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Amongst the gravest objections raised by the progress of modern science against Theism, the possibility of miracles, free-will, the immateriality of the human soul, its creation and immortality, are, according to many thoughtful men, those based on the Law of the Conservation of Energy. Consequently, as full a treatment of this topic in its philosophical aspects as the limits of space will allow, is here attempted.

The word energy comes from the Greek ’enérgeia, "operation", "actuality". This term is itself a compound of ’en and ’érgon, "work". In modern physical science the notion of energy is associated with mechanical work. It is commonly defined as "the capacity of an agent for doing work". By "work" scientists understand the production of motion against resistance. Such energy, whilst existing in many forms, is considered especially in two generically distinct states known as kinetic energy, or energy of motion, and potential energy, or energy of position. The power of doing work in the former case is due to the actual motion possessed by the body, e.g. a cannon-ball on its course, or a swinging pendulum. Potential energy, on the other hand, is exemplified by a wound-up spring, or by the bob of a pendulum when at its highest point; as the bob swings upwards its velocity and kinetic energy continuously diminish, whilst its potential energy is increasing. When at its highest point its potential energy is at a maximum, and its kinetic is nil. Conversely, when, moving downwards, it reaches its lowest point, it will have recovered its maximum kinetic energy, whilst its potential will have vanished. Energy is also recognized in the heat of a furnace, or the fuel of the same, in explosives, in an electric current, in the radiations of the ether which illuminates and warms the earth. Now, it has been found that these different forms of energy can be changed into one another. Further, the amount of a sum of energy in different forms can be measured by the quantity of work it can accomplish. A weight suspended over a pulley can be employed to do work as it sinks to a lower level; likewise a steel spring as it expands, heat as it passes to a cooler body, electric current as it is expended, and chemical compounds in the course of decomposition. On the other hand, a corresponding amount of work will be required in order to restore the original condition of the agents. Perhaps the greatest and most fruitful achievement of modern physical science during the past century has been the establishment of a law of quantitative equivalence between these diverse forms of energy measured in terms of work. Thus a certain amount of heat will produce a definite amount of motion in a body, and conversely this quantity of motion may be made to reproduce the original amount of heat—assuming that in the actual process of transformation there were no waste. In other words, it is now accepted as established that, in any "conservative" or completely isolated system of energies, whatever changes or transformations take place among them, so long as no external agent intervenes, the sum of the energies will always remain constant. The Principle of Law of the Conservation of Energy has been thus formulated by Clerk Maxwell: "The total energy of any body or system of bodies is a quantity which can neither be increased nor diminished by any mutual action of these bodies, though it may be transformed into any other forms of which energy is susceptible" (Theory of Heat, p. 93). Thus stated, the law may be admitted to hold the position of a fundamental axiom in modern physics; the nature of the evidence for it, we shall consider later. But there is a further generalization, advancing a considerable way beyond the frontiers of positive science, which affirms that the total sum of such energy in the universe is a fixed amount "immutable in quantity from eternity to eternity" (Von Helmholtz). This is a proposition of a very different character; and to it also we shall return. But first a brief historical account of the doctrine.

The doctrine of the Conservation of Energy was long preceded by that of the Constancy of Matter. This was held vaguely as a metaphysical postulate by the ancient materialists and positively formulated as a philosophical principle by Telesius, Galileo, and Francis Bacon. Descartes assumed in a somewhat similar a priori fashion that the total amount of motion (MV) in the universe is fixed—certam tamen et determinatam habet quantitatem (Princip. Philos., II, 36). But the effort to establish such assumptions by accurate experiment begins later. According to many we have the principle of the conservation of energy virtually formulated for the first time in Newton's Scholion developing his third law of motion (action and reaction are equal and opposite), though his participation in the current erroneous conception of heat as a "caloric", or independent substance, prevented his clearly apprehending and explicitly formulating the principle. Others would connect it with his second law. Huyghens, in the seventeenth century, seems to have grasped, though somewhat vaguely, the notion of momentum, or vis viva (MV²). This was clearly enunciated by Leibniz later. The fundamental obstacle, however, to the recognition of the constancy of energy lay in the prevalent "caloric theory". Assuming heat to be some sort of substance, its origin and disappearance in connextion with friction, percussion, and the like seemed a standing contradiction with any hypothesis of the constancy of energy. As early as 1780, Lavoisier and Laplace, in their "Mémoire sur la chaleur", show signs of approaching the modern doctrine, though Laplace subsequently committed himself more deeply to the caloric theory. Count Rumford's famous experiments in measuring the amount of heat generated by the boring of cannon and Sir Humphry Davy's analogous observations (1799) on the heat caused by the friction of ice, proved the death-blow to the caloric theory. For the view was now beginning to receive wide acceptance among scientists, that heat was "probably a vibration of the corpuscles of bodies tending to separate them". Dr. Thomas Young, in 1807, employed the term energy to designate the vis viva or active force of a moving body, which is measured by its mass or weight multiplied by the square of its velocity (MV²). Sadi Carnot (1824), though still labouring under the caloric theory, advanced the problem substantially in his remarkable paper, "Réflexions sur la puissance motrice du feu", by considering the question of the relation of quantity of heat to amount of work done, and by introducing the conception of a machine with a reversible cycle of operations. The great epoch, however, in the history of the doctrine occurred in 1842, when Julius Robert Mayer, a German physician, published his "Remarks on the Forces of Inanimate Nature", originally written in a series of letters to a friend. In this little work, "contemptuously rejected by the leading journals of physics of that day" (Poincaré), Mayer clearly enunciated the principle of the conservation of energy in its widest generality. His statement of the law was, however, in advance of the existing experimental evidence, and he was led to it partly by philosophical reasoning, partly by consideration of physiological questions. At the same time, Joule, in Manchester, was engaged in determining by accurate experiments the dynamical equivalent of heat—the amount of work a unit of heat could accomplish, and vice versa; and "Colding was contributing important papers on the same subject to the Royal Scientific Society of Copenhagen, so that no particular man can be described as the Father of the doctrine of the Conservation of Energy" (Preston). Between 1848 and 1851, Lord Kelvin (then Sir William Thomson), Clausius, and Rankine developed the application of the doctrine to sundry important problems in the science of heat. About the same time Helmholtz, approaching the subject from the mathematical side, and starting from Newton's Laws of Motion, with certain other assumptions as to the constitution of matter, deduced the same principle, which he termed the "Conservation of Forces". Subsequently, Faraday and Grove illustrated in greater detail the extent and variety of the transformation and correlation of forces, not only heat being changed into work, but light occasioning chemical action, and this generating heat, and, and heat producing electricity, capable of being again converted into motion, and so on round the cycle. But it further became evident that in such a series there inevitably occurs a waste in the usableness of energy. Though the total energy of a system may remain a constant quantity, since work can be done by heat only in its transition from a warmer to a cooler body, in proportion as such heat gets diffused throughout the whole system it becomes less utilizable, and the total capacity for work diminishes owing to this dissipation or degradation of energy. This general fact is formulated in what has been called the principle of Carnot or of Clausius. It is also styled the second law of thermodynamics and has been made the basis of very important conclusions as to the finite duration of the universe by Lord Kelvin. He thus enunciates the law: "It is impossible by means of inanimate material agency to derive a mechanical effect from a portion of matter by cooling it below the temperature of the coldest surrounding bodies."

Living organisms

The successful determination of the quantitative equivalent of one form of energy in some other form, obviously becomes a far more difficult problem when the subject of the experiment is not inanimate matter in the chemical or physical laboratory, but the consumption of substances in the living organism. Scientific research has, however, made some essays in this direction, endeavouring to establish by experiment that the principle of the constancy of energy holds also in vital processes. By the nature of the case the experimental evidence is of a rougher and less accurate character. Still it tends to show at all events approximate equivalence in the case of some organic functions. Among the best investigations so far seem to be those of Robner, who kept dogs in a calorimeter, measuring carefully the quantity of food received and the heat developed by them. The chemical energy of the substances consumed manifests itself in heat and motion, and the heat generated in the consumption of different substances by the animals seems to have corresponded rather closely to that resulting in laboratory experiments; hence it is affirmed that the observations all point to the conclusion that "the sole cause of animal heat is a chemical process" (Schäfer). This, however, is a long way from experimental proof that the conservation of energy holds in all vital processes with such rigid accuracy that every faintest change in the motor or sensory nerve-cells of the brain must have been completely determined by a preceeding physical stimulus. Whether this proposition be true or not, there is not as yet even a remote approach to experimental proof if it (cf. Ladd).

Character and range

About the character and range of the law and its bearing on sundry philosophical problems, there has been and still is much dispute. As a rule, however, the most eminent scientists, e.g. men like Clerk Maxwell and Lord Kelvin, are most cautious and guarded in their enunciation of the law. Be it noted that, when strictly stated, this proposition, "The sum of the kinetic and potential energies of a conservative system amid all changes remains constant", first applies only to an isolated or closed system. But such systems are hypothetical or ideal. As a matter of fact, no group of agents in the present universe is or can be thus isolated. Next, the proposition may be stated, as a legitimate generalization, only of inanimate bodies and material energies. The law affords no justification for the assertion that the only energies in any particular system, still less in the universe as a whole, are material energies. Clerk Maxwell himself explicitly reminds us that "we cannot assert that all energy must be either potential or kinetic, though we may not be able to conceive of any other form". Again many physicists insist that this concept of energy contained in the formula proves, when examined closely, to be vague and elusive. H. Poincaré asks: "What exactly remains constant?" And he concludes a searching analysis with the statement that "of the principle nothing is left but an enunciation: There is something which remains constant" (Science and Hypothesis, p. 127). As eminent a physicist as George F. Fitzgerald tells us that "the doctrine of the conservation of energy is most valuable, but it only goes a very little way in explaining phenomena" (Scientific Writings, p. 391). Helmholtz's extension of the principle in the statement, that "the total quantity of all the forces capable of work in the whole universe remains eternal and unchanged throughout all their changes", is a hazardous leap from positive science into very speculative metaphysics. This should be recognized. For even supposing the proposition true, it cannot be demonstrated a priori. It is not self-evident. It is obviously beyond the possibility of experimental proof. It assumes the present universe to be a closed system into which new agents or beings capable of adding to its energy have never entered. Lucien Poincaré's contention is just: "It behooves us not to receive without a certain distrust the extension by certain philosophers to the whole Universe of a property demonstrated for those restricted systems which observation can alone reach. We know nothing of the Universe as a whole and every generalization of this kind outruns in singular fashion the limit of experiment." James Ward's account of its character is much the same: "Methodologically, in other words as a formal and regulative principle, it means much, really it means very little." It furnishes very little information about the past, present, or future of the universe.

Proof of the Law

On what evidence precisely, then, does the principle rest? Here again we find considerable disagreement. E. Mach tells us: "Many deduce the principle from the impossibility of perpetual motion, which again they either derive from experience or deem self- evident…Others frankly claim only an experimental foundation for the principle." He himself considers the justification of the law to be in part experimental, in part a logical or formal postulate of the intellect. We have already alluded to the view that it is implicit in Newton's laws of motion. The principle of causality, according to others, is its parent. Mayer himself quotes ex nihilo nil fit, and argues that creation or annihilation of a force lies beyond human power. Even Joule, who laboured so diligently to establish an experimental proof, would reinforce the latter with the proposition, that "it is manifestly absurd to suppose that the powers with which God has endowed matter can be destroyed". Preston judiciously observes: "The general principle of the conservation of energy is not to be proved by mathematical formulæ. A law of nature must be founded on experiment and observation, and the general agreement of the law with facts leads to a general belief in its probable truth. Further, the conservation of energy cannot be absolutely proved even by experiment, for the proof of a law requires a universal experience. On the other hand, the law cannot be said to be untrue, even though it may seem to be contradicted by certain experiments, for in these cases energy may be dissipated in modes of which we are as yet unaware" (p. 90). In view of the extravagant conclusions some writers have attempted to deduce from the doctrine, it is useful to note these serious divergencies of opinion as to what is its true justification among those who have a real claim to speak with authority on the subject.

We shall best approximate to the truth by distinguishing three different parts of the doctrine of energy: the law of constancy; the law of transformation; and the law of dissipation or degradation. The law of transformation, that all known forms of material energy may be transmuted into each other, and are reconvertible, is a general fact which can only be ascertained and proved by experience. There is no a priori reason requiring it. The law of dissipation, that, as a matter of fact, in the course of the changes which take place in the present universe there is a constant tendency for portions of energy to become unusable, owing to the equal diffusion of heat through all parts of the system—this truth similarly seems to us to rest entirely on experience. Finally, with respect to the principle of quantitative constancy, the main proof must be experience—but experience in a broad sense. It has been shown by positive experiments with portions of inanimate matter that the more perfectly we can isolate a group of material agents from external interference, and the more accurately we can calculate the total quantity of energy possessed by the system at the beginning and end of a series of qualitative changes, the more perfectly our results agree. Further, modern physics constantly assumes this principle in most complex and elaborate calculations, and the agreement of its deductions with observed results verifies the assumption in a manner which would seem to be impossible were the principle not true. In fact, we may say that the assumption of the truth of the law, when correctly formulated, lies now at the basis of all modern physical and chemical theories, just as the assumption of inertia or the constancy of mass is fundamental to mechanics. At the same time we must not forget the hypothetical character of the conditions postulated, and the limitations in its application to particular concrete problems. Bearing this in mind, even if there occurs some novel experience, as, e.g., the fact that radium seemed capable of sustaining itself at a higher temperature than surrounding objects and of emitting a constant supply of heat without any observable dimination of its own store of energy, science does not therefore immediately abandon its fundamental principle. Instead, it rightly seeks for some hypothesis by which this apparently rebellious fact can be reconciled with so widely ranging a general law—as, for example, the hypothesis that this eccentric substance possesses a peculiar power of constantly collecting energy from the neighbouring ether and then dispensing it in the form of heat; or, that the high complexity of the molecular constitution of radium enables it, while slowly breaking down into simpler substances, to continue expending itself in heat for an extraordinarily long time. Such an exception, however, is a useful reminder of the unwarranted rashness of those who, ignoring the true character and limitations of the law, would, in virtue of its alleged universal supremacy, rule out of existence, whether in living beings or in the universe as a whole, every agent or agency which may condition, control, or modify in any way the working of the law in the concrete. As we have before indicated in regard to some changes of a chemical and mechanical character in the living beings, the principle of conservation may hold in much the same way as in non-living matter; whilst, in regard to other physiological or psycho-physical processes, the necessary qualifications and limitations may be of a different order. The kind of evidence most cogent in regard to inanimate matter—both direct experiment and verified deduction—is wanting here; and many of the vital processes, especially those connected with consciousness, are so unlike mechanical changes in many respects that it would be scientifically unjustifiable to extend the generalization so as to include them. The possibility of reversion, for instance, applicable in a cycle of changes in inanimate matter, is here unthinkable. We could conceivably recover the gaseous and solid products of exploded gunpowder and convert them into their original condition, but the effort to imagine the reversion of the process of the growth of a man or a nation brings us face to face with an absurdity.

The philosophical conclusions which some writers have attempted to deduce from the law affect the question of God's existence and action in the world, the possibility of Divine interference in the form of miracles, the nature of the human soul, its origin and relation to the body, and its moral freedom.

The materialistic mechanical theory

This theory, which seeks to conceive the world as a vast self-moving machine, self-existing from all eternity, devoid of all freedom or purpose, perpetually going through a series of changes, each new state necessarily emerging out of the previous and passing into the subsequent state, claims to find its justification in this law of the conservation of energy. To this it may be replied in general, as in the case of the old objections to Theism based on the indestructibility of matter, that the constancy of the total quantity of energy in the world or the convertibility of different forms of material energy, does not affect the arguments from the evidences of intelligent design in the world, the existence of self-conscious human minds and the moral law. These things are realities of the first importance which every philosophical creed that pretends to be a rational system of thought must attempt to explain. But the mere fact that the sum of material energies, kinetic and potential, in any isolated system of bodies, or even in the physical universe as a whole, remains constant, if it be a fact, affords no rational account or explanation whatever of these realities.

Herbert Spencer's doctrines

As Spencer is the best-known writer who attempts to deduce a philosophy of the universe from the doctrine of energy, we shall take him as representative of the school. Though the term force is confined by physicists to a narrower and well-defined meaning—the rate of change of energy per distance—Spencer identifies it with energy, and styles the conservation or constancy of energy the "Persistence of Force". To this general principle, he tells us, an ultimate analysis of all our sensible experience beings us down, and on this a rational synthesis musty build up. Consequently, from this principle his "Synthetic Philosophy" seeks to deduce all the phenomena of the evolution of the universe. With respect to its proof he assures us that "the principle is deeper than demonstration, deeper than definite cognition, deep as the very nature of the mind. Its authority transcends all other whatever, for not only is it given in the constitution of our consciousness, but it is impossible to imagine a consciousness so constituted as not to give it" (First Principles, p. 162). The value of this assertion may be gauged from the fact that Newton and all the ablest scientists down to the middle of the last century were ignorant of the principle, and that it required the labour of Mayer, Joule, Helmholtz, and others to convince the scientific world of its truth. "Evolution is an integration of matter and concomitant dissipation of motion during which matter passes from an indefinite incoherent homogeneity to a definite heterogeneity, and during which the retained motion undergoes a parallel transformation. Owing to the ultimate principles the transformation among all kinds of existence cannot be other than we see it to be. The redistribution of matter and motion must everywhere take place in those ways and produce those traits which celestial bodies, organisms, societies alike display, and it has to be shown that this universality of process results from the same necessity which determines each simplest movement around us…In other words the phenomena of evolution have to be deduced from the Persistence of ‘Force’." Spencer's proof is merely a description of the changes which have taken place. He does not show, and it is impossible to show, from the mere fact that the quantity of energy has to remain constant, that the particular forms in which it has appeared—the Roman Empire, Shakespeare's plays, and Mr. Spencer's philosophy—must have appeared. The principle can only tell us that a constant quantitative relation has been preserved amid all the qualitative transformations of the physical universe, and that it will be preserved in the future. But it furnishes no reason for the order and seemingly intelligent design which abounds, and it offers not the faintest suggestion of an explanation why the primitive nebulæ should have evolved into life, minds, art, literature, and science. To describe the process of building a cathedral is not to deduce a masterpiece of architecture from so many tons of stone and mortar. To show even that the law of gravitation prevailed during every event in the history of England would not be a deduction of the history of England from the law of gravitation. Yet this is precisely the sort of undertaking Spencer's "Synthetic Philosophy" is committed to in seeking to deduce the present world from the conservation of energy, and so to dispense with an intelligent Creator. The same holds for every other project of a similar kind. A more remarkable feature still in Spencer's handling of the present subject is that he seats this "Persistence of Force" in the Absolute itself. It really "means the persistence of some Power which transcends our knowledge and conception…the Unknown Cause of the phenomenal manifestations" of our ordinary experience. This is a complete misconception, misrepresentation, and misuse of the principle of conservation, as known to science. Mayer and Joule never attempted to establish that some noumenal power or unknown cause behind the phenomena of the universe has a constant quantity of energy in itself. Nor is it a self-evident datum of our consciousness that, if there be such an unknown cause, its phenomenal manifestations must be always quantitatively the same throughout all past and future time". The scientific principle merely affirms constant quantitative equivalence amid the actual transmutations of certain known and knowable realities, heat, mechanical work, and the rest. This, however, would afford no help towards an explanation of the universe. Consequently, it had to be transformed into something very different to serve as the basis of the Synthetic Philosophy.

Professor Ostwald

Professor Ostwald, on the other hand, apparently opposed to mechanical theories, carries us little farther by his special doctrine of energy. Matter, the supposed vehicle or support of energy, he rejects as a useless hypothesis. Every object in the universe is merely some manifestation of energy of which the total amount retains a constant value. Energy itself is work, or what arises out of work, or is converted back into work. It is the universal substance of the process of change in the world. Mass is merely capacity for energy of movement, density is volume-energy. All we can know of the universe may be expressed in terms of energy. To accomplish this is the business of the savant. Hypotheses are to be abandoned as worthless crutches; and the aim of science is to catalogue objects as forms of energy. But surely this is merely to abandon all attempt at explanation. The mere application of a generic common name to diverse objects furnishes no real account of their qualitative differences. We do not advance knowledge by the easy process of assigning new properties to energy, any more than the ancients did by the liberal allotment of occult qualities. The simple truth is that the quantitative law of constancy supplies not the faintest clue to the fundamental problem, how and why the present infinitely varied allotropic forms of reality have come into existence.

Not only does the modern scientific doctrine of energy fail to provide a foundation for a materialistic theory of a mechanical self-existing universe, but a most important part of that doctrine—the second law of thermodynamics and its consequences—presents us with the materials for a very powerful argument against that theory. Lord Kelvin, the most eminent authority on this point, working from data established by Carnot and Clausius, has shown that "although mechanical energy is indestructible, there is a universal tendency to its dissipation, which produces throughout the system a gradual augmentation and diffusion of heat, cessation of motion and exhaustion of the potential energy of the material Universe" (Lectures, vol. II, p. 356). The heat becoming thus diffused at an equally low temperature throughout the entire universe, all living organisms will perish of cold. In fact, the conclusion which Kelvin deduces from the modern scientific doctrine of energy is that the physical world, so far from being a self- existing machine endowed with perpetual motion, much more closely resembles a clock which has been put together and wound up at some definite date in the past and will run down to a point at which it will stop dead in the future.

According to the ordinary Catholic doctrine, philosophical and theological, the soul is a spiritual principle, distinct from matter, yet by its union with the organism constituting one substantial being, the living man. It is the source of spiritual activities, thought, and volition. It is endowed with free-will. It originates and controls bodily movements. In its origin it has been created; at death it is separated from the body and passes away from the material universe. Now if the soul or mind, though itself not a form of material energy, acts on the body, originates, checks, or modifies bodily movements, then it seems to perform work and so to interfere with the constancy of the sum of energy. Moreover, if thus being sources of energy individual souls are created and introduced into this material universe and subsequently pass out of it, then their irruptions seem to constitute a continuous infringement of the law. For clearness we will handle the subject under separate heads.

I. Does the soul or mind initiate or modify in any way movements of matter, or changes in the forms of energies of the material world? Yes, assuredly; the soul through its activities, does thus act on matter—Clifford, Huxley, Hodgson notwithstanding. The thoughts, feelings, and volitions of men have had some influence on the physical events which have constituted human history. All the movements of every material particle in the world would not have been precisely the same if there had been no sensation or thought. Art, literature, science, invention have had their origin in ideas, and they involve movements of material bodies. The mental states called feelings and desires have really influenced war and trade. If these feelings and ideas had been different, war, trade, art, literature, and invention would have been different. The movements of some portions of matter would have been other than they have been. The mind or soul, therefore, does really act on the body.

II. Is the soul, or the activities by which it acts on the body, for instance its conscious states, merely a particular form of energy interconvertible with the other material forms of heat, motion, electricity, and the rest? Or is the soul and psychic activity something distinct in kind, not interchangeable with any form of material energy? Yes. That mental or psychical states and activities are realities, utterly distinct in kind from material energy, is the judgment of philosophers and scientists alike. These states are subjective phenomena perceptible only by the internal consciousness of the individual to whom they belong. Their existence depends on their being perceived. In fact, their esse is percipi. They are not transmutable into so much material energy. As Tyndall says, "the chasm between the two orders of reality is intellectually impassable." The phenomena of consciousness are not a fixed sum; though incapable of proper quantitative measurement they seem to grow extensively and intensively and to rise in quality in the world. Wundt, indeed, embodies this fact in his contrasted "principle of the increase of psychical energy", a law of qualitative value, which he attaches as the reverse or subjective side of the quantitative constancy of physical energy. The psychical increase, being indefinite, holds only under the condition that the psychical processes are continuous. Mental states or activities are thus movements of matter, whilst on the other hand they are different in nature from all material energies and unconvertible with any of the latter. The soul, mind, or whatever we call the subject or source of these immaterial states or activities, must be therefore some kind of hyperphysical agent or power.

III. This brings us to the central crux of the subject. If the soul, or mind, or any of its activities, causes or modifies the movement of any particle of matter, then it seems to have produced an effect equivalent to that of a material agent, to have performed "work", and thereby to have augmented or diminished the previously existing quantity of energy in the area within which the disturbance took place. The vital question then arises: Can this real influence of the soul, or of its activities, on matter be squared with the law of conservation? At all events, if it cannot, then so much the worse for the law. The law is a generalization from experience. If its present formulation conflicts with any established fact, we may not deny the fact; we must instead reformulate the law in more qualified terms. If our experience of radium seems to contradict the law of conservation, we are not at liberty to deny the existence of radium, or the fact that it emits heat. We must either give up the universality of the law, or devise some hypothesis by which the law and the new fact may be reconciled. Now we are certain that volition and thought do modify the working of some material agents. Consequently, we must devise some hypothesis by which this fact may be reconciled with the law, or else alter the expression of the law.

Diverse solutions, however, have been advanced. (1) Some writers simply deny the application of the law to living beings, or at least its rigid accuracy, if referred to the entire collection of vital and psychical phenomena. They urge with much force that the living, conscious organism, endowed with the power of self-direction, differs fundamentally in nature from a mere machine, and that it is therefore illegitimate to extend the application of the law to organisms in precisely the same sense as to inanimate matter until this extension is rigidly justified by experimental evidence. But evidence of this quantitative accuracy is not forthcoming—nor at all likely to be. As a consequence, scientists of the first rank, such as Clerk Maxwell and Lord Kelvin, have always been careful to exclude living beings from their formulation of the law. Moreover, they remind us that, in certain respects, the animal structure resembles a very delicate mechanism in which an extremely minute force may liberate or transform a relatively large store of latent energy preserved in a very unstable condition, as, e.g., the pressure of a hair- trigger may explode a powder magazine.

(2) Again, many physicists of high rank (Clerk Maxwell, Tait, Balfour Stewart, Lodge, Poynting), who suppose, for sake of argument, the strict application of the law even to living beings, aim to harmonize the real action of the soul on the body with the law by conceiving this action as exercised merely in the form of a guiding or directing force. They generally do so, moreover, in connection with the established truth of physics that an agent may modify the direction of a force, or of a moving particle, without altering the quantity of its energy, or adding to the work done. Thus, a force acting at right angles to another force can alter the direction of the latter without affecting its intensity. The pressure of the rail on the side of the wheel guides the train-car; the tension of gravitation keeps the earth in its elliptical course round the sun without affecting the quantity of energy possessed by the moving mass. If the enormous force of gravitation were suddenly extinguished, say, by the annihilation of the sun, the earth would fly away at a tangent with the same energy as before. The axiom of physics, that a deflecting force may do no work, is undoubtedly helpful towards conceiving a reconciliation, even if it does not go the whole way to meet the difficulty.

(3) At the same time, the philosophy of Aristotle and St. Thomas provides us with a clue which assists us farther than any modern theory towards the complete solution of the problem. For this, four distinct factors must be kept in mind:—

(a) The entire quantity of the work done by the living being must in this view be accounted for by the material energies—mechanical, chemical, electrical, etc.—stored in the bodily organism. The soul, or mind, or vital power merely administers these, but does not increase or diminish them. The living organism is an extremely complex collection of chemical compounds stored in blood and cellular tissue. Many of these are in very unstable condition. A multitude of qualitative changes are constantly going on, but the quantity of the work done is always merely the result of the using up of the material energies of the organism. The soul, within limits, regulates the qualitative transformation of some of these material energies without altering the sum total.

(b) The action of the soul, whether through its conscious or its merely vegetative activities, must be conceived as primarily directive.

(c) But this is not all. The soul not only guides but initiates and checks movements. The most delicate hair-trigger, it is urged, requires some pressure to move it, and this is work done, and so an addition to that of the machine. The trigger, too, presses with equal reactive force against the finger, and through this emits some of its energy back to another part of the universe. Consequently, any action of the soul upon the body, even if the pressure or tension be relatively small, involves, it is said, a double difficulty: the pressure communicated by the soul to the body and that returned by the body to the soul. In reply: First, what is needed in order to originate, guide, or even inhibit a bodily movement is a transformation of the quality of some of the energy located in certain cells of the living organism. Whilst physics, which seeks to reduce the universe to mass-points in motion, is primarily interested in quantity, qualitative differences cannot be ignored or ultimately resolved into quantitative differences. Direction is the qualitative element in simple movement, and it is as important as velocity or duration. Now, although the initiation of movement, or the origination of a change in the quality of the material energy located in particles of inanimate matter, needs a stimulus involving the expenditure of some energy, however small, it does not seem necessary, and there is no proof, that every transformation of energy in living beings requires a similar expenditure of energy to occasion the change. Be it noted also that the energy of the stimulus often bears no relation to the magnitude of the change and that in many cases it is not incorporated in the main transformation. Indeed, the explosive materials of the earth might conceivably be so collocated that the action of an infinitesimal force would suffice to blow up a continent and effect a qualitative transformation of energy vaster than the sum total of all the changes that have gone on in all living beings since the beginning of the world. This should be remembered when it is alleged that any action of the human mind on the body would constitute a serious interference with the constancy of the sum total of energy.
     However, as a matter of fact, some qualitative changes of energy in the living organism which result in movement at least appear not to be excited by anything of the nature of physical impact. Psycho-physics teaches that concentration of thought on certain projected movements, and the fostering of certain feelings, are speedily followed by qualitative changes in organic fluids with vascular and neuromotor processes. States of consciousness becoming intense seem to seek expression and find an outlet in bodily movement, however this is actually realized. This brings us to the further step in the solution of the problem which the Aristotelico-Scholastic conception of the relation of body and mind, as "matter" and "form", contributes. In that theory the soul or vital principle is the "form" or determining principle of the living being. Coalescing with the material factor, it constitutes the living being. It gives to that being its specific nature. It unifies the material elements into one individual. It makes them and holds them a single living being of a certain kind. Biology reveals that the living organism is a mass of chemical compounds, many of them most complex and in very unstable equilibrium, constantly undergoing change and tending to dissolution into simpler and more stable substances. When life ceases, the process of disintegration sets in with great rapidity. The function, then, of this active informing principle is of a unifying, conserving, restraining character, holding back, as it were, and sustaining the potential energies of the organism in their unstable condition. From this view of the relation of the soul to the material constituents of the body, it would follow that the transformation of the potential energies of the living organism is accomplished in vital processes not by anything akin to positive physical pressure, but by some sort of liberative act. It would in this case suffice simply to unloose, to "let go", to cease the act of restraining, and the unstable forms of energy released will thereby issue of themselves into other forms. In a sack of gas or liquid, for instance, the covering membrane determines the contents to a particular shape, and conserves them in a particular space. Somewhat analogously, in the Scholastic theory the soul, as "form", determines the qualitative character of the material with which it coalesces, while it conserves the living being in its specific nature. A "form" endowed with consciousness exerts a control, partly voluntary, partly involuntary, over the qualitative character of the constituents of the organism, and in this view it would occasion qualitative changes in some of these by a merely liberative act, without adding to or taking from the quantity of physical energy contained in the material constituents of the organism. The illustration is of course imperfect, like all such analogies. It is given merely to aid towards a conception of the relations of mind and body in the Aristotelean theory.

(d) Finally, in this theory, the action of the soul, or vital principle, upon the material energies of the living organism, must be conceived not as that of a foreign agent, but as of a co-principle uniting with the former to constitute one specific being. This most important factor in the solution is not sufficiently emphasized, or indeed realized, by many physicists who seek to harmonize the law with the real action of the soul. Accepting the philosophy of Descartes, many of these adopt a very exaggerated view of the separateness and mutual independence of soul and body. In that philosophy soul and body are conceived as two distinct beings merely accidentally conjoined or connected. The action of either upon the other is that of an extrinsic agent. If an angel or a demon set a barrel rolling down a hill by even a slight push, the action of such a spirit would involve the invasion of the system of the material universe by a foreign energy. But this is not the way the soul acts, according to the philosophy of St. Thomas and Aristotle. Here the soul is part of the living being, a component principle capable of liberating and guiding the transformation of energies stored up in the constituents of the material organism, which along with itself combines to form a single complete individual being. This point is a vital element in the solution, whether the basis of the difficulty be the conservation of energy, the conservation of momentum, or Newton's third law. The directing influence is not exercised as the pressure of one material particle on another outside of it. The soul is in the body which it animates and in every part of it. Neither is "outside" the other.

This solution obviously provides an answer at the same time to the objections deduced from the conservation of energy against the creation of human souls or the freedom of the will. If the soul were a fount of energy distinct from and added to the material energies of the organism, and if the freedom of the will involved incursions of a foreign physical force into the midst of existing material energies, then infringement of the law of constancy would seem inevitable. But if the soul merely diverts the transformation of existing reserves of energy in the manner indicated, no violation of the law seems necessary. Similarly, the departure of such an immortal soul from the physical universe would not involve any withdrawal of material energy from the total sum. Finally, if human thought and volition can interfere in any degree with the movements of matter, and exercise a guiding influence on any of the processes of the bodily organism, a fortiori must it be possible for an Infinite Intelligence to intervene and regulate the course of events in the material universe; and if the human mind can effect its purposes without infringement of the law of conservation of energy, assuredly this ought to be still more within the powers of a Divine Mind, which, according to the Scholastic philosophy, sustains all beings in existence and continuously co-operates with their activity.