:33 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 discussed the materials at his disposal with great ingenuity and industry ; but adequate statistics, sorted according to the various classes of society, are still wanting.
The families are usually large to which scientific 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 scientific 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