THE STRUCTURE OF THE UNIVERSE.* Du. OSBORNE REYNOLDS, who is
Professor of Engineering in the Owens College, Manchester, has been engaged for twenty years upon a research which promises to have a very remarkable effect upon our ideas as to the structure of the universe and the ultimate constitution of matter. Incidentally it attempts to explain the cause of gravitation and to tell us what electricity is, besides being full of side-lights , on all physical problems. The outlines of this great discovery are traced in the little volume now before us, which contains Dr. Reynolds's notes for the Rede Lecture which he delivered at Cambridge last June. Unfortunately, they are presented in a fashion somewhat difficult for the ordinary reader, who will find his attention fully taxed in mastering the meaning of Dr. Reynolds's new theory as to the nature of matter. We do not here profess to criticise this theory, a task to which probably only half-a-dozen of the most eminent physicists in this country are equal. Whilst we wait to hear what Lord Kelvin and Sir Oliver Lodge, Professor J. J. Thomson and Professor Larmor, have to say on the matter, however, it seems worth while to present, in a more popular form than Dr. Reynolds has seen fit, to adopt, some general notion of his theories.
From the time of Thales and Plato down to our own day, many attempts have been made to go behind the appearances of things and deal in thought with the material basis on which the physical universe must be supposed to rest. No coherent and completely satisfactory solution of the problem has hitherto been given. The difficulties of the research are sc great—at least to beings of our finite powers—that many philosophers have been tempted to assume, with Berkeley, that there is really no material basis below the appearances. Men of science have mostly contented themselves with working at the immediate and tangible elements in the problem, and have only handled theories of the ultimate structure of the material universe as convenient working hypotheses. The latest of these, which holds the field in so far that it is accepted on all hands as the most convenient way of explaining the phenomena of light and other forms of radiant energy—such as the sun's rays and Marconi telegrams—is that of the so-called luminiferous ether, which is conceived as filling all space and serving as the medium by which the messages of light and heat and electricity are conveyed from place to place. The main idea, which originated two centuries ago in the mind of Huygens, and was elaborated by Thomas Young, is that of " space occupied by an incompressible elastic jelly yielding to tangential stress, baying a density which is all but infinitely small." All the most common radiations can be ex- plained as waves in this elastic jelly, propagated just like the ripples caused when a stone is flung into a pond. Mathema- ticians have been able to work out the conditions of wave-motion in such a medium, and thus to explain nearly all the observed phenomena of light and other forms of radiant energy on the hypothesis of its existence, pervading all apace, both that which we call empty and that which is occupied by material bodies, through the network of whose atoms the ether is supposed to flow as freely as water under the Tower Bridge. The reason why such an ether has been invented is that the human mind is incapable of conceiving the possi- bility of " action at a distance," or an effect produced by one body on another without any physical connection. How far this inconceivability is due to the obsession of our own muscular sense is hotly disputed by metaphysicians, but few readers will deny that it exists. Newton put this, once for all, very clearly in a passage which remains the corner-stone of all meditations as to the structure of the universe :—" It is incon-
Inversion of Ideas as to the Structure of the Universe. By Osborn* Cambridge ; At the University Press. [Lk ed. net.]
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ceivable, that inanimate brute Matter should, without the Mediation of something else, which isnot material, operate upon, and affect other Matter without mutual Contact, as it must be, if Gravitation in the Sense of Epicurus be essential
and inherent in it. That Gravity should be innate, inherent and essential to Matter, so that one Body may act upon another at a Distance, through a Vacuum, without the Mediation of anything else, by and through which their Action and Force may be conveyed from one to another, is to me so great an Absurdity," says Newton, " that I believe no Man who has in philosophical Matters a competent Faculty of thinking, can ever fall into it." Inconceivability to man may not really be an infallible test of truth—" there are more things in heaven and earth," &c.—but it is the most cogent test that we can apply, though higher beings—living perhaps on that elastic body in the fourth dimension by which an eminent physicist has endeavoured to explain gravitation— may smile leniently at our impudence in making it so.
It is admitted, then, that all space must be filled with some medium which transmits the various influences which we know as radiant energy : for Newton's own theory that they might consist in the actual trans- mission of material particles has been completely disproved. The luminiferous ether has held its ground because it was adequate to explain most of the phenomena ; but it has always been felt that our inability to assign any way in which it could possibly transmit the attraction of material bodies for one another, which we call gravitation, was a serious deficiency. Indeed no one has yet assigned a cause for gravitation—the fundamental property of all matter as we know it—which is even plausible. Such theories as Le Sage's bombardment of corpuscles, or Lord Kelvin's hypothesis of " sinks" and " sources " of matter, have been set aside, on the double ground that we have no proof of their existence, and that they presuppose such an incredible development of energy— gravitation being made a mere difference effect—as to be exceedingly improbable. But Dr. Osborne Reynolds tells us that his new theory of the universe accounts for gravitation on Newton's original hypothesis that it is the effept of a state of stress in the medium surrounding all bodies. That medium, as Dr. Reynolds believes that he has discovered it, is not the homogeneous infinitely rare jelly which is understood by those who have hitherto spoken of the ether, but a definite granular structure, comparable to an illimitable heap of shot or sand piled in a regular fashion so that each grain is at the same mean distance from each of its twelve neigh- 'ours. By a method which is intelligible only to the trained mathematician, Dr. Reynolds has been able to work out from his experiments a complete series of measures for the grains of this primordial substance which he believes to fill all space. The result is one of the most amazing propositions ever laid down by a serious physicist. We are told that the size of these grains is inconceivably small, though it has been definitely measured by mathematical analysis as being the seven-hundred- thousand-millionth part of the wave-length of violet light, a unit which is itself roughly equal to the sixty-thousandth part of an inch. In a normal condition these grains are in motion with a mean relative velocity of about one and one-third feet per second, though the mean path of each grain is restricted by its neighbours to the four-hundred-thousand-millionth part of its own diameter. From this it follows that the mean density of such a medium must be ten thousand times that of water, or four hundred and eighty times greater than that of the densest matter known on the earth ; whilst it must be normally in a state of stress such that its mean pressure is seven hundred and fifty thousand tons on the square inch, or three thousand times greater than the strongest material known to us can bear. If, now, the reader will try to conceive the real meaning of Dr. Reynolds's assertion that the whole of space—which we call empty—is filled by this extraordinary medium—recalling Wordsworth's description of " The heavy and the weary weight
Of all this unintelligible world "
The will have some idea of the epoch-making nature of this discovery.
Dr. Reynolds goes on to state—the detailed proof is reserved, and, as we have said, only a very few men can be competent to criticise it—that the assumption of such a medium affords "a complete, quantitative, purely mechanical explanation of the cause of gravitation." It is enough to say here that this cause is found in the tendency of any system of grains arranged in the hypothetical manner to expand under pressure, a tendenoy most ingeniously illustrated by the behaviour of indiarubber bags filled with sand and water, one of which the author proudly calls "the first experimental model universe." Another almost equally striking consequence is that the hypothesis gives us "a purely mechanical explanation of electricity." What, then, one asks, is matter? The answer to this question also is ready, and not wholly novel to those who are familial with Lord Kelvin's beautiful theory of vortex atoms,—matter, as we know it, is simply a mode of motion in the assumed granular medium. " We are all waves," says Dr. Reynolds, recalling Montaigne's description of man as " divers et ondoyant." We have given but a bald account of Dr. Reynolds's fascinating, and perhaps epoch-making, theories, but it is with the greatest interest that we await the opinion on them of the few men of science whose judgment will carry weight.
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