The division of the sciences reflects the diversity of human interests; it represents the economical adaptation of organized thought to the conditions of reality; and it likewise recognizes the intrinsically and objectively distinct realms and aspects, in which and under which phenomena occur. It is obvious that the sciences were shaped by human needs; that physics and chemistry and geology and biology and psychology do not constitute independent departments of nature's régime, but only so many aspects of complex natural activities; that a cross-section of the composite happenings of a cosmic moment would reveal an endlessly heterogeneous concomitance of diverse forms of energy acting upon diverse types of material; that, as we confine our attention somewhat arbitrarily to one or another component of the aggregate, we become physicists, or chemists, or geologists, or biologists, or psychologists; that, indeed, Nature is all things to all men. There is, furthermore, a community of spirit between the several sciences, as there is a logical unity of method and purpose within the realm of each. However ignorant they may be of one another's facts, the chemist and the psychologist readily appreciate one another's purposes, and find a bond of sympathy in the pursuit of a commonly inspired though differently applied method. The search for objective truth, the extension of the realm of law and regularity, the expansion and organization of the army of facts constantly marshaled and reviewed and made ready for service, the ever widening development of principles and the furthering of a deeper insight into their significance,--these are ideals for the advancement of science, far easier of expression than of execution, but the clear and accepted formulation of which itself attests a highly developed stage of accurate thought. A clear-cut conception of the purposes and methods of scientific investigation and of the scope of the several sciences is a dearly bought product of generations of well-directed, as also of misdirected, effort. The path of progress leading to this achievement has been tortuous and indirect; there has been much expenditure of energy that resulted merely in marking time, in going through the movements of locomotion but with no advance, in following a false trail, or, through a loss of the sense of direction, in coming back after a circuitous march to an earlier starting-point. It is easy, when a certain height is reached, to look down and back, and see how much more readily the ascent might have been accomplished; but it is a very different matter to form a successful plan for attaining the next higher commanding point. It is inevitable that there shall be differences of opinion as to course and manœuvre, and errors of judgment of commission and omission; but such diversity is quite consistent with an underlying coöperation and singleness of purpose. It is in the inspiration and in the