular
constitution than with that of a perfect fluid. Finally, the mere
fact that the velocity of light is finite, tends also in the same
direction. But if the visible universe be developed from a material
which is not a perfect fluid, then the argument deduced by Sir W.
Thomson in favour of the eternity of ordinary matter disappears,
since this eternity depends upon the perfect fluidity of that out of
which it was developed. In fine, if we suppose the material universe
to be composed of a series of vortex-rings developed from something
which is not a perfect fluid, it will be ephemeral, just as the
smoke-ring which we develop from air, or that which we develop from
water, is ephemeral, the only difference being in duration, these
lasting only for a few seconds, and the others it may be for billions
of years.
153. In our last chapter, we came to the conclusion that the
available energy of the visible universe will ultimately be
appropriated by the ether, and we may now perhaps imagine, that as
a separate existence itself the visible universe will ultimately
disappear, so that we shall have no huge useless inert mass existing
in far remote ages to remind the passer-by of a species of matter
which will then have become long since out of date and functionally
effete. Why should not the universe bury its dead out of sight?[50]