256 HEREDITY. 



you to deracinate that root, there is little philosophy 

 on the globe that could be depended upon to per- 

 petuate the family. [Applause.] 



Suppose that we have here a marking-machine 

 or a vertical plank [illustrating on the blackboard], 

 against which a million men, one after the other, 

 stand, while the height of each is dotted upon it. 

 Let the measurement be repeated with other millions 

 of the same race, living under the same conditions 

 with the first million. It will be found that there is 

 a substantially unchanged average height for any 

 million, year after year. The dots representing the 

 height of the different individuals will range over 

 quite a space. There will be a few very short men, 

 and a few very tall ones. Let a line representing 

 the average height of a million be drawn through the 

 cloud of dots. On both sides of that average line 

 the dots will diminish in number as they recede from 

 the average. Notice where the dot representing the 

 least height stands, and where the dot representing 

 the greatest height stands. Divide the distance from 

 the lowest to the highest point into equal spaces. 

 We find but a very few dots in the upper space, and 

 a very few in the lower ; but if you will tell me where- 

 this average lies, and how many points there are in 

 that upper square, I can calculate, according to 

 mathematical law, what the number of points would 

 be in the other squares. Experience and theory 

 correspond with marvellous closeness inside the 

 range of such spaces. This is the famous law of 

 deviation from an average, of which such extensive 



