148 NATURAL INHERITANCE. [CHAT'.
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., IT., 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 law 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 ; " Gl for " a grandparent of S ; " G2 for " a greatgrandparent 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 possessed by F is equal to D, and that nothing whatever