POPULATION OF THE UNITED STATES. 53 



1920 114,416,000 



1930 136,887,000 



1940 162,268,000 



1950 190,740,000 



1960 222,067,000 



1970 257,688,000 



1980 296,814,000 



1990 339,193,000 



2000 385,860,000 



2100 1,112,867,000 



2500 11,856,302,000 



2900 40,852,273,000 



The law governing the increase of population, as generally stated, 

 is, that when not disturbed by extraneous causes such as emigration, 

 wars and famines, the increase of population goes on at a constantly 

 diminishing rate. By this is meant that the percentage of increase 

 from decade to decade diminishes. It will be noticed that the figures 

 just given involve such a decrease in the percentage of growth. A 

 simple differentiation of the formula gives as the percentage of in- 

 crease of the population per decade 32 per cent, in 1790, 24 per cent, 

 in 1880, 13 per cent, in 1990, while in one thousand years it will have 

 sunk to a little less than three per cent. But according to the formula 

 this percentage of increase will become zero, or the population become 

 stationary, only after the lapse of an indefinite period. 



The figures just quoted are, to say the least, suggestive. Forming, 

 as they do, the most probable estimate we can make for the population 

 of the future, they suggest possibilities of the highest social and eco- 

 nomic interest. Within fifty years the population of the United States 

 (exclusive of Alaska, of Indians on reservations and of the inhabitants of 

 the recently acquired islands) will approximate 190 millions, and by the 

 year 2000 this number will have swelled to 385 millions of people; 

 while should the same law of growth continue for a thousand years the 

 number will reach the enormous total of 41 billions. 



How great a change in the conditions of living this growth of popu- 

 lation would imply is, perhaps, impossible for us to realize. Great 

 Britain, at present one of the most densely populated countries of the 

 globe, contains about 300 inhabitants to the square mile. Should the 

 present law of growth continue until 2900 the United States would 

 contain over 11,000 persons to each square mile of surface. 



With the growth of population our civilization is becoming more 

 and more complex and the drafts upon the stored energy of the earth 

 more enormous. As a consequence of all this, it would seem that life 

 in the future must be subject to a constantly increasing stress, which 

 will bring to the attention of individuals and of nations economic ques- 

 tions which at our time seem very remote. 



