University of Virginia Library

10. CHAPTER X.
NECESSARY LIMITATIONS OF SCIENTIFIC AND
RELIGIOUS THOUGHT.

I HAVE endeavored to show that the evidence which all nature affords of a personal God is wholly independent of the theories of cosmogony we may assume. But although our doctrine of causation may not impair the evidence of an original design, it is not so with the other bearings of the subject. For if nature be a mere machine, weaving the complex web of destiny with the same precision and certainty with which a carpet-loom weaves the pattern of a carpet, then the Christian's idea of a superintending Providence cannot be true. If nature has been evolved solely under necessary conditions and laws, with which the Creator has never interfered since he wound up the immense weight which set the whole in motion and still maintains the preordained beats of the great pendulum of the universe,—if with an archangel's intellect we could predict every event in nature with the same certainty with which we now foretell the phases of an eclipse,—then I say again that the visions of an overshadowing Providence which have appeared to

us at those milestones on our life's journey where, wearied and disheartened, we have sat down to rest, are nothing but a delusion and a dream. It does not remove the difficulty here referred to, to say that our lives are parts of this preordained plan, or even to admit that God may interfere in the moral world by influencing the will of man; for every one is conscious that his will has not been thus directly influenced, and knows, moreover, that the circumstances of his condition have always concealed, at the time, the kind Providence by which he has been led. And when your theory leads to this, that man has been put into a world of probation and trial, and there left to walk over pitfalls with his eyes blinded, every unsophisticated mind will feel—say what you will—that the character of the God you worship is more truly symbolized by the car of Juggernaut than by the cross.

A great deal of false prejudice against scientific study arises from a mistaken impression that the materialist's interpretation of nature is the natural and necessary result of all scientific thought. Hence not a few religious minds have concluded that the methods of science must be all wrong, and its conclusions wholly untrustworthy. It will not, therefore, be out of place in this connection to consider briefly whether the materialist's idea of causation is the necessary, or even the probable conclusion to which the observed facts of nature and the legitimate methods of science lead. We must remember, however, while discussing this subject, that we have passed the limits of human knowledge, and

cannot therefore expect by our unaided processes of thought to prove or disprove anything. We cannot determine absolutely whether the materialist's theory be true or false; for science has not the knowledge which would enable it to form a decision. The only question for us is, whether this theory is the necessary theory, or even the most probable theory; and if it is not either the one or the other, then the theory is of no weight. One man's theory is as good as another's, provided both are equally consistent with facts. If, then, we can show, on scientific grounds alone, that the Christian's theory of causation is as probable as the materialist's, we shall in regard to this point also fully sustain the position we have taken in regard to scientific studies. Surely science is no more responsible for the excesses of theorists than is religion for the crimes of bigots, and it should be sufficient to satisfy any religious mind, that there is a Christian theory which is perfectly consistent with all known facts.

It is easy to understand the relative position of the two theories of causation after we have become acquainted with the facts which both must necessarily explain. Let us review, then, very briefly, these facts, which are more or less familiar to every one. An innate principle of the human mind compels us to believe that every change must have an adequate cause, and leads us to refer the phenomena of nature to what we call forces. Thus the falling of an avalanche, the flowing of the tides, the beating of the waves, the blowing of the winds, the crashing of the lightning, the burning of the fire,

the moving power of steam, and the impression of light, must all have an adequate cause, and to this cause we give the name of force. We use this word so frequently and so familiarly that we are apt to think that we associate with it a definite conception; but a moment's reflection will show that in regard to the nature or origin of force we have no absolute knowledge. This word is merely our name for the unknown cause of natural phenomena. The uneducated mind naturally refers the origin of all force to the bodies from which it appears to emanate, and regards it either as a quality inherent in matter, as in the phenomena of gravitation, or as a property superimposed upon matter, as in the phenomena of light, heat, magnetism, and electricity. In either case, however, it is regarded as a quality of matter. Moreover, the uneducated mind, impressed most of all by the great diversity in physical phenomena, naturally infers that a similar diversity exists in the forces which produce them, and thus is led to the idea that there are different kinds of force. Hence men have been led to refer the falling of bodies towards the earth to a distinct force called gravitation, the motion of a steam-engine to another force called heat, the burning of a candle to a third force called chemical affinity, and in like manner to each class of phenomena they have assigned a peculiar and separate force.

Such ideas as these are natural in the infancy of knowledge, and we must remember that, with all our boast of progress, the human race, so far at least as physical science is concerned, is yet in its childhood.

The law of gravitation was discovered only two centuries ago, and almost the whole of the present sciences of chemistry and physics has been developed within the lifetime of men now living. Many of the present generation were educated in those very natural, but crude notions, and it is not until a comparatively recent period that even scientific men have been persuaded that these primitive ideas must be wholly abandoned, or at least radically modified. We are now in a transition stage, and hence arises a great difficulty in discussing the subject. The language even of modern science is based upon the old ideas, and we cannot describe natural phenomena without using terms which imply what almost all thinkers now believe to be erroneous notions. Hence, when we attempt to present spiritual views of the origin and nature of force, we are obliged to use terms which imply the opposite, and our very language appears to condemn us, or at least prejudices our theory. This is especially true of the word force itself, and we must carefully bear in mind that the origin of phenomena is not explained because, in the language of science, they have been referred to an assumed force with a high-sounding name. Names are not things, and we know nothing more of the cause which brings the apple to the ground because Newton has called it the force of gravitation, than we did before. He gave us the law of the motion, and enabled us to predict how every apple would fall, and how every planet would move throughout space, but the cause of the motion is as closely hidden as ever. In regard to the law of gravitation we know a great deal; but in regard to the force of gravitation—whatever we may think or believe about it—we know absolutely nothing, and the same is true of every other force.

The most remarkable feature of modern science has been the constant tendency of all investigations, during the last fifty years, to show that the same energy, if only differently applied, may produce the most diversified phenomena; and now almost all the so-called forces of the old philosophy appear to be mutually convertible. Thus—to begin with a lump of coal—as we have seen, a certain amount of latent energy resides in that black mass, which has been called the force of chemical affinity. Burn the coal,—that is, combine it with oxygen,—and the affinity is satisfied, but the energy reappears as light and heat. If the coal is burnt under a steam-boiler, the heat expands the water and converts it into vapor, and then we find the energy again in the expansive force of steam. The steam expands against the piston of the locomotive, and the energy passes into the moving train. The rapidly moving mass, in forcing its way through the air and over the iron track, is constantly losing its moving power in consequence of the friction it encounters; but the energy is not lost, and if we could follow it, we should find it reappearing somewhere as heat. Suddenly the engineer opens a valve, and a portion of the energy of the steam gives motion to the air, and the effect is a shrill whistle. The brakeman applies the brakes, and the train after a few moments comes to rest. Its moving power is gone, but the energy is not lost.

The motion has been transformed into heat, and the smoking brake shows where the energy has gone.

Return now again to the lump of coal, and, instead of burning it under a steam-boiler, heat it in a properly constructed furnace in contact with roasted zinc ore. This ore is a compound of zinc and oxygen. The coal, in order to satisfy its intense affinity, seizes on the oxygen and sets the zinc free. But although the chemical affinity of the coal has been satisfied, no power has been lost; for the energy which was before latent in the carbon is now latent in the zinc. Dissolve the zinc in dilute sulphuric acid, and the chemical affinity of the zinc will be satisfied, and, if certain conditions are fulfilled, the energy will take the form of a current of electricity. Cause this current to flow through a platinum wire, and this energy will appear in the heat and light radiated from the glowing metal. Cause the same current to flow in spiral lines around a bar of iron, and we find the energy again in the attractive force of an electro-magnet. Connect with the electro-magnet appropriate machinery, and the same energy may be so applied that it will move a light boat or turn a small lathe. Lastly, connect with the dissolving zinc four thousand miles of iron wire, and the energy will be transmitted across a continent with the velocity of thought, and write in a distant city the message which it carries.

Illustrations like these might be multiplied indefinitely; but enough, I think, has been said to show that, to all appearance at least, the same energy may be transferred from one mass of matter to

another, and that thus, while nothing but the mode of application has been changed, the power may reappear under entirely different manifestations, and produce phenomena wholly unlike those in which it was but a moment before the active cause. The truth of this principle becomes still more evident when we apply in our experiments exact measurements; for we find that in all these transfers of energy from mass to mass the power reappears undiminished. It may remain latent for a time, as in a mass of coal, but sooner or later it will reappear without having undergone the slightest loss.

We must here dwell for a moment upon an important distinction, which has already been implied, between latent and active energy. It is a distinction with which every one is practically familiar, and it may therefore be made clear by referring to a few examples. A weight falling to the ground from a given height is an example of active energy, while an equal weight suspended at the same height represents an equivalent amount of latent energy. In winding up a clock, muscular energy becomes latent in the suspended weight, but reappears in mechanical motion as the clock runs down. So also a lump of coal, as already stated, represents a certain amount of latent energy. When the coal burns, its energy becomes active, and takes the form of heat. Again, in smelting zinc ore there is transferred to the product a portion of the latent energy of the coal used in the furnace; and if in a voltaic battery the resulting zinc dissolves in sulphuric acid, this energy becomes active, and reappears in a current of electricity.

Some persons do not like the term latent energy, and speak of energy which is not in action as possible or potential. In like manner they speak of energy in action as actual or kinetic. But terms are of no importance, if only the ideas which they express are fully understood.

Keeping this distinction in view, we shall better understand the bearings of the important principles just before stated. When energy, in passing from one body to another, changes its mode of manifestation, it seldom flows wholly into one channel, and almost invariably more or less of it becomes latent. Thus—to go back to the example of the steam-engine—of the energy, which is latent in the coal and becomes active in the form of heat when the coal burns, not more than one-tenth, at the most, produces any useful mechanical effect. The rest becomes again latent in changing the water into steam, and in heating and expanding the iron, the bricks, the water, and the air in contact with which the fuel burns. All this heated matter represents a large amount of latent energy. It is in the condition of the wound-up weight of a clock, and, as it cools, this energy is distributed to surrounding bodies. Were it possible, at a given instant after the burning of the coal, to sum up all the energy, both active and latent, which could be traced directly back to the burning fuel, it would be found that not the smallest fraction of the energy originally in the mass of coal had been lost. In this case, of course, accurate experiments are out of the question; but wherever it has been possible to apply

measurements, it has been found that the principle here illustrated holds true. I should not be able to make the methods of such investigations intelligible without occupying a great deal of time. Let it then be sufficient to state, that all those who have most carefully studied the subject have arrived at the same results. There is, therefore, every reason to believe that the principle we have been illustrating is universally true. Let us then embody it in a definite statement. All natural phenomena are the manifestation of the same omnipresent energy, which is transferred from one portion of matter to another without loss.

But if the principle as thus stated be accepted, we cannot rest here; for it involves this further conclusion, which, however marvellous, must be true. The sum total of all the active and latent energies in the universe is constant and invariable. In other words, power is as indestructible as matter. [*]

This grand truth is generally called the law of conservation of energy, and, if it cannot as yet be regarded as absolutely verified, there can be no question that it stands on a better basis to-day than did the law of gravitation one hundred years ago.

But how can I give you any conception of the sublimity of the truth which this formal language implies, but which no language is adequate to express? Even poetry, in the highest flights of fancy, has never seen such a vision as these vistas of actual

realities open to the intellect and imagination of man. Review in the light of this grand generalization the subsidiary truth which from time to time I have endeavored to illustrate in this work, —namely, that all terrestrial energy comes from the sun. The accumulated power of the sun's delicate rays produces, as we before saw, every motion and every change which takes place on the surface of this planet, from the falling of an avalanche to the crawling of a worm. But that energy, as we now know, is not exhausted on the earth. To use the eloquent language of another: "Our world is a halting-place where this energy is conditioned. Here the Proteus works his spells; the selfsame essence takes a million shapes and hues, and finally dissolves into its primitive and almost formless form. The sun comes to us as heat; he quits us as heat; and between his entrance and departure the multiform powers of our globe appear. They are all special forms of solar power,—the moulds into which his strength is temporarily poured, in passing from its source through infinitude.''[*]

Attempt now to bring together in imagination all the energies acting at one moment on the earth, and unite them in one tremendous aggregate. Begin with the moving power of the air, the hurricanes, the tornadoes, the storms, and the gentler winds which are everywhere at work from the Arctic to the Antarctic Pole, omitting in making the estimate, if

you choose, the lightning and the thunder, which, though brilliant and noisy demonstrations of power, would hardly increase by a unit the vast sum. Add to this the mechanical power in the mighty flow of waters, the ocean currents, the rivers, the cataracts, the glacier-streams, and the avalanches, all over the globe. Bring into the calculation the forces at work in the various phases of animal and vegetable life. Remember the conflagrations, the furnaces, the fires, and the other manifestations of the terrible energies of the atmospheric oxygen, whenever it is aroused. Do not even forget the comparatively insignificant power which man is wielding with the aid of powder and of steam. Making now an immense allowance for what you must have overlooked, sum this all up, —if you can without bewilderment,—and what part is it of the whole? Why, it has been calculated that it is equal to but one 2,300,000,000th of the force which the sun is every moment pouring into space. And what is the sun? A small star in the infinitude of space, where shine Sirius and Arcturus, Regulus and Aldebaran, Procyon and Capella, with unnumbered others, all shedding forth a far mightier effluence than our feeble star: yet the grand total of the powers streaming from all the suns which human eye has seen, or which still lie undiscovered in the depths of space, alone represents the active energy of the universe. My friends, there are two theories of causation. One regards this energy as an unintelligent power. The other sees in it simply the will of the Almighty. They are both theories. We cannot substantiate either. But which do you think is the more probable? Let us not pass hasty judgment, but soberly weigh all the testimony, and base our decision on the best scientific evidence we can obtain, and on that alone.

Thus far in our discussion we have been dealing with facts and principles which every theory of causation must explain. But we now pass into what is rather the region of speculation, and we must step more cautiously. I have used thus far the terms energy and transfer of energy, without expecting that you would attach to them any more definite meaning than that which is conveyed by the words in their most familiar use. Energy is a definite thing, which is as palpable to our senses as matter, and which, in most cases at least, we can measure as accurately. Any one who has been stunned by a blow, bruised by a fall, burnt by a fire, dazzled by the sun, or paralyzed by a shock of electricity, knows well enough what energy is; and the doctrine of the conservation of energy is wholly independent of any theory which men may entertain in regard to its essence. For this reason, I have aimed to present the grand doctrine of modern science entirely free from all speculations whatsoever; but now that we are seeking to go behind the external phenomena, it will be well for us to consider very briefly a theory which, although it does not profess to explain what energy is in its essence, nevertheless may give to the mind a more definite conception of its mode of action. The theory, it is true, cannot be regarded as fully established; but it represents the undoubted tendency of science,

and the materialists would, of all others, be the first to accept it. According to the modern view, all energy appears as motion, and this too whether it be manifested in mechanical work, or in the more subtile phenomena of sound, light, heat, chemical affinnity, electricity, or magnetism. We must, however, extend our idea of motion, and not limit it, as is usually done, to the motion of visible masses of matter.

Even the smallest material masses perceptible to our senses must be regarded as aggregates of still smaller masses, which we call molecules. These molecules, moreover, even in the densest bodies, cannot be in contact, and we must picture them to our imagination each as a tiny world poised in space. The same relation which the worlds bear to the cosmos, we conceive that these molecules bear to the microcosmos which every mass of matter represents, and it is believed that the motions of suns and systems have their miniature in the motions of these molecules. The ether, also, of which I spoke in the second chapter as filling celestial space, is supposed to pervade equally the molecular spaces, to surround each molecule with a highly elastic atmosphere, and to be the medium by which motion is transmitted throughout a universe which includes the infinitesimal as well as the infinite. Moreover, we conceive that the motion of the molecule is the exact counterpart of the motion of a world or of the motion of a ball, and that all motion obeys the selfsame laws. As when an ivory billiard-ball strikes another, it gives up the whole or a part of its motion to the second ball, so we believe that one molecule may

transmit motion to another. In like manner, as an impulse is transmitted through a long line of billiard-balls, and the last ball only appears to move, so also we conceive that the electrical impulse is transmitted from molecule to molecule through the telegraph wire, and produces perceptible motion only when transformed into magnetism at the end of a thousand miles. Again, motion may be transmitted from molecules to masses of matter; for although the impulse imparted by a single molecule may be as nothing, the accumulated effect of millions on millions of these impulses may be immense. In this way, as we conceive, the motions of the ether particles in the sunbeams unite to produce all the grand phenomena of nature. On the other hand, the motion of great masses may be suddenly resolved into the motions of the molecules composing these masses, and thus, when motion outwardly appears to cease, it may only be transferred from the previously moving body to the molecules within. When the cannon-balls, with their immense velocity, strike the iron-clad frigate and fall harmlessly from her armor-plates, the particles of iron take up the motion of the ball, and indicate by a higher temperature that the energy has not been lost.

Understanding, then, the term motion in the extended sense just explained, we shall comprehend more clearly the theory stated above. This theory supposes that the phenomena of sound, light, heat, and electricity are produced by the motions of molecules, in the same way that the grander phenomena of mechanics and astronomy are caused by the motion

of large masses of matter. The transmission of energy is, then, the direct result of the transmission of motion, and the conservation of energy is fully explained by the well-known law of inertia, which the motions of all matter necessarily obey. I have not time to enter into any details in regard to the mode of motion by which light, heat, and all this class of phenomena are produced, other than those already given in the previous chapters of this book; but I take great pleasure in referring my readers to the work of Professor Tyndall, already frequently quoted, as by far the best popular statement of the subject that has ever been made. Indeed, great differences of opinion in regard to the mode of the molecular motion are entertained by those who accept the theory in its general statement, and in many cases we can form no conception of the peculiar phase which the motion assumes. It is sufficient for my purpose if I have been able to make clear the general principle, and I will only add a few numerical results, which will show what a precise form the theory has taken in the minds of scientific men.

According to the modern theory, when we heat a body we merely impart to its molecules a greater velocity of motion. Now, according to the experiments of Professor Joule, when we raise the temperature of a pound of water two Fahrenheit degrees, we distribute among the molecules of the liquid an amount of motion equal to that acquired by a weight of two pounds in falling 772 feet, and a simple calculation will show that this is represented

by a Minie ball, weighing one-eighteenth of a pound, moving with a velocity of 1,338 feet in a second. [*] The amount of motion, therefore, which is imparted to the particles of water in an ordinary tea-kettle during the process of boiling, must be in the aggregate vastly greater than that ever acquired by any projectile. We shall arrive at a still more remarkable result if we examine in the light of our theory the process of chemical combination by which water is formed. In this process of burning, one pound of hydrogen gas combines with eight pounds of oxygen gas to form nine pounds of water. Although the distances which separate the atoms of the two gases before combination are utterly inappreciable by our senses, yet, in passing over these distances, they acquire a velocity which causes them to clash together with tremendous energy, and in the collision this form of atomic motion is transmuted into that other mode of motion which we call heat. Incredible as it may appear, the amount of motion which in the act of combination alone is thus transmuted into heat corresponds to the fall of a ton weight down a precipice 22,320 feet high. Such illustrations might be multiplied indefinitely; but you will see from these how purely mechanical the idea is which we associate with the motion of a molecule, and you must have been impressed by the magnitude of the energy which these molecular motions represent. "I have seen,'' says Professor Tyndall, "the wild stone avalanches of the Alps, which smoke and thunder down the declivities with a vehemence almost sufficient to stun the observer. I have also seen snow-flakes descending so softly as not to hurt the fragile spangles of which they were composed; yet to produce from aqueous vapor a quantity of that tender material which a child could carry, demands an exertion of energy competent to gather up the shattered blocks of the largest stone avalanche I have ever seen, and pitch them to twice the height from which they fell.'' If such, then, be the measure of these atomic motions, we can easily conceive how the motion of the cannon-ball might be transferred to the particles of the armor-plate without much apparent result, and even how the energy of a world might be maintained by the motion of the molecules in the sunbeam.

Accepting, then, this new theory of science, and admitting that all energy is manifested in motion, we reduce at once our discussion of the doctrine of causation to this simple question,—What is the primary cause of motion? If we can explain the simplest case of motion, we have solved the problem for the universe. Take, for example, a boy's ball, moving through the air under the impulse of a well-directed blow. Do we not know something of the cause of that motion? Is it not connected with the muscular contraction of the boy's arm, produced by his will? Is not his volition, acting mysteriously on matter, at least the occasion of the motion? It is perfectly true that the will does not create the motion. The ball is impelled by a portion of that

energy in nature which man can neither increase nor diminish. But still the boy's will is the occasion of the motion. It has opened the channel through which the energy of nature has flowed to produce the specific result which the boy desired. So, in a thousand other ways, man is able to come down, as it were, upon nature, and to introduce a new condition into the chain of causation. Place the point of contact as far back as you please, theorize about the subject as you may, the fact still remains the same. Our will does act on matter, and does act to produce most efficient results. Here is energy exerted of whose cause we have the consciousness within our selves, and, if the analogy is worth anything, it points to but one conclusion,—namely, that motion is always the manifestation of will. As the boy's will acted on that particle of matter, which, though moved perhaps but an atom's breadth from its position, set in action—as if by the touching of a spring—the train of natural causes which gave motion to the ball, so we may suppose that the Divine will acts in nature. According to this view, the energy which sustains the universe is the will of God, and the law of conservation is only the manifestation of His immutable being—"the same yesterday, and to-day, and forever.''

We do not say that this theory can be proved— for certainty here is out of the question—but we do claim that it is based on the only analogy which nature affords, that it is a legitimate deduction of science, and that it is perfectly consistent with Christian faith. On a subject where science can only

grope, the wildest theories are possible; but these should not trouble a well-balanced mind, so long as there exists an equally probable theory which can be reconciled with the purest faith. It has been my aim in this chapter to show, not only that such a theory is tenable, but also that the Christian theory of causation is the most probable theory of science; and my earnest hope is, that, for some minds at least, the considerations I have offered will help to reconcile the apparent conflict between science and religion which materialism is ever striving to foment. Allow me to add, in concluding, one or two other suggestions which may be of value in the same direction.

I cannot but believe that the appearance of clashing between science and religion would be wholly avoided, if the teachers both of God's unwritten and of His written word would pay more regard to the necessary limitations of scientific and religious thought. On subjects where the methods of acquiring knowledge are so utterly unlike, where the relations of knowledge to the human understanding are so different, it is in vain to expect literal accordance. Science, both in its methods and its results, addresses the understanding exclusively; Christianity appeals chiefly to the heart. Science aims to instruct; Christianity aims to persuade. Science is attained by study, and is possible only for the few; Christianity is a free gift from God to all men who will receive His Son. The results of science are fully comprehended, and can be expressed in definite terms; the truths of Christianity stand on a level

above man's intellect, and can only be shadowed forth in types and symbols. The forms of science are constantly changing; the types and symbols of Christianity are permanent. Lastly, while the language of science may be so varied from time to time as to express accurately the current ideas, Christianity necessarily retains the forms through which it was first revealed. Under such conditions, how can it be expected that the letter of revelation should agree with the language of science? One might as reasonably find fault with nature because its crystals are not perfect, as criticise the Bible because its language, although embodying divine truth, is not free from the necessary limitations and imperfections of the human medium of thought.

Consider in this connection the method of science which we have already discussed at some length in a previous chapter. Remember that in nature we observe only a sequence of phenomena. The idea of a cause is supplied by our own minds, and every phenomenon is so surrounded and obscured by adventitious circumstances that it is frequently very difficult to establish the causal connection with the antecedents. Science endeavors to discover this connection by a process of elimination, which it conducts in various ways. It notices, for example, that while certain antecedents invariably accompany a given effect, others are sometimes absent, and in this way the accidental concomitants may be to a greater or less extent eliminated. The process of elimination is more rapid and satisfactory when the phenomenon is so far under our control that we can vary the

conditions by experiment. If, then, we find that a given condition may be omitted or varied without influencing the result, we can conclude with great safety that this antecedent is not essential. On the other hand, if we find, either from experiment or observation, that the effect varies with the condition any change in the antecedent being followed by a corresponding change in the phenomenon we are studying, then we feel great confidence that we have found one at least of the causes we are seeking. When a connection of this kind is established, the effect is said to be a function of its antecedent, and it is frequently possible to express this function by a mathematical formula, so that we can predict with absolute certainty the nature and extent of the effect which will under any given circumstances be produced; and in this case our certainty in regard to the immediate cause of the phenomenon is of the highest order which can be reached in science. An illustration will make the point clearer.

A few years ago, Professor Crookes, of London, having observed that light pith balls delicately suspended in a vacuous tube were under certain conditions repelled by the sun's rays, was led on from step to step until he had constructed the instrument now so well known as the radiometer, in which a delicate wheel is rapidly turned by the rays of the sun, or by the rays of any source of bright light, shining on its blackened vanes.

At first sight the effect seemed to be the result of a direct mechanical action of the rays of light, and this explanation was for a time generally received.

But it soon appeared that if the heat-giving rays were absorbed by passing the beam of light through a solution of alum, the motion of the vanes was arrested, or at least very greatly retarded, while, on the other hand, when the light-giving rays were absorbed by a solution of iodine, a medium which although opaque to light is pervious to heat, the motion was maintained with nearly its full activity. Further, it was soon found that the motion could be produced by any cause which determined a slight difference of temperature between the blackened faces of the vanes and the surface of the inclosing glass bulb, and that while the motion was in one direction when the vanes were warmer than the glass, the motion was in the opposite direction when these conditions were reversed; and further, that, other things being equal, the greater the difference of temperature the more rapid was the motion. Hence, after a long series of experiments, it was concluded that the motion of the radiometer was an effect of a difference of temperature between its parts, or, in other words, that the radiometer is, like the steam engine, simply an example of a heat engine. Thus Professor Crookes was able to discover the proximate cause of the remarkable phenomenon he had observed, and having done this he had learned all that could be known with certainty in regard to it.

This example is a fair illustration of the method of science, and scientific ability is shown in the power of so directing observations or making experiments as to establish the true causal relations in any case. No one supposes, however, that having

established this relation we have discovered an "efficient cause.'' We have found out which are essential and which are accidental antecedents, and established possibly what we may call the law of succession, but nothing more. There may be a whole chain of such antecedents—we frequently know that there is—and, behind all, the true cause as much concealed as ever. The mind, moreover, refuses to stop at this point, or to rest satisfied with such a result. It at once begins to theorize. Why is it that a difference of temperature causes the steam engine to work, or the radiometer wheel of our illustration to turn? We cannot answer the question with certainty, but this is our theory:

"Heat is a mode of motion,'' and its phenomena are the effects of the motion of molecules of matter. Molecules, although of an order of magnitude far removed from our limits of perception, are as real masses as cannon-balls or bullets, and their motions as rapid and as real, and although the moving power of single molecules is as nothing, yet collectively their motion is capable of producing effects compared with which the mightiest bombardment is insignificant.

Now, although the air has been exhausted to a very high degree from the bulb of the radiometer, the interior still contains a vast number of molecules of gas, which, unless our calculations are greatly at fault, must be counted by the million million for every cubic inch of capacity. Moreover, at the degree of exhaustion reached in the bulb, the amplitude of the motion of the little masses becomes

so considerable that they bound to and fro between the vanes of the wheel and the surface of the inclosing glass, and according to our theory the motion of the wheel is the result of this reaction. This theory is supported by the fact that if we exhaust the air from the bulb of the instrument beyond a certain limit we arrest the motion. It is also true, however, that the motion stops if the amount of air be only slightly increased, for the evident reason that there is then less free room for the motion of the separate molecules, and they do not move far enough to cause any reaction between the wheel and the surrounding walls.

To those who have become familiar with the conception of molecular magnitudes this theory is very plausible. If you ask whether the theory is true, I can only answer that we may perhaps regard it as relatively true, seeing that it has explained a great many facts and suggested lines of investigation which have led to new discoveries. But it certainly is not absolutely true in the sense of expressing the whole truth. These molecules are creatures of the scientific imagination, and may be mere fictions, but the value of the theory lies in its power of directing research, and, as I have before said, I believe that all theories which have this power are partial truths; but no one can regard them as perfect representations of the realities of nature. Men who, in the first flush of discovery, feel the guiding power of a theory, are wont to associate with it an undue reality, but they soon learn their error by experience.

What we have just said is true of all the great theories of science, but it is especially true of that

form of the atomic theory which is now the chief guide in chemical investigation.

The chemist is acquainted with numerous groups of substances which we call isomeric compounds, and two substances are said to be isomeric when they not only consist of the same elements united in the same proportions, but also have the same density in the state of vapor, so that according to the molecular theory their molecules must have the same weight. For example, the two substances called butyric acid and acetic ether are isomeric bodies. The vapor density, as we call it, of both substances is forty-four times that of hydrogen, and they both consist of carbon, hydrogen, and oxygen united in precisely the same proportions, yet the two substances differ from each other in their properties most widely. Butyric acid is an oily liquid, with whose offensive smell we are only too familiar, since it is the noticeable ingredient of rancid butter. It does not boil until the temperature reaches 302° on our Fahrenheit scale, and does not readily inflame. Acetic ether, on the other hand, is a limpid liquid with a pleasant fruity smell, highly volatile, boiling at 165°, and inflaming with the greatest ease. What, now, is the cause of this most marked difference? The phenomenon demands an explanation, and invites theorizing, and the theory we have formed is as follows:

The molecules of all compound substances are themselves groups of elementary atoms, and the molecules of two isomeric compounds, like butyric acid and acetic ether, although consisting of the

same number of the same atoms, and therefore having the same weight, differ from each other in that these atoms are differently grouped. Nay, we go much further than this, for we have formed a scheme of the manner in which the atoms are grouped in each case, thus:

In these diagrams the capitals stand for atoms of the elementary substances of whose names they are the initial letters, and it is obvious that not only two isomeric compounds, but a great number, might be formed by differently grouping these same atoms; although the number of possible combinations is greatly diminished by conditions imposed by well-known chemical principles, which it would be out of place to discuss in this connection. Our diagrams, moreover, indicate a great deal more than the general theory, that the differences between isomeric compounds depend on differences in the grouping of the same atoms; for the exact grouping in each case is based on the known chemical relations of the substances. There is a reason for the position of each letter in these structural symbols, as they are called.

We have here given one of the simplest illustrations

of the theory of molecular structure which is the basis of modern theoretical chemistry. It is the chief object of chemical investigation at the present time to discover the molecular structure of chemical compounds, and there is frequently as earnest discussion about the position of a letter in one of these structural symbols as there is in natural history about the origin of species, and if there were a point of theological doctrine involved in the controversy, the discussion would be doubtless as personal and as bitter. Yet no one in his sober senses dreams that these diagrams represent realities. If there are such things as atoms and molecules, all analogy would lead us to believe that the parts must sustain relations to the whole similar to those of the members of the solar system, and like the sun and planets must have their orbits and periods of revolution. Still our diagrams give us correct representations of the relations between a large number of facts which they serve to group together, and this theory of molecular structure has been one of the most successful aids in directing investigation which science has known. It has led to the discovery of a process of manufacturing artificially the valuable madder dye called alizarine—a discovery which has revolutionized one of the most important industries of the world—and this is but one of hundreds of new discoveries with which it has enriched the arts of life or extended chemical science. In a word, it has been a most valuable "working theory,'' and no other theory except the law of gravitation can be compared with it in efficiency. Hence, absurd as our conceptions of molecular structure certainly would be, if we supposed them realized in the crude forms which our diagrams suggest, yet we cannot but regard these representations as the rude symbols of a real truth which in its essence transcends the limits of our present knowledge. That which is true of the molecular theory of modern chemistry is equally true of the two great conceptions which are always cited as examples of the most perfect theories of physical science. The undulatory theory of light involves assumptions in regard to the alleged ether which are simply preposterous, and even the law of gravitation takes for granted action at a distance which is opposed to all experience and to all philosophical thought. Still, to abandon these theories, because we cannot accept their postulates, would be as foolish as to throw away our compass because we cannot agree about the theory of magnetism.

Now we are told by the naturalists that Darwinism is just such another working theory, and they are, with reason, impatient when blamed for following its guidance because it cannot be reconciled with certain cherished theological dogmas. And, assuming that the dogmas are right, you might as reasonably find fault with the mariner for using the magnetic needle, because it does not always point to the true north. Like the needle, our theory points out the path of discovery, and, although the way may at times seem to lead backward, and men, like Columbus, may become frightened at the evident aberrations of their guide,

yet if, with the brave navigator, they persevere, the trusted guide will certainly conduct them to the true goal in the end, unless truth is a fiction, and the whole issue of the human faculties a lie. Nevertheless there may be as blind dogmatism in science as has ever existed in theology, and it is dogmatism when men claim as absolute certainty what is at most merely relative truth, and treat with superciliousness all who do not accept their authority as final. Certainly, let us be true to our convictions, and hold fast to our theories as the earthen vessels which contain a precious treasure, but let us remember,

Such, then, being the credentials, and such the methods of science, let us turn for a few moments to the credentials and methods of theology, and ask, in all humility, whether the conditions do not impose limits on human thought in this direction as well as in the other. In theology, as in science, there are certain facts which, although chiefly facts of consciousness, and not facts of observation, are no less facts than the phenomena of nature. Prominent among these facts are the moral judgments, the affections, and the aspirations of the soul, which, explain them as you will, are the most important factors of human life—the most potent agents in human society. Corresponding to these affections and aspirations are certain religious beliefs which we

have inherited from our ancestors, and which have come down to us with the authority of eighteen centuries of human experience. During that period these beliefs have satisfied the highest aspirations of humanity, and have led many of the purest and noblest men whom the world has known to encounter peril, endure cruel torments, and suffer ignominious death, in attestation of their faith. The origin of this faith was a life which, as portrayed to us in the Gospels, has aroused in every generation of men from its birth the noblest enthusiasm and the warmest love; a life which has appeared more and more transcendent as civilization has advanced, and which has been the one power that has redeemed man from his selfishness, and enthroned charity among the chief rulers of the earth. Such, then, are the credentials of Christianity—a real want, an adequate satisfaction. Learned men have endeavored to formulate the principles of religious beliefs, and hence have come systems of theology, in regard to which we might repeat very nearly the same statements that we have already made in regard to the theories of science. These systems have certainly satisfied the great mass of mankind, and have done a good work in defining and preserving the faith; but they are all earthen vessels, and, like the working theories of science,

Let us remember that as Christianity was revealed in a life, it ever abides as a life in the heart of the believer, and only those who have lived that life can

know how real it is. To all such, however, it is the most real thing in the world, and the theological forms in which it finds expression have the same reason for their being as the forms of science, and are held the more sacred as the truths symbolized are the more dearly cherished. Moreover, it is a fact most worthy of notice, that Christianity is almost co-extensive with civilization, or, as Coleridge has expressed it, "Christendom is the best evidence of Christianity.''

While, however, the "internal evidences'' of Christianity, which we may not inappropriately call the credentials of theology, are so similar to the credentials of physical science, the methods of theology are, for the most part, utterly unlike the scientific methods we have been discussing. In the first place, the very data on which the whole body of Christian theology rests cannot be verified by observation. The phenomena of nature are ever with us, and can be closely scrutinized at each repetition; but the events from which Christianity arose occurred once for all more than eighteen centuries ago; and if we take the summary of those events given in the primitive creeds as representing what is common to the beliefs of the great body of Christians, and as authenticated by the experience of the Church, and present this as the subject-matter of theology, we must claim belief in these data on grounds of faith, and not on scientific evidence. We accept these supernatural facts not solely on account of the historical evidence adduced in their support, but largely in deference to a certain "witness in our hearts,''

which disposes us to accept them. To men who know nothing by experience of this inner witness, beliefs thus accredited may appear foolishness, and this is too often the case with those who, occupied exclusively with the study of nature, are not accustomed to accept any statement as true which cannot be verified by experiment or observation, and who regard the order of nature as the one standard from which there is no appeal. On the other hand, those who have felt its power are persuaded that the witness in themselves is the voice of God speaking to the heart.

The basis thus established, Christian theology is built up on the textual criticism, interpretation and collation of a written record, a form of study which involves historical research, critical analysis, philological investigation, and metaphysical inquiries. Thus a great mass of learning has been accumulated to which various minds will attach very different degrees of value, according as they are more or less familiar with the methods employed. These, however, are so unlike the methods of physical science that it would be the height of presumption for a physicist to pass any judgment on the results. But certainly no one can claim for them a greater value than for the best working theories of science.

Seeing, then, that the limits of positive knowledge are so well defined, both in natural science and in theology, we certainly need not be troubled by the apparent conflict between the two modes of thought, so long as the controversy is confined to the debatable ground which has not been fully explored by

either party. Within the well-explored limits there never has been and never can be any actual disagreement, and something has been gained if we have been able to make evident that such limits exist, however imperfectly we have succeeded in defining them. The bearing of such considerations is obvious, and they lead to important practical conclusions. In the first place, they should teach men of science to honor and reverence the forms of religion. They are the types and symbols of a truth higher than any which Science can teach. Let Science vindicate her own methods, and allow no interference within her proper sphere; but unless she learn that there are other sources of knowledge than material nature, and other channels of truth than the intellect, her own philosophy will be confounded, and her light will go out in darkness. On the other hand, it is equally the duty of the ministers of religion to honor and respect the methods of science. They have been ordained by God, and through these processes of thought He is constantly revealing eternal truths to the mind of man. Insist as strongly as you please that Science should be allowed no voice in matters of faith. Scrutinize as closely as you can every step of her logic; but so long as she keeps within her legitimate province, allow her the largest liberty, and extend to her the most generous encouragement. Watch sharply her results, and expose her fallacies wherever you can find them; but if your judgment condemns, let it be on scientific grounds, and not by any arbitrary standard of your own. Above all, even if you think your most cherished SCIENTIFIC AND RELIGIOUS THOUGHT. opinions are in danger, do not withdraw your fellowship hastily, or be betrayed into undiscriminating censure. Science is paramount within her own province. Do everything in your power to consecrate her aims and sanctify her spirit, but do not attempt to control her investigations or restrict her free thought. Await God's time. If Science be wrong, she will sooner or later correct her error. If she be right, the "Lord of Hosts'' is on her side, and you will find yourself "fighting against God.''

Again, a proper appreciation of the necessary limits of scientific and religious thought should lead all men to reverence the "Word of God'' as it has been handed down to us through history. In view of the facts already intimated, I cannot look with favor on any attempts at Biblical criticism which aim to square the language of Scripture with the results of modern science. They leave a most unpleasant impression on my mind. Seeing the large element of human ignorance, incapacity, and frailty, which the history of both so conspicuously exhibit, I cannot stake my faith either on the "Infallibility of the Church'' or the "Infallibility of the Book.'' But I do believe that the Bible is inspired with spiritual truth, from the grand epic of creation, with which it opens, to the glorious vision of the New Jerusalem at its close. I feel that its very words are consecrated by the associations of the ages, and if you are so ready to accommodate any part of them to the shifting phases of science, what certainty can I have in regard to the whole? The Bible is no text-book of science, and the attempt to impose an equivocal or

mysterious meaning on its simple and obvious statements degrades and dishonors it in the minds of devout men. The methods by which its truths are expressed may be at times rough and uncouth; but they are the methods chosen by God, consecrated by the blood of martyrs, and hallowed by the tears of saints; and they have therefore a power which no other language could have. Break not the mould in which the forms of faith have been cast, before they have become firm and hard, lest the precious metal should itself be lost. Finally, leave religion and science to their respective methods, and encourage both alike in their noble callings. Let science, by cultivating man's intellect, elevate him to nobler and more spiritual views of God's wisdom and power. Let religion, by purifying man's heart, open to him clearer visions of God's purity and love; and, at last, when this material shall have vanished, and when the waters of controversy shall have ceased to roll, the heart and the intellect, made one and washed clean in the blood of the Lamb, shall unite in the song of the angels around the throne, saying, "Blessing, and glory, and wisdom, and thanksgiving, and honor, and power, and might, be unto our God for ever and ever.''

But while insisting upon the necessary limitations of scientific and religious thought, I must not forget that all such considerations bear with peculiar force upon the questions I have discussed in this book. Therefore, although I have most carefully endeavored to guard my argument from the slighestexaggeration, I should not feel justified in concluding without distinctly stating how far, in my opinion,

the argument of natural theology may be safely carried, and to what extent unaided science may be said really to prove the fundamental truths of Christianity.

In the first place, then, I believe that the existence of an intelligent Author of nature, infinite in wisdom and absolute in power, may be proved from the phenomena of the material world with as much certainty as can be any theory of science. In the second place, I am of opinion that the facts of nature are throughout consistent with the belief that the Author of nature is a personal being, and the one only and true God revealed to us in the Bible. Lastly, I think that the relations of the human mind to the material world, viewed in the light of modern science, give us strong reason to believe, on scientific grounds alone, that the universe is still sustained in all its parts by the same omnipotent and omniscient Will which first called it into being.

To the extent I have indicated, I regard the argument of natural theology as logically valid. Moreover, I am persuaded that science confirms and illustrates the priceless truth which Christ came on earth to reveal; but I do not believe that the unaided intellect of man could ever have been assured of even the least of these truths independently of revelation. And, as I stated in my introductory chapter, I feel that the best service which science can render to religion is in the way of confirmation and illustration, rather than in that of absolute proof, and for this reason I have preferred to discuss my subject chiefly from that point of view.

The subject, as prescribed by the founder of the "Graham Lectures,''[*] was "The power, wisdom, and goodness of God as manifested in His works,'' and to this form of statement, if interpreted in the sense just indicated, I have nothing to object. I do not believe, however, in any sense, that nature proves the goodness of God. When the heart has been once touched by the love of God, as manifested on Calvary, the tokens of God's goodness are visible everywhere; but before this, nature, to one who has seen its terrors and felt its power, looks dark indeed; and the pretence that the material universe, unexplained by revelation, manifests a God of unmixed beneficence, not only does harm to religion, but places science in a false light. The most superficial observation shows that this is not true. Lightning and tempest, plague, pestilence, and famine, with all their awful accompaniments, are no less facts of nature than the golden sunset, the summer's breeze, and the ripening harvest; and who does not "know that the whole creation groaneth and travaileth in pain together until now''? It does not change the terrible fact to say that nature has been disordered by man's sin; for sin is itself the greatest evil in the world, and its ghastly forms meet us at every step. So prominent, indeed, is the evil in nature, and so insidiously and mysteriously does it pervade the whole system, that an argument to prove the malignity of God could be made to appear quite as plausible as the arguments which are frequently

urged to prove His pure beneficence; and when the unaided human intellect has attempted to make to itself a beneficent God, it has usually made a malignant deity as well. Nature seems to manifest God's wrath no less than His love, and it is a false and sickly philosophy which attempts to keep the awful fact out of sight. God is our Father; but nature could not teach it, and "the Word was made flesh'' to declare it. God is love; but nature could not prove it, and the Lamb was "slain from the foundation of the world'' to attest it. Nature is but a part of God's system, and not until the natural and the supernatural shall be made one will the mystery of evil be solved.