Chapter VIII: Introduction: To Part III (3)

Consider, for example, the group of beliefs which may be described generally as beliefs in persistence, or beliefs in conservation—the kind of belief which has been applied at different periods, and by different schools of scientific thought, to matter, mass, bulk, weight, motion, force, heat, and energy. As every one knows, these ascriptions have not always been correct. But this only emphasises the strength of the tendency. Weight was at one time supposed to be invariable. We know now that the weight of a body varies with its position relatively to other bodies. It is different, for example, at the poles from what it is at the Equator. But how was the error discovered? Not by experiment. There were experiments, no doubt. But those who undertook them already believed in the law of gravitation; and the law of gravitation made it necessary to distinguish the mass of any given fragment of matter both from its weight and from the occult quality of gravity, which is one of the factors on which its weight in any given situation depends. The desire for conservation was not, however, defeated; since physicists, till within the last few years, regarded both mass and gravity as unalterable characteristics of all material bodies.

Again, consider the case of heat. This also has been regarded by powerful schools of scientific thought as a substance that was “conserved.” It is so regarded no longer. But is the inclination to believe in conservation thereby defeated? Not at all. Though heat may vanish, energy remains, and heat is a form of energy.

This doctrine of the conservation of energy is indeed the crowning triumph of the tendency I am discussing, and provides the best illustrations of its strength. For natural philosophers, intent on finding conservation wherever they could, started too boldly on their quest. Descartes regarded the conservation of motion as a self-evident inference from the rationality of God. It is true that he neither had experimental evidence of his doctrine, nor could he, under any circumstances, have obtained it; for the energy of motion, as he incorrectly described it, is not conserved. Leibnitz described it correctly, and had as great a confidence as his predecessor in its conservation, and as little proof to support him. So confident indeed was he, and so independent of experimental evidence was his faith, that he dogmatically asserted that, when motion seemed to disappear, what was lost by the bodies which we see, was exactly taken up by their component elements which we do not see; so that nothing in the nature of what he called _vis viva_ was either lost or created. That this transformation of energy from molar to molecular motion is constantly occurring we now have sufficient proof. But Leibnitz had no proof; and apparently thought none was required other than the Cartesian deduction from the rationality of God. He made a bold anticipation of experience, with nothing to support him but _a priori_ inclination.

His anticipation, however, was not only bold; it was fortunate. Kinetic energy may really be transformed from molar to molecular motion, and suffer no variation. It is conserved. On the other hand, it may not. It may altogether cease, and what becomes of conservation then?

The scientific formula which satisfies both the facts of the case and our desire for conservation is well known.[13] Energy, we are taught, is of two kinds: kinetic and potential energy—energy in act and energy in possibility. Each may turn into the other, and is continually so turning. Each, therefore, may vary in quantity, and does vary in quantity. It is only their sum which is indestructible.

Few scientific generalisations have been more fruitful; few have been accepted on more slender evidence; none are more certain; none more clearly illustrate our natural appetite for beliefs of conservation. For, indeed, to the over-critical this sort of conservation must needs leave something to be desired. When we assert the indestructibility of matter we mean that a real entity continues through time unchanged in quantity. But the word has a less obvious meaning when it is applied to energy. The propriety of describing motion as energy seems indeed clear enough; and if all energy were energy of motion, and if energy of motion were always conserved, the conservation of energy would be on all fours with the conservation of matter. But this is not the case. In spite of Leibnitz, the amount of _vis viva_ is not indestructible. What, then, happens when some of it is destroyed? In that case, says science, energy changes its form but not its quantity. Energy of motion becomes energy of position. What was kinetic becomes potential; and, as the transformation is effected without loss, the principle of conservation is saved.

When, however, energy thus becomes potential, in what sense does it still exist, and why do we still call it energy? Energy suggests “doings” and “happenings.” In the case of “potential” energy there are no “doings” and no “happenings.” It is “stored”; and stored it may for ever remain, hibernating (as it were) to all eternity, neither changing nor causing change.

I do not quarrel with this; but I ask myself why “energy” should be treated more leniently than “force.” Though force is now known not to be “conserved,” ordinary thought attributes to it a certain continuity of existence even when it does not show itself in motion. Force may be exerted though nothing moves; as, for example, by a book pressing on a table. But this view is profoundly unsatisfactory to many scientific thinkers. For them force is nothing apart from “acceleration”; it does not represent a cause, it only measures an effect. And if in our ordinary moments we think otherwise, this (they think) is simply because we illegitimately attribute to matter something which corresponds to muscular effort in man.

It is not, perhaps, so easy as these critics suppose to extrude from scientific thought (I say nothing of scientific language) this notion of latent force—force which would produce movement if it could; and is actively, though imperceptibly, striving to show itself in motion. But why should they try? They welcome potential energy—why should they anathematise latent force?

I think the answer is to be found in the fact that, whether force has, or has not, any being apart from acceleration, it is certainly _not_ conserved; while, if energy be as real when it is potential as when it is kinetic, it certainly _is_ conserved. A lapse into anthropomorphism, therefore, is without excuse in the first case, while a lapse into metaphysics is justified in the second. Any heresy may be forgiven, and any evidence is worth respectful attention when conservation is the thing to be proved.

I have sometimes amused myself by wondering what would have happened about the year 1842 if the conservation of energy had been a theological dogma instead of a scientific guess. Descartes, as I mentioned just now, inferred the conservation of motion from the attributes of God. Colding and Joule used the same argument in favour of the conservation of energy. Now, if a belief in the conservation of energy had been an integral part of religious orthodoxy in the early forties of the last century surely some positivist philosopher would have used Joule’s first investigation on Work and Heat to upset the very dogma they were intended to establish. “Here” (he would have said) “you have a believer in these metaphysico-theological methods of discovering the laws of nature; and mark what happens. In true medieval fashion he begins with some fanciful deductions from the way in which he thinks God must have made the world. Fortunately, however, though his principles are medieval, his methods are modern. Not only is he a most brilliant experimenter, but he has the courage to put his own speculations to an experimental test. He takes the minutest precautions, he chooses the most favourable conditions, and what happens? Does he prove his case? Do his results square with his theories? Does he find a fixed relation between work and heat? Does he justify his views of God? Not at all. Between his lowest determination of the mechanical equivalent of heat, and his highest, there is an immense and lamentable gap. What does he do? He takes their mean value:—a very proper method if he knew there _was_ a mechanical equivalent of heat; a very improper method if the reality of such an equivalent was the thing to be proved. Clearly, if he had not put his theological opinions into his scientific premises when he began his experiment, he never would have got them out again as scientific conclusions when he had reached its end.”

For my own part, I think this imaginary critic would, at that date, have had something to say for himself—supposing always we are prepared to accept his presuppositions about scientific method. If sound reason and intellectual integrity require us to follow the lead of observation and experiment with no antecedent preference for one class of conclusions rather than another, then no doubt Joule and a long line of distinguished predecessors were the spoilt children of fortune. They made their discoveries in advance of their evidence, and in spite of their methods. If they turned out to be right, or, at least, on the right road, what can we do but criticise their credulity and wonder at their luck? unless, indeed, their luck be a form of inspiration.

Before leaving beliefs of conservation, I must say one more word about the most famous of them all—the belief in the conservation of matter. This was an important article in the scientific creed of the early atomists, who had no better evidence for it than they had for the Atomic Theory itself. The material “substance” of the medieval Aristotelians was, I imagine, also conserved; though as all that could be known about it were its qualities, and as these were not necessarily conserved, the doctrine in practice did not, perhaps, amount to much. Then came the theory which, chiefly in the hands of Boyle[14] at the end of the seventeenth century, initiated modern chemistry. What was conserved, according to this view, was not a metaphysical substance with detachable qualities, but elementary kinds of matter with inseparable qualities; and out of these qualified entities was compounded the whole material universe. I may incidentally observe that a company promoter who should issue a prospectus based on no better evidence than Boyle could advance for this tremendous theory would certainly be in peril of the law. Yet Boyle was right: and, notwithstanding subsequent developments, his conjecture remains the corner-stone of modern chemical research.

Now, what is it that we intend to assert when we say that matter is conserved, or is indestructible? We certainly do not mean that its qualities never suffer change: for most of those which are obvious and striking are always liable to change. If you sufficiently vary temperature or pressure; if you effect chemical composition or decomposition, the old characteristics will vanish and new characteristics will take their place. What, then, is conserved?

In the first place, the lost qualities can (in theory) always be restored, though not always without the expenditure of energy. Water never ceases to be convertible into steam, nor steam into water. The characteristics may vanish, but in appropriate conditions they will always reappear.

Now science, as we have just seen, is tolerant of this notion of latency or potentiality, and is ready enough to use it in aid of beliefs in conservation. It was so used in connection with heat when heat was regarded as a material substance. It is still so used in connection with energy, which is sometimes described as an immaterial substance. But (as I have already noted) it has never been so used in connection with matter. The reason, I suppose, is that the conservation of matter is much more a belief of common sense than the conservation of energy. Energy is a conception which has but recently been disengaged from other conceptions, like force and momentum, and has but recently been associated with heat, with chemical reactions, with changes of physical phase, and with electro-magnetic phenomena. It is, therefore, a remote and somewhat abstract product of scientific reflection; and science may do what it will with its own.

The notion of matter, on the other hand, is the common possession of mankind. Whatever difficulties it may present to reflective analysis, it presents none to our work-a-day beliefs. We are quite ready to regard it as indestructible; but we are not ready to combine this conviction with the view that it possesses no single characteristic which may not be temporarily etherealised into a “potentiality.” On such terms the eternal and unchanging identity of this or that parcel of matter would seem a difficult and elusive doctrine, inappropriate to the familiar and substantial world in which we suppose ourselves to live. A belief in the conservation of matter has therefore always, or almost always, carried with it a belief in the unchanging continuity of at least _some_ material qualities; though as to what these qualities are there has been much dispute.

Descartes, though not consistent, found unchanging continuity in the attribute of size; so also did Hobbes. I presume that the older atomists, who explained the appearances of matter by the shape of its constituent atoms, would have regarded both atomic form and atomic magnitude as persistent. But it was the assumption that the same piece of ponderable matter always possessed the same gravitating power, and that the same gravitating power was always associated with the same mass, which, in the hands of Lavoisier, made so great a revolution in eighteenth-century chemistry. Matter might change its size, its shape, its colour, its phase, its power of acting and reacting; but its mass and the quality which caused its weight it could not change; these characteristics were always associated with each other, and were never in abeyance.

To Lavoisier this double principle seemed self-evident. It was not a hypothesis that required testing, but a touchstone by which other hypotheses might safely be tested. If, in the course of some chemical operation, weight increased, then no further proof was required to show that mass had increased also, and that matter had been added. If, on the other hand, weight diminished, then no further proof was required to show that mass had diminished also, and that matter had been subtracted. Whatever other qualities matter might gain or lose, mass and gravity were indestructible and unchanging.

Men of science seemed, on the whole, content silently to assume these principles of conservation without inconveniently raising the question of evidence. Philosophers have not always been so cautious. Kant supposed himself to have demonstrated them _a priori_. Schopenhauer followed suit. Spencer declared their contraries to be inconceivable. Mill said they were proved by experience. In short, all these eminent thinkers vied with each other in conferring upon this doctrine the highest honours permitted by their respective philosophies. But apparently they were hasty. Recent discoveries have changed our point of view. Mass (it seems) is no longer to be regarded as unchanging. When bodies move at speeds approaching the velocity of light their mass rapidly increases; so that this quality, which is peculiarly characteristic of matter, must be removed from the category of those which persist unchanged, and placed in the category of those which change but can always be restored. Are we so to class gravitation? Would the weight of a body moving nearly at the speed of light increase as, in like circumstances, its inertia increases? If the answer is “no,” then the link is broken which has for long been thought to connect gravity and mass. If the answer is “yes,” then what Kant regarded as certain _a priori_ is false; what Spencer regarded as “inconceivable” is true; another carrier of “persistence” is lost, and some fresh characteristic must be found which will remain unchanged through all time, and under all conditions.

If this characteristic should turn out to be electric charge, what a curious light it will throw upon our tendency to “beliefs of conservation”[15]. After long seeking for some indestructible attribute of matter; after taking up and rejecting size, shape, weight, mass, and (perhaps) impenetrability, we shall at last find the object of our quest in a conception which has (I suppose) been clearly realised only within the last hundred years, about which our senses tell us nothing, and of which the general run of educated mankind are still completely ignorant!

III

It is possible, but not, I hope, probable, that some hasty reader may suppose that in this and the preceding lectures I am recommending a new method or instrument of discovery. “If you want to reach truth, follow your unreasoned inclination,” may be his summary of my doctrine: brief—but also unjust.

Of the manner in which discoveries are going to be made I say nothing, for I know nothing. I am dealing with the past: and in the historic movements of scientific thought I see, or think I see, drifts and currents such as astronomers detect among the stars of heaven. And, as the law of gravitation will hardly (I suppose) explain the last, so observation, experiment, and reasoning will hardly explain the first. They belong to the causal, not to the cognitive, series; and the beliefs in which they issue are effects rather than conclusions.

Those who feel little sympathy for such a view may be inclined to regard the relatively faint inclinations dealt with in this lecture as ordinary scientific hypotheses confirmed by ordinary scientific methods. This view, as I have already observed, is not applicable to the inevitable beliefs dealt with in earlier lectures. Whatever philosophers may say after the event the conviction that we live in an external world of things and persons, where events are more or less regularly repeated, has never been treated as a speculative conjecture about which doubt was a duty till truth was proved. Beliefs like these are not scientific hypotheses, but scientific presuppositions, and all criticism of their validity is a speculative after-thought. The same may be said, though with less emphasis and some qualification, about beliefs fostered by the intellectual tendencies considered in this chapter. These, as we have seen, are many. They are often inconsistent; they are never inevitable; and they perpetually change their form under the pressure of scientific discovery. Atomism in one shape follows atomism in another; doctrines of conservation rise, fall, and rise again; incredulity about “action at a distance” breeds explanations whose failure (in the case of gravity) leaves the hope of final success untouched.

Now, it would be an error to say that science does not, when it can, apply to these various theories its ordinary methods of verification. They are in a different position from inevitable beliefs, which can hardly be verified because the process of verification assumes them. Yet they must not be confounded with ordinary scientific hypotheses, for they are something more and something different. Like these, they are guesses, but they are guesses directed, not by the immediate suggestion of particular experiences (which indeed they sometimes contradict), but by general tendencies which are enduring though sometimes feeble. Those who make them do not attempt the interrogation of Nature wholly free from certain forms of bias. In cross-examining that most stubborn and recalcitrant of witnesses they never hesitate to ply her with leading questions; and, whether this procedure be logically defensible or not, no lover of truth need regret its results.

Readers of M. Bergson’s “Creative Evolution” may remember the picture he draws of the _élan vital_—the principle of life—forcing its way along different paths of organic evolution, some without issue or promise of progress; others leading on through regions hitherto untraversed to ends remote and unforeseen. The secular movements of science, as I conceive them, somewhat resemble this process, even though it be faintly and at a distance. There is in both a striving towards some imperfectly foreshadowed end; and in both the advance is irregular, tentative, precarious, with many changes of direction, and some reversals. Yet I would not press the parallel over-far or plunge too deeply into metaphor. It is enough to say that as, according to M. Bergson, the course followed by organic evolution cannot be wholly due to Selection, so the course followed by scientific discovery, as I read its history, cannot be wholly due to reasoning and experience. In both cases we seem forced to assume something in the nature of a directing influence, and (as I should add, though perhaps M. Bergson would not) of supramundane design. And if “a Power that makes for truth” be required to justify our scientific faith, we must surely count ourselves as theists.

NOTE

_Extracts from a letter from Sir Oliver Lodge on certain passages in this lecture relating to Energy and its transformations._

* * * * *

You say, on page 226, “Energy, we are taught, is of two kinds: kinetic and potential energy—energy in act and energy in possibility.”

So long as emphasis is laid upon the words “we are taught,” I have no objection. People _have_ taught that, though I strongly object to such teaching, because I object to the idea “Energy in possibility” or “possible Energy” of any kind. I teach the identity of Energy in much the same terms as the identity of Matter; not merely the conservation, with the idea that one quantity can disappear and another quantity reappear. It is not another quantity, but the same; though it may have been locked up for any length of time. But then it has not been usually taught so, and I think you are dealing with what is usual.

* * * * *

Again, you say on page 227, “Energy suggests ‘doings’ and ‘happenings.’” No, say I, _activity_ suggests doings and happenings, and activity is Energy in transformation. Energy alone is something stored, like Capital. The earth’s rotational energy, for instance, is stored just as really as, and for a longer time than, the vegetation of the carboniferous epoch.

Lower down you observe that “Force may be exerted though nothing moves.” Certainly it may, when resisted by an equal opposite force. But I fully admit that a lot of nonsense has been talked about the acceleration measure of force, as if it were the only measure, and that some criticism on this procedure is useful. But I should not speak of “latent” force; it is real force you have in mind, or at least real stress—_i.e._ two equal and opposite forces. It is latent Activity which becomes active when the other factor, viz. Motion, is supplied or allowed—_e.g._ by the release of a bent bow, or a wound-up spring, or a raised weight.

So it is also with the Energy of a fly-wheel. That, too, is latent Activity until the other factor, viz. Force, is supplied, _i.e._ when it is employed to overcome resistance, and therefore do work. Otherwise its Motion will be stored to all eternity.

In short, activity, or doing of work, has two factors, Force and Motion. When both are present, work is done; when either is present alone, Energy is stored. Static Energy is the Force factor, with the possibility of a certain range of effectiveness understood; like a head of water, for instance, a certain height above the sea. Kinetic Energy is the Motion factor, with a certain inertia or possibility of Force understood; not Motion alone, but a mass in motion, so that it may be able to overcome resistance.

There is no real reason why one form of Energy should be considered more “actual” or real than another; our eyes appreciate the one form, our muscles could appreciate the other.

* * * * *

In considering cases of Potential Energy, it is wise to realise that our knowledge about Gravitation is altogether too vague to make the case of a raised weight useful. And our knowledge of solid elasticity, though not so insignificant, is small enough to make the case of a bent bow or wound spring not very easy for fundamental contemplation. A case of chemical Energy, like gun-cotton, is in much the same predicament.

But a typical and satisfactory example of Potential Energy is the case of a vessel of compressed air. Here is Energy stagnant enough, and violent enough when released, and one that can be locked up apparently to all eternity, and yet released by the pulling of a trigger. It represents, however, a case of which we know something concerning the internal mechanism; and we have learnt that in this case the force statically exerted on the walls of a vessel is really a kinetic bombardment of the molecules. In other words, we recognise in this case that Potential Energy is ultimately resolvable into Kinetic. It may be so in the other cases. And on Kelvin’s Kinetic Theory of Elasticity, which he showed a tendency in later life to abandon, all strain or stress in Ether may be ultimately due to its ultramicroscopic vortex circulation.

But none of this is yet proven.

* * * * *

The general argument of your lecture deals with the ease with which certain general propositions are accepted as it were intuitively, without real conclusive evidence. I am entirely with you. And the way we feel secure about general laws, when adequate evidence for them is really impossible, has often struck me as remarkable. Even when facts appear to go against them, we question the facts, and find after all that in so doing we have been right.

FOOTNOTES:

[12] See Lecture VI.

[13] See note at the end of the Lecture.

[14] I got this view of Boyle’s relation to modern chemistry from Ostwald’s work.

[15] In this chapter, especially in that part of it which deals with beliefs of conservation, I am greatly indebted to Meyerson’s “Identité et Réalité.” This acute and learned work is not written from the same point of view as that which I have adopted; but this in no way diminishes the amount of my obligation to its author.