This preliminary scheme, though more extensive than that of the London Laboratory, is plainly co-ordinate with the latter over a very large range of subjects. One is tempted to ask, then: What will be done in the anthropometric laboratory proper? Or, to give the question a more general form: What constitutes the difference between a psychological and an anthropometrical experiment?
Obviously, a number of investigations – those into height, weight, span of arms, size and shape of head, and so forth – can be ruled out at once. They have no direct connection with psychology. Where, in the other cases, does anthropometry end, and psychology begin? Let us consider a typical instance; that of reaction time. To the psychologist, the reaction experiment has a threefold importance. Firstly, it presents a means of training the student of psychology in the exclusively psychological method, – introspection. Secondly, the reaction is the exact type of a voluntary action: practice in it is practice in control of attentional direction. Thirdly, its time value may be useful for the temporal definition of mental processes; though this, its most patent aspect, has up till now proved itself the most difficult to turn to true psychological account. And all this implies that psychological experimentation in the sphere of reaction is no easy matter. The subject must be educated by a long course of practice; all disturbing influences must be eliminated, whether they are external or internal; the recording apparatus must be the most accurate possible. More than that: not every one is capable of acting as subject. The psychological Anlage is necessary here, just as is the physiological in experiments upon the nervous system. Of seven normal persons who offered to take part in an investigation of my own into the reaction time of visual discrimination, only two proved to possess the needful power of concentration of the attention, patience, and ability to control their results at all constantly by introspection. Nor is this by any means an isolated experience.
With the anthropometrical reaction it is quite different. The experiment is not controlled, as regards direction of the
