Popular Science Monthly/Volume 18/March 1881/Mind as a Measure of Nature



IT has been said that every man is born a Platonist or an Aristotelian. This is an epigrammatic way of stating the fact that the general tendency in the pursuit of knowledge is to approach it from one or the other of two different standpoints, variously called the subjective and the objective; the mental and the material; the theological, or metaphysical, and the scientific. While this tendency is pretty clearly marked, yet the saying has the fault common to most apothegms, of sacrificing correctness to brevity—of overlooking the delicate gradations in Nature's continuity in its attempt to express her more salient diversities in a pithy utterance. This is the imperfection of all classifications. They necessarily separate what is continuous. It is only as they refer to genetic relationships that they most nearly correspond with nature, and this they can do in only a few of the natural sciences. For the most part, the act of classifying is the application of a mental scale to incommensurable quantities. The very impossibility of grouping phenomena into natural kinds renders an artificial classification necessary. Before science can advance a single step, the innumerable phenomena of nature must be reduced into classes. If not susceptible of natural arrangement, they must be arranged artificially; and, as long as the artificial character of the classification is comprehended, no harm is done; but when men, with but little knowledge of the objects dealt with, proceed to construct a procrustean bed to which they expect Nature to conform, and then, from this tortured witness, attempt to extort unwilling testimony, they may expect Science to enter a demurrer. As this method, however, has the merit of simplicity, as might be expected, it has long been the favorite with a certain class of philosophers.

Turning back to the early progress of human speculation, especially so far as it has reference to material objects, we see that all the first attempts at physical knowledge consisted, principally, of deductions from mental notions, with but little, if any, reference to phenomena. Beginning with the theories of the universe propounded by the Greek philosophers, we see that whatsoever progress was made in scientific acquisition was only in proportion to the occasional reactions from the excessive subjectivity that mostly prevailed. This reaction found expression in men like Archimedes and Hipparchus, and under their influence science had apparently attained a foothold when the intolerance of a religious supremacy, which held sway over Europe during the dark ages, banished it from Christendom, and thus became debited to humanity for a thousand years of stagnation.

Not until the time of Copernicus was there any new impetus to research. The appeal to objective facts was, then, although in a small degree, made the avowed basis of scientific speculation. Then began the progress of knowledge which, with constantly accelerating speed, has continued to our times, and which, we trust, may not again be slackened.

The experience of our predecessors teaches us a lesson that we ought not soon to forget. In the practical affairs of life, experience is considered the best guide. The man who learns nothing from its teachings does not succeed. It is no less important in the life of the race. If we learn nothing from others' failures, we can expect to learn nothing from their successes.

The attempts to construct the universe a priori are analogous to the attempts to construct a perpetual motion. As long as there was no direct reference to experience, it appeared by no means improbable that a machine might be so constructed that, when once set in motion, it would never stop. Any one, who has had any experience with a class in mechanics, knows how crude are the notions they possess with reference to the very elements of physics. It is safe to assert that today not one person in ten possesses a thorough certainty of belief in the validity of the third law of motion, namely, that action and reaction are always equal; or, to put it in more familiar language, that, when a horse pulls a wagon, the wagon pulls the horse equally hard. It is not until correct mechanical notions become wrought into the very warp and woof of one's mental fabric that his deductions from them may fairly be presumed to be correct. Witness the absurd notions current only a very few years ago as to the possibility of constructing a "motor" that should, in some mysterious way, evolve force enough from a pint of water to propel a train of cars from Philadelphia to New York! Mechanics went on inventing "perpetual motions," but, however plausible they looked, somehow or other they wouldn't work. Do away with friction to the greatest possible extent; overcome one obstacle here and another there; increase the time the machine would run indefinitely—still, to a state of equilibrium would it come at last. From these empirical observations mechanics learned, what philosophers might have learned years ago, that experience affords the only sure test of the validity of our notions.

After numberless failures had taught the empirical lesson that attempts to construct a perpetual motion were fruitless, the gradual development of the law of the conservation of energy showed the reason for it. In like manner, we have sufficient reason, judging merely from the observation of previous speculation, to warrant us in abstaining from attempts to deduce a knowledge of material nature from mental concepts. Add to this fact that other, that all knowledge has its basis in experience, and we supplement our empirical conclusion by a deduction from a fundamental law of nature, and show their entire congruence.

Early physical speculation, with hardly an exception, proceeds on the assumption that knowledge is derived primarily from the mind—thus completely inverting the true order. Would some of those persons who in our day attribute so much power to the unaided mind carefully peruse a history of science in the early centuries of our era and the centuries immediately preceding it, we think they would become convinced that purely mental speculation can never lead to any exact knowledge, but must, on the contrary, invariably be a source of obscurity and error.

With but two or three exceptions, the most eminent men of the early and middle ages, except as in a few instances they recorded interesting facts, contributed absolutely nothing to scientific progress. The principal cause of the difference in the civilization of our times and those of the ancients is the progress of exact knowledge. What would the most mystical of metaphysicians of to-day say to Socrates's assertion that those things are called like which partake of the quality of likeness? or to Aristotle's argument against a void in nature, that a void is a negation, and in a negation there could be no differences, and where there were no differences there could be no up or down, consequently bodies could not move up or down in a void, but it is the nature of bodies to move up and down, therefore there is no void? or to his argument in support of circular motion, that it is the best, therefore the most natural? The mental ability of the "Father of Logic" is unquestioned. He follows logical methods closely enough. What, then, is there unscientific in his reasoning? Simply that he allows abstract terms and mental notions to pass current for facts—thus using an irredeemable currency as though it possessed intrinsic value.

The modern astronomer can not but wonder at the daring speculations of the Pythagoreans, that, as ten was a perfect number, there must be ten heavenly bodies, notwithstanding nine only were then known. Before such vaticinations the predictions of a Leverrier sink into insignificance.

We find the whole history of science, up to the time of Copernicus, a history of the conflict of facts with preëstablished notions. The problem of astronomers was to reconcile the apparent motions of the heavenly bodies with their assumed circular motions. Thus, when it was found that the motions of the planets were not uniformly circular, it was naïvely suggested that an uncertain motion could not be tolerated even in a man, much less in a planet, hence the theory of epicycles, or wheels revolving on the rims of other wheels, was introduced. Notwithstanding its questionable parentage, and the fundamental error on which it is based, this theory, as established by Hipparchus and extended by Ptolemy, is about the only example of a scientific working hypothesis previous to the fourteenth century.

Physics, equally with astronomy, suffered from the anti-scientific method. The study of nature was not only neglected, but discountenanced by the Church. A priori arguments were urged against the existence of antipodes, and, but a short time before they were visited by Columbus, a belief in their existence was denounced as heretical. The direction of knowledge during the middle ages was retrogressive rather than progressive. Scholastic physics was based upon the assumption that analysis of mental concepts would give all requisite knowledge. Why wonder at the result? Weight being the cause of bodies falling, it was assumed that heavy bodies would fall faster than light ones. Personal qualities being attributed to inanimate objects, there were supposed to be different degrees of perfection in the metals, and thus arose alchemy, whose aim it was to extract gold—the most perfect metal—from the baser metals.

The contagion of scholasticism became epidemic, even infecting able men, and establishing its parasitic growth upon sound theories. Astronomy gave birth to astrology, to whose weird influence even a Bacon could succumb. One of the arguments brought forward in support of the Copernican theory was that it placed the noble element, fire, in the center of the universe, thus satisfying the tendency toward mythical explanations. So prevalent was this method of considering nature, that Kepler himself entered into complex speculations concerning the relations of music to the motions and distances of the planets; and even Galileo was led into an erroneous theory of motion in consequence of assuming that it must be the simplest possible. In support of true hypotheses, as well as false, metaphysical reasons were given. The fact that from them anything wished for can be proved, constitutes the great danger in their use. From the immutable laws of God Descartes deduced the first law of motion, while, from the same source, the Church had previously demonstrated the immovability of the earth. Borelli conjectured that the motions of the planets were controlled by two forces—one the centrifugal force, and the other the appetite a planet must have for the body about which it revolves. Suction was explained by the famous principle that Nature abhors a vacuum, and, had it not been discovered that the abhorrence ceased at certain fixed limits, this explanation would probably have done service even to our day, for that class of philosophers for whom the kindred principle of vitality is a sufficient explanation of the various phenomena of life.

The few examples that have been cited give a fair sample of the science of the middle ages. During that long period the men imbued with a spirit of scientific research could be counted on one's fingers. It is a striking fact in the history of man that, out of the many centuries he has inhabited the earth, so few have been productive of any useful knowledge. Throw away everything that had been done previous to the fifteenth century, and the loss would have been by no means irreparable. Add to the productive period twenty centuries, and we embrace the whole. Think of the average life of fourscore men spanning the totality of human knowledge! Truly, science is in its infancy. What were the speculations of the men who existed a few centuries prior to our era, we have no record. After the dim poetical aspirations which compose the earliest known philosophy, there emerges a pseudo-scientific natural philosophy, which, disdaining the shackles that a constant reference to the phenomena of nature would impose upon its flights, attempts at once to solve the problem of the universe. Like the famous German, who, instead of going to see the camel he was to describe, pursued the easier and more fascinating method of evolving him from his own inner consciousness, the Greek philosopher evolved the universe from his.

A modern writer, who certainly can not be accused of want of sympathy with a deductive philosophy, in comparing the relative merits of the a priori and a posteriori methods, observes that, although the latter may in general come somewhat nearer the facts of nature, yet, as it can never embrace all the phenomena in its inductions, it can never arrive at the whole truth; while the a priori method, if it chance to hit upon the right formula, has the whole universe, so to speak, at its fingers' ends. While we may readily admit the sublimity of the attempt to reach out and grasp the hidden springs of nature, stubborn facts constrain us to assert its impracticability. The diffuse light of mental theory must be concentrated to a small focus in order to produce any visible effect.

Knowledge is the concomitant of the progressive limitation of our powers. As long as man assumes that he contains within himself the premises of knowledge, so long will it elude his grasp. Not until experience has compelled him to doubt the validity of his mental concepts when applied to nature, and has forced him to have recourse to facts only, has man taken the first steps in the paths of science.

That one learns the boundlessness of knowledge only in proportion to his own acquirements is a saying famous only for its triteness. What are certainties to the ignorant are uncertainties to the intelligent. What are dogmas to the blind followers of a fanatical priesthood are for ever insoluble problems to the man of science. The ignorant savage—who can not count beyond five; who has no abstract names in his vocabulary; who knows nothing of the use of pronouns; who uses words denoting the commonest things and most usual actions only—possesses knowledge differing so widely in degree from ours as almost to constitute a difference of kind. For him nature has no problems. The universe, of which he knows so little, is but in a slight degree a mystery. Wonder—the first sense of philosophy, as it has been so aptly termed by Aristotle—exists in his mind only as superstition. We are too apt to think that primitive or savage man must be appalled by the presence of nature, forgetting that his universe is limited to his own unaided senses. We forget that, in our own life, philosophic problems present themselves only as we approach maturity, and, generally, then only if our studies have led us in their direction. To see how little the "natural man" comprehends these problems, observe the answers he gives to those questions in which it is customary to assume that the wayfaring man, though a fool, does not err.

Man is naturally a "realist." Things are to him what they seem. Mind is his sole measure of nature. He looks nowhere else for an interpreter, and knows no other source of knowledge. He interprets natural phenomena by mental qualities, and this prepossession colors all his theories. The history of science is the history of the gradual demolition of this tendency. The mental distance from a savage that personifies the tree, the forest, and the stream, to a Kepler that conceives it necessary to place a guiding spirit in the planets to keep them in their courses, is, of course, immense, and each is indicative of the thought of his time; but we now know that each was in error in positing some utterly unknowable substance to explain the unknown elements.

The person who to-day expects to make the phenomena of life more clear by attributing them to the effects of "vitality" is making a dangerous mental concept do duty in place of exact knowledge, however limited. The frequency with which this attempt occurs, even among men eminent in science, shows that continued protests are needed. However little real knowledge we may possess upon a given subject, our only way to get more is to approach it humbly and laboriously as a question that can be solved only by constant reference to the facts that appertain to it. All experience teaches that an analysis of mental notions has never yet yielded a particle of natural knowledge, but, on the contrary, has often proved a barrier to the acceptance of true theories. We can not expect to be more fortunate ourselves. The principal objection to the development theory has been on the ground of its opposition to preconceived notions as to the reality of the mental conception "species," and to certain beliefs in vogue concerning the genesis of man, rather than to its assumed opposition to the facts of nature. Every theory has to run the gantlet of this extra-scientific criticism, and only when it is shown to have no possible bearing upon preconceived notions is it allowed to be settled simply upon its merits and by scientific methods.

Instead of reverting to the experience of our ancestors and showing the futility of all previous attempts to extract light from mental sunbeams, we might have deduced the same conclusion from the known laws of thought. No psychological theory has greater probability than that which bases the units of knowledge in experience. Since the time of Locke and Hume, the drift of speculation has been steadily in the direction of a more or less modified empiricism. The more far-sighted of the intuitionists cast aside everything they thought could embarrass their theory, and were content to allow that the matter of thought was based upon experience, while reserving as the province of intuition the mental forms by which knowledge was possible. The theory of evolution explains this intuitional residue by extending the experience of the individual to the experience of the race, and showing that what may be intuitive (in every sense, except the supernatural, in which that word was formerly used) to the individual is so in consequence of inherited tendencies corresponding to the aggregate experience of his ancestors.

But we do not need to urge mental theories, however probable, to show that our knowledge of the universe is dependent upon our surroundings. A little difference in the physical condition of the earth would have sufficed to have utterly changed our conception of nature. Make the not very inconceivable supposition that our earth bore the same relation to the sun that the moon does to the earth—rotating once on its own axis to each revolution about the sun, and remaining nearly perpendicular to the ecliptic, thus always presenting the same side to the sun's rays—how would it have affected our knowledge of nature? To what modest proportions would not only science have shrunk, but also our mental or intuitive conceptions of nature!

Astronomy has been well called the mother of the sciences. The apparent motions of the sun, moon, and stars through the heavens, and the motions of the planets among the stars, contributed to produce a wonder in the minds of the beholders that might well cause astronomy to be the first studied of the sciences. In our hypothetical world, the sun would appear stationary in the heavens, more or less removed from the zenith according to the position of the observer. On the center of the earth's surface would be a torrid zone upon which the vertical rays of the sun would pour down with unremitting severity, with no alternation of day and night to temper its influence. Outside of this would be a temperate zone well adapted, it might be, to the existence of human beings, but having no change of seasons, only one monotonous summer day, varying in temperature according to location. The temperate zone would gradually give place to a frigid zone, and, as the day darkened into an eternal night, this would be succeeded by an impenetrable region in which the degree of cold would vastly exceed anything we have on earth at present. Thus man, confined to somewhat less than half the globe, would see nothing of the moon or stars, and the earth, with the sun shining on it, would be the only bodies visible. There would be no natural divisions of time into days, weeks, months, or years. Mathematicians might calculate the hemispherical form of the earth, but the elephant and the tortoise would be more than ever necessary to support it. There would be no science of astronomy, no knowledge of the law of gravitation, none of physics, so far as it was dependent upon astronomy. The sciences so act and react on one another that it is difficult to say just how far the absence of one would affect the others, but we know it would greatly. Such suppositions as we have made may be more or less fully realized in other worlds, and we can thus see that their science may differ very widely from ours and still be no less correct. Science is everywhere relative to the facts with which it has to deal. The difficulty of conceiving physical and spatial relations different from those we are familiar with does not prove them non-existent; nor does the ease of such conceptions prove their existence.

Helmholtz has very ably shown that our geometrical axioms have a truth relative only to the space they are applied to. He supposes beings, of the same mental capacity as ourselves, but of two dimensions only, to inhabit a plane surface. They would possess a plane geometry like ours, but would have no solid geometry whatsoever. Thickness would be as inconceivable to them as a fourth dimension in space is to us. Transplant these beings to the surface of a sphere, and their planimetry would change to a spherical geometry. Defining a straight line as the shortest distance between two points, all their straight lines would be arcs of great circles, and every straight line, when sufficiently extended, would return to itself. Between two points, half the circumference of a great circle apart, an infinite number of straight lines, of equal length, could be drawn; and, as two points would always cut the great circle on which they were situated into two arcs of unequal length, there would always be, besides the shortest straight line connecting the points, a longer straight line (i. e., a line made up of shorter lines, each of which is the shortest distance between its extremities) also connecting them. There could be no parallel straight lines and no similar triangles. The sum of the angles of a triangle would always be more than two right angles, and the amount of the excess would depend upon the length of the sides.

Helmholtz again supposes these beings of two dimensions to be placed upon (what has been called by Beltrami) a pseudo-spherical surface—a surface shaped somewhat like the sides of an hour-glass. Here our axiom of parallels does not hold good. Through a given point, a whole pencil of straight lines may be drawn, none of which shall cut a given line, though infinitely produced, and limited, at the two extremes, by lines that cut the given line at infinite distances in the opposite directions. Helmholtz makes other suppositions which it is unnecessary to follow, as we have already gone far enough to show that even the fundamental axioms of geometry are quite as dependent upon the conditions under which they are used as upon any intuitive necessity we may think belongs to them.

It is well known that but a portion of the phenomena of nature are cognizable by us—how small a portion it is not known. A person born blind has no conception of color; one born deaf, none of sound. The disease of color-blindness affords a good illustration of the limitation of knowledge in consequence of the limitation of sensibility in certain directions. One affected with this disease, while able to see outlines with perfect distinctness, as well as some of the colors, is insensible to others; and this insensibility does not affect alone the ability to discriminate between colors nearly alike, but also those that are apparently widely divergent. It is related of Dalton, from whom color-blindness takes its name of daltonism, that some wag exchanged the robe of sober drab which this demure Quaker was in the habit of wearing, for one of scarlet, and that, unconscious of the difference, he went forth, much to the amusement of the bystanders. Undoubtedly many accidents are due to the inability to discriminate between different colored signals. This subject is just beginning to receive the attention its importance demands, and it is found much more prevalent than was even suspected. Like short-sightedness and, probably, all maladies due to the absence or the imperfection of any of the senses, the subject of it is unconscious of its existence until something particular calls it to his attention. To a greater or less extent we may all be said to be color-blind. Only a part of the rays that are known to proceed from the sun are visible to any of us. Vision is produced only by waves of a certain definite length. The rays of longer wave-length than the red are known to us by their heat producing effects only; those of shorter wave-length than the violet, by their chemical effects. It is not improbable that, at some future time, a race may exist capable of seeing rays invisible to us—just as we perceive many invisible to some of the lower animals. In the development of sight there must, at first, have been simply a power to distinguish light from darkness; then, the ability to distinguish outlines; and, finally, the sensibility to color. Until this sensibility was developed, objects would present merely an alternation of light and shade, similar to the view we get in a stereoscopic picture.

Sounds inaudible to us are heard by insects, and odors that we can not distinguish are smelled by animals. So we might go through the whole category of sensations and resulting ideas, and show their variation under different conditions; and yet, whatever may be the theory of knowledge we espouse, it is from these sensations and ideas that we form our conception of nature. How different our mental conceptions would be if our senses were indefinitely magnified, we can but guess. A drop of water, it has been estimated by Sir William Thomson, if magnified to the size of the earth, would be seen to consist of molecules of the size of cricket-balls; and these molecules are themselves of great complexity. The internal motions of a drop of blood are more complex than the motions of the solar system. Place it under a microscope of high power, and the corpuscles are seen hurrying hither and thither as if (to use a quite appropriate simile) their life depended upon it. Repeat the process, and new complexities are seen. Increasing the power of our senses artificially by the use of instruments has given us a vastly enlarged conception of nature; but every increase in knowledge shows us more clearly the limitation of the knowledge we possess. Truly, there are more things in heaven and earth than are dreamed of in our philosophy.

Science is continually teaching us the lesson that the universe is larger and more complex than formerly supposed. Old geographers, guided by an egoistic impulse, placed their own country in the center of the known earth; early astronomers placed the earth in the center of the universe. Later, that position of honor was given to the sun. The influence of mental concepts and the desire for system, even where none is discernible, induce some astronomers to locate the center of the sidereal system somewhere in the region of the Pleiades; but, even should this attempt prove successful, we should be no nearer the discovery of the center of the universe. Place a grain of sand thirty feet from an orange, and you have, approximately, the relative distances and dimensions of the earth and sun. Nearly one thousand feet beyond would be the planet Neptune—the outermost planet of our system—while more than twelve hundred miles would have to be traversed before arriving at the nearest fixed star. Even on this miniature scale, our fractions of inches grow to miles, and man finds himself immeasurably dwarfed, even in the presence of the known. He sees whole systems drifting through space. In a much broader sense than Emerson meant, we are like ships upon an unknown ocean, knowing neither whence we came nor whither we are bound.

It is fascinating, no doubt, to construct theories of universe-reaching proportions. It has been truly said that—

". . . Our nimble souls

Can spin an insubstantial universe
Suiting our mood, and call it possible,
Sooner than see one grain with eye exact,

And give strict record of it."

Perhaps such employments are elevating. Such, at least, is the claim of those who affect to despise what they superciliously term the bread-and-butter sciences. Admit all they claim; still, their conceptions of nature are worthless until verified.

In this brief sketch of past thought, we have seen that it was only as man has been content to acquire knowledge patiently, slowly, and arduously, by what are now known as scientific methods, that his knowledge has been of any practical value. Theorize as widely as he may, constant verification is the only criterion of a theory's validity. Fact must be the point of departure and the point of return of all theories. Mental notions can aid us only as they are reflections of nature. Even scientific hypotheses have but a relative validity. In time, as in space, the extent of knowledge follows a law analogous to the law of spherical diffusion. It has been held that the record of any historic event is wholly invalidated by the lapse of sufficient time; much more is this true of future prediction. The baseline of our knowledge is sufficient but for a limited survey. The very distant future has no mental parallax.

We have seen every far-reaching theory become obsolete; and there is no reason to suppose that, at the present time, we shall be more successful. There is but one course that it is safe to pursue, namely, to be content to let insoluble problems remain as such—not attempting any mental theory concerning them—and confine ourselves to those problems that may offer some probability of solution, with the assurance that, however far the boundaries of knowledge may be extended, each successful solution will enlarge the horizon of the unknown beyond.