HEREDITY 303 



this? My brother-in-law, J. Hamilton Dickson of 

 Peterhouse, loves problems and wants new ones. 

 Send it to him." I did so, under the form of a 

 problem in mechanics, and he most cordially helped 

 me by working it out, as proposed, on the basis 

 of the usually accepted and generally justifiable 

 Gaussian Law of Error. So I begged him to allow 

 his solution to be given as an appendix to my paper 

 [91], where it will be found. 



It had appeared from observation, and it was 

 fully confirmed by this theory, that such a thing 

 existed as an " Index of Correlation " ; that is to say, 

 a fraction, now commonly written r, that connects 

 with close approximation every value of deviation 

 on the part of the subject, with the average of all 

 the associated deviations of the Relative as already 

 described. Therefore the closeness of any specified 

 kinship admits of being found and expressed by a 

 single term. If a particular individual deviates so 

 much, the average of the deviations of all his brothers 

 will be a definite fraction of that amount ; similarly 

 as to sons, parents, first cousins, etc. Where there 

 is no relationship at all, r becomes equal to o ; when 

 it is so close that Subject and Relative are identical 

 in value, then r= 1. Therefore the value of r lies 

 in every case somewhere between the extreme limits 

 of o and 1. Much more could be added, but not 

 without using technical language, which would be 

 inappropriate here. 



The problem as described above is by no means 

 difficult to a fair mathematician. Mr. J. H. Dickson 

 set it to a class of his higher students, most of whom 

 answered it. It has since been remarked that this 



