‘Felix qui potuit rerum cognoscere causas,atque metus omnis et inexorabile fatumsubjecit pedibus, strepitumque Acherontis avari.’Vergil.
‘Felix qui potuit rerum cognoscere causas,atque metus omnis et inexorabile fatumsubjecit pedibus, strepitumque Acherontis avari.’Vergil.
‘Felix qui potuit rerum cognoscere causas,
atque metus omnis et inexorabile fatum
subjecit pedibus, strepitumque Acherontis avari.’
Vergil.
‘Who shall tempt with wandering feetThe dark, unbottomed, infinite abyss,And through the palpable obscure find outHis uncouth way; or spread his airy flightOver the vast abrupt, ere he arriveThe happy isle?’—Milton,Paradise Lost.
‘Who shall tempt with wandering feetThe dark, unbottomed, infinite abyss,And through the palpable obscure find outHis uncouth way; or spread his airy flightOver the vast abrupt, ere he arriveThe happy isle?’—Milton,Paradise Lost.
‘Who shall tempt with wandering feetThe dark, unbottomed, infinite abyss,And through the palpable obscure find outHis uncouth way; or spread his airy flightOver the vast abrupt, ere he arriveThe happy isle?’—Milton,Paradise Lost.
‘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 theAtom. The outlines of the atomic theory were laid down very precisely by Democritus and Leukippus (circa400B.C.), who taught that the whole universe is made up of empty space and eternal atoms, differing only in form (asΑandΝ), order (asΑΝandΝΑ), and posture (asΖandΝ). 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 poethimself:—
‘Omnia enim stolidi magis admirantur amantque,inversis quæ sub verbis latitantia cernunt,veraque constituunt quæ belle tangere possuntauris et lepido quæ sunt fucata sonore.’[44]
‘Omnia enim stolidi magis admirantur amantque,inversis quæ sub verbis latitantia cernunt,veraque constituunt quæ belle tangere possuntauris et lepido quæ sunt fucata sonore.’[44]
‘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, dangerof 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 aplenum: 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 isslower 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 avery 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 overcomingit:—
‘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.’ BookIII.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.’ BookIII.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 dispensewith the atom altogether, substituting in its place the conception (which mathematicians often find useful) of a mere geometrical point, which is acentre of force, as it is called. Here we get rid of the idea ofsubstanceentirely, 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 theoneessential 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 forceof 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 inthe 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 ofstufforsubstancewhich 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 subsequentexperiment shows to be correct, at least within the limits of accuracy of our methods of observation and measurement. But as towhat it iswe 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 nolifesuch 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 considerablyless 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, tulitnos nequiores, mox daturosprogeniem vitiosiorem.
Aetas parentum, pejor avis, tulitnos nequiores, mox daturosprogeniem vitiosiorem.
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 timesmenfought withmen,—irrepressible energy,rather than any sordid passion or uncontrolled vice, constantly pulling the trigger!Nowcreatures 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 experimentsin 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 theformof 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 havebeen 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, forgiven 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 calledpotentialenergy. Not that there will cease to be a profound difference in kind between it and ordinarykineticenergy; but thatBOTHmust 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 ofvis 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 theEther.
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 thenature 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 sourceof 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 apun:—
‘The grinding swordwith discontinuous woundPassed through him—but the ethereal substance closedNot long divisible.’
‘The grinding swordwith discontinuous woundPassed through him—but the ethereal substance closedNot long divisible.’
‘The grinding swordwith 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 least11,000,000,000of 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 anumerator 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 isfinite, 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, andthat 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 bethe 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 thanthose visible with the 10-foot, was erroneous. He would, in fact, have been able to see little more thantwiceas far.
It will be obvious now that an enormous increase of the so-calledspace-penetratingpower 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 orderin 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 aforce 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 inherentproperties, 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 perfectfluid, 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]