PSYCHOLOGICAL APPARATUS. The object of the psychological laboratory is, in brief, to standardize the conditions of intro spection (see PSYCHOLOGY) ; to make it possible that psychological observations shall be taken in the most favorable circumstances, so that they may be repeated (by the same or by other observers), isolated and varied. It is only under these experimental conditions that the results of introspection can lay claim to universal validity. The single, hap-hazard observation, made under all the distractions of ordinary life, is worth as little in psychology as it would be in physics or physiology. Hence it was nothing less than a revolution in psychology when W. Wundt founded in 1879, at Leipzig, the first psycholog ical laboratory that the world had known. Wundt's example was quickly followed in America by G. S. Hall, who founded a labora tory in 1881 at the Johns Hopkins University. At the present time all the more important seats of learning in Germany and the United States are equipped with psychological laboratories, while there are a large number distributed through the other civilized countries of the world.
To give an idea of the problems with which the experimental psychologist is busied, we may mention some of Wundt's early apparatus and the questions which he hoped to solve by their aid. In 1861 Wundt devised the complication pendulum (Fig. 1) in order to determine the behavior of attention under the influence of two simultaneous stimuli. Suppose that I am sub jected, at one and the same time, to a sight and a sound. Do I hear and see together? Do I see before I hear or hear before I see? The question was of great practical import ance, since it was involved in the "eye and method then in vogue for a certain type of astronomical observations. Its general psy chological importance is obvious. The instru ment now "consists of a large, heavy, wooden pendulum. The bulb carries a pointer, which as the pendulum swings passes over a circular scale. Near the point of rotation m there is fixed to the stem a horizontal metal bar ss. A movable vertical standard Is has attached to it a metal spring, also in the horizontal line.
The spring is fixed in such a way that the bar ss in passing by produces a short single click, the end of the bar and the point of the spring just touching each other, while the shock is so slight that the course of the heavy pendulum is not noticeably affected. By watching the course of the pointer attached to the bulb of the pendulum, while the upper part of the instru ment remains concealed, we can determine at what point of its passage to or fro the click of the spring takes place. For example, if the pointer appears to be at e' at the moment of the sound, the bar ss will be in the position di, and this will mean that the passage is put too early. If the pointer seemed to be at e", the bar would be in the position cd, and this would mean that the passage was put too late. If we know the duration and amplitude of the pendular vibra tion and measure the angular difference between e' or e" and the actual point at which the bar ss comes in contact with the spring, we can easily calculate the interval between the giving of the sound and its apperception? The instru ment has been gradually refined and its scope extended until it now has the form shown in Fig. 2.
Another of Wundt's early experiments was made to determine the range of consciousness for auditory impressions. I hear a number of similar sounds; say, of metronome strokes. How large a group can I keep in mind at once? I must not count; for that would mean a sep arate attention and a verbal association to every sound. Suppose that a group of 20 strokes, marked off by bell-tones, is followed by a group of 21 marked off in the same way. Do the two groups appear the same or can I tell that they are of different lengths? This question was answered by Wundt by aid of the instru ments shown in Fig. 3. The metronome M gave the series of sounds, and the limits of the series were indicated by the bell G. Fig. 4 shows a later and better instrument for the determination of the range of consciousness to visual impressions.