CHAPTER V 
HOW POPULATION INCREASES 
THE question how any particular population increases, 
and why its rate of increase may change at different 
stages of its development, is not only interesting per se, 
it is, as we have seen, a question of great practical 
importance, and is specially so whenever an attempt 
is made to forecast its future growth. It may be 
mentioned that, between 1909 and 1923, the world 
was increasing at a rate which would double its popu- 
lation in 104-32 years, or say in round numbers 10§ 
years. This may be taken as one of the most recent 
fairly accurate estimations covering a sufficient period 
to give results of value. 
Accepting this, and assuming—to suppose the 
impossible—that this rate of increase is to go on 
unchanged, it is instructive to inquire what the effect 
would be as regards the total population at different 
dates, how many persons this would give to the square 
mile, and further what area, on the average, each would 
occupy. The answers to these queries enables us 
better to envisage the significance of the numbers. In 
the table below the date-years are Iog apart, the 
population being always doubled. The second line 
gives their numbers in millions. The third is the 
number per square mile. The fourth gives the side of 
a square, which each would occupy if they could be 
distributed uniformly over the 52-5 millions of square 
miles of land-surface. The fifth line gives the name 
of the country whose average density of population 
most nearly agrees with that shown on line three, 
Bl