Page:Philosophical Review Volume 2.djvu/334

320 science, because they are able to treat only a few equations amid an indefinite number. The complexity of both physical and mental phenomena is very great, but the order of the universe is perfect.

The psychology with which this paper is concerned is not a part of physiology. Measurements of the mind, on the one hand, and of the body, on the other, may teach us that there is a complete correlation between the mental and the physical order. Should this correlation be established and its nature determined, it would be possible to measure either the physical or the mental phenomena, as might be found the more convenient. But the measurements to be treated here are of mental quantities or, at all events, of quantities which are functions of mental conditions. It seems, indeed, that our knowledge of the mind is less partial and uncertain than our knowledge of the nervous system. We have, for example, a considerable mass of fact and systematic knowledge concerning the nature and interaction of sensations. Starting from this knowledge, theories have been elaborated concerning the physiological processes in the eye and ear. The mental data are admitted by all, while the physiological hypotheses are in dispute. There is, again, some settled knowledge concerning feeling, attention, etc., whereas we are in absolute ignorance concerning the molecular changes in the brain which may accompany these mental processes. The advance of science will demand a more exact definition of the subject-matter of physics, of physiology, and of psychology, in which psychology must be allotted the measurements and quantitive relations considered in this paper.