3o ENGLISH MEN OF SCIENCE. [CHAP. 



able period for the survival of mother and child, 

 and therefore probably the best in every sense, is 

 when she is 20 25 at the time of giving birth. 

 The important question of the effect of the age of 

 the parent on the wellbeing of the offspring seems 

 never yet to have been treated as strictly and as 

 copiously as it deserves. Dr. Duncan, in the 

 chapter of his work above referred to, has dis- 

 cussed the materials at his disposal with great 

 ingenuity and industry ; but adequate statistics, 

 sorted according to the various classes of society, 

 are still wanting. 



FERTILITY. 



The families are usually large to which scien- 

 tific men belong. I have two sets of returns the 

 one of brothers and sisters, excluding, for the 

 most part, those who died in infancy ; and the 

 other of brothers and sisters who attained 30 years. 

 In these several cases I have included the scien- 

 tific man himself, and find, on an average of 

 about 100 cases, that the total number of brothers 

 and sisters is 6*30 in the first case, and 4*80 in 



