292 Prof. K. Pearson. Mathematical Contributions [Jan. 20, 



think, we may safely assert that 400 at least are not included in my 

 series. She found : Mean age,* 12-7177 ; mean head-length, 184-8182 ; 

 and slope of regression line, 1 -2040, giving the formula 



Hp = 169-5061 + 1-2040 A, 

 a result in substantial agreement with mine. 



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O I 2 3 4-5 6 7 3 9 10 II 12 A3 14 IS 16 17 13 19 20 



Age of Boy. 



In Diagram 1 the formula (e) is represented with the observed 

 mean values at each year of life. The results for the 4th, 5th, and 

 19th years of life ought not to be considered, for they are based on 

 only 2, 10, and 12 observations respective^. It will clearly hardly 

 be possible to express the growth curve better than by a straight 



* The mean age is less, because brother-sisters are obtained chiefly from 

 primary s not secondary, schools. 



