Let us take for our ill.u.s.tration the best example, that experience and observation afford, that of the atmosphere surrounding the earth. The a.n.a.logy is so perfect, that one is almost tempted to believe that the atmosphere and the Aether are in some way intimately a.s.sociated with each other. Some years ago Lord Kelvin was of the opinion that the Aether was but an extension of the atmosphere, though I am not certain whether he holds that view at the present time. Clerk Maxwell, writing in the _Phil. Mag._ in May 1861, writes: "I have deduced from this result the relation between statical or dynamical electricity, and have shown that the elasticity of the magnetic medium in air is the same as that of the luminiferous medium, _if these two coexistent, coextensive, and equally elastic media are not rather one medium_."
Now for the comparison. Both the atmosphere and Aether are matter. Both are atomic, both are gravitative, both possess elasticity, and both possess density. The atmosphere also possesses different degrees of density, so does the Aether. In the case of the atmosphere, however, experience and experiment teach us that the atmosphere is denser nearer the earth than farther away.
When we ascend mountains, it is a matter of common knowledge that the higher we ascend, that is the further we get from the earth, the rarer the atmosphere becomes. When we ascend in balloons, we find that the air becomes so rare and so light, that the blood will flow from the nose, on account of the reduced pressure exerted on it, the pressure inside the body being greater than that outside. Now in accordance with our second Rule of Philosophy, if experience is to be any guide at all, then it most conclusively teaches us that the Aether being subject to the same laws as the atmosphere, the same results inevitably follow. Therefore the Aether nearest the earth is denser than any layer immediately above it, and that layer denser than the one above it, and so on for great distances, with the result that the only conclusion we can come to in regard to the density and rarity of Aether in relation to all gravitating bodies is, that the densest part of the Aether is nearest to them, and the rarest, the farthest away from them. So that while Newton"s suggestion in his nineteenth query is correct in principle, it is incorrect in application to s.p.a.ce.
I would like to point out here, that what is true of the earth in relation to the density of the surrounding Aether, must also be true, according to our second Rule of Philosophy, of every other planet, or sun, or star. So that every planet, satellite, every sun or star has its atmosphere, if I may so term it, of Aether, which obeys and follows the same laws as the earth"s atmosphere does.
This is a most important fact, and has a most important bearing upon the physical cause of Gravitation as applied to each planet, and sun and star, as I shall afterwards show.
I wish now to bring the reader into contact with a Theory of Gravitation that was given to the world by Professor Challis of Cambridge, 1872. In the _Philosophical Magazine_ of June of that year he writes: "I a.s.sume that all the active forces of Nature are different modes of pressure under different circ.u.mstances of a universal elastic Aether, which presses always proportionately to its density."
Now what I wish to point out is, that while Prof. Challis admits the density of the Aether, and also varying degrees of density, as he states that the Aether presses proportionately to the density, he does not show how that varying density is accounted for. If there is this varying density, then there must be some underlying principle which governs the variation in density, and I know of only one principle or law which can regulate that variation in density, and that is that Aether is gravitative, and being gravitative it not only possesses density, but also variations in density.
Thus by admitting that Aether is gravitative, because it is matter, we have at once a satisfactory explanation for the density of the Aether and also for different degrees of density both in the atomic world, and in the planetary and stellar world.
ART. 47. _Aether is Elastic._--In Art. 39, matter was shown to be elastic, and on the a.s.sumption that Aether is matter, the elasticity of the Aether, which has been postulated for it by various scientists, can be logically and philosophically accounted for.
In view of the transmission of light through s.p.a.ce with a definite and finite velocity, we are compelled to regard Aether as possessing elasticity, similar to that of an elastic solid body.
If we take the a.n.a.logy of sound, we find that sound is transmitted and propagated through matter, by waves of alternate condensation and rarefaction, and that transmission is regulated by the relation of the density of the medium to its elasticity. Light has been proved to be due to the undulatory wave-motions of the Aether, and in order to account for the transmission of the wave-motion, it is essential that the Aether should possess the property of elasticity.
As Young points out in his First Hypothesis,[6] the Aether possesses this property of elasticity, but with the advance of scientific knowledge and research, the elasticity of the Aether may be said to have pa.s.sed out of the hypothetical stage, into the state of actual fact and experiment. Both McCullagh and Fresnel have a.s.sumed this property of elasticity for the aetherial medium in order to account for certain phenomena of light.
Apart, however, from the atomicity of the Aether, it is exceedingly difficult to understand how such a property can belong to it. Atoms are exceedingly small particles, possessing the property of elasticity, or the power to recover their original shape after distortion or change of shape. If the Aether therefore be atomic, as is pointed out in Art. 44, it can at once be readily understood how the Aether as a whole can possess the property of elasticity. The atoms of the Aether must be inconceivably small, as the light-waves travel with the enormous velocity of 186,000 miles per second.
What must therefore be the atomic vibration which such a statement implies? If, on the other hand, the Aether is a.s.sumed to be continuous and non-atomic, it must be seen how exceedingly difficult it is to account for the elasticity of the Aether, as it seems absolutely impossible for a medium which is continuous, and non-atomic, to be able to transmit the waves of light with a finite velocity.
Apart, therefore, from atomicity of some kind or other, elasticity of the Aether is an a.s.sumption philosophically incorrect, as it is contrary to that simplicity of conception laid down by Newton, and is also contrary to all experience, and thus violates the second Rule of Philosophy.
Aether therefore must be said to be perfectly elastic; so perfectly elastic, that it is susceptible to the least touch of any natural thing, so that even an atom, so small that it cannot be seen with the most powerful microscope, yet so elastic is this Aether medium, that the least motion or vibration of one of these atoms, though the motion did not exceed the 20- or 40-millionth part of an inch, yet even this would create in the aetherial ocean, Aether-waves, just as a body moving in water creates water-waves, which, radiating from the place of their birth, beget and create others, the process continuing until they reach the margin of the water in which they were generated. It is precisely so with these Aether-waves, when once generated and set in motion. They create others, the process being continued and perpetuated; and, unless arrested in their course, may continue until they reach the very limits and confines of material immensity and s.p.a.ce.
It is, perhaps, only necessary to say, regarding the perfection of the elasticity of the Aether medium, that though it takes from 40,000 to 69,000 waves to complete the s.p.a.ce of one inch in extent, yet it is done with such miraculous rapidity, as to speed the distance of 186,000 miles in the short s.p.a.ce of a second of time; or, taking the number of Aether-waves to complete an inch as 50,000, its elasticity is such that it makes 50,000 186,000 12 5280 vibrations in one second of time.
We have already seen in Art. 39, that according to Boyle and Marriotte"s Law, the velocity of a wave-motion, as sound in the air, is determined by the relation of the elasticity of the medium to its density. If the temperature of the atmosphere remains the same, then the _elasticity_ varies in the same proportion as its density.
According to Art. 45, Aether is gravitative, and that fact produces different degrees of density in the aetherial atmosphere of an atom or planet or meteor, sun or star; that part of the Aether being densest nearest the central body, and rarer the further we go away from that body.
Now the question at once arises, what is the effect of the increased density of the Aether near the body upon the elasticity of the Aether?
From the a.n.a.logy of sound in air, we arrive at the conclusion that Boyle and Marriotte"s Law equally applies to the Aether, as it does to the atmosphere of any planet. That is, if the temperature of any stratum or layer of the Aether remains the same, then the elasticity of the aetherial medium in that layer is proportionate to its density, so that while the gravitating property of the Aether makes it denser nearest the central body, the fact that the elasticity is proportionate to the density, does not affect the transmission of any wave-motion.
[Footnote 6: _Phil. Trans._, 1802.]
ART. 48. _Aether possesses Inertia._--From Art. 40 we have seen that all matter possesses inertia, inertia being that property of matter by which it cannot of itself change its state of motion or of rest.
If Aether be matter, therefore, then it must also possess inertia. This property of inertia is already postulated for Aether by scientists, and to that extent is conformable to the Rules of Philosophy. Professor Tyndall, with reference to the inertia of the Aether, writes: "The motion of Aether communicated to material substances throws them into motion. It must be therefore itself a substance. Aether is a substance endowed with inertia, and capable, in accordance with the established laws of motion, of imparting its motion to other substances."[7]
Again, Lord Kelvin in his Address to the British a.s.sociation, 1901, on the "Cl.u.s.tering of Gravitational Matter in any part of the Universe,"
states: "Aether we relegate to a distinct species of matter which has inertia, etc." Aether, therefore, according to Tyndall, "is a substance or medium endowed with inertia, and capable, in accordance with Newton"s Laws of Motion, of imparting its motion to other substances."
If, however, the Aether is frictionless, as has generally been supposed, then it cannot possess inertia, because to the extent that a body possesses inertia, to that extent it is opposed to being frictionless.
Inertia is really the equivalent of ma.s.s, or the amount of matter measured by gravity, and if Aether possesses ma.s.s in any sense at all, as it must do if it is matter, then, possessing ma.s.s or weight, it must offer resistance to any body moving through it, and to that extent cannot be frictionless. To suppose that the Aether is frictionless, and yet possesses inertia, is to suppose something altogether opposed to all the Rules of Philosophy and therefore of experience.
I have already shown that a frictionless medium is opposed to all philosophy and experience, and is an anomaly in the universe.
On the strictly philosophical a.s.sumption that Aether is matter, and therefore atomic and gravitative, the whole question of the inertia of the Aether is reduced to one of common experience. It is, at least to my mind, difficult to conceive of ma.s.s without weight or without atomicity, and yet that is the unphilosophical position of the present state of science in relation to the Aether. In other words, while the Aether is supposed to possess inertia, which is dependent upon ma.s.s, as measured by gravity, yet it is supposed not to be gravitative, that is, that the ma.s.s of the Aether has no weight at all, and therefore is not ma.s.s, which a.s.sumption contradicts itself. From Arts. 44 and 45, however, we have seen, to be strictly philosophical, that Aether must be atomic and also gravitative. It can now be easily understood how it can possess inertia like any other matter, and is therefore capable of receiving motion from other matter, and also of imparting that motion to other matter.
So that, wherever there is motion of any kind in the Aether, either in the form of vibratory motion as heat, or undulatory motion as light, or rotatory motion as electricity, those motions will affect adjoining matter in the same way that the motion of any other moving matter affects any body with which it comes into contact.
From the fact that Aether possesses inertia, and is also gravitative, we have now to alter our conception of this universal s.p.a.ce-filling medium, and in place of a frictionless medium, which is incapable of imparting motion to any body, we have now to remember henceforth that the Aether is matter, which possesses inertia, and therefore has the capacity not only of offering resistance to any body moving through it, as a comet or meteor, but also of imparting the motion which it may receive in any manner to any other matter, as a planet, satellite, or sun, that may be floating in it.
With this philosophical view of the Aether, which is entirely in harmony with our first and second Rules of Philosophy, we shall be able to give a physical explanation of the Law of Gravitation, as we have now a physical medium existing in all atomic, solar, and stellar s.p.a.ce, which can both accept motion, and transmit that motion to other bodies. In other words, we have a medium which can both push and pull.
[Footnote 7: _Lectures on Light._]
ART. 49. _Aether is Impressible._--Another characteristic property of this Aether medium is, that it is as perfectly impressible as it is elastic. So perfectly impressible, that it receives, retains, and perpetuates for thousands of years, and for distances to human mind incalculable, every impression given to it of light, form, colour, tint, and shade; and that, too, with a perfect fidelity that nothing mars, even to the least and most infinitesimal detail.
Therefore, irrespective of distance, wherever there is matter to arrest and reflect the impressions received, there those impressions of light (and all that in the luminosity is involved and contained) become visible and revealed, and wherever there is power of vision to receive and concentrate these Aether- or light-waves, there, not only luminosity or light, but all that const.i.tutes and is involved in that luminosity, becomes at once visible and seen.
It is by this means we see the colour, tints, shades, and forms of suns and planets; of stars, constellations, etc., with all the varied forms, configurations, and movements of the celestial phenomena. Each and every one, small or great, glittering or blazing, sun or planet, are ever creating or generating Aether-waves, and impressing them with all the details and particulars of their nature and existence; and these Aether-waves ever bear upon their mystic wings the impressions received, carrying the information given with lightning speed to the very confines and limits of infinite s.p.a.ce or the material universe; beyond which exists nothing but the ever-living and active energy of the Divine, the only unlimited, unbounded, and absolute infinitive.
It is by the interception and concentration of these waves by our perceptive powers, aided with the giant powers of the telescope, that we obtain the information given, or become cognizant of the nature and existence of the varied lights, colours, tints, and shades of the celestial bodies.
The vision, a.s.sisted by the giant power of the telescope, collects and concentrates these Aether-waves into a perfect image of those things that gave them birth, and by this means reveals to us the knowledge of things afar, their existence, nature, characteristics, properties, and powers.
Thus it is we see the solar orb, with its huge fires all aglow, obtain a knowledge of its character and powers, see its huge spots, its quivering fringe of flame, and high-leaping prominences, or watch its slowly revolving form.
Thus we see the planets that around it sweep and roll; swift-footed Mercury with his wondrous speed, and dazzling Venus with her silver sheen; Mars the G.o.d of war with his ruddy glow, and mighty Jupiter with his orange hue, and the yellow Saturn with her mysterious rings, the blue Ura.n.u.s, and the more distant Neptune, with all the satellites that to it belong.
Then far far away the brilliant Sirius--the Dog Star, Cygnet, Centauri, the Great Bear, and a thousand others.
The Pleiades and the twenty millions of suns that form our own galaxy and the Milky Way, with all their varied colours, tints, and hues of white, golden, orange, ruby, red and blue, green and grey, silver, purple and yellow, buff and fawn, emerald and green, lilac and coppery.
Thus we see the distant Orion, so far away that swift-footed Light, with its speed of more than eleven million miles per minute, has to travel for more than thirty thousand years before it spans the gulf that intervenes between it and us, and brings to us the news of its existence there.
Then the spectroscope with its revealing power literally tears asunder wave from wave, and reveals the mystic message which each doth bear, of the distant things from which they come, of each and every sort and kind.
Thus we know, that in the solar fires there ever burn such things as hydrogen, oxygen and nitrogen, and also, in a vaporous state, aluminium, sodium, iron, magnesium, cobalt, calcium, chromium, copper, manganese, zinc, and others.
Thus light-waves are speeding everywhere, and from all material things.
They come from our own sun, and rush in, and flood the earth"s aerial veil, the atmosphere; and "Each little atom of matter, like a mirror, reflects and re-reflects them as if in sport, buffeting each luminous ray from one to another, increasing and amplifying it by an infinity of repercussions" (Herschel), and then in their entirety and whole, like a huge multi-mirror, so blend and mingle them that they come to earth"s surface in that soft radiance we call Light, and bathe it as in a sea of mellowed glory.
ART. 50. _Aether: its Motions._--The question of the exact motions of the Aether is a question which has involved the attention of scientific men for many years, and which is at the present time receiving the attention of some of our most advanced scientists, not only in this country but in other countries also.
Whether the Aether in s.p.a.ce is at rest, or is moving along with all the bodies that float in it, so to speak, is a question of the greatest importance to scientists and philosophers generally, as the particular character of the motions of the Aether, which are either suggested or ascribed to it from the a.n.a.logies of Nature, are sure to have a most important bearing not only on the motions of all the planets and satellites, but also upon such questions as the aberration of light, and such difficulties as presented by Lord Kelvin in his paper on "Clouds on the Undulatory Theory of Light" (_Phil. Mag._, July 1902).