October 6, 1911] 



SCIENCE 



433 



PAST AND PROSPECTIVE POPULATION OP MAINLAND 

 UNITED STATES 



living) ; but already the railways are passing 

 under regulation in the public interest by the 

 Interstate Commerce Commission, vphile v?ith 

 that proper development of waterways des- 

 tined to come before the next decennial census 

 the aggregate cost of freight movement will 

 be reduced 20 per cent, or 30 per cent. So on 

 the whole any apparent paralysis in growth 

 arising in imperfect economic balance would 

 seem to be more apparent than real, and at the 

 worst of temporary character. 



The decennial percentage increment of pop- 

 ulation decreases normally with growth. Dur- 

 ing the twelve decades covered by the United 

 States census the increments have varied from 

 36.4 per cent. (1800-1810) to 20.7 per cent. 

 (1890-1900), averaging 30.4 per cent; the 

 mean for the earlier six being 34.4 per cent. 

 and for the later six 25.9 per cent. The de- 

 creases have not been uniform; during the 



second decade there was a slight increase, 

 during the sixth a decided increase, during 

 the ninth (following the civil war decade) a 

 still greater increase, and during the twelfth 

 a slight increase (from 20.7 per cent, to 21 

 per cent.). 



In the extrapolation based on (1) past 

 growth, (2) current promise of prospective 

 growth and (3) limitation of growth by water 

 supply, it may be assumed that the percentage 

 increment will diminish steadily at the rate 

 of 1 per cent, during each decade for a cen- 

 tury, and then more slowly (1 per cent, during 

 each two decades) for two centuries more, 

 when the population limit fixed by water sup- 

 ply may be reached. Reckoned on this as-' 

 sumption, the prospective population is shown 

 in the accompanying table and diagram (the 

 figures from 1790 to 1810 from Census Bulle- 

 tin 109), in which Gannett's estimates are 

 introduced for comparison, and extended from 

 A.D. 2100 to A.D. 2210 on the basis of per- 

 centage increments decreasing conformably 

 with his figures for the two preceding cen- 

 turies. 



It is true that in the era of commercial 

 interchange on which the world has fairly 

 entered no country exists wholly unto itself, 

 but subsists in part on the resources of other 

 lands and in prospectively increasing degree 

 on those of the waters ; theoretically, the pop- 

 ulation-estimate for any country should take 

 account of the capacity of other countries for 

 yielding and exchanging necessaries of life — 

 i. e., the materials for food and clothing; but 

 practically, the cost of exchange (including 

 transportation) imposes a burden directly on 

 the consumers and less directly on the pro- 

 ducers of commodities, and if these are prime 

 necessaries this burden tends quickly to be- 

 come unbearable — ^when the people on whom 

 it rests must cease increasing and may even 

 decrease until an economic balance is at- 

 tained. Yet by reason of areal extent and 

 variety of resources, mainland United States 

 is potentially self-contained in exceptional de- 

 gree (unexcelled natural wealth in materials 

 for manufacturing and the development of 

 power are combined with a large capacity for 



