iology and physics. How the methods and results of these sciences could be turned to profit, without any sacrifice of its own method or autonomy, was, for psychology, not easy to determine. Fortunately, with some friendly discussion regarding metes and bounds, psychology has not only held its own, but has also rendered service to its neighbors.
It has not abandoned its traditional method. For the analysis of the various states, processes, tendencies and activities which appear in the individual consciousness, introspection cannot be dispensed with. If it is supplemented, as we nowadays say, by other methods, this implies not that self-observation of a keener sort is our prerogative, but rather that, with clearer knowledge of the conditions upon which our mental life depends, we are enabled to study each process both in itself and in its manifold relations. Comparison is thus a conspicuous and even an essential feature of modern psychological methods.
Psycho-physical research, as the name indicates, seeks to determine the relations between mental processes and physical processes. Whether this determination and its quantitative results should be called measurement, is still a subject for discussion. But there can no longer be any question as to the value for psychology of experimental methods. With the aid of these it is now possible to compare accurately changes in sensation and variations in the quality and intensity of external stimuli, to observe closely the organic modifications which accompany emotion, and to fix, within reasonable limits, the time-rate of the most complex processes. In a general way, of course, it has always been known that there was some sort of connection between the psychical and the physical; what modern psychology accomplishes is the more detailed and more exact investigation of that connection. Similarly with the phenomena of association, memory, attention, inhibition and fatigue; their importance has long been recognized, but their thorough analysis is the outcome of experimental work.
A complete solution of the problems that are offered in this portion of the field would leave on our hands the larger problem as to the development of consciousness. That mind is a growth, that its behavior in any given moment is affected by its behavior in all the past moments, all psychologists admit. But there is much to be learned regarding the successive phases of this growth. By what steps does the mind advance from the earliest impressions of childhood to the complex activities of adult life? What share in the process shall be assigned respectively to heredity, to the influence of environment, to the mind's own reaction by impulse, imitation and the growing consciousness of ends to be attained? The answer to such questions involves obviously a comparison between later forms of mental life and its simpler beginnings which may lead us far into the province of biology. Certainly no theory of evolution can afford to disregard the mental factors any
