_What is involved in a Full Study of the Relative Density of Populations._--A full treatment of the subject of the comparative density of population in different places would include an extended study of the kinds of industry which find their natural homes in densely peopled countries and of those which flourish in sparsely peopled ones, and a much more detailed tracing than it is possible here to undertake of those changes in the character of industries everywhere which result from a leveling out of differences in population. Clearly, if all America were to become as crowded with inhabitants as are Holland and Belgium we should develop industries of a different type from those that we now have, and the change would be in the direction of producing relatively more form utilities and relatively less of the elementary utilities. Labor and capital would move from the subgroups which in our table we have called _A_, _B_, and _C_ toward _A'''_, _B'''_, and _C'''_. We should spend more of our energy in making finished goods and less in getting raw materials. I shall note in a very general way the changes in social industry caused by increase of population without looking forward to that remote time when the density of population shall be equalized. _Why an Approximately Static Adjustment of Industries within the Central Area permits Unequal Density of Population in Different Parts of It._--We exclude from view the ultimate static adjustment of the whole world, and content ourselves with an approximate adjustment within society as we have defined it. Even within this limit there are inequalities in the density of population which it would require a very long time to remove, and a perfectly static state cannot be reached till they are leveled out. The selection of industries in Texas and in Belgium cannot be, in the ultimate sense, natural till population in these two regions is so adjusted that there is no longer an economic motive for migrating from the one to the other. If, in order to determine what an absolutely static condition for the central society would be, we were to apply the rule of imagining all new dynamic influences precluded and of allowing time enough to elapse to bring about a normal apportionment of population within that limited area, we should encounter a measure of the same difficulty which confronted us when we proposed to attain a similar static state for the entire world, though the trouble would be less serious in degree. In waiting long enough for population to distribute itself naturally, we cut off influences that, within that period, will affect production and distribution far more than the change in population will affect them. In so far as Texas or any newly occupied region is concerned, the changes thus precluded are those which would have tended to reverse the effect of the redistribution of population. Migrations from Belgium to Texas, if extensive and long continued,