102   ENGLISH MEN OF SCIENCE.   [char.

affected ; mother' delicate and phthisical." I can find only two cases, neither very strongly marked, in which both parents are described as unhealthy, although marriages between such persons are not infrequent. The returns seem to show that the issue of these marriages are barely capable of pushing their way to the front ranks of life. All statistical data concur in proving that healthy persons are far more likely than others to have healthy progeny ; and this truth cannot be too often illustrated, until it has taken such hold of the popular mind, that considerations of health and energy shall be of recognized importance in questions of marriage, as much so as the probabilities of rank and fortune.

I may mention, as a fact that corroborates my belief in the exceptionally good physique of scientific men, that I find the average height of those who have sent me returns, to be half an inch above that of their fathers.