[1] Exceptional local conditions may make an influx of population for a time a cause of greater productivity rather than of less. The general and permanent effects are otherwise, and it is on these that the present argument rests. [Illustration] If the line _BB'_ represents the unequal level of _natural_ wages in different localities, on the assumption that populations remain unequal, the undulating curve _DD'_ which crosses and recrosses the line _BB'_ represents actual local rates fluctuating about the standard ones. _How a Static Adjustment for the World is a Dynamic Influence within a Limited Part of It._--Commodities are, by traffic, crossing the social boundary in both directions, and with the goods there go and come influences that affect the economic life of the central society. Methods and modes of organizing business are taught by each region to the other, though most of the teaching is done by the people of the center and most of the learning by those of the environment. All this affects the center and falls within our study. It has dynamic effects within the center, though it is only a part of a static adjustment for the world as a whole. If the grand bank of Newfoundland were to subside to the level of the middle of the Atlantic, there would be a great rush of water toward the place that the banks now occupy, but this would be only what is required in bringing the general level of the sea to an equilibrium. It would be essentially a static phenomenon, but for the region of the banks it would be dynamic in the highest degree. A rush of population from China to America would be a change tending to establish an equilibrium of population in the world, but it would be a startling bit of dynamics for America. Teaching the Chinese all the mechanical arts that we know would be creating an equilibrium of another sort, in which methods would be similar in the two countries; but for China itself this acquiring of practical arts would be dynamics acting on a vast scale. What is a static adjustment for the world is a dynamic change for parts of the world, and all such changes that can occur within the area of economic society proper and within the period we can wisely include in our study we need to take into account. Changes in population, wealth, method, and organization must be studied, however they may originate. CHAPTER XV PERPETUAL CHANGE OF THE SOCIAL STRUCTURE