In one of a series of articles in "Engineering," Vol. XXV., on Repulsion from Radiation, we find, at page 155, what follows:
"With the same apparatus, Mr. Crookes conducted a long series of experiments for determining the conductivity of the residual gas to a spark from the induction coil. In air he found, at a pressure of 40 millionths (1/25,000th) of an atmosphere, which will be seen from the diagram, is the pressure at which the force of repulsion is at a maximum, that a spark whose striking distance at the normal pressure of the atmosphere is half an inch will illuminate a tube whose terminals are 3 millimetres apart. By pushing the exhaustion farther, the half-inch spark ceases to pass, but a one-inch spark will illuminate the tube, and as a vacuum is approached more electromotive-force is required to force the spark to cross the space separating the terminals within the tube, until at still higher exhaustion a coil capable of giving a 6-inch spark in air at the pressure of the atmosphere is required to show any indication of conductivity in the residual air. It was found, however, in experimenting with so powerful a spark that occasionally the glass was perforated by the discharge taking place through the bulb; but it is a remarkable fact that the perforation in such cases was so excessively small that several days were occupied before equilibrium of pressure was established between the inside and outside of the bulb."
Here we notice first—and it was the reason why we have made the first and longest part of the quotation—that the spark whose striking distance was half an inch at the normal pressure of the atmosphere, fell to under one-fourth of its power in a vacuum of only 1/25,000th of that pressure; that when a one-inch spark was required to illuminate the tube, it must have decreased to one-eighth in a vacuum of 1/50,000th; and, if it be admissible to follow the same proportion, the 6-inch spark must have been exhibited in a vacuum of 1/250,000th an atmosphere at least. Perhaps all this experiment was carried on in vacua produced by pumping alone, and the final vacuum may have reached a greater height than that which we have just mentioned; but the most interesting part of it is the perforation of the bulb by the 6-inch spark. In it we have to consider what was the conveyer which carried the electric spark through the glass of the bulb, instead of to the other terminal of the coil so close at hand, and it is a very difficult problem to solve. We naturally recur for some solution to the stratification of light given out when an electric current traverses a gas at very low pressure and gives rise to zones alternately light and dark as noted in the reference we made, at [page 229], to Professor Balfour Stewart's experiments. We cannot think it unreasonable to suppose that the dark zones contained no matter at all that could be lighted up, and that it was the lighted zones alone which contained carrying matter for the electricity. If so, we can easily imagine one of these zones or strata carrying the perforating spark from the induction terminal to the nearest part of the glass of the bulb, for it was as possible for it to lie in that direction as in the direction of the other terminal, and the difference of distance between the first terminal and the glass, and between the two terminals, would not be so great as it appears to be on simply reading the accounts of the experiments; but we have still to think of how it managed to force itself through the glass of the bulb.
To get over this difficulty, we can refer to what we have said, that is, that glass may be thoroughly pervaded by the ether in an almost infinitesimal degree, and suppose that the electricity may have discovered, or rather been led to, the ether contained in the glass tube or bulb, and so found its way to one of the oozing holes we have said might exist in the glass; even the oozing hole may not have passed quite through the glass, and there might remain a very thin film to be burst open before perforation was complete. Also we may note that the zone which performed the office of carrier to the side of the bulb was much more probably composed of residual ether than residual air or gas, or at the least formed a preponderating part of the carrying element. The fact of the hole being so minute "that several days were occupied before equilibrium of pressure was established between the inside and outside of the bulb" on such occasions, goes far to prove that the carrying agent through the glass must have been the natural carrier of electricity, light, and heat. We cannot conceive that an eruptive force could open such a small passage through the glass of the bulb, but we can conceive that it should be able to force itself through a very minute passage already open, and even join two or more such passages into one. This conception makes us think of the many oozing passages there may be through a glass bulb; passages so minute that the ether might pass through them, but nothing so gross as any of our known gases; in fine, so minute that glass, for all the compact look it presents to us, may be only as a very fine sponge in respect to the ether. However, that the perforations related in the above quotation were large enough for air to pass through them there can be no doubt, otherwise the equilibrium between the pressures on the inside and outside of the bulb could not have been re-established even after many days; for there still remains the idea that the oozing holes might be so small that nothing but the ether could pass through them.
Should the glass of a vacuum tube or bulb be pervaded by the ether in the manner we have supposed it to be, and we believe there can be no doubt that it is so, it is obvious that its glowing when a current of electricity is passed through it must be caused by the electricity and consequently of its light, being carried into the body of the glass by means of the ether imbedded in, and forming a constituent part of, it. In connection with this we have to remember that the air in the tube does not glow when it is at full atmospheric pressure, but only when a certain degree of vacuum has been produced in it; and therefore it is equally obvious that it is only when the ether enclosed in the tube is reduced to the same degree of tenuity as that imbedded in the glass forming the tube, that the light of the electricity can be carried by it into the glass and make it glow. But to show this more clearly, it is necessary to refer to the steps by which we believe we have made very plain what must undoubtedly be the nature of the ether.
(1) First of all we have shown that, if there be such a thing as the ether, it can be pumped out of a close vessel of any kind; which proves that it must be a material substance, and in consequence can be expanded, or rarefied, and compressed the same as any other material substance; and that if there is no such thing, something else, having these qualities, has to be invented to take its place. (2) In showing this it has been made abundantly clear by the example of the hair of a cat in variable weather, to which we may add the exhibition of lightning in daylight, that it cannot make electricity visible, or illuminate any matter, unless the quantity of electricity it has to carry bears some certain proportion to the density of the ether in the matter that is illuminated. (3) In proof of this we have shown how, through its carrying power it can convey electricity of adequate force up to very great heights, so as to illuminate very rarefied air and cause auroras; the conveying being done either directly from the earth or by means of the ether mixed with the air carried up by whirlwinds to those great heights; and (4) how electricity is carried into the body of a tube of glass and makes it glow.
With these examples we can extend our ideas to other exhibitions of light, which, otherwise, we could hardly avoid looking upon as mysterious. We can see how marsh gas, rising up from boggy ground, becomes mixed with common air till it reaches a certain density, and forms the Will-o'-the-wisp when there is sufficient electricity in the air to make the diffused marsh gas visible, through the medium of the ether always mixed with it; or, perhaps, rather when the density of the diffused gas corresponds to the density of the ether. Then we have the phenomena of films of matter on the surfaces of certain liquids glowing with appropriate colours; which films must be pervaded by the ether in proportion to their conducting powers, the same as we have seen must be the case with all kinds of matter, the light given off corresponding as is natural to the composition of the films; and of course this same reasoning, or exposition, applies to the films formed on, or near, the surface of the sea which produce what sailors call "fire-on-the-wave." Lastly, and akin to the glowing caused in a vacuum tube, we cite the case of the glow-worm, the radiation from which must of necessity contain a certain amount of the ether in it, and may either glow constantly or intermittently according to its capacity for carrying electricity or light of any kind, constant or inconstant. Or if there is no radiation from it, its skin may possess the properties of a film on the surface of a liquid. We have seen in the "Times" of September 21, 1896, in its report for that day of the Meeting of the British Association at Liverpool, that in experimenting with glow-worms Dr. Dawson Turner had found some difficulty in getting them to glow when he wanted, but found they gave off the radiation whether glowing or not. Perhaps his interference with them destroyed the balance of force between the electricity present and the density of the ether in it without stopping the radiation.
Hitherto the light given out by a nebula, and any light of the kind not easily accounted for, has been attributed to incandescent gas not burning or being consumed, but only glowing. Now it is time to look upon it as belonging, at least in part, to the ether, and to look upon the bright line in the spectrum of a nebula as the Ether Line. We shall have to return to this later on.
We said, at [page 248], that a fluid of some kind, elastic or not elastic, is necessary to enable us to pump solid matter out of a vessel of any kind, and went on to show that a gas as described by Dr. Crookes, or that can be described, in its own independent state of existence, by anybody, could not supply the want; because it consists of particles, molecules, atoms—any name that can be given to them—which have no power in themselves to move or to give motion to anything; they can be moved but cannot impart motion to anything, even to one another, until they are first set in motion by attraction. This in its turn led us to see that the only elastic fluid we have is the ether, and our work since then has taught us that we were wrong in saying at [page 250] that a non-elastic fluid would suit for pumping solid matter out of a vessel; for we now see that what we have been in the habit of looking upon as non-elastic fluids, must owe their fluidity, such as it is, to the ether, which, in proportionate degree, pervades them the same as it does all other matter. In this way we are run down to the only conclusion we can come to, namely, that the ether is the only connecting medium and carrying agent of matter that we have, or even initiator of motion, except attraction; and being matter of the nature of an elastic fluid, there is no reason why we should not at once consider it to be attraction itself. It has been looked upon, for no one can exactly tell how long, as the connecting mechanism of the universe, thus having, in reality, assigned to it the attributes of the law of attraction, and all that we have to do is to put it in its right place. We are, in a manner, taught to look with suspicion on two agents being required to do one kind of work, or even two kinds of work that are so closely allied that we cannot separate them in a way that satisfies us; and this is precisely a case in which we can have one agent that can connect matter, and at the same time carry immaterial elements from one place to another.
Having got this length we have still to go one step farther. We cannot now doubt that the ether is a material substance, and if it is, there is nothing to prevent us from considering it to be the primitive matter; in fact it would be absurd to look upon it in any other light. We cannot conceive of anything having been created before the ether, or ordained before the law of attraction, and thus we have the two coeval and one. It is long years since physicists, chemists especially perhaps, began to think that the great number of chemical elements cannot all have existed from the beginning of things, and that it is far more probable that they have all been evolved from one primitive substance, and this idea must now be gathering more strength from day to day in view of the new elements that are being constantly discovered; the unknown is being made known, and the air we breathe instead of being one in four elements, as in former times it was considered to be, is now not far from double that number in one. Adopting this notion, then, the ether is much more likely to have been the primitive element than any other material substance that can be thought of. If it has never been thought of in this light, it has come to be very remarkably near it, as may be seen by referring to the long quotation we made in [Chapter VII]., beginning at [page 129], where the idea of the ether being the connecting medium of matter is made use of to compute its density. Little thought we of this when we made the quotation, but there was the idea whether the author saw or not all that was implied in it.