BASIS OF INVESTIGATION. 



at the rate of twenty per cent, then at the end of fifty-year periods 



the population will stand as follows: 



This shows that at the end of three hundred years the rapidly 

 increasing- blacks would be 13.6 times as numerous as the slowly 

 increasing whites. But a time comes in each community when 

 the population cannot further increase, or can only increase slowly. 

 This stoppage of numerical increase takes place gradually, and is 

 assumed to first affect those which are normally less prolific, so 

 that before the time when increase ceases for the community, the 

 less prolific have begun to decrease if they have not become wholly 

 extinct. 



LOWER CLASSES MOST PROLIFIC. 



In the civilized communities of Europe and America there 

 exist two classes of people, known respectively as the intelligent 

 or upper class, and the ignorant or lower class. There is no dis- 

 tinct line of demarkation between them, as they grade into each 

 other through innumerable intermediate degrees. Yet we all recog- 

 nize these two classes by the intellectual power of the individuals 

 which compose them. While there is no natural line of division 

 between them we may, for convenience, draw an arbitrary line and 



