Ch. xi. On the Fruitfuhwss of Marriages. 475 



a number of births nearly equal to the births 

 produced by all the marriages included in the 

 period; and of course the prolifickness of these 

 marriages. But if the population of a country be 

 increasing regularly, and the births, deaths and 

 marriages continue always to bear the same pro- 

 portion to each other, and to the whole popula- 

 tion, it is evident that all the births of any period 

 will bear the same proportion to all the births of 

 any other period of the same extent, taken a cer- 

 tain number of years later, as the births of any 

 single year, or an average of five years, to the 

 births of a single year, or an average of five years, 

 taken the same number of years later ; and the 

 same will be true with regard to the marriages. 

 And consequently, to estimate the prolifickness 

 of marriages, we have only to compare the mar- 

 riages of the present year, or average of five years, 

 with the births of a subsequent year, or average 

 of five years, taken 3-| years later. 



We have supposed, in the present instance, 

 that each marriage yields four births; but the 

 average proportion of births to marriages in Eu- 

 rope is 4 to 1 ;* and as the population of Europe 

 is known to be increasing at present, the proli- 

 fickness of marriages must be greater than 4. If, 

 allowing for this circumstance, we take the 

 distance of 4 years instead of 3^ years, we 

 may not be far from the truth. And though 



* The true proportion will be greater, if, as before stated, there 

 is reason to believe that in all registers the omissions in the births 

 and deaths are more numerous than in the marriages. 



