386 THE POPULAR SCIENCE MONTHLY 



A. P = 89.7 C. P = S9.7 E. P = 91.4 



B. P = 89.3 D. P = 91.4 F. P = 91.3 



It will be observed that these forecasts fall into two classes, in one 

 of which the numbers run between eighty-nine and ninety millions and 

 the other a little over ninety-one millions. The former are based more 

 strictly upon the formula as it stands, including the entire set of ob- 

 servations. In the latter, greater weight is given to more recent obser- 

 vations, as it is supposed that they represent more nearly the present 

 rate of increase in the population. The last formula (F) is based upon 

 three observations only, those for 1880, 1890, and 1900. It is probable 

 that while the formulae yielding the lower results conform more nearly 

 to the population of our country in the past, the results which are 

 yielded by the other set of formulas are more correct for 1910. As an 

 illustration of the closeness with which the formula? conform to past 

 conditions, we will determine the results for each census by means of 



formula : 



P = 5.13 + 0.358X + 0.666X 2 . 



The formula published by Dr. H. S. Pritchett, in The Populak 

 Science Monthly, of November, 1900, agreed more closely with the 

 results of past censuses than the one used here. It will be noted that 

 while the sum of the various deviations resulting from each application 

 of the formula is 6.7 millions, that from Dr. Pritchett's formula is only 

 about 4 millions. This formula, however, does not seem to fit the 

 future conditions so well as the one employed here, for it gives a popu- 

 lation of 77.5 millions for 1900, while the census returns show it to be 

 76.3 millions. 



As a method of determining the population of the United States 

 during the coming decades, the application of these formulae is inter- 

 esting. By the use of formula E — 



P = 5.4 + 0.12X+ 0.7X 2 



