MECHANICS AND USEFUL ARTS. 137 



2. The Law of Numerical Relation between the Sexes. There is a natural 

 law of relations between the sexes, -which is found to vary at different 

 ages, according to the different dangess to which they are exposed. This 

 is one of the most curious of the natural laws, and one of the most 

 interesting demonstrating the admirable economy of adaptations between 

 the several parts of the natural system. If the number of males and 

 females born was exactly equal, the result would be, that, before they 

 reached middle age, the female sex would be reduced too low, and become 

 inadequate to the purposes which it has to fill. In fact, the number of 

 males born is always greater than the females by about four per cent. To 

 illustrate the changes in the numerical relations perfectly, take the follow- 

 ing example from the last two censuses : 



In IS 10, under five years of age . . . 1,270,750 males. 

 In 1840, under five years of age . . . 1,203,349 females. 



Excess (o per cent.) .... 67,4-41 males. 

 In 1850, under five years of age . . . 1,472.052 males. 

 In 1850, under six years of age . . . 1,424,325 females. 



Excess (4 per cent.) .... 47,727 males. 



Now, let us pass on to the age of puberty, and see what a change has 

 taken place : 



In 1850, from 15 to 20 years .... 1,087,GOO females. 

 In 1850, from 15 to 20 years .... 1,041,116 males. 



Excess (4 per cent.) .... 46,484 females. 



The females have now passed the males ; but let us go 011 and see what 

 influence motherhood has had on females : 



\ 



In 1850, from 30 to 40 years .... 1,288,682 males. 

 In 1850, from 30 to 40 years .... 1,128,257 females. 



Excess (14 per cent.) .... 160,425 males. 



At 70 years of age, the females are again in advance, and the same fact 

 is developed in each census. Above we see an immense change in this 

 relation. From birth to 20 years, the loss of males to females by death was 

 nearly 2 to 1 ; but from 20 to 40, the death of females was much the great- 

 est so that the males are again the most numerous. Bast 40, the deaths of 

 females are the smallest. The numerical law of the sexes, then, is this : 



1. There are more males than females born by about 4 per cent. 



2. At 20 years of age, this preponderance is entirely lost, and there are 

 more females than males. 



3. At 40 years, the balance is again the other way, and there are more 

 males than females. 



4. At 70, the sexes are about even, and the ultimate age of the human 

 being is reached without any decided advantage to either sex. 



