events, in order to explain , must themselves be psychical and not physiological. However important such knowledge as that of which we have just been speaking may be for physiology, it has of itself no value for psychology. It tells simply what and how physiological elements serve as a basis for psychical acts; what the latter are , or how they are to be explained, it tells us not at all. Physiology can no more, of itself, give us the what, why, and how of psychical life, than the physical geography of a country can enable us to construct or explain the history of the nation that has dwelt within that country. However important, however indispensable the land with all its qualities is as a basis for that history, that history itself can be ascertained and explained only through historical records and historic conditions. And so psychical events can be observed only through psychical means, and interpreted and explained by psychical conditions and facts. What can be meant, then, by saying that the rise of this physiological psychology has produced a revolution in psychology? This: that it has given a new instrument, introduced a new method ,-- that of experiment, which has supplemented and corrected the old method of introspection. Psychical facts still remain psychical, and are to be explained through psychical conditions; but our means of ascertaining what these facts are and how they are conditioned have been indefinitely widened. Two of the chief elements of the method of