# Popular Science Monthly/Volume 51/October 1897/Some Unrecognized Laws of Nature

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* "SOME UNRECOGNIZED LAWS OF NATURE."
By C. HANFORD HENDERSON.
IN Some Unrecognized Laws of Nature, Mr. Singer and Mr. Berens have restated the riddle of the universe, and have made a brave attempt to solve it.
It has not been the good fortune of modern science to give us a coherent philosophy of things so much as it has been to give us a very nice measurement of them. Its triumphs have been for the most part quantitative. "We have only so much science as we have mathematics." One might almost say that science has become a branch of applied mathematics. In the case of the luminiferous ether, and in some other departments of physical inquiry, one might even go a step further, and assert that science is mathematics, pure and simple, dealing only with signs and symbols, and quite unregardful of the realities of experience. Brilliant and successful as this treatment has been, it does not satisfy all the demands of the spirit. The old sense of wonder and inquiry is still unappeased. One is often tempted to stop in the midst of one's measuring rods and balances, and put again the old question, the eternal Why?
It is this sentiment which makes us turn with some eagerness to such a book as the one before us. It is an inquiry not into the phenomena of Nature, but into their causes, and more particularly into the cause of gravitation. At the present time, we have no theory of gravitation. The several guesses that have ​been made at it, have never been taken seriously enough to merit the name of theory. With the strictly orthodox, indeed, the cause of gravitation is no longer open to discussion. It has been relegated once for all to the region of the unknowable. A book, therefore, which throughout five hundred pages not only proposes to discuss this forbidden problem, but also professes to solve it, will attract attention for its boldness, if for nothing else. One begins to read with large sense of expectation.
The volume is divided into four books, which deal respectively with methods of inquiry; with first principles; with phenomenology, or "the interconvertibility of forces"; and finally with gravitation. All the books seem to us of value. They have been arranged with considerable cleverness, for the effect is cumulative.
The first book is largely psychological. Its main content has to do with methods of inquiry and of verification, and with sources of error. It maintains, and we think very properly, that our greatest need at the present time is a revision of our conceptions rather than any further confirmation of our observational or experimental data. In all cases the causes of phenomena are inferential, and are necessarily colored by our prior conceptions along the same lines of inquiry. Our stock in trade, when we come to philosophize, is simply the report of our own imperfect senses, helped or hindered, as the case may be, by our equally imperfect reasoning. The same facts may come into different minds, but they have far from equivalent values. It is comparatively easy to agree about the facts, but far from easy to agree about their interpretation. The interpretation is necessarily subjective, and is conditioned by many factors outside the phenomena themselves. Remembering this, one will be disposed to agree with the authors that apparent absurdity is not a legitimate refutation of any new and strange theory. It is only the absence of similar conceptions that makes the new view absurd. Nor does the correspondence of any theoretical view with prior conceptions offer the least confirmation of the view itself. Its agreement with preconceived ideas may prevent its seeming absurd, but does not prevent its being untrue. The so-called "confirmations" of philosophy and science will always bear re-examination, indeed demand such periodical re-examination, and the more so in proportion to their seeming certainty. The shores of the ocean of truth are thickly strewn with the wrecks of many a fair theory, as beloved in its day as the most cherished beliefs of our own day. Equally true is it that agreement between phenomena and theory, however perfect it may be, is not confirmation, for it is to be remembered that the theory itself was deduced from these very phenomena. The argument that such agreement constitutes proof ​is very plain reasoning in a circle—from which Heaven defend us all, and particularly our neighbor! The only evidence of this sort that is confirmatory must be a posteriori. If, from the consideration of things in general, a universal principle is brought to light, then the agreement of subsequently discovered or subsequently considered phenomena with this principle is strong evidence in favor of the probable truth of the principle itself. These considerations apply nowhere perhaps with greater force than in the investigation of gravitation. The problem is practically where Newton left it, unless indeed it has been rendered even more difficult by our inheritance of debarring ideas. The concluding chapter of the first book is wisely given to a psychological study of the current view of gravitation. The basic principle is not far to seek. It lies in the doctrine that gravitation is proportional to mass, and that mass is constant. With this conception firmly fixed in the mind, the interpretation of the phenomena of gravitation becomes a foregone conclusion. Yet the present authors show that this conception is far from being a necessary deduction from the facts of gravitation, is indeed probably a false deduction. Their experiments and reasoning lead them to believe, and the belief is supported by other observers, that either mass is not constant, or else that gravitation depends upon other factors than simple mass and distance. This alternative, however, as we shall see, is merely verbal.
Many of the psychological considerations in this first book are very obvious, yet they are none the less necessary, and we commend most highly the skillful vestibule which Mr. Singer and Mr. Berens have constructed to their new Temple of Truth.
The second book has to do with first principles. These the authors find to be four—persistence, resistance, reciprocity, and equalization. The four primary principles represented by these terms are at the basis of the whole work, and of their truth and adequacy the authors express themselves as having no misgivings whatever. They believe that the entire phenomena of the visible universe can be explained by referring them to these principles.
The principle of persistence grows out of a consideration of Newton's first law of motion: "Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon." This is, of course, only the principle of inertia, which is simply another, and it has always seemed to us an unnecessary, statement of the principle of causation. Nothing happens without a cause. It is perhaps well to emphasize this principle when fighting superstitions and other hobgoblins; but in an intelligent world it may be taken for granted as one of those primary conditions of thought which need neither statement nor discussion. The habit of ​speaking of inertia as if it were a "property" of matter, and the use made of it in current mechanics, has long seemed to us mischievous. The present authors modify this law to read, "All matter tends to persevere in whatever state it may happen to be and to resist change." In this form the law is more catholic. By persistence the authors mean "the tendency of all matter to remain in any given state, even after the conditions are altered (i. e., a quality), while the term resistance is used to denote the intensity of this persistence (i. e., a quantity)." The gain is not simply one of terminology. It is a real gain, since it allows us to substitute a simple idea, that of relative persistence or resistance, for the somewhat complex and dissimilar ideas represented by such terms as impact, inertia, latency, conductivity, charge, etc.
The principle of reciprocity is founded on another dictum of Newton's, that "all reactions are mutual and are directed to contrary parts." This means very simply that every change involves at least two bodies, and that no body acts upon another, but rather that two or more bodies react with one another. This follows, indeed, from the principle of persistence. Since a change of state in any body can be brought about by external agencies only, it must follow that the persistence of this body can only be overcome by the expenditure of a certain amount of resistance on the part of the second or reacting body, and a corresponding change in its own state.
The two corollaries growing out of this law are also very important:
"1. Bodies can react with each other only when there is a difference of state in respect of any quality or tendency; and— "2. The extent or intensity of the reaction will be proportional to this difference, and will cease altogether when relative equalization has been reached."
This second corollary really involves the fourth primary principle, that of equalization, in virtue of which all bodies tend to come to a common state, and the drama of the universe, the flux and flow of things, goes on eternally. It might at first seem that with the operation of this principle of equalization the universe would at last, like a spent clock, run down and stop. Such a view has indeed found expression in that modern and now famous doctrine, the dissipation of energy. A universe completely run down, a dead uniformity of condition, are among the striking spectacles of modern scientific speculation. It is not that we see any loss of action in the cosmic drama. On the contrary, it goes on unceasingly. It is only that a limited conception of the principle of equalization requires such ultimate uniformity. But there is another element that must needs be taken into consideration. The establishment of relative equilibrium ​between any two bodies would at once disturb the equilibrium existing between them and other bodies, and so tend to produce an unending series of readjustments. Furthermore, equalization with respect to any one quality or tendency does not mean equalization with respect to all. We have thus a twofold source of variation, and the conception of eternal change becomes at once less impossible than the conception of eternal rest. In addition, the doctrine of the dissipation of energy involves a fatal contradiction. If the world be running down by the conversion of all available energy into heat, how comes it about that the universe is at the same time cooling off by the loss of heat? The answer that the heat energy is being transferred to the ether is not satisfying, and it is particularly unsatisfying if one does not believe in the ether. An examination of the phenomena would lead one to the very contrary conclusion—that the world machine is not running down and that the universe is not cooling off.
The third book, on phenomenology, starts out with the denial of "force" and "energy" as separate physical entities, and seeks to find an explanation of acceleration and retardation, heat and molecular reaction, electricity and magnetism, conduction and induction, in terms of persistence, resistance, reciprocity, and equalization. Energy is regarded not as a cause of phenomena, but as a result, while "force" is dismissed as a metaphysical pitfall which has already claimed too many victims. The attempt is necessarily somewhat lengthy (it occupies two hundred pages), and the more so since the milk of human kindness in these two writers has not yet been condensed, but in the main it is a very successful attempt. It proceeds upon the true scientific principle—the search for similarities rather than for differences.
The same book also takes up the much-discussed question of action at a distance. We all remember Newton's words: "That gravitation should be innate, inherent, and essential to matter, so that one body may act on 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 that I believe no man who in philosophical matters has a competent faculty of thinking can ever fall into it." But experience shows that equalization between two bodies in different states of excitation takes place the more readily in proportion as the intervening resistance is less. It is a natural inference, therefore, that the very most favorable condition for such equalization would be the absence of all resistance—that is, the absence of any intervening medium. Experiments with vacuum tubes confirm this inference. The more perfect the exhaustion the more perfect the transmission; and this is true not only of heat, light, and electricity, but as well of gravity itself, ​since bodies fall more readily in vacuo than in air. There is an important distinction between kinematic and dynamic reactions. The first, or primary reactions, not only can but always do take place at a distance, and in view of the undoubted fact any discussion of the possibility is idle in the extreme. But it is very different in the case of secondary or dynamic effects. There is, strictly speaking, no reaction between the bodies concerned. They have no attraction for each other. They merely happen to get in each other's way when one or both are undergoing some kinematic reaction. A falling body may meet a second body thrown upward, and the path of each will be notably altered, but the reaction will be purely dynamic, and as such absolutely dependent on contact. These secondary reactions happen to be the ones with which we are the more familiar and upon which we have allowed our minds to play the more freely. The old question, "Can a body act where it is not?" is only applicable to dynamic reactions, but is not at all pertinent in the discussion of kinematic reactions. In the first case, no one doubts the inability of a body to push or pull another without actual contact. In the second case, the facts leave no room for discussion.
The concluding book, on gravitation, is naturally the pièce de resistance of the whole, and seems to us of high interest and importance. The other books lead up to it very cleverly. Newton himself, as we have seen, had no theory of gravitation, or at least was extremely careful not to publish it if he ever had one. Later disciples, however, have been less cautious, and the Newtonian view has been erected into something of a theory. This assumes that all matter attracts all matter, and this quite independently of its state of excitation. The intensity of the attraction has been formulated in the well-known law that gravity is proportional to the mass and inversely proportional to the square of the distance. But mass, as Newton used the term, is synonymous with weight, and weight is simply the measure of gravity, so that this fine-sounding phrase amounts only to this, that gravity is proportional to gravity, a statement which can not be said to materially help on the cause of truth. The Newtonian view assumes the constancy of mass or weight, but does so without the least experimental verification, and indeed in the teeth of much contrary evidence. It is true that modern physicists distinguish between mass and weight, making the former term stand for amount of matter (whatever that may mean) and the latter for the measure of gravity. But in this sense mass is a purely metaphysical quantity.
Now, there are two classic experiments for determining the density of the earth that seem at first sight to establish the current view that all matter attracts all matter. These are the ​Cavendish experiment, in which the attraction of lead balls of known mass is measured by means of a torsion balance, and so compared with the attraction of the earth; and the Schiehallion experiment, in which a plumb line is suspended near a mountain of known mass, and the deflection of the line from the vertical carefully measured. But both experiments proceed upon the assumption that all matter attracts, and prove nothing.
This review of the Newtonian conception serves as a preface to the authors' own theory, which is a direct outgrowth from the four primary principles deduced in an earlier book persistence, resistance, reciprocity, and equalization. Briefly stated, their theory is that two bodies in different states of excitation and free to move will move toward each other, the intensity of attraction being proportional to the difference in the excitation. Bodies in the same state—that is, in equilibrium—have no attraction for one another, and there will be no gravitation manifested between them. This is a direct contradiction of the Newtonian position that gravitation is universal. The excitation of a body may be increased by heat, light, electricity, or magnetism, and consequently the attraction, weight, or mass may be changed by a change in the physical conditions. This has been repeatedly shown by experiment, but with the idea of the unchangeableness of gravity firmly fixed in the mind the results of the experiments have always been explained on other grounds. According to the new view, terrestrial gravitation is entirely due to the different states of excitation which prevail on the outside of the globe and on the inside, and notably to the difference in thermal condition. Heating a body on the surface of the earth ought, by lessening this difference, to reduce the attraction—that is to say, the weight—and such is actually the case. Every one who has worked in the laboratory knows that a hot platinum crucible weighs several milligrammes less than the same crucible when cold. This was formerly attributed to ascending currents of hot air, but the explanation no longer holds. These and other similar experiments have recently been repeated under conditions which do not admit the existence of convection currents, and the loss of weight is still observable.
With permission we quote from a letter recently received from Mr. Paul R. Heyl, of Philadelphia: "I have been making a curious experiment since I got back within reach of an analytical balance. I took a piece of three-quarter-inch glass tubing, sealed it at one end, and choked it slightly about one inch from the sealed end. In the lower chamber thus formed I placed dilute sulphuric acid, and dropped in a piece of solid caustic potash, which was arrested at the choke. I then sealed off the upper end of the tube about two inches above the choke. This arrangement I then ​packed in cotton in a light glass cylinder, one and three quarter inches diameter by six and a half inches high, and closed the mouth of the cylinder by a flat cork carefully paraffined so as to be air-tight. The apparatus was then placed upright on the balance and counterpoised carefully. The balance beam was then lowered and the apparatus removed from the pan, held inverted for a second or two, and replaced on the pan. On raising the beam and releasing the pans a distinct loss of weight made itself immediately apparent, some seven to nine scale divisions. (The apparatus weighed from one hundred and ten to one hundred and twenty grains.) After some three quarters of an hour the normal weight returned.
"This loss of weight could not be due to the fact that I was weighing a vessel filled with air partially rarefied by the heat produced, for both vessels were closed air-tight. Nor could it be due to currents of hot air rising (the usual explanation in text-books) for two reasons: first, because the loss of weight was immediate, and, owing to the cotton packing, the outside of the apparatus did not become perceptibly warm to the touch for three quarters of a minute, and never became more than barely warm; secondly, because the effect noticed was too great to have been produced by convection. . . . It would seem, then, that convection currents have been greatly overestimated, and that the loss of weight noticed in weighing hot bodies is in large part a true effect. Either mass is a function of temperature, or else (which is more probable) heat weakens gravitation just as it weakens magnetic attraction, only that the magnetic attraction does not come back when the steel cools."
Furthermore, the authors show that the combining weights of the elements vary with the temperature, and they record a series of very interesting experiments. When applied to celestial gravitation, to the motion of the earth and other planets, and to their apparent irregularities, the new theory leads to surprising conclusions. If it stand the test of a more widespread examination, it will entirely change our conception of astronomical physics, and make necessary a radically different cosmology. The speculations in this department, however, are put forward very tentatively, and more by way of suggestion than as settled convictions. It will be noticed here, as elsewhere throughout the book, that the observed phenomena of Nature are not called in question, but only our conceptions and interpretation of them.
In conclusion—and it is quite time that we should stop we—are disposed to believe that Mr. Singer's and Mr. Berens's book is destined to attract wide attention, perhaps to provoke warm controversy, and certainly to stimulate wholesome doubt and inquiry. It has a high value quite aside from whether one accepts the ​main conclusions or not, and we commend it to the serious consideration of those interested in the world-riddle. We can not forbear the remark, however, that even if we accept the conclusions, the cause of gravity is still to be sought. If we attribute it to the mutual attraction of bodies in different states of excitation, we have advanced a proximate cause for the attraction, but we have not explained why this is a cause or how it acts. We have but carried the inquiry one step further back.
"Veil after veil will lift—but there must be Veil upon veil behind."