I. ON THE MOVEMENT OF POPULATION IN GENERAL The races of European stock doubled their numbers between 1700 and 1800, and between 1800 and 1900 more than trebled them, rising from about 175 millions to 580 millions,1 Among the European races the population of England numbered about 8 millions in 1800, and four times that figure in 1900;2 and besides this enormous addition to the population at home millions of men and women were sent out to America and the colonies. Reflecting over such multiplications men have become fearful for the future. By means of a little arithmetic they have calculated that at such a speed of expansion the human race will amount to so and so by 1950, so and so by 2000, and obtain figures that are beyond any means now known, or beyond any means feasibly predictable, of raising food and clothing for them. In order to show the dangerous potentialities of human reproductive power, one expert has computed that two persons could multiply to 1,700 millions persons in two thousand years, which is about the present population on the earth. Competent sociologists and competent statisticians are alike of the opinion that the recent rate of population growth could not safely continue.3 This can be granted. The rate of the nineteenth century could not continue for many centuries, and it is doubtful whether it could continue for another century.