598 THE AMERICAN JOURNAL OF SOCIOLOGY
chemistry, biology, and psychology, confront the same problem. In sociology, however, the problem is more complicated than in the other sciences. In every case equilibrium results from a certain internal arrangement which is in harmony with external conditions. For example, take an instantaneous view of each of the consecutive positions of a runner. At each moment his body is in equilibrium. At each moment it is in a static condition. At each moment, and with each movement, it is in a state of repose. Even his fall is an inferior equilibrium, a return to equilibrium which has been disturbed by a maladroit adaptation of the internal parts to the external conditions. Like- wise in every apparent state of repose his structure is in the dynamic state. Social equilibrium, like biologic statics, is always an unstable equilibrium, always changing ; changing because of variations of the environment, or because of the action of the aggregate upon the environment corresponding continually to variations of the structure of the aggregate; also because of vari- ations of the aggregate corresponding to variations of the dif- ferent social environments.
By virtue of the laws of continuity of the mass, and of cor- relation of all its parts laws which we shall explain later every variation in any one of the parts corresponds to a varia- tion of the whole. The variation of the whole may, moreover, precede, accompany, or follow variation in any one of the parts, but the phenomenon is unavoidable and constant. Finally, when social statics is brought to its simplest conditions, it may be reduced to equations of forces, in the same way as mechanical statics.
Statistics, because it notes the frequency, intensity, and dura- tion of the properties of the social forces, is the natural prepara- tion for statics and its natural instrument. By means of statistics we are able not only to determine the abstract, qualitative conditions of social equilibrium, but also the concrete, quantita- tive conditions, so that we may measure them exactly. For example, when we learn by means of statistics that the nourish- ment of the laboring or productive force in the social aggregate, the Belgian nation, is less than the physiological expendi-
