The Ether a Material Substance, proved by its Behaviour.

We have said in a former part of this work, pages 153 and following, that if the ether is capable of performing all the functions that are attributed to it, it must have some consistence or substance of some kind; that it must be matter of some kind in some form, and consequently must have density in some degree however low; and we might, for the same reasons, suppose that it must have some temperature; but as long as we believe that without motion there can be no heat, we cannot conceive it to have any temperature. No doubt we might suppose it to be in a constant state of vibration, and to have the temperature corresponding to that state, whatever that may be; but this, in addition to leaving us just where we were, would only entail upon us the task of supplying temperature as well as density to a body of whose existence no positive proof has hitherto been given, whatever we may believe about it. At the same time, the evident necessity of taking its temperature into consideration, seems to supply another reason for concluding that it is a material substance, over and above those we have cited now and before.

The general belief regarding the ether has been, ever since it was invented, that it is a substance of some kind (imponderable and impalpable?) which fills and pervades all space and matter; but a little consideration will show that this belief requires to be modified. The ether is supposed to be the connecting link of the universe, and the agent for carrying light, heat, electricity, and magnetism from the sun to the earth and planets, and all over space; but it has been found that electricity will not pass through a vacuum, such as has been produced by experimenters, unless it be with a very powerful current. This, of course, would seem to prove that there must be almost no ether in such a vacuum; because if there was ether in it, of the same density as there is in space, electricity would pass through it with the same ease as it does from one body to another on the earth or in space; it would seem, also, to justify us in inferring that electricity would not pass through an absolute vacuum at all, however powerful the current might be, because there would be absolutely no ether to carry it; and, likewise, that the quantity of ether remaining in the experimenter's receiver had as much to do with the passing of a very powerful current of electricity through it—perhaps a great deal more—as the small quantity of air, or gas, or dust not altogether exhausted from it, to which the experimenters attribute its passage. Moreover, it would appear that when air or any gas is pumped out of a receiver, the ether mixed with it is pumped out along with it; consequently it must be a material, tangible substance, possessing density in some degree, however low it may be. Here, then, we have, it would appear, proof positive that there is such a carrying substance as the ether has been supposed to be. It is a thing which we have not to conceive of, fabricate, or build up in our minds. It is a thing we can pump out of a tube, and is as much a material substance, in that respect, as air or any other gas that is as invisible as itself—yet nevertheless in the tube until it is pumped out.

Against this idea of the nature of the ether, and what may be done with it, it may be argued that light and heat pass freely through a tube or receiver in vacuo, when electricity refuses to pass; but are we sure that they do pass? It would be a much more difficult matter to prove that they do, than to prove that electricity does not, because our eyesight gives us evidence in the latter case. Besides, there are facts which, when thoroughly looked into, induce us to believe that light actually does disappear gradually from a vacuum as it is being formed.

In an article on "The Northern Lights," in "Science for All," Vol. II., reference is made to a well-known laboratory experiment in the following words: "We take a glass cylinder, covered at the ends with brass caps, one of which is fitted with a stop-cock, which we can screw to the plate of an air-pump. To the brass caps we now attach the terminals of a powerful induction coil, but as yet we perceive no result. We now begin to exhaust the air from the cylinder, and as the exhaustion goes on we soon see a soft tremulous light beginning to play about the ends of the cylinder; and this, when the air is sufficiently rarefied, gradually extends right through the cylinder. As we continue the exhaustion these phenomena will be reversed, the light gradually dying away as the exhaustion increases. We shall at once perceive how very much this resembles an aurora on a small scale, and so we have electricity suggested to us as the agent which produces the aurora." Farther on in the same article we find that: "Aurora displays usually take place at a great height—sometimes so high as 300 miles—while their average height is over 100 miles. At such heights the air must be extremely rarefied, and we should be disposed to expect that the electric discharge could not take place through it."

Now, at the beginning of this experiment, it must be granted that light was passing freely through the glass cylinder from side to side, and also that, when the electric current was turned on, the electricity was passing freely through the air in the cylinder though it was not visible. It could not pass through the glass on account of its being a non-conductor. Then, when the air had been partially exhausted from the cylinder, and the "soft tremulous light" began to appear about its ends, it is clear that some interference with, or change in, the free passage of light through it must have been produced, both transversely and longitudinally, which occasioned the difference in the appearance of the light and caused its tremulous motion. And as change in the appearance of the light extended through the length of the cylinder as the exhaustion increased, and finally died away—light, change and all—when it approached more nearly that of an absolute vacuum, we cannot help concluding that the light disappeared because there was no medium left in the cylinder, of sufficient density at least, through which it could pass; which, of course, means that light cannot pass through a vacuum any more than electricity can.

The experiment we have cited above may be considered antiquated, but similar results are presented to us in Professor Balfour Stewart's "Elementary Physics," where he says at page 399 of the Reprint of 1891: "Another peculiarity of the current is the stratification of the light which is given out when it traverses a gas or vapour of very small pressure. We have a series of zones alternately light and dark, which occasionally present a display of colours. These stratifications have been much studied by Gassiot and others, and are found to depend upon the nature of the substance in the tube." [The ether?] "If, however, the vacuum be a perfect one, Gassiot has found that the most powerful current is unable to pass through any considerable length of such a tube."

[In passing, we take the opportunity to assert, with confidence, that there can be no perfect vacuum on the earth.]

Here we see the gas or vapour in the tube divided into zones alternately light and dark, which occasionally present a display of colours, and are led to infer, from the colours depending upon the nature of the substance in the tube, that they disappear altogether when the exhaustion is sufficiently great; and are finally told that the most powerful current is unable to pass through such a tube of any considerable length. In this case also, we can say with perfect confidence that there can be no ether left in the tube, in sufficient quantity, or else it would be able to carry the electricity through it much more easily than from the sun to the earth, or from one part of the earth to another. If we refuse to acknowledge that the ether has been removed from the tube or cylinder, we are forced to conclude that it is not the carrying agent, for which alone it has been called into existence by the imagination of scientists; and we have to invent new theories, new methods for explaining what we have been accustomed to think we thoroughly understood. We have to look for a new dog to carry and fetch. Furthermore, all that has been said about electricity is equally applicable to light, whether we can prove it or not. If light could pass freely through the experimental cylinder from side to side, as it was certainly doing before the exhaustion was begun, we cannot understand why there should be, first tremulous light which finally disappeared, and why dark strata were displayed in it by the forced passage of electricity; unless it was that the carrier of the light was removed, and then we naturally think of why there should be dark strata in the tube. We can understand electricity lighting up darkness, but not its darkening light—it lightens up midday—and we must conclude that both the one and the other were driven through the cylinder, or similarly conducted through it, by the same force, or were left behind.

Following up the quotations we have already made from "Science for All," Vol. II., we now add another for further illustration of what we have been saying, to wit: "Let us now return to the laboratory, and see whether we can make any experiment which will throw light upon this difficulty. If we send the electric discharge through one of the so-called vacuum tubes—choosing one which consists, through part of its length, of tube which is much narrower than the main portion—we find that when the discharge is passing the pressure is greater in the narrow part of the tube, showing that in some way gas is being carried along by means of the current, and Professor A. S. Herschel suggests that in some similar way air may be electrically carried up to these great heights." This quotation, of course, refers to the Northern Lights, but it serves to illustrate what we are seeking to show with respect to the ether.

In this experiment, the explanation of the pressure being greater in the narrow part of the tube, is exactly the same as that for water passing through a conduit which is narrower at one place than another. The same quantity of water has to pass through the narrow as through the wide part, consequently the velocity and pressure (head) have to be greater than in the wide part—the water arranges that for itself; and the seeming difficulty of explanation arose from the idea "that in some way gas is (was) being carried along by the current," when it was only the gas that was being lighted up more vividly by the electricity passing through it, because the same amount of electricity had to be carried through the narrow part as the wide one. No portion of the gas could be carried along with the electricity, else it would very soon have been all accumulated at one end of the tube, or a reverse current must have been set up to restore the balance, which would speedily have shown itself. Had the said tube been filled with copper instead of gas, the experimenter must have known that the electricity, in passing through it, would have spread itself all through the wide part, and contracted itself to pass through the narrow part, spreading itself out again through the other wide part, thus giving rise to differences of pressures and velocities at the different widths of the tube; but, of course, he would not have been able to see this, because the electricity could hardly be in sufficient quantity to light up the copper, or to impart to it sufficient heat to make it visible. Neither would the electricity carry with it part, or the whole, of the copper when passing through the narrow part. It would be the gas lighted up more vividly, not set in motion, by the electricity that the operator saw in the experiment under discussion, and, no doubt, if the tube had been sufficiently exhausted of gas, the light would have disappeared the same as in the first quoted experiment, and the electricity would have ceased to pass because there was nothing, in sufficient quantity at least, to carry it along, not even the universally commissioned monopolist the ether. Let us ask here: Does not all this seem to prove that electricity is a carried, not a carrying, agent?

In the quotation made, at page 229, from "Elementary Physics," we are told that when electricity passes through a gas or vapour of very small pressure, "We have a series of zones alternately light and dark." Now we ask, Why should part of these zones be dark? and the only answer to be given is—simply because there is no light in them, nothing in them to carry or hold light. Otherwise, we cannot understand why they should appear to be dark. We cannot imagine a glass tube with light and dark zones in it longitudinally—we have understood the zone to be longitudinal; transverse sections would not be zones—at the same time that light is passing freely through it transversely, i.e. from side to side, unless it is that in the dark zones there is nothing, not even the all-pervading ether, to carry or hold light in; therefore, we conclude again that there is no light where there is no ether.

For an explanation of the existence of light and dark zones in the almost exhausted cylinder or tube, we refer to Professor Tait's treatise on "Heat," where he says, in section 358, "What happens at exceedingly small pressures is not certainly known. In fact, if the kinetic gas theory be true, a gas whose volume is immensely increased, cannot in any strict sense be said to have one definite pressure throughout. At any instant there would be here and there isolated impacts on widely different portions of the walls of the containing vessel, instead of that close and continuous bombardment which (to our coarse senses) appears as uniform and constant pressure." Admitting the truth of the kinetic theory of gases, we can see that in a vacuum so rare that only electricity at a very high pressure could be forced (carried?) through it, we have the prescribed conditions in which there cannot be "one definite pressure throughout" the whole tube; in other words, we shall have some places in a vacuum tube where there is no gas at all, or perhaps even ether, and others where the gas is so rare that it takes a powerful stream of electricity to light it up in passing through, whether the lighted-up zones be composed of gas, or of ether, or part of both. If it did not pass, there would be no light-streak even. And further, we have to notice that the light and dark streaks would be changing places constantly, owing to the collisions of the small number of atoms or molecules of the gas, still not exhausted from the tube, driving each other from place to place.

All this makes us think of what is the real carrier of electricity through a partial vacuum, through a gas, or through a substance of any kind whatever, and we can only imagine it to be the ether. In that case the conductivity of any substance would depend upon the quantity of ether contained in it, and we can give no other reason for there being conductors and non-conductors of electricity. All matter has been thought to be pervaded by the ether, but we have said before that this must be the case in a limited sense only. It can be shown that glass is permeable to ether, and is therefore not an absolute non-conductor. Metals are supposed to consist of atoms bombarding and revolving around each other under the control of ether. Intermediate conductors may have the quantity in them of ether corresponding to their conductivity; and the compressibility of water, or any liquid, may depend upon the quantity of the ether mixed with its ultimate atoms.

Although we consider it to be going rather beyond the course we had laid out for ourselves, we cannot help returning to the article on the "Northern Lights" in "Science for All," quoted above in connection with electricity in the presence of a vacuum; because it helps to illustrate the subject we are dealing with.

In the regions where these Lights are seen, we know that there can be no want of ether, because it is supposed to pervade all space; but we know that there must be a very great want of air, or vapour of any kind, due to the height above the earth at which they are seen. Here, then, we have a great field for differences of pressures being caused all through it, by the collisions among themselves of the molecules or atoms of the extremely attenuated air; we have the higher or lower pressed zones of the laboratory experiment spread out before us, and if we suppose currents of electricity to be passed through them, we have an aurora in the high heavens, a counterpart of what was seen in the vacuum tube. The bombardment of the molecules continually shifting their positions and creating zones of different pressures, when lighted up by electricity, would easily account for the flashes, coruscations, and changes of the aurora; but, how does the air get up so high as is stated in the quotation at page 228?

We cannot accept the supposition of Professor A. S. Herschel that the air is carried up to the height of from 100 to 300 miles by electricity. We must believe, till evidence is given to the contrary, that electricity is a carried, not a carrying, power. Conductors of sound are all material substances; sound is not. It seems logical, therefore, to conclude that the ether is a material substance, because it conducts light, heat, etc. etc., which are not material substances. Proof is therefore required that electricity is a material substance, before it can be called a carrier. That air does somehow get up so high there can be little doubt, as is satisfactorily proved by the burning of meteorites when they come into our atmosphere at heights said to be more than 300 miles. How it does mount up so high is not so wonderful as it seems, when we take into consideration the causes of the trade winds, which are: The upward currents of the air created by the heat of the sun; the centrifugal force inherent in it at the time of leaving the earth; and its angular motion, which may be, at a guess, from 10 to 16 miles per minute, seeing that the equator has an angular velocity of over 1000 miles per hour. Then, from the time it leaves the earth, the air must begin to lose its angular velocity, the impelling power being cut off, and form a bank higher up, opposing the motion forward of all the air following it, so that immediately above the tropics there must be forward motion and obstruction, producing whirlwinds of which we can see or know really nothing, though they must exist, and which may carry air or vapours up to very great heights, carrying with them densities far beyond what would correspond to the simple attraction of the earth. At these heights this attraction would be very much diminished, and almost the only way in which the density of the whirlwinds could be diminished would be by expansion, which would not be very active in bodies already very considerably attenuated, as the whirlwinds would naturally be. Their movement towards the poles would be the same as that of the trade winds has always been supposed to be; and we can now see how there can be air at great heights in the aurora regions, not carried up by electricity. In fact, the air may, or rather must, have carried the electricity up with it, as we shall, we believe, presently see.

We have not supposed that all the air, raised from the earth by the heat of the sun, is carried up to such altitudes and to its polar regions, but only a very small part of it; and we have to add that there is perhaps not always electricity present in sufficient quantity to illuminate the air when it is carried up, which would, from the nature of its ascent, be undoubtedly divided into zones, streams, or belts at different degrees of tenuity. We do not doubt, or rather we believe, that electricity is always present in the atmosphere; but we are not sure that it is always so in sufficient force to make itself manifest. A very homely example of this is: Stroke a cat's back in ordinary circumstances, and it will only arch it up in recognition of the caress; but stroke it on a frosty night and it will emit sparks of electricity. The cat's hair does not shine—perhaps fortunately for the cat—because the electricity in it is not present in sufficient force, and only shows itself when the hand acting like a brush collects it into sparks. This shows not only that electricity is more abundant in the air at one time than at another, but that it is more so in cold and dry than in warm and moist air. It also shows one of the reasons why auroras of great brilliancy and extent are not continually in play in their own special regions, which is the want of a sufficient supply of electricity; another reason being, the absence of the requisite zones, or masses of air in cyclonic motion at different pressure and in sufficient quantity. We understand from what we have read that the glow of the aurora is seldom awanting in clear weather in the far north, and can imagine that there is always a sufficient supply of electricity and attenuated air to maintain the glow constantly; and also that the brilliant displays are only made when there is a sufficient influx of whirlwinds of air at low and varying pressures, and of electricity in sufficient force to light them up. We should suppose that the bright flashes would take place where the pressure was greatest, and the illuminated darkness, so to speak, where it was least. Electricity does not carry up air to these heights, neither does magnetism bring it down from the sun; still a magnetic storm produces brilliant auroras.

Confronting these reflections with the laboratory experiment we have cited at page 228, we see that they are very fully confirmed by it; perhaps it would be more true to say that they were originated by it. When the current of electricity was first turned into the glass cylinder, no result was perceived. This must undoubtedly be construed into showing that the light in the cylinder, passing through it from side to side, was more powerful than the diffused light of the electricity passing through it from end to end; which was the reason why there was no result. By diffused, we mean that the electricity, turned into the cylinder through a thin wire, would immediately spread out over the whole of its width (or cross section) and thus very much weaken its light-giving power. When exhaustion had proceeded to a sufficient extent to produce the soft tremulous light, we can only conceive that the transverse light had decreased so far that the diffused light of the electricity, passing longitudinally, had begun to balance it, which caused the tremulous appearance on account of the one beginning to disappear and the other to take its place. And when the light extended through the whole length of the cylinder and the phenomena were reversed; and when the light died away altogether, when the vacuum became sufficiently pronounced; we can only believe that there was no light at all in it; neither natural light passing through it transversely, nor light of electricity passing longitudinally. Should any one object to this demonstration, as we may call it, we refer him to the quotation, made at page 229, from Professor Balfour Stewart's "Elementary Physics," and ask him, How could there be dark zones in a tube, through which light ought to pass freely from side to side? The thing appears to be tremendously absurd. There were dark streaks in the tube and other streaks of gas, or vapour of some kind at very low pressures (see also quotation from Professor Tait at page 232) that were lighted up to some extent by the current of electricity, but even these died away. We do not pretend to impugn the idea that the stratification of light and dark zones depended upon the nature of the substances in the tube, we only want to insist that the substances left in it were so extremely rare that electricity could not pass freely through it longitudinally, nor daylight transversely, else there could have been no dark zones in it; and that even the ether was in such small force that it could not perform the carrying duties assigned to it.

We have often wondered whether any experiments have ever been made to ascertain whether any changes, as far as the presence of light is concerned alone, have been brought about by producing a vacuum in a tube. The gradual dying away of light, and its final disappearance, are certainly suggestive of changes, and may have excited curiosity to know what actually happens. That there are changes cannot be denied, and it would be satisfactory to know what they are. It appears to us that one simple and easily made experiment would give a good deal of information on the subject. Let a glass tube of cylindrical form—one of those prepared for vacuum experiments—be placed in a slit in the window-shutter of a dark room, so that absolutely no light can pass into the room except through the hollow part of the tube; which might be effectually managed by burying two opposite sixth parts of its circumference in the wood of the shutter, and there would still be left one-third of its diameter for the free passage of light from side to side. When so arranged, and when still full of air, let a spectrum be taken of sunlight passing through it, to serve for comparison. Then let a high vacuum be produced in the tube, and another spectrum taken and compared with the first. This will at once show whether any change has been produced or not. Should the difference we expect be found, the experiment might be extended by spectra being taken at different degrees of exhaustion, from which some useful information might be derived.

We have said, at page 129, that the ether does not pervade all bodies of all classes, and such must be the case in some measure at least, otherwise there would be no non-conductors of electricity, no insulators for our electric telegraphs and deep sea cables. Were glass, for instance, pervaded freely by the ether, and the ether is in reality the carrier of electricity, then electricity could pass freely through glass, but it does not; therefore, there can be no, or at all events very little, ether in glass or any other insulator. We can see, then, the possibility of the ether being removed from a glass tube, provided it is a material substance, by shutting up one end of it with a stopper of glass and passing a perfectly-fitting glass piston through it to the other end. Suppose this done, it would be quite safe to say that electricity could not pass through the tube, because there would be nothing—absolutely nothing—to carry it, not even the piston-rod, for we could have that not only made of glass but on the outside of the piston. In this case the result would be exactly the same as when the contents of the tube were pumped out of it, and the residue left, if any, would be the same, that is, an immeasurably small quantity of the ether which had filtered through the glass. It may be argued that it would be impossible to make such an experiment as we have proposed, but that does not damage in the slightest degree the correctness of the consequences deduced from it; any more than the impossibility of constructing a perfect heat engine destroys the deductions drawn by Sadi Carnot, from the study of such an ideal machine. We can grant that glass being not an absolute non-conductor, the ether might, in course of time, ooze through it and fill the tube again, while gas, air, or dust could not so ooze through it, and thus re-establish the current of electricity that was stopped for want of it; but we cannot grant that there was any very perceptible quantity of ether in the tube, when the electric current could not pass through it without dismissing the ether altogether, and dropping back into the difficulties out of which it has in many cases lifted us.

The evident fact that the ether cannot pass through glass freely, and therefore cannot carry electricity with it, may be disputed by referring to the free passage of light, and also of heat, through glass and other substances, in virtue of transparency and diathermancy, two terms that have the same meaning, at least, as nearly as that light and heat mean the same thing; but we believe that this free passage, instead of invalidating our reasoning, only tends to prove that the ether is a material substance; because, if it is not, it might pass through transparent bodies just as easily as light and heat do. Of course, this belief obliges us to show how light and heat do pass through a transparent body such as glass, and the mode is exactly the same as of heat passing through any other body that is a conductor of heat. Glass is a substance that is known to be a bad conductor, but it is also known that it is not an absolute non-conductor of heat; therefore, there is no difficulty in supposing that it, and its companion light, can be conducted through glass with velocity proportioned to its thickness. We know that in the case of a pane of glass in a window it is practically instantaneous, but that does not mean that it is absolutely so. We know also, that in passing through, both are refracted, and that comparatively little heat is imparted to the glass, even under bright sunshine, which may be very well accounted for by the ether on the other side of the window pane carrying them (light and heat) off, in the same direction they were going, quite as fast as they could be conducted through the glass. But, supposing there was no ether in the room to which the window gave light, or gas, or elementary matter of any kind—a condition which could be obtained by making the room of glass and pumping out its contents as was done with the vacuum tube—What would be the result? There would be no wave motion to carry on light and heat into the room, and it would be in the same state as the exhausted tube, except that there would be no electricity in the room—no current being passed through it—nor anything in sufficient quantity to be lighted up if there was; the light would be stopped and reflected back from the glass, and nothing inside the room could be seen; not even that it was dark, because there would be no electricity to make dark zones visible. The window, or rather the whole room, would become a many-sided mirror, for reasons almost identical with those that account for a sheet of glass being made into a mirror.

We confess that all these deductions have startled us, but we can see no flaw in the reasonings which have led to them. If it is not for want of ether—in sufficient quantity at least—and the admission of variable quantity is to admit that it is a material substance, that electricity will not pass through a highly exhausted tube, we cannot imagine what can be the reason why it does not; simply accepting it as a fact is by no means satisfactory. In the dilemma between renouncing the ether altogether or acknowledging its disappearance—effective at least—it occurred to us that it might be for want of heat, and that in terms of the inter-dependency of temperature and pressure in a gas, heat disappeared in proportion to the decrease of pressure in the air or gas that was being exhausted from the tube, or from cold being applied to it from without; but that notion has already been disposed of by our own work, when we have seen that a gas in a close vessel can be heated or cooled to any degree, altogether independently of pressure.

When, acknowledging that the ether ought to have some temperature as well as density, we have said that it might have the temperature of vibration whatever that might be, thereby admitting that we could not pretend to determine what it is; nevertheless, we may take a look at it from a distance, and at least see what it cannot be, anywhere within the limits of our system. We have shown, at page 220, that when the original nebula was about 29,000,000 miles in diameter, its density must have been 0·179 that of air at atmospheric pressure, and its temperature -225°, and that these could be neither the density nor temperature of space. With this temperature, then, it is evident that there was still heat enough and to spare in the ether—considering it to be a material substance—to cause it to vibrate and perform its assigned offices; and, therefore, it could not be for want of heat that neither it, nor light, nor electricity could be carried through the vacuum tube, but for want of the ether in due quantity; consequently, the temperature of vibration cannot be so great as -225°. Turning back now to page 129, we find the density of the ether estimated at 1/5,264,800th of an atmosphere, which corresponds to an absolute temperature of 0·000052° or -273·999948°; but on the following page we expressed our opinion—well founded, we believe—that the estimate was too high, i.e. too dense, and that it might be 2, 3, or 4 times, or more, too great. Be this as it may, we can see that if the ether alone occupies space—beyond a comparatively very limited distance from any body belonging to the solar system—it must be almost absolutely free from temperature of any degree, for the difference between -273·999948° and -274° is virtually nothing; or it must have a special temperature derived from the collisions of its own atoms, or from the sun. We have said more than once that the temperature of space cannot be so high as minus 225°, and now we cannot believe that it can be so low as absolute zero, because the ether in it is credited with the motion of vibration, which must be either the cause or effect of heat. What then shall we say? We can only speculate.

We can suppose that when the chemical elements were created, or evolved by some process, and began to attract each other, they had the ether to carry them into collision and produce heat; and that it, being also a material substance, became heated to the same degree as the other matter, always increasing in proportion to its state of condensation, the ether mixed with the other matter being also, of course, condensed. Then, following up this supposition, we can see that when the sun came to be condensed to its present state, the ether must have had the same degree of heat as itself at its surface, and be of the same density as it would in our air at the earth's surface condensed to the pressure of nearly 28 atmospheres; knowing as we do that the attraction of the sun at the surface of its photosphere is almost 28 times greater than that of the earth at its surface. Under this supposition, therefore, the ether might emit light just as surely as any other matter that may exist, or can be seen, in the corona or atmosphere of the sun, and might be the cause of the Zodiacal Light, probably more naturally than any other cause that has been imagined for it.

Mr. Proctor, in his "Sun," has given us a most elaborate description of how the Zodiacal Light could be produced by the swarms of meteorites and meteors, that are generally supposed to be floating around the sun and continually showering in upon it, and we confess that his reasoning is very plausible; but it, along with other similar hypotheses, has one very serious defect which it is hard to get over, under our existing ideas about matter and its origin. If there is a constant rain of meteorites and meteors falling into the sun now, and the same has been going on during the multitude of millions of years that it is supposed to have existed, we have to acknowledge that it must either come to an end some day, or that there is going on a constant creation or evolution of matter to keep up the supply. It will not suffice to accept the hypothesis that the supply comes from other suns, or any idea of that kind, because each one of them would finally find itself alone with its planets, etc., if it has any, in its domains the same as our sun. Neither would it suit the ideas of those who consider that matter has existed from all eternity and has made itself into all sorts of bodies or systems to suit them. Without continued creation, or evolution, matter must end in condensation into one mass. There can be no self-evolution to keep up the supply of matter. It would require another and exactly opposite power to unmake the final mass, and another change to original matter to start anew on the old course.

But we are speculating too soon. It may be said that if the Zodiacal Light is caused by the ether, and if the ether is a material substance, it must be exhausted sooner or later, just the same as all other matter and the whole universe to one mass the same as before; and also that we have no authority for supposing that the ether can be heated and cooled or condensed and expanded. But we think that with what we have done in this chapter, and what we will be able to show in the following one, we shall be able to get over all these difficulties, and also show how the universe might be dissolved and renewed by the ordained process of evolution.