196 NATURAL INHERITANCE. [CHAP 



accounted for, but the factor of stability of type has 

 to be reckoned with, and this has not yet been 

 adequately discussed. 



The ratio of filial Eegression is found to be so bound 

 up with co-fraternal variability, that when either is 

 given the other can be calculated. There are no 

 means of deducing the measure of fraternal variability 

 solely from that of co-fraternal. They differ by an element 

 of which the value is thus far unknown. Consequently 

 the measure of fraternal variability has to be calculated 

 separately, and this cannot be done directly, owing to 

 the small size of human families. Four different and 

 indirect methods of attacking the problem suggested 

 themselves, but the calculations were of too delicate a 

 kind to justify reliance on the R.F.F. data. Separate 

 and more accurate measures, suitable for the purpose, 

 had therefore to be collected. The four problems were 

 then solved by their means, and although different 

 groups of these measures had to be used with the 

 different problems, the results were found to agree 

 together. 



The problem of expressing the relative nearness of 

 different degrees of kinship, down to the point where 

 kinship is so distant as not to be worth taking into 

 account, was easily solved. It is merely a question of 

 the amount of the Eegression that is appropriate to the 

 different degrees of kinship. This admits of being 

 directly observed when a sufficiency of data are acces- 

 sible, or else of being calculated from the values found 

 in this inquiry. A table of these Regressions was given. 



