152 NATURAL INHERITANCE. [CHAP. 



them 0*50 of the peculiarity of S, the four grand- 

 parents, together with what they imply of the previous 

 ancestry contribute 0'32, being an aggregate of 0*82, 

 leaving a residue of 0'18 to be rateably assigned as 

 0'12 to light, and 0'6 to dark. A hazel-eyed Parent 

 is here reckoned as contributing 0'16 to light and 0'9 to 

 dark; a hazel-eyed Grand-Parent as contributing 0*5 

 to light and O f 3 to dark. All this is tabulated in 

 Table 17, and its working explained by an example in 

 the columns headed III. of Table 18. 



Results. A mere glance at Tables 19 and 20 will 

 show how surprisingly accurate the predictions are, and 

 therefore how true the basis of the calculations must be. 

 Their average correctness is shown best by the totals 

 in Table 19, which give an aggregate of calculated 

 numbers of light-eyed children under Groups I., II., and 

 III. as 623, 601, and 614 respectively, when the observed 

 numbers were 629 ; that is to say, they are correct in 

 the ratios of 99, 96, and 98 to 100. 



Their trustworthiness when applied to individual 

 families is shown as strongly in Table 20 whose results 

 are conveniently summarised in Table 21. I have there 

 classified the amounts of error in the several calculations : 

 thus if the estimate in any one family was 3 light- 

 eyed children, and the observed number was 4, I should 

 count the error as 1 '0. I have worked to one place of 

 decimals in this table, in order to bring out the different 

 shades of trustworthiness in the three sets of calcula- 

 tions, which thus become very apparent. It will be 



