4 76 On the Friiitfulness of Marriages. Bk. ii. 



undoubtedly the period will differ in different 

 countries, yet it will not differ so much as we 

 might at first imagine ; because in countries 

 where the marriages are more prolific, the births 

 generally follow at shorter intervals, and where 

 they are less prolific, at longer intervals ; and 

 with different degrees of prolifickness, the length 

 of the period might still remain the same.* 



It will follow from these observations, that the 

 more rapid is the increase of population, the more 

 will the real prolifickness of marriages exceed the 

 proportion of births to marriages in the registers. 



The rule which has been here laid down at- 

 tempts to estimate the prolifickness of marriages 

 taken as they occur ; but this prolifickness should 

 be carefully distinguished from the prolifickness 

 of first marriages or of married women, and still 

 more from the natural prolifickness of women in 

 general taken at the most favourable age. It is 

 probable, that the natural prolifickness of women 

 is nearly the same in most parts of the world ; but 

 the prolifickness of marriages is liable to be af- 

 fected by a variety of circumstances peculiar to 

 each country, and particularly by the number of 

 late marriages. In all countries the second and 

 third marriages alone form a most important con- 



* In places where there are many migrations of people, the 

 calculations will of course be disturbed. In towns, particularly, 

 where there is a frequent change of inhabitants, and where 

 it often happens that the marriages of the people in the neigh- 

 bouring country are celebrated, the inferences from the proportion 

 of births to marriages are not to be depended on. 



