NATURAL DEATH, PUBLIC HEALTH 255 



comes into play some factor not now known, and which 

 has never operated during the past history of the country, 

 to make the rate of growth more rapid. The latter con- 

 tingency appears improbable. The 1920 census confirms 

 the result, indicated by the curve, that the period of most 

 rapid population growth was passed somewhere in the 

 last decade. The population at the point of inflection 

 works out to have been 98,637,000, which was, in fact, 

 about the population of the country in 1914. 



The upper asymptote given by the equation has the 

 value of 197,274,000 roughly. This means that the maxi- 

 mum population which continental United States, as now 

 areally limited, will have, will be roughly twice the pres- 

 ent population; provided no fundamental new factor 

 comes into play in the meantime, different in its magni- 

 tude and mode of operation from any of the factors which 

 have influenced population growth in the past. This 

 state of affairs will be reached in about the year 2,100, a 

 little less than two centuries hence. Perhaps it may be 

 thought that the magnitude of this number is not suffi- 

 ciently imposing. It is so easy, and most writers on 

 population have been so prone, to extrapolate population 

 by geometric series or by a parabola or some such purely 

 empirical curve, and arrive at stupendous figures, that 

 calm consideration of real probabilities is most difficult 

 to obtain. While we regard the numerical results as 

 only a rough first approximation, it remains a fact that 

 if anyone will soberly think of every city, every village, 

 every town in this country having its present population 

 multiplied by 2, and will further think of twice as many 

 persons on the land in agricultural pursuits, he will be 

 bound, we think, to conclude that the country would be 



