needed, beside endurance and industry, was a quick power of perception accompanied by quick responsive action.  He knew that the psychological laboratory has developed methods for a very exact measurement of the time needed to react on an impression with the quickest possible movement; it is called the reaction time, and is usually measured in thousandths of a second.  He therefore considered it advisable to measure the reaction-time of the girls, and to eliminate from service all those who showed a relatively long time between the stimulus and reaction.  This involved laying off many of the most intelligent, hardest-working, and most trustworthy girls.  Yet the effect was the possibility of shortening the hours and of reducing more and more the number of workers, with the final outcome that thirty-five girls did the work formerly done by a hundred and twenty, and that the accuracy of the work at the higher speed was two thirds greater than at the former slow speed.  This allowed almost a doubling of the wages of the girls in spite of their shorter working-day, and at the same time a considerable reduction in the cost of the work for the factory.  This excursion of an efficiency engineer into the psychological laboratory remained, however; an entirely exceptional case.  Moreover, such a reaction-time measurement did not demand any special development of new methods or any particular mental analysis, and this exception thus confirms the rule that the followers of scientific management principles have recognized the need of psychological inquiries, but have not done anything worth mentioning to apply the results of really scientific psychology.  Hence the situation is the same as in the field of vocational guidance.  In both cases a vague longing for psychological analysis and psychological measurement, but in both cases so far everything has remained on the level of helpless psychological dilettantism.  It stands in striking contrast with the scientific seriousness with which the economic questions are taken up in the field of vocational guidance and the physical questions in the field of scientific management.  It is, therefore, evidently the duty of the experimental psychologists themselves to examine the ground from the point of view of the psychological laboratory.

VII

THE METHODS OF EXPERIMENTAL PSYCHOLOGY

We now see clearly the psychotechnical problem.  We have to analyze definite economic tasks with reference to the mental qualities which are necessary or desirable for them, and we have to find methods by which these mental qualities can be tested.  We must, indeed, insist on it that the interests of commerce and industry can be helped only when both sides, the vocational demands and the personal function, are examined with equal scientific thoroughness.  One aspect alone is unsatisfactory.  It would of course be possible to confine the examination to the individual mental