412 C. C. HURST 



the one is typically English and modern, while the other includes eleven 

 different nationalities and is spread over a period of several centuries. 



DEFINITION OF INTELLECT 



Throughout this investigation the concept "intellect" is taken to represent 

 natural mental ability as expressed in general mental activities and achieve- 

 ments, on the lines and definitions laid down by Galton (1869), Woods 

 (1906) and Spearman (1927). The concept therefore corresponds with Gal- 

 ton's "natural ability," Woods' "intellect" and Spearman's "general fac- 

 tor g." 



Spearman's remarkable psychological discovery of a statistical factor "g" 

 representing the general mental ability which enters into every act of cog- 

 nition, has cleared the way for a genetical investigation of the inheritance of 

 intellect. Experimental tests show that Spearman's "g" is generally con- 

 stant for any normal individual from the age of puberty up to the onset of 

 senility, while it is greatly variable in degree or power in different indi- 

 viduals. In grading intellect we are measuring Spearman's "g." 



RELIABILITY OF THE GRADINGS 



Woods' historical material was rated and graded by histriometric methods 

 originally devised by himself. Numerous careful tests made with different 

 controls and criteria showed clearly that his subjective consensus rating by 

 adjectives was a more delicate and accurate method of grading intellect 

 than other methods which were more mechanical and objective. Tested 

 by Mendel's Laws of Heredity, Woods' gradings of intellect in Royalties 

 have a reliability of 94.7 per cent. The reliability of the ratings and grad- 

 ings of intellect in my own investigation of the Leicestershire families was 

 checked and tested in various ways. In the course of the twenty-five years 

 research several repetition re-ratings have been made and where possible 

 all individuals have been re-graded after a few years' interval. 



In numerous cases the same individuals have been independently rated 

 by parents, teachers and colleagues. There is a remarkable conformity of 

 the intellect gradings of individuals with their occupations and vocations in 

 accordance with the scales laid down by Barr, Taussig and the American 

 Army Reports. Tested by Mendel's Laws of Heredity, the gradings of in- 

 tellect in the Leicestershire families have a reliability of 99.8 per cent. So 

 far as achievement can be regarded as a test or measure of ability, the ratings 

 and gradings made are probably as approximately accurate as those ob- 

 tained by standardised tests. Owing to personal objections and other seri- 

 ous difficulties it was found impracticable to apply the conventional batteries 



