108 NATURAL INHERITANCE. [chap. 



Thus 56 is written in the position of 60 '48 inches, which 

 is equal to 56 x 1*08. Similarly, 60 is written in the 

 position of 64*80, which is equal to 60 x 1*08. 



It is obvious that raising M will cause F to fall, and 

 vice versa, without affecting the wheel AB, and there- 

 fore without affecting SD ; that is to say, the Parental 

 Differences may be varied indefinitely without affecting 

 the Stature of the children, so long as the Mid-Parental 

 Stature is unchanged. But if the Mid-Parental Stature 

 is changed to any specified amount, then that of SD 

 will be changed to § of that amount. 



The weights M and F have to be set opposite to the 

 heights of the mother and father on their respective 

 scales ; then the weight SD will show the most probable 

 heights of a Son and of a Daughter on the corresponding 

 scales. In every one of these cases, it is the fiducial 

 mark in the middle of each weight by which the reading 

 is to be made. But, in addition to this, the length of 

 the weight SD is so arranged that it is an equal chance 

 (an even bet) that the height of each Son or each 

 Daughter will lie within the range defined by the upper 

 and lower edge of the weight, on their respective scales. 

 The length of SD is 3 inches, which is twice the Q of 

 the Co-Fraternity ; that is, 2 x 1*50 inch. 



d. Fraternal : In seeking for the value of Fraternal 

 Eegression, it is better to confine ourselves to the 

 Special data given in Table 13, as they are much 

 more trustworthy than the E.F.F. data in Table 12. 

 By treating them in the way shown in Fig. 13, which 

 is constructed on the same principle as Fig. 10, page 96, 



