It was the great intellectual service of Copernicus that he conceived of a world in motion instead of a world at rest. So anthropo-geography must see its world in motion, whether it is considering English colonization, or the westward expansion of the Southern slave power in search of unexhausted land, or the counter expansion of the free-soil movement, or the early advance of the trappers westward to the Rockies after the retreating game, or the withdrawal thither of the declining Indian tribes before the protruding line of white settlement, and their ultimate confinement to ever shrinking reservations. In studying increase of population, it sees in Switzerland chalet and farm creeping higher up the Alp, as the lapping of a rising tide of humanity below; it sees movement in the projection of a new dike in Holland to reclaim from the sea the land for another thousand inhabitants, movement in Japan's doubling of its territory by conquest, in order to house and feed its redundant millions. The whole complex relation of unresting man to the earth is the subject matter of anthropo-geography. The science traces his movements on the earth's surface, measures their velocity, range, and recurrence, determines their nature by the way they utilize the land, notes their transformation at different stages of economic development and under different environments. Just as an understanding of animal and plant geography requires a previous knowledge of the various means of dispersal, active and passive, possessed by these lower forms of life, so anthropo-geography must start with a study of the movements of mankind. [Sidenote: Mobility of primitive peoples.]