Popular Science Monthly/Volume 66/November 1904/The Methods of the Earth-Sciences

1422632Popular Science Monthly Volume 66 November 1904 — The Methods of the Earth-Sciences1904Thomas Chrowder Chamberlin


By Professor T. C. CHAMBERLIN


IT is my assigned task to review the methods of the earth-sciences. The technical processes of the constituent sciences are peculiar to each and are inappropriate subjects for discussion before this composite assemblage; but the fundamental methods of intellectual procedure are essentially common to all the earth-sciences, and to these the address will confine itself.

That which passes under the name earth-science is not all science in the strict sense of the term. Not a little consists of generalizations from incomplete data, of inferences hung on chains of uncertain logic, of interpretations not beyond question, of hypotheses not fully verified and of speculation none too substantial. A part of the mass is true science, a part is philosophy, as I would use the term, a part is speculation, and a part is yet unorganized material. However, I like to think of the aggregate, not as an amorphous mixture of science, philosophy and speculation, but as a rather definite aggregation of these, not unlike that of the earth itself. The great mass of our subject material may be regarded as a lithosphere of solid facts. Around this gathers an atmosphere of philosophy, rather dense near the contact zone, but thinning away into tenuous speculation in the outer regions. For myself, I like to think of the nucleus as solid and firm throughout, not as a thin fractured crust floating on a fiery liquid of plutonian suggestiveness. I like to think of the philosophic and speculative atmosphere as no mere gas-zone of forty-five miles' depth, as of old, but as an envelope of intense kinetic life, in the denser zone, where the logical molecules touch one another with marvelous frequency, and where there is frictional contact with the solid but rather inert lithosphere. In the outer tenuous zone, the molecular flights are freer and the excursions are without assignable limits. I believe an appropriate atmosphere of philosophy is as necessary to the wholesome intellectual life of our sciences as is the earth's physical atmosphere to the life of the planet. None the less, it must ever be our endeavor to reduce speculation to philosophy, and philosophy to science. For the perpetuation of the necessary philosophic atmosphere, we may safely trust to the evolution of new problems concurrently with the solution of the old.

But granting the importance of the philosophic element, we doubtless agree without hesitation that the solid products of accurate and complete observation, natural or experimental, are the bed-rock of our group of sciences. The first great object sought by laudable methods is, therefore, the promotion of the most accurate, searching, exhaustive and unbiased observation that is possible. One of the primary efforts in behalf of our sciences, therefore, was naturally directed to the task of promoting the best observational work. It was soon discovered that two chief dangers threatened the worker—bias and incompleteness. To guard against the first there was evolved

The Method of Colorless Observation.

Under its guidance, the observer endeavors to keep his mind scrupulously free from prepossessions and favored views. However tensely he may strain his observing powers to see what is to be seen, he seeks solely a record of facts uncolored by preferences or prejudices. To this end, he restrains himself from theoretical indulgence, and modestly contents himself with being a recorder of nature. He does not presume to be its interpreter and prophet. At length, in the office, he gathers his observations into an assemblage, with such inferences and interpretations as flow from them spontaneously, but even then he guards himself against the prejudices of theoretical indulgence.

Laudable as this method is in its avoidance of partiality, it is none the less seriously defective. No one who goes into the field with a mind merely receptive, or merely alert to see what presents itself, however nerved to a high effort, will return laden with all that might be seen. Only a part of the elements and aspects of complex phenomena present themselves at once to even the best observational minds. Some parts of the complex are necessarily obscure. Some of the most significant elements are liable to be unimpressive. These unobtrusive but yet vital elements will certainly escape observation unless it is forced to seek them out, and to seek them out diligently, acutely and intensely. To make a reasonably complete set of observations, the mind must not only see what spontaneously arrests its attention, but it must immediately draw out from what it observes inferences, interpretations, and hypotheses to promote further observations. It must at once be seen that if a given inference is correct, certain collateral phenomena must accompany it. If another inference be correct, certain other phenomena must accompany it. If still a third interpretation be the true one, yet other phenomena must be present to give proof of it. Once these suggestions have arisen, the observer seeks out the phenomena that discriminate between them, and, under such stimulus, phenomena that would otherwise have wholly escaped attention at once come into view because the eye has now been focused for them. It may be affirmed with great confidence that without the active and instantaneous use of these concurrent processes the observer will rarely, if ever, record the whole of any one set of significant elements, much less the whole of all sets. His record will contain incomplete parts of different sets of significant elements, but no complete set of any one. The obscure factors of each set are quite sure to be overlooked and the obtrusive factors of several sets indiscriminately commingled. The method of colorless observation is thus seriously defective in the completeness of its products, while it successfully guards them from bias.

Standing over against it, in strong contrast, is the method which at once endeavors to seek out and put together the phenomena that are thought to be significant. This leads promptly to the construction of a theory or an explanation which soon comes to guide the work and gives rise to

The Method of the Ruling Theory.

The chief effort here centers on an elucidation of phenomena, not on an exhaustive determination of the facts. Properly enough the crown of the work is the end, explanation is brought to the forefront and eagerly made the immediate end of endeavor. As soon as a phenomenon is presented, a theory of elucidation is framed. Laudable enough in itself, the theory is liable to be framed before the phenomena are fully and accurately observed. The elucidation is likely to embrace only the more obtrusive phenomena, not the full complement of the obtrusive and the unimpressive. The field is quite likely to present many repetitions of the leading phenomena and a theory framed to fit those that first arrest attention naturally fits the oft-recurrent phenomena of the same class. While there may be really no new evidence, nor any real test, nor any further inquiry into the grounds of the theory, its repeated application with seeming success leads insidiously to the delusion that it has been strengthened by additional investigation. Unconsciously then it begins to direct observation to the facts it so happily elucidates. Unconsciously the facts to which it gives no meaning become less impressive and fall into neglect. Selective observation creeps insidiously in and becomes a persistent habit. Soon also affection is awakened with its blinding influence. The authorship of an original explanation that seems successful easily begets fondness for one's intellectual child. This affection adds its alluring influence to the previous tendency toward an unconscious selection. The mind lingers with pleasure upon the facts that fall happily into the embrace of the theory, and feels a natural indifference toward those that assume a refractory or meaningless attitude. Instinctively, there is a special searching-out of phenomena that support the theory; unwittingly also there is a pressing of the theory to make it fit the facts and a pressing of the facts to make them fit the theory. When these biasing tendencies set in, the mind soon glides into the partiality of paternalism, and the theory rapidly rises to a position of control. Unless it happens to be the true one, all hope of the best results is gone. The defects of this method are obvious and grave. It is safe to say, however, that under this method, with all its defects, many facts will be gathered that an observer of colorless attitude would have quite overlooked. The reverse may doubtless also be said. An effort to avoid the dangers at once of the colorless Scylla and the biasing Charybdis gave rise to

The Method of the Working Hypothesis.

This may be regarded as the distinctive feature of the methodology of the last century. This differs from the method of the ruling theory in that the working hypothesis is made a means of determining facts, not primarily a thesis to be established. Its chief function is the suggestion and guidance of lines of inquiry; inquiry not for the sake of the hypothesis, but for the sake of the facts and their final elucidation. The hypothesis is a mode rather than an end. Under the ruling theory, the stimulus is directed to the finding of facts for the support of the theory. Under the working hypothesis, the facts are sought for the purpose of ultimate induction and demonstration, the hypothesis being but a means for the more ready development of facts and their relations, particularly their relations.

It will be seen that the distinction is somewhat subtile. It is rarely if ever perfectly sustained. A working hypothesis may glide with the utmost ease into a ruling theory. Affection may as easily cling about a beloved intellectual child under the name of a working hypothesis as under any other, and may become a ruling passion. The moral atmosphere associated with the working hypothesis, however, lends some good influence toward the preservation of its integrity. The author of a working hypothesis is not presumed to father or defend it, but merely to use it for what it is worth.

Conscientiously followed, the method of the working hypothesis is an incalculable advance upon the method of the ruling theory, as it is also upon the method of colorless observation; but it also has serious defects. As already implied, it is not an adequate protection against a biased attitude. Even if it avoids this, it tends to narrow the scope of inquiry and direct it solely along the lines of the hypothesis. It undoubtedly gives acuteness, incisiveness and thoroughness in its own lines, but it inevitably turns inquiry away from other lines. It has dangers therefore akin to its predecessor, the ruling theory.

A remedy for these dangers and defects has been sought in

The Method of Multiple Working Hypotheses.[2]

This differs from the method of the simple working hypothesis in that it distributes the effort and divides the affections. It is thus in some measure protected against the radical defects of the two previous methods. The effort is to bring up into distinct view every rational explanation of the phenomenon in hand and to develop into working form every tenable hypothesis of its nature, cause or origin, and to give to each of these a due place in the inquiry. The investigator thus becomes the parent of a family of hypotheses; and by his paternal relations to all is morally forbidden to fasten his affections unduly upon any one. In the very nature of the case, the chief danger that springs from affection is counteracted. Where some of the hypotheses have been already proposed and used, while others are the investigator's own creation, a natural tendency to bias arises, but the right use of the method requires the impartial adoption of all into the working family. The investigator thus at the outset puts himself in cordial sympathy and in the parental relations of adoption, if not of authorship, with every hypothesis that is at all applicable to the case under investigation. Having thus neutralized, so far as may be, the partialities of his emotional nature, he proceeds with a certain natural and enforced erectness of mental attitude to the inquiry, knowing well that some of the family of hypotheses must needs perish in the ordeal of crucial research, but with a reasonable expectation that more than one of them may survive, since it often proves in the end that several agencies were conjoined in the production of the phenomenon. Honors must often be divided between hypotheses. In following a single hypothesis, the mind is biased by the presumptions of the method toward a single explanatory conception. But an adequate explanation often involves the coordination of several causes. This is especially true when the research deals with complicated phenomena such as prevail in the field of the earth-sciences. Not only do several agencies often participate, but their proportions and relative importance vary from instance to instance in the same class of phenomena. The true explanation is therefore necessarily multiple, and often involves an estimate of the measure of participation of each factor. For this the simultaneous use of a full staff of working hypotheses is demanded. The method of the single working hypothesis is here incompetent.

The reaction of one hypothesis upon another leads to a fuller and sharper recognition of the scope of each. Every added hypothesis is quite sure to call forth into clear recognition neglected aspects of the phenomena. The mutual conflicts of hypotheses whet the discriminative edge of each. The sharp competition of hypotheses provokes keenness in the analytic processes and acuteness in differentiating criteria. Fertility in investigative devices is a natural sequence. If therefore an ample group of hypotheses encompass the subject on all sides, the total outcome of observation, of discrimination and of recognition of significance and relationship is full and rich.

Closely allied to the method of multiple working hypotheses is

The Method of Multiple Series.

In many of the more complex problems of the earth-sciences the basal facts are but imperfectly determined, e. g., the rate of rise of internal temperature, the rigidity of the earth's body, the thermal conductivity of the earth's interior, the amount of the earth's shrinkage, the extent of lateral thrust in the formation of folded mountains and many others, indeed most others. There is need to deal with these problems notwithstanding the imperfection of the basal data, for in many cases these must long remain imperfect. Moreover, there is need to treat these problems tentatively to determine what fundamental facts are really needed, how these can best be secured, and with what precision they must be determined. Preliminary trial may save much tedious and expensive experimentation. It is as foolish to cultivate sterile soil in science as in agriculture, and preliminary tests may show that given soils are necessarily sterile. In many cases, all the needs of the problem may be met by a multiple series of assumptions covering the full range of a probable fact. In most cases it is easy to see that the value of a given fundamental factor can not range beyond certain extremes on either hand. If a series of values ranging from the one extreme to the other be used simultaneously in the inquiry, the full range of results dependent on this factor may be covered. In some inquiries this serves as well as if the exact truth were known, for whatever the assignable value, certain deductions Can not stand. In other cases, it will be shown that a very slight change in the value of the basal factor will wholly change the outcome, and hence that extremely accurate determinations must be made before any trustworthy solution can be reached. Expensive determinations in the first case are folly; very accurate determinations in the second are to be sought at any cost. Conclusions on imperfect data in the one case are perfectly safe; conclusions without precise determinations in the other are folly. It is to be hoped that, with the wider adoption of the method of multiple series, tables of serial determinations covering the data of the more vital phenomena of the earth-sciences will be constructed, as tables of physical constants now are.

The Method of Regenerative Hypotheses.

In the method of multiple hypotheses, the members of the group are used simultaneously and are more or less mutually exclusive, or even antagonistic. Supplementary to this method is the use of a succession of hypotheses related genetically to one another. In this the results of an inquiry under the first hypothesis give rise to the assumptions of the succeeding hypothesis. The precise conclusions of the first inquiry are not made the assumptions of the second, for the process would then be little more than repetitive, but the revelations and intimations, perhaps the incongruities and incompatibilities of the first results beget, by their suggestiveness, the basis of the second. The latter is the offspring of the former, but between parent and offspring there is mutation with an evolutionary purpose. A cruder first attempt generates a more highly organized and specialized working scheme fitted to the new state of knowledge developed. The method is specially applicable to elaborate inquiries, particularly those in which the premises are imperfect and a long logical chain is hung upon them. The discussions of our great fundamental conceptions furnish the best examples, chiefly examples of the lack of a systematic regenerative method. Among these, two general classes may be recognized, (1) those of a rather rigorous type, as, for a distinguished example, the researches of George Darwin on tidal reaction and the history of the earth and moon, and (2) those of a looser and sometimes rather metaphysical type, which I shall try to illustrate by the doctrine of determinism. In all cases, assumptions are made the basis of the procedure. Absolute premises are not available. Taking its start from these assumptions, the process pursues a long course and at the end conclusions of great import are often drawn. Usually the process rests there, and in this lies a serious shortcoming. It should give rise to a new process of a higher order. Not seldom, a critical study of the results will reveal features that were not recognized nor suspected in the original assumptions, though really there. Out of these revelations should grow new assumptions and a new process. The second conclusion may in like manner betray unsuspected qualities and these should beget still other assumptions, and so the procedure should continue until the field is exhausted.

To choose a specific illustration is not a little delicate, for to be most familiar it must be of the negative type, but I fear such an illustration is the only way to clearly convey the meaning here intended. I therefore venture to choose one so eminent and so admirable, even with its limitations, that any suggestion of shortcoming will in no wise dim the luster of a great achievement. In the classic investigations of George Darwin on tides and their astronomic consequences, a viscous earth is assumed as the starting-point, with properties such that the tidal protuberance is carried forward by the rotation of the earth to the point which gives the maximum effect on the motions of the earth and moon. These assumptions run potentially through the whole train of brilliant mathematical deduction. At the end of the inquiry, or if not of this particular inquiry, at least of collateral inquiries, the conclusion is reached that the earth is a rigid body comparable to steel. Between such a rigid body and such a viscous earth as was assumed at the outset of the inquiry, there is a seeming incongruity. This, under the regenerative method, suggests a new investigation on the assumption that the earth is a very rigid body, with the further assumption that it has high elasticity of form, such that its protuberance may perhaps not be carried forward to the degree previously postulated. These new assumptions are the more imperative, because they are supported by inquiries based on quite independent lines. In framing the new hypothesis an advance in detail and in organization is to be sought on the evolutionary principle already indicated. If the earth as a whole is as rigid as steel, and the outer part is, as we know, formed of rock much less rigid than steel, the interior must be much more rigid than steel and there must be a differential distribution of rigidity. The new inquiry may then well start with the assumption of increasing rigidity toward the center. Postulating an earth so constituted, a first step of the regenerated inquiry might well be an effort to learn not only the amount of the tidal protuberance, but also the position of the protuberance, since its position is as essential as its amount in influencing the motions of the earth and moon. As a geologist I venture to entertain the belief that exhaustive inquiry on such regenerative lines would bring forth results in harmony with geological evidences, with which the well-known conclusions heretofore reached seem to be at fatal variance.

The earth-sciences are not purely physical sciences. They concern themselves with life and with mentality, as well as with rocks, ocean and atmosphere. Our group is exceptionally comprehensive in the range of its subjects. Our methods should hence be such as to encompass the whole field. They should give us ultimately a complete working system of thought relative to all the earth is or holds. In some sense the earth sciences must come to comprehend the essentials of all the sciences. At least as much as any other scientists we are interested in the fundamental assumptions of all the sciences and in their consistent application. To touch hastily this broader field, I choose a second illustration of the method of regenerative hypotheses from the relations between the assumptions of science and the conclusions of science.

As our working basis, we assume that our perceptions represent reality, when duly directed and corrected, but that error and illusion lurk on all sides and must be scrupulously avoided. We assume that we are capable of detecting error and of demonstrating truth; and that, as requisite means, we have choice, and some measure of volitional command over ourselves and over nature.

Starting thus with assumptions that embrace choice and the possibility of error, and going out into physical research, most of us have concluded that antecedents are followed rigorously by their consequents. Going out a step further into the chemico-biological field and noting the close interrelations between physical and vital phenomena, many of us have been led to a belief in their ultimate identity. Going out a step further into the mental field, not a few of us have concluded that an unvarying sequence of antecedents and consequents reigns here also. But this seems to contradict the assumptions with which we started. Our primary assumptions embraced choice, volitional control, and the alternative of reaching truth or falling into error according to our self-directed discrimination.

What is to be done in the face of this seeming contradiction? The method of regenerative hypotheses answers that a new set of assumptions begotten of the contradictory conclusion should be made the basis of a new inquiry, and if possible of a new working hypothesis. Instead of the usual assumption of choice, and of the possible alternative of reaching truth or falling into error, let the assumption be that all acts of the mind are parts of a rigorous chain of antecedents and consequents. Let it be assumed that no swerving from the predetermined sequences is possible, that every thought and every act follows its antecedents with absolute rigor, no real choice, or volition, or alternative between accuracy and error being possible.

Let this set of assumptions be tried as a working hypothesis. If investigation be possible under it, let such investigation cover the whole ground of what we call truth and error. Let a distinction be drawn between absolutely predetermined mental actions corresponding to truthfulness on the one hand, and falsity on the other, if this be possible, and out of the former let science be constructed and let it be shown why it is science, and let the latter be disposed of in some suitable way. In other words, let the doctrine of determinism be put into workable form, and carried into effect in all its applications, with every step true to the primary assumptions. If this can be done successfully, we shall have a wholly new working basis for the production of science, with new criteria of science. If it can not be done and the hypothesis of determinism is unworkable, let it be cast aside like any other unworkable hypothesis. Whatever metaphysicians may think of an unworkable scheme, scientific investigators may as well send it to the junk shop.

Huxley once delivered himself of an able exposition of determinism. It was severely criticized by a fellow countryman who seemed to Huxley to have dealt with him unjustly, and he poured out the vials of his rhetorical wrath upon him as only Huxley could. But if determinism be true, I do not see how Huxley's critic could have swerved by a turn of a phrase from what he wrote, and Huxley's wrath was not more consistent than that assigned to Xerxes when he lashed the stormy Hellespont because it thwarted his purpose. But in this I may be wholly wrong. Let determinism prove itself by giving rise to a complete and systematic working hypothesis.

Whether this can be clone or not, let any other basal assumptions suggested by the inquiry be made the ground of like attempts and be developed into full working hypotheses, if possible, and so continue the effort until the whole field is covered. Let it be seen what can and what can not be put into the form of a working system.

In this second illustration of the method of regenerative hypotheses, I have touched questions not usually thought to belong to the earth-sciences. It is none the less true that they are basal to the earth-sciences, as they are to all science, and to all true philosophy as well. The earth-sciences are entitled to probe for their own bottom as well as other sciences, or any philosophy, and it is altogether wholesome that they should do so. The most serious source of error in the development of the earth-sciences, in my judgment, is our relative neglect to probe fundamental conceptions and to recognize the extent to which they influence the most common observations and interpretations. We need a method of thought that shall keep us alive to these basal considerations. To this end I believe it to be conducive to soundness of intellectual procedure to regard our whole system of interpretation as but an effort to develop a consistent system of workable hypotheses. I think we should do well to abandon all claims that we are reaching absolute truth, in the severest sense of that phrase, and content ourselves with the more modest effort to work out a system of interpretation which shall approve itself in practise under such tests as human powers can devise. Wherein lie

The Basal Criteria of Our Sciences?

I believe they lie essentially in the working quality. Whatever conforms thoroughly to the working requirements of nature probably corresponds essentially to the absolute truth, though it may be much short of the full truth. That may be accepted, for the time being, as true which duly approves itself under all tests, as though it were true. Whenever it seems to fail under test in any degree, confidence is to be withdrawn in equal degree, and a rectification of conceptions sought. This may well hold for all conceptions, however fundamental, whether they relate to the physical, the vital, or the mental phenomena which the earth presents. Let us entirely abandon the historic effort of the metaphysicians to build an inverted pyramid on an apex of axioms assumed to be incontestable truth, and let us rear our superstructure on the results of working trials applied as widely and as severely as possible. Let us seek our foundation in the broadest possible contact with phenomena. I hold that the working test when brought to bear in its fullest, most intimate and severest forms is the supreme criterion of that which should stand to us for truth. Our interpretative effort should, therefore, be to organize a complete set of working hypotheses for all phenomena, physical, vital and mental, so far as appropriate to our sphere of research. These should be at once the basis of our philosophy and of our science. These hypotheses should be constantly revised, extended and elaborated by all available means, and should be tested continually by every new relation which comes into view, until the crucial trials shall become as the sands of the sea for multitude and their severity shall have no bounds but the limits of human capacity. That which under this prolonged ordeal shall give the highest grounds of assurance may stand to us for science, that which shall rest more upon inference than upon the firmer modes of determination may stand to us for our philosophy, while that which lies beyond these, as something doubtless always will, may stand to us for the working material of the future.

  1. An address at the International Congress of Arts and Science, St. Louis, September, 1904.
  2. In this sketch I have drawn freely upon my paper on 'The Method of Multiple Working Hypotheses,' Journ. Geol., V., 1897.