the Young-Helmholtz theory of color, presents investigations about which psychologists are bound to trouble for many a day.
Thus, the significance of Helmholtz's career may be traced to his combination of the mathematical and exact-scientific with the humanistic interest, a union to which we may attribute our greatest advances alike in science and in intellectual insight. And this fitted him rarely to execute work of abiding value for physiological psychology. No one has contrived to reach better results in those unplumbed reaches of experience where the joint action of body and mind can be studied with a measure of success. Proceeding from the theory of "specific energy" of his master Müller, he wrought it out in detail, eminently for the mechanism of sight and hearing, by experimental methods and by mathematico-physical analyses. Upon the romantic interest in nature stimulated by Schelling he superimposed the critical processes of Kant, armed with all the resources of the most delicate apparatus and rigid analytic procedure. This coalition of endowment and outlook continued in the three leaders who were destined to build psychology into an independent science—Lotze, Fechner and Wundt. To them we shall turn next.