K. Pearson 
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the regression is linear. What results shall we obtain by thus assuming perfect 
continuity between the physical and the psychical ? No doubt the drums will 
begin to beat the tattoo, we shall hear talk of the hopeless materialism of some 
men of science. But to use Huxley's appropriate words : " One does not battle 
with drummers." I cannot free myself from the conception that underlying every 
psychical state there is a physical state, and from that conception follows at once 
the conclusion that there must be a close association between the succession or the 
recurrence of certain psychical states, which is what we judge mental and moral 
characteristics by, and an underlying physical confirmation be it of brain or liver. 
Hence I put to myself the problem as follows : — Assume the fundamental laws of 
distribution which we know to hold for the physical charactei's in man, and see 
whither they lead us when applied to the psychical characteristics. They must : 
(a) Give us totally discordant results. If so, we shall conclude that these laws 
have no application to the mental and moral attributes. Or, (b) Give us accordant 
results. If so, we may go a stage farther, and ask how these results compare with 
those for the inheritance of the physical characters : are they more or less or equally 
subject to the influence of environment ? Here are the questions before us. Let 
us examine how they are to be answered. As an illustration I take Ability in 
Girls. 1 measured intelligence by the following seven classes, (i) Quick Intelligent; 
(ii) Intelligent] (iii) Slow Intelligent; (iv) Sloiu; (v) Slow Dull; (vi) Very Dull; and a 
quite distinct category (vii) Inaccurate-Erratic. Some explanation of these terms 
is given in Appendix Ia., which contains the general instructions for observation, 
and the terms themselves were practically formulated by a schoolmaster of 
considerable pedagogic and psychological experience. 
My next stage was to ask two or tliree different teachers in several schools 
to apply the classification to 30 to 50 pupils known to each of them. The 
classifications were made quite independently, often by teachers of quite different 
subjects, and a comparison of the results showed that 80 to 8-5 per cent, of the 
children were put into the same classes by the different teachers, while about 
10 per cent, more only differed by one class. This gave one very great confidence 
not only in the value of this scale, but of other psychical classifications when used 
by observant teachers. The next stage was to obtain exactly, as in the case of 
Health, a general scale of intelligence*. 
Diagram XL gives the normal distribution of intelligence in a population of 
2014 girls. It is a curious, if a common result of experience, to find that the modal 
ability is on the borderland between the Intelligent and Slow Intelligent. We have 
here for the first time a quantitative scale of intelligence, and we can at once apply 
it to the problem of the degree of resemblance between sisters as regards ability. 
Just as in the case of Health, all the girls of a given class are taken, say the Slow 
Intelligents, and at the average value of this class, is plotted upon this scale of 
intelligence, the average value of the intelligence of the sisters of these girls on 
* I should say at once that the Inaccurate -Erratics turned out a surprisingly small class, a fractional 
per cent, of the community, and that they were not further dealt with. 
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