78 Life and Letters of Francis Galton 



the variability of the sibship or fraternity proceeding from that generant, 

 where a is the standard deviation or variability of the general population. 

 If r be the correlation of brothers in the ordinary sense, then owl— r 2 is 

 the variability of an array or co-fraternity of brothers. The connecting link 

 missed by Galton is : R 2 = r*. 

 The second topic is : 



" the fundamental distinction that may exist between two couples whose personal faculties 

 are naturally alike. If one of the couples consist of two gifted members of a poor stock, and 

 the other of two ordinary members of a gifted stock, the difference between them will betray 

 itself in their offspring. The children of the former will tend to regress ; those of the latter will 

 not. The value of a good stock to the well-being of future generations is therefore obvious, and 

 it is well to recall attention to an early sign by which we may be assured that a new and gifted 

 variety possesses the necessary stability to easily originate a new stock. It is the refusal to 

 blend freely with other forms. Some among the members of the same fraternity might possess 

 the characteristics in question with much completeness, and the remainder hardly or not at all." 

 (pp. 197-8.) 



It will be perceived from this paragraph that Galton does not hold the 

 absence of regression in the " gifted " stock to be due to less mediocrity in 

 the ancestry, but to the creation of a " new " stock by some trick of falling 

 into a fresh position of stability, which enables the stock, at any rate in 

 some of its members, to breed true. That is, he appeals to mutations for the 

 source of " gifted " stocks. 



Whether this be true or not, Galton I think reached his views owing to 

 a misinterpretation of the statistical phenomena of regression. It was a 

 misfortune that he really did not get beyond the idea of regression in two 

 variates, because to be clear as to the true relation between his "mid- 

 parental heredity " and his " Law of Ancestral Hei'edity " a knowledge of 

 multiple regression is essential. But it was the greatest good fortune that 

 he got as far as he did; he blazed the track, which many have followed 

 since, and if he left unsolved or half-solved problems, his disciples ought to 

 be grateful that the master has provided the problem as well as the tool, 

 rather than be stern critics of his pioneer workf. Natural Inheritance is a 

 great book even if it has its obvious blemishes. 



The work concludes with the reproduction of tables from the memoirs 

 on percentiles, on stature and on eye-colour, etc. Also with a series of Ap- 

 pendices. A gives particulars of Galton's own works and memoirs. B reprints 

 Hamilton Dickson's paper (see our p. 12). C describes the experiments on 

 sweet-peas, never fully dealt with. D reprints the Fortnightly Review paper 

 on Temper (see our pp. 69-70 and Vol. n, p. 271). E reproduces Galton's 

 paper on the Geometric Mean (see Vol. II, pp. 227-8). F reprints Galton 

 and Watson on the Probable Extinction of Families (see Vol. u, pp. 341-343). 

 G deals with the orderly arrangement of hereditary data, in particular with 



* See Biometrika, Vol. xvir, p. 131. 



t We have in a case in the Oalloniana of the Galton Laboratory the first map of Damara- 

 land. Is it of less value because it is not an Ordnance map of what was once German 

 South- West Africa 1 



