The range of psychological instruments is very wide. In the sphere of sensation we have apparatus for work on color mixture, contrast, adaptation, after-images, color blindness and the spatial distribution of the retinal sensitivity; for work on tonal fusion, beats, combination tones; for work on the sensations of pressure, warmth and cold, on the sensations of taste and smell and on the organic (muscular, articular, etc.) sensations. In the sphere of affection we have instruments which register exactly the bodily changes that accompany change in the affective disposition (pleasantness and unpleas antness) : pulse recorders or sphygmographs, breathing recorders or pneumographs, volume recorders or plethysmographs and strength re corders, ergographs and dynamographs. In the sphere of attention we have instruments for measuring the duration and the range or span of the attentive state. In the sphere of perception we have, for example, all sorts of instruments for the analysis and synthesis of visual space perception: among them the famil iar stereoscope and its converse, the pseudo scope; instruments for the measurement of the various types of optical illusion, and so on. Memory and association have a whole labor atory of apparatus of their own; one of these, which exposes at regular intervals a series of words or syllables to be memorized, is shown in Fig. 12.
It should be clear, even from this hasty and imperfect survey that the arrangement and fur nishing of a modern psychological laboratory is a very complicated matter. There must be a large lecture-room, fitted with all conveniences for desk demonstrations and class experiments. There must be a dark room for work in psy chological optics, and an absolutely quiet room for work in psychological acoustics. There should be a special room, specially ventilated, for work on olfactory sensation and perception.
There must be a series of fairly large and well lighted rooms for the group work of under graduate students. There must be a series of closet-rooms for the research students. There must be research laboratories for the instruct ing staff. There must be a workshop, or rather there should be two workshops•— one in the general laboratory, in which the students them selves may assemble complicated pieces, and make the necessary modifications in existing in struments, and another sacred to the •mechani cian, who is an indispensable part of the staff of an adequate laboratory. Every new investi gation — and experimental psychology presents far more novel problems than can be solved, at the present rate of work, in a human genera tion— demands its own new set of instruments. It must be confessed that, as things are, psy chology is for the most part rather shabbily housed. The science of mind appeared on the scene later than the science of life and of in organic nature; and, when it came, funds and buildings were very largely pre-empted. There are, however, some signs that it is coming to its rights in this regard; and the next 10 years should see a very considerable improvement in the material conditions under which experi mental psychologists are called upon to work in colleges and universities.
Bibliography.— Wundt, W. M.,