CH. iv] HEREDITY 33 



the analysis of the individual instance' [25, 'Math. 

 Contrib. III.' Phil. Trans. Roy. Soc. A, 1896, p. 255]. 

 The second method on the other hand has been used 

 in cases where the causes of variation appear to be 

 few and definite, and seeks to isolate these causes. 

 The first method is thus clearly adapted especially to 

 characters which vary continuously and which can 

 be measured ; the second to characters which vary 

 discontinuously and can be sharply separated into 

 classes. The first method gives on the whole the 

 average intensity of inheritance, but little information 

 with regard to its probable development in individual 

 cases ; the second attempts to answer the question 

 in what manner the character will be distributed 

 among the offspring in any family. 



The founder of the modern statistical, or as it is 

 now often called, the biometrical study of heredity was 

 Sir Francis Galton, and its leading exponents have 

 been Professor Karl Pearson and the late Professor 

 Weldon. In this chapter an attempt will be made to 

 explain the fundamental principles on which the 

 biometric methods rest, and to outline the chief 

 results obtained ; the methods themselves frequently 

 require mathematics of an advanced order, and for 

 the study of them the reader is referred to the books 

 and papers dealing with the subject mentioned in the 

 bibliography. 



It has already been seen that in the case of a 



D. 3 



