6 Statement of the Subject. Ratios of Bk. i. 



population. Very severe labour is requisite to 

 clear a fresh country ; such situations are not in 

 general considered as particularly healthy ; and 

 the inhabitants, probably, are occasionally subject 

 to the incursions of the Indians, which may de- 

 stroy some lives, or at any rate diminish the fruits 

 of industry. 



According to a table of Euler, calculated on 

 a mortality of 1 in 36, if the births be to the 

 deaths in the proportion of 3 to 1 , the period of 

 doubling will be only 12 years and 4-5ths.* And 

 this proportion is not only a possible supposition, 

 but has actually occurred for short periods in 

 more countries than one. 



Sir William Petty supposes a doubling possible 

 in so short a time as ten years.f 



But, to be perfectly sure that we are far within 

 the truth, we will take the slowest of these rates 

 of increase, a rate in which all concurring testi- 

 monies agree, and which has been repeatedly 

 ascertained to be from procreation only. 



It may safely be pronounced, therefore, that 

 population, when unchecked, goes on doubling 

 itself every twenty-five years, or increases in 

 a geometrical ratio. 



The rate according to which the productions of 

 the earth may be supposed to increase, it will not 

 be so easy to determine. Of this, however, we 

 may be perfectly certain, that the ratio of their 



* See this tabic at the end of chap. iv. book ii. 

 t Polit. Arith. p. 14". 



