they differ from the average mind which the theoretical psychologist may construct as a type. Still more frequently we have to act with reference to smaller groups or to single individuals whose mental physiognomy demands careful consideration. As long as experimental psychology remained essentially a science of the mental laws, common to all human beings, an adjustment to the practical demands of daily life could hardly come in question. With such general laws we could never have mastered the concrete situations of society, because we should have had to leave out of view the fact that there are gifted and ungifted, intelligent and stupid, sensitive and obtuse, quick and slow, energetic and weak individuals.

But in recent years a complete change can be traced in our science. Experiments which refer to these individual differences themselves have been carried on by means of the psychological laboratory, at first reluctantly and in tentative forms, but within the last ten years the movement has made rapid progress. To-day we have a psychology of individual variations from the point of view of the psychological laboratory.[1] This development of schemes to compare the differences between the individuals by the methods of experimental science was after all the most important advance toward the practical application of psychology. The study of the individual differences itself is not applied psychology, but it is the presupposition without which applied psychology would have remained a phantom.

II

THE DEMANDS OF PRACTICAL LIFE

While in this way the progress of psychology itself and the development of the psychology of individual differences favored the growth of applied psychology, there arose at the same time an increasing demand in the midst of practical life. Especially the teachers and the physicians, later the lawyers as well, looked for help from exact psychology. The science of education and instruction had always had some contact with the science of the mind, as the pedagogues could never forget that the mental development of the child has to stand in the centre of educational thought. For a long while pedagogy was still leaning on a philosophical psychology, after that old-fashioned study of the soul had been given up in psychological quarters. At last, in the days of progressive experimental psychology, the time came when the teachers under the pressure of their new needs began to inquire how far the modern laboratory could aid them in the classroom. The pedagogical psychology of memory, of attention, of will, and of intellect was systematically worked up by men with practical school interests. We may notice in the movement a slow but most important shifting. At first the results of theoretical psychology were simply transplanted into the pedagogical field. Experiments which were carried on in the interest of pure theoretical science were made practical use of, but their application remained a mere chance by-product. Only slowly did the pedagogical problems themselves begin to determine the experimental investigation. The methods of laboratory psychology were applied for the solving of those problems which originated in the school experience, and only when this point was reached could a truly experimental pedagogy be built on a psychological foundation. We stand in the midst of this vigorous and healthy movement, which has had a stimulating effect on theoretical psychology itself.

We find a similar situation in the sphere of the physician. He could not pass by the new science of the mind without instinctively feeling that his medical diagnosis and therapy could be furthered in many directions by the experimental method. Not only the psychiatrist and nerve specialist, but in a certain sense every physician had made use of a certain amount of psychology in his professional work. He had always had to make clear to himself the mental experiences of the patient, to study his pain sensations and his feelings of comfort, his fears and his hopes, his perceptions and his volitions, and to a certain degree he had always tried to influence the mental life of the patient, to work on him by suggestion and to help him by stimulating his mind. But as far as a real description and explanation of such mental experiences came in question, all remained a dilettantic semi-psychology which worked with the most trivial conceptions of popular thinking. The medical men recognized the disproportion between the exactitude of their anatomical, physiological, and pathological observation and the superficiality of their self-made psychology. Thus the desire arose in their own medical circle to harmonize their psychological means of diagnosis and therapy with the schemes of modern scientific psychology. The physician who examines the sensations in a nervous disease, or the intelligence in a mental disease, or heals by suggestion or hypnotism, tries to apply the latest discoveries of the psychological laboratory. But here, too, the same development as in pedagogy can be traced. The physicians at first made use only of results which had been secured under entirely different points of view, but later the experiments were subordinated to the special medical problems. Then the physician was no longer obliged simply to use what he happened to find among the results of the theoretical psychologist, but carried on the experiments in the service of medical problems. The independent status of experimental medical psychology could be secured only by this development.

In somewhat narrower limits the same may be said as to the problems of law. A kind of popular psychology was naturally involved whenever judges or lawyers analyzed the experience on the witness stand or discussed the motives of crime or the confessions of the criminal or the social conditions of criminality. But when every day brought new discoveries in the psychological laboratory, it seemed natural to make use of the new methods and of the new results in the interest of the courtroom. The power of observation in the witness, the exactitude of his memory, the character of his illusions and imagination, his suggestibility and his feeling, appeared in a new light in view of the experimental investigations, and the emotions and volitions of the criminal were understood with a new insight. Here, too, the last step was taken. Instead of being satisfied with experiments which the psychologist had made for his own purposes, the students of legal psychology adjusted experiments to the particular needs of the courtroom. Investigations were carried on to determine, the fidelity of testimony or to find methods for the detection of hidden thoughts and so on. Efforts toward the application of psychology have accordingly grown up in the fields of pedagogy, medicine, and jurisprudence, but as these studies naturally do not remain independent of one another, they all together form the one unified science of applied psychology.[2]

As soon as the independence of this new science was felt, it was natural that new demands and new problems should continue to originate within its own limits. There must be applied psychology wherever the investigation of mental life can be made serviceable to the tasks of civilization. Criminal law, education, medicine, certainly do not constitute the totality of civilized life. It is therefore the duty of the practical psychologist systematically to examine how far other purposes of modern society can be advanced by the new methods of experimental psychology. There is, for instance, already, far-reaching agreement