In the year 1796 the Reverend Nevil Maskelyne, director of the Greenwich observatory, noticed that the transits recorded by his assistant, Kinnebrook, showed a gradually increasing difference from his own, finally amounting to almost a full second. He suspected his assistant of having deviated from the prescribed method of observation, the so-called eye and ear method, and of having substituted some unreliable method of his own. He admonished the young man to return to the correct method and do better in the future. But his admonition was in vain, and he found himself obliged to part with his otherwise satisfactory assistant. Kinnebrook lost his position on account of the deficient psychological knowledge of his time. It was not until two decades later that Bessel discovered that such differences between the results of observations by different individuals were quite general and normal, and that in Kinnebrook’s case they were only unusually great. They depend on the manner of giving attention to both the sound of the pendulum and the sight of the moving star, which naturally differs in different individuals.
At first this question of the so-called personal equation remained a purely practical astronomical problem. But a few decades later it gave rise to two classes of investigations of psychological importance, both of the experimental kind. The first was an investigation of a comparatively simple problem—the duration of the mental processes. Among such processes measured were the simple perception, the discrimination of several perceptions, the simple reaction to them, the reproduction of any suggested idea, the reproduction of a specific suggested idea, and so forth. Not only was the duration of these processes studied, but also their dependence on differences of stimulation, the accompanying circumstances, the individual differences, the subject’s trend of thought. The second class of investigations was concerned with the more complex mental processes of attending and willing. As examples may be mentioned inquiries into the attention of a person confronted by a multitude of impressions, a study of the order in which the several impressions are perceived, a determination of the largest number of impressions perceptible as a mental unit, and research into the causal relations between ideas and actions.
A more recent contribution of natural science to the advancement of psychology has come from investigations in the physiology and pathology of the central nervous system since the discovery about 1870 of the so-called speech center by Broca, and of the motor areas of the brain cortex by Fritsch and Hitzig. Some have placed a rather low value on this contribution and, noticing the errors and immature conceptions of this or that investigator, have arrived at the conclusion that psychology can learn nothing worth mentioning from the work of these men. This, it seems to me, is a great mistake.
Quite aside from innumerable details, psychology owes to the investigations made in recent years concerning the physiology of the brain two fundamental conceptions. In the first place it has come to be generally recognized that the search of centuries for the exact seat of the soul in the brain—for the point where mind and body come into interaction—is without an object. There is no seat of the soul in this sense; the brain is the embodiment of almost absolute decentralization. Our mind receives the impressions of the external world by means of widely separated parts of the brain, as different sensations, according to the peripheral organs stimulated. And our mind controls our actions by means of widely separated parts of the brain according to the local differences of the muscle groups which are called into action. All the parts of the brain are connected, but they function in relative independence, without being controlled from a single point. Now, it is clear that insight into this fact is of no little significance for our conception of the nature of mind.
In the second place it is only through the work of these neurologists that psychologists have come to realize how enormously complicated are even those mental functions which have always been regarded as comparatively simple. That the speech function, for example, involves consciousness of sound, of movement, and sometimes of sight, may be recognized immediately, and has been recognized. That our images of things are directly nothing but revived sense impressions of various kinds, visual, auditory, olfactory, and so on, and that our skill in handling things depends upon our experience obtained through running our fingers over them, is also recognized. But that all these images are more than abstractions, that they have a concrete significance even though the subject may not be aware of them, has been recognized only after the study of pathological cases, where, in consequence of peculiar lesions of the brain a dissociation has occurred among those factors which usually work together harmoniously, and where some of them are perhaps entirely lost. It was not until these pathological facts were known that psychology was able to give a definite formulation to certain of its problems. It then became clear that many former problems which took their origin from those popular simplifications, will, judgment, memory, or from the seeming simplicity of ideas and movements, were perfect nonsense, considering the actual complexity of the facts. Now, after having learned how to formulate its problems, psychology can at last hope to understand the phenomena of mental life.
The study of the brain has also had an indirect influence upon psychology through the strong impulse which it gave to psychiatry. The knowledge gained in the study of the abnormal mind gave a new insight into the processes of the normal mind. And since psychiatrists most often came into contact with the highly complex mental states, such as emotion, intelligence, self-consciousness, the impulses which they gave to psychology were a happy supplement to those other influences which concerned chiefly sensation and perception.
During the last decades of the nineteenth century all these buds of a new psychology were—first by Wundt—grafted on the old stem and so united into an harmonious whole. They have rejuvenated the apparently dying tree and brought about a strong new growth. The psychology of the text-book and the lecture room has become a different science. The most conspicuous sign of this new conception of the science of the mind is the establishment of numerous laboratories exclusively devoted to psychological research.
In earlier times psychology was but the handmaid of other interests. Psychological research was not an end in itself, but a useful or necessary means to higher ends. Usually it was a branch or a servant of philosophy. Men took it up particularly in order to understand the foundations of knowledge, or how our conceptions of the natural world originated, and this again in order to draw metaphysical or ethical conclusions, to settle the controversy between idealism and materialism, to answer the question as to the relation of body and mind, to derive rules for a rational conduct of life, often also with the mere purpose of confirming views springing from some other source. Others took up the study of psychology with a practical aim, for example, in order to find out how to make the most of their lives, or how to improve their memories. It is, to be sure, greatly to be hoped that psychology will not entirely lose its connection with philosophy, as natural science has unfortunately done. At no time, indeed, has the practical importance of psychology, its great usefulness in education, psychiatry, law, language, religion, art, been more strongly felt, or given rise to more numerous investigations than at present. But it is now recognized that, here as elsewhere, it is more fruitful for the true and lasting advancement of philosophical ends, instead of always thinking of advancing them, to forget them for the time, and to work on the preliminary problems as if these preliminary problems were the only ones existing. And so psychology, formerly a mere means to an end, has come to be regarded as a special science, to which a man can well afford to give his full time and energy.
A few data may illustrate what we have just said. Until the last decades of the nineteenth century psychology has not been able to support a journal of its own. A few attempts in this direction were made in the eighteenth century, when two psychological periodicals were started; but neither published more than a few volumes. Even in the middle of the last century magazine articles of psychological content were rare enough and appeared only in philosophical, physiological, or physical journals. During the last thirty years a complete revolution has taken place in this respect, more remarkable than in any other branch of science. First at longer intervals, then in quick succession, numerous purely psychological journals were founded in the principal civilized countries, of which none thus far has been compelled to retire on account of lack of either contributors or readers. We count at present at least fifteen, six of them in German, four in English, three in French, one in the Italian language, and one representing the Scandinavian peoples. And there is an equal number of periodical publications of single investigators and institutions, and also numerous writings of psychological importance published in philosophical, physiological, psychiatrical, pedagogical, criminological, and other journals.
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