THE INHERITANCE OF DURATION 167 



from Foster's "Peerage." The second series consisted 

 of a thousand pairs of fathers and sons, the latter 

 dying beyond the age of 20, taken from Burke's 

 "Landed Gentry." The third series consisted of ages 

 at death of one thousand pairs of brothers dying 

 beyond the age of 20 taken from the "Peerage." It 

 will be noted that all these series considered in this first 

 study dealt only with inheritance in the male line. The 

 reason for this was simply that in such books of record 

 as the "Peerage" and "Landed Gentry" sufficiently ex- 

 act account is not given of the deaths of female relatives. 

 In a second study the material was taken from the pedi- 

 gree records of members of the! English Society of Friends 

 and from the Friends' Provident Association. This ma- 

 terial included data on inheritance of longevity in the 

 female line and also provided data for deaths of infants, 

 which were lacking in the earlier used material. The 

 investigation was grounded upon that important branch 

 of modem statistical calculus known as the method of 

 correlation. For each pair of relatives between whom it 

 was desired to study the intensity of inheritance of longe- 

 vity a table of double entry was formed, like the one shown 

 here as Table 17. 



The figures in each cell or compartment of this table 

 denote the frequency of occurrence of pairs of fathers 

 and adult sons having respectively the durations of life 

 indicated by the figures in the margins. Thus we see, 

 examining the first line of the table, that there were 11 

 cases in which the average duration of life of the father 

 was 48 years and that of the adult son 23 years. Farther 

 down and to the right in the table there were 13 cases in 

 which the average duration of life of the father and the 

 son was in each case 83 years. These cases are men- 



