7. The magnitudes of physical science are, on the one hand, number and direction, and, on the other hand, time, mass, and distance.
We are not here concerned with the metaphysics of these magnitudes, nor even with such critical discussion as may fall within the limits of a scientific theory of knowledge. Students of the physical sciences would disagree entirely as to such matters, and yet they coöperate everywhere in attempting to express the material world in terms of these magnitudes. As regards number and direction, it is evident that the units of measurement are given in the nature of things, and these units were used in the beginnings of science. As regards time, mass, and distance, the units of measurement are conventional, and are being slowly adjusted as science advances. Astronomy seems to have been the earliest of the sciences, and consisted at first of the relative positions and times due to the movements of the heavenly bodies. Distance was soon measured in surveying, architecture, and music. Mass was measured somewhat later, and the development of the idea of energy belongs to modern times. The question we have to consider is, whether there are mental magnitudes analagous to those of the physical world, and, if so, whether they may be measured and correlated. Is a mental mechanics possible?
8. Number and statistics may be used in psychology.
Number occupies a peculiar position, all measurement depending on ratios. The place of pure enumeration in the physical sciences has not perhaps been exactly defined. But it seems to be mostly unimportant, as when it is said that there
sui generis, and even though quantitive determinations were impossible, the laws governing the interaction and sequence of changes of consciousness could be determined apart from any question of the relation of mind to body. Aristotle might hold that the chief use of the brain is to supply the eyes with tears, and yet be a far better psychologist than M. Luys, who is considered an authority on the brain, but who writes: "Judgment is the principal operation of cerebral activity," etc. (The Brain and its Functions, 289.) Nor is psychology an art to "charm a chronic insane delusion away" (James: Phil. Review, I. 153). Professor James's Psychology would not be the important work it is, were it confined to the correlation of brain changes and consciousness, and the therapeutic value of hypnotism.
