148 NATURAL INHERITANCE. [chap. 



Principles of Calculation. — I .have next to show 

 how the expectation of Eye-colour among the children 

 of a given family is to be reckoned on the basis of 

 the same law that held in respect to stature, so that 

 calculations of the probable distribution of Eye-colours 

 may be made. They are those that fill the three last 

 columns of Tables 19 and 20, which are headed I., 

 II. , and III., and are placed in juxtaposition with 

 the observed facts entered in the column headed 

 " Observed." These three columns contain calculations 

 based on data limited in three different ways, in order 

 the more thoroughly to test the applicability of the 



. that it is desired to verify. Column I. contains 

 calculations based on a knowledge of the Eye-colours 

 of the Parents only ; II. contains those based on a 

 knowledge of those of the Grand-Parents only ; 

 III. contains those based on a knowledge of those 

 both of the Parents and of the Grand-Parents, and 

 of them only. 



I. Eye- colours given of the two Parents — 



Let the letter S be used as a symbol to signify the 

 subject (or person) for whom the expected heritage is to 

 be calculated. Let F stand for the words " a parent of 

 S ; " G x for " a grandparent of S ; " G 2 for "a great- 

 grandparent of S," and so on. 



We must begin by stating the problem as it would 

 stand if Stature was under consideration, and then 

 modify it so as to apply to Eye-colour. Suppose then, 

 that the amount of the peculiarity of Stature pos- 

 sessed by F is equal to D, and that nothing whatever 



