No one would deny the right of forming a provisional a.s.sumption to the intelligence officer interpreting a cipher, or to the detective unravelling the mystery of a crime. The first a.s.sumes that the message is in a certain language, and, perhaps, that each symbol employed is the equivalent of a letter, his a.s.sumption is put to the proof of getting a reasonable and consistent meaning from the cipher. The detective a.s.sumes a motive for the crime, or the employment of certain means of escape; even if his a.s.sumption does not clear up the mystery, it may have value as leading to a new and more adequate a.s.sumption.

Henri Poincare has pointed out that one of the most dangerous forms of hypothesis is the unconscious hypothesis. It is difficult to prove or disprove because it does not come to clear statement. The alleged devotee of facts and of things as they are, in opposing the a.s.sumptions of an up-to-date science, is often, unknown to himself, standing on a platform of outworn theory, or of mere vulgar a.s.sumption. For example, when Napoleon was trying to destroy the commercial wealth of England at the beginning of the nineteenth century, he unconsciously based his procedure on an antiquated doctrine of political economy. For him the teachings of Adam Smith and Turgot were idle sophistries. "I seek," he said to his Minister of Finance, "the good that is practical, not the ideal best: the world is very old, we must profit by its experience; it teaches that old practices are worth more than new theories: you are not the only one who knows trade secrets." We are not here especially concerned with the question of whether Napoleon was or was not pursuing the best means of breaking down English credit. He did try to prevent the English from exchanging exports for European gold, while permitting imports in the hope of depleting England of gold. But in pursuing this policy he thought he was proceeding on the ground of immemorial practice, while he was merely pitting the seventeenth-century doctrine of Locke against the doctrine of Adam Smith which had superseded it.

According to one scientific hypothesis, "Species originated by means of natural selection, or, through the preservation of favored races in the struggle for life." This a.s.sumption was rightly subjected to close scrutiny in 1859 and the years following. The ephemeral nature of the vast majority of hypotheses and the danger to progress of accepting an unverified a.s.sumption justify the demand for demonstrative evidence. The testimony having been examined, it is our privilege to state and to support the opposing hypothesis. It was thus that the hypothesis that the planets move in circular orbits, recommended by its simplicity and aesthetic quality, was forced to give way to the hypothesis of elliptical orbits. Newton's hypothesis that light is due to particles emitted by all luminous bodies yielded, at least for the time, to the theory of light vibrations in an ether pervading all s.p.a.ce. The path of scientific progress is strewn with the ruins of overthrown hypotheses. Many of the defeated a.s.sumptions have been merely implicit errors of the man in the street, and they are overthrown not by facts alone, but by new hypotheses verified by facts and leading to fresh discoveries.

According to John Stuart Mill, "It appears ... to be a condition of a genuinely scientific hypothesis, that it be not destined always to remain an hypothesis, but be of such a nature as to be either proved or disproved by that comparison with observed facts which is termed Verification." This statement is of value in confirming the general distrust of _mere_ hypothesis, and in distinguishing between the unverified and unverifiable presupposition and the legitimate a.s.sumption which through verification may become established doctrine.

REFERENCES

J. c.o.x, _Beyond the Atom_, 1913 (Cambridge Manuals of Science and Literature).

R. K. Duncan, _The New Knowledge_, 1905.

H. Poincare, _Science and Hypothesis_.

E. Rutherford, _Radioactive Substances and their Radiations_.

F. Soddy, _The Interpretation of Radium_.

F. Soddy, _Matter and Energy_ (Home University Library).

Sir William A. Tilden, _Progress of Scientific Chemistry in our Own Time_, 1913.

CHAPTER XIX

THE SCIENTIFIC IMAGINATION

Psychology, or the science of mental life as revealed in behavior, has been greatly indebted to physiologists and to students of medicine in general. Any attempt to catalogue the names of those who have approached the study of the mind from the direction of the natural sciences is liable to prove unsatisfactory, and a brief list is sure to entail many important omissions. The mention of Locke, Cheselden, Hartley, Cabanis, Young, Weber, Gall, Muller, Du Bois-Reymond, Bell, Magendie, Helmholtz, Darwin, Lotze, Ferrier, Goltz, Munk, Mosso, Maudsley, Carpenter, Galton, Hering, Clouston, James, Janet, Kraepelin, Flechsig, and Wundt will, however, serve to remind us of the richness of the contribution of the natural sciences to the so-called mental science. Indeed, physiology would be incomplete unless it took account of the functions of the sense organs, of the sensory and motor nerves, of the brain with its a.s.sociation areas, as well as the expression of the emotions, and the changes of function accompanying the development of the nervous system, from the formation of the embryo till physical dissolution, and from species of the simplest to those of the most complex organization.

At the beginning of the nineteenth century the French physician Cabanis was disposed to identify human personality with mere nervous organization reacting to physical impressions, and to look upon the brain as the organ for the production of mind. He soon, however, withdrew from this extreme position and expressed his conviction of the existence of an immortal spirit apart from the body. One might say that the brain is the instrument through which the mind manifests itself rather than the organ by which mind is excreted. Even so, it must be agreed that the relation between the psychic agent and the physical instrument is so close that physiology must take heed of mental phenomena and that psychology must not ignore the physical concomitants of mental processes. Hence arises a new branch of natural science, physiological psychology, or, as Fechner (1860), the disciple of Weber, called it, psycho-physics.

Through this alliance between the study of the mind and the study of bodily functions the intelligence of the lower animals and its survival value, the mental growth of the child, mental deterioration in age and disease, and the psychological endowments of special cla.s.ses or of individuals, became subjects for investigation. Now human psychology is recognized as contributing to various branches of anthropology, or the general study of man.

Wilhelm Wundt, who, as already implied, had approached the study of the mind from the side of the natural sciences, established in 1875 at the University of Leipzig the first psycho-physical inst.i.tute for the experimental study of mental phenomena. His express purpose was to a.n.a.lyze the content of consciousness into its elements, to examine these elements in their qualitative and quant.i.tative differences, and to determine with precision the conditions of their existence and succession. Thus science after contemplating a wide range of outer phenomena--plants, animals, earth's crust, heavenly bodies, molecules and atoms--turns its attention with keen scrutiny inward on the thinking mind, the subjective process by which man becomes cognizant of all objective things.

The need of expert study of the human mind as the instrument of scientific discovery might have been inferred from the fact that the physicist Tyndall read before the British a.s.sociation in 1870 a paper on the Scientific Use of the Imagination, in which he spoke of the imagination as the architect of physical theory, cited Newton, Dalton, Davy, and Faraday as affording examples of the just use of this creative power of the mind, and quoted a distinguished chemist as identifying the mental process of scientific discovery with that of artistic production.

Tyndall even chased the psychologists in their own field and stated that it was only by the exercise of the imagination that we could ascribe the possession of mental powers to our fellow creatures. "You believe that in society you are surrounded by reasonable beings like yourself....

What is your warrant for this conviction? Simply and solely this: your fellow-creatures behave as if they were reasonable."

On the traces of this brilliant incursion of the natural philosopher into the realm of mental science, later psychologists must follow but haltingly. Just as in the history of physics a long series of studies intervened between Bacon's hypothesis that heat is a kind of motion (1620) and Tyndall's own work, _Heat as a Mode of Motion_ (1863), so must many psychological investigations be made before an adequate psychology of scientific discovery can be formulated. It may ultimately prove that the pa.s.sages in which Tyndall and other scientists speak of scientific _imagination_ would read as well if for this term, intuition, inspiration, unconscious cerebration, or even reason were subst.i.tuted.

At first glance it would seem that the study of the sensory elements of consciousness, motor, tactile, visual, auditory, olfactory, gustatory, thermal, internal, pursued for the last half century by the experimental method, would furnish a clue to the nature of the imagination. A visual image, or mental picture, is popularly taken as characteristic of the imaginative process. In fact, the distinguished psychologist William James devotes the whole of his interesting chapter on the imagination to the discussion of different types of imagery. The sensory elements of consciousness are involved, however, in perception, memory, volition, reason, and sentiment, as they are in imagination. They have been recognized as fundamental from antiquity. Nothing is in the intellect which was not previously in the senses. To be out of one's senses is to lack the purposive guidance of the intelligence.

The psychology of individuals and groups shows startling differences in the kind and vividness of imagery. Many cases are on record where the mental life is almost exclusively in visual, in auditory, or in motor terms. One student learns a foreign language by writing out every word and sentence; another is wholly dependent on hearing them spoken; a third can recall the printed page with an almost photographic vividness. The history of literature and art furnishes us with ill.u.s.trations of remarkable powers of visualization. Blake and Fromentin were able to reproduce in pictures scenes long retained in memory. The latter recognized that his painting was not an exact reproduction of what he had seen, but that it was none the less artistic because of the selective influence that his mind had exerted on the memory image.

Wordsworth at times postponed the description of a scene that appealed to his poetic fancy with the express purpose of blurring the outlines, but enhancing the personal factor. Goethe had the power to call up at will the form of a flower, to make it change from one color to another and to unfold before his mind's eye. Professor Dilthey has collected many other records of the hallucinatory clearness of the visual imagery of literary artists.

On the other hand, Galton, after his cla.s.sical study of mental imagery (1883), stated that scientific men, as a cla.s.s, have feeble powers of visual representation. He had appealed for evidence of visual recall to distinguished scientists because he thought them more capable than others of accurately stating the results of their introspection. He had recourse not only to English but to foreign scientists, including members of the French Inst.i.tute. "To my astonishment," he writes, "I found that the great majority of men of science to whom I first applied protested that mental imagery was unknown to them, and they looked on me as fanciful and fantastic in supposing that the words 'mental imagery'

really expressed what I believed everybody supposed them to mean. They had no more notion of its true nature than a color-blind man, who has not discerned his defect, has of the nature of color." One scientist confessed that it was only by a figure of speech that he could describe his recollection of a scene as a mental image to be perceived with the mind's eye.

When Galton questioned persons whom he met in general society he found "an entirely different disposition to prevail. Many men and a yet larger number of women, and many boys and girls, declared that they habitually saw mental imagery, and that it was perfectly distinct to them and full of color." The evidence of this difference between the psychology of the average distinguished scientist and the average member of general society was greatly strengthened upon cross-examination. Galton attributed the difference to the scientist's "habits of highly generalized and abstract thought, especially when the steps of reasoning are carried on by words [employed] as symbols."

It is only by the use of words as symbols that scientific thought is possible. It is through cooperation in work that mankind has imposed its will upon the creation, and cooperation could not have been carried far without the development of language as a means of communication. Were it not for the help of words we should be dependent, like the lower animals, on the fleeting images of things. We should be bound to the world of sense and not have range in the world of ideas. Words are a free medium for thought, for the very reason that they are capable of shifting their meaning and taking on greater extension or intension. For example, we may say that the apple falls because it is heavy, or we may subst.i.tute synonymous phraseology that helps us to view the falling apple in its universal aspects. The mind acquires through language a field of activity independent of the objective world. We have seen in an earlier chapter that geometry developed as a science is becoming gradually weaned from the art of surveying. Triangles and rectangles cease to suggest meadows, or vineyards, or any definite imagery of that sort, and are discussed in their abstract relationship. Science demands the conceptual rather than the merely sensory. The invisible real world of atoms and corpuscles has its beginning in the reason, the word. To formulate new truths in the world of ideas is the prerogative of minds gifted with exceptional reason.

To be sure, language itself may be regarded as imagery. Some persons visualize every word spoken as though it were seen on the printed page; others cannot recall a literary pa.s.sage without motor imagery of the speech organs or even incipient speech; while others again experience motor imagery of the writing hand. With many, in all forms of word-consciousness, the auditory image is predominant. In the sense of being accompanied by imagery all thinking is imaginative. But it is the use of words that permits us to escape most completely from the more primitive forms of intelligence. So directly does the printed word convey its meaning to the trained mind that to regard it as so much black on white rather than as a symbol is a rare and rather upsetting mental experience. Words differ among themselves in their power to suggest images of the thing symbolized. The word "existence" is less image-producing than "flower," and "flower" than "red rose." It is characteristic of the language of science to subst.i.tute the abstract or general expression for the concrete and picturesque.

When, therefore, we are told that the imagination has been at the bottom of all great scientific discoveries, that the discovery of law is the peculiar function of the creative imagination, and that all great scientists have, in a certain sense, been great artists, we are confronted with a paradox. In what department of thought is imagination more strictly subordinated than in science? Genetic psychology attempts to trace the development of mind as a means of adjustment. It examines the instincts that serve so wonderfully the survival of various species of insects. It studies the more easily modified instinct of birds, and notes their ability to make intelligent choice on the basis of experience. Does the bird's ability to recognize imply the possession of memory, or imagery? Increased intelligence a.s.sures perpetuation of other species in novel and unforeseen conditions. The more tenacious the memory, the richer the supply of images, the greater the powers of adaptation and survival. We know something concerning the motor memory of rodents and horses, and its biological value. The child inherits less definitely organized instincts, but greater plasticity, than the lower animals. Its mental life is a chaos of images. It is the work of education to discipline as well as to nourish the senses, to teach form as well as color, to impart the clarifying sense of number, weight, and measurement, to help distinguish between the dream and the reality, to teach language, the treasure-house of our traditional wisdom, and logic, so closely related to the right use of language. The facts of abnormal, as well as those of animal and child psychology, prove that the subordination of the imagination and fancy to reason and understanding is an essential factor in intellectual development.

No one, of course, will claim that the mental activity of the scientific discoverer is wholly unlike that of any other cla.s.s of man; but it leads only to confusion to seek to identify processes so unlike as scientific generalization and artistic production. The artist's purpose is the conveyance of a mood. The author of _Macbeth_ employs every device to impart to the auditor the sense of blood-guiltiness; every lurid scene, every somber phrase, serves to enhance the sentiment. A certain picture by Durer, a certain poem of Browning's, convey in every detail the feeling of dauntless resolution. Again, a landscape painter, recognizing that his satisfaction in a certain scene depends upon a stretch of blue water with a yellow strand and old-gold foliage, proceeds to rearrange nature for the benefit of the mood he desires to enliven and perpetuate.

It is surely a far cry from the att.i.tude of these artists manipulating impressions in order to impart to others an individual mood, to that of the scientific discoverer formulating a law valid for all intellects.

In the psychology of the present day there is much that is reminiscent of the biological psychology of Aristotle. From the primitive or nutrient soul which has to do with the vital functions of growth and reproduction, is developed the sentient soul, concerned with movement and sensibility. Finally emerges the intellectual and reasoning soul.

These three parts are not mutually exclusive, but the lower foreshadow the higher and are subsumed in it. Aristotle, however, interpreted the lower by the higher and not vice versa. It is no compliment to the scientific discoverer to say that his loftiest intellectual achievement is closely akin to fiction, or is the result of a mere brooding on facts, or is accompanied by emotional excitement, or is the work of blind instinct.

It will be found that scientific discovery, while predominantly an intellectual process, varies with the nature of the phenomena of the different sciences and the individual mental differences of the discoverers. As stated at the outset the psychology of scientific discovery must be the subject of prolonged investigation, but some data are already available. One great mathematician, Poincare, attributes his discoveries to intuition. The essential idea comes with a sense of illumination. It is characterized by suddenness, conciseness, and immediate certainty. It may come unheralded, as he is crossing the street, walking on the cliffs, or stepping into a carriage. There may have intervened a considerable period of time free from conscious effort on the special question involved in the discovery. Poincare is inclined to account for these sudden solutions of theoretical difficulties on the a.s.sumption of long periods of previous unconscious work.

There are many such records from men of genius. At the moment the inventor obtains the solution of his problem his mind may seem to be least engaged with it. The long-sought-for idea comes like an inspiration, something freely imparted rather than voluntarily acquired.

No mental process is more worthy to command respect; but it may not lie beyond the possibility of explanation. Like ethical insight, or spiritual illumination, the scientific idea comes to those who have striven for it. The door may open after we have ceased to knock, or the response come when we have forgotten that we sent in a call; but the discovery comes only after conscious work. The whole history of science shows that it is to the worker that the inspiration comes, and that new ideas develop from old ideas.

It may detract still further from the mysteriousness of the discovery-process to add that the illuminating idea may come in the midst of conscious work, and that then also it may appear as a sudden gift rather than the legitimate outcome of mental effort. The spontaneity of wit may afford another clue to the mystery of scientific discovery. The utterer of a witticism is frequently as much surprised by it as the auditors, probably because the idea comes as verbal imagery, and the full realization of their significance is grasped only with the actual utterance of the words. The fact that to the scientific discoverer the solution of his problem arrives at the moment when it is least sought is a.n.a.logous to the common experience that the effort to recall a name may inhibit the natural a.s.sociation.

The tendency to emphasize unduly the role played by the scientific imagination springs probably from the misconception that the imagination is a psychological superfluity, one of the luxuries of the mental life, which should not be withheld from those who deserve the best. The view lingers with regard to the aesthetic imagination. James could not understand the biological function of the aesthetic faculty. On the alleged uselessness of this phase of the human mind A. J. Balfour has recently based an argument for the immortality of the soul. This view is strikingly at variance with that which inclines to identify it with that mental process which creates scientific theories and thus paves the way for the adjustment of posterity to earthly conditions.

REFERENCES

Baldwin, J. M., _History of Psychology_, 1913. 2 vols.

Dessoir, Max, _Outlines of the History of Psychology_, 1912.

Klemm, Otto, _A History of Psychology_, 1914.

Merz, J. T., _History of European Thought in the Nineteenth Century_, vol. II, chap. XII, On the Psycho-physical View of Nature.

Rand, Benjamin, _The Cla.s.sical Psychologists_, 1912.

Ribot, T. A., _English Psychology_, 1889.

Ribot, T. A., _German Psychology of To-day_, 1886.

CHAPTER XX