484 On the Fruitf ulness of Marriages. Bk. ii. 



about 20 out of 35, instead of twenty out of 27, 

 will live to marry.* The marriages compared 

 with the births 4 years later, according to the rule 

 laid down, will in this case give 5*58 for the pro- 

 lifickness of marriages. The calculations of Mr. 

 Barton respecting the age to which half of the born 

 live, cannot possibly be applicable to America in 

 general. The registers, on which they are founded, 

 are taken from Philidelphia and one or two small 



* If the proportions mentioned by Mr. Barton be just, the ex- 

 pectation of life in America is considerably less than in Russia, 

 which is the reason that I have taken only ten years for the dif- 

 ference between the age of marriage and the age of death, instead 

 of fifteen years, as in Russia. According to the mode adopted 

 by Dr. Price, (vol. i. p. 272,) of estimating the expectation of life 

 in countries the population of which is increasing, this expecta- 

 tion in Russia would be about 38, (births -$ 6 , deaths Jg, mean - s l E ), 

 and supposing the age of marriage to be 23, the difference would 

 be 15. 



In America the expectation of life would, upon the same prin- 

 ciples, be only 32 J, (births,^, deaths, ^, mean ^Vi); and sup- 

 posing the age of marriage 22^, the difference would be 10. 



Since this was written, I have seen reason to believe, from some 

 calculations of Mr. Milne, actuary to the Sun Life Assurance So- 

 ciety, that Dr. Price's mode of estimating the expectation of life 

 in countries that are increasing is by no means correct, and that 

 the true expectation of life in such countries lies very much nearer 

 the proportion of the annual mortality, than a mean between the 

 annual mortality and the proportion of annual births ; but I retain 

 the mean proportion in the calculations of this chapter, because I 

 find that this mean expresses more nearly the period when the 

 deaths will equal the present births, or accord with the present 

 marriages, than the distance of the expectation of life. In a pro- 

 gressive country, where the annual births considerably exceed the 

 annual deaths, the period at which the annual deaths will equal the 

 present annual births is less distant than the expectation of life. 



