70 NATURAL INHERITANCE. [chap. v. 



will call b. Now, if the lateral distance of a particular 

 green mark from M is given, what is the most jprobable 

 distance from M of the red mark at which it was aimed ? 



It is V-A_y 



cr + b 



(5) What is the Prob: Error of this determination ? 



In other words, if estimates have been made for a great 



many distances founded upon the formula in (4), they 



would be correct on the average, though erroneous in 



particular cases. The errors thus made would form a 



normal system whose Q it is desired to determine. Its 



n • be 

 value is — jj- 5,. 



By the help of these five problems the statistics of 

 heredity become perfectly manageable. It will be 

 found that they enable us to deal with Fraternities, 

 Populations, or other Groups, just as if they were units. 

 The largeness of the number of individuals in any of 

 our groups is so far from scaring us, that they are actu- 

 ally welcomed as making the calculations more sure 

 and none the less simple. 



