An Introduction to a Biology 



a being whose faculties are so sharpened that he can follow 

 every molecule in its course, such a being, whose attributes 

 are still as essentially finite as our own, would be able to 

 do what is at present impossible to us. For we have seen 

 that the molecules in a vessel of air at uniform temperature 

 are moving with velocities by no means uniform, though 

 the mean velocity of any great number of them, arbitrarily 

 selected, is almost exactly uniform. Now let us suppose 

 that such a vessel is divided into two portions, A and B, 

 by a division in which there is a small hole, and that a being 

 who can see the individual molecules opens and closes this 

 hole, so as to allow only the swifter molecules to pass from 

 A to B, and only the slower ones to pass from B to A. He 

 will thus, without expenditure of work, raise the temperature 

 of B and lower that of A, in contradiction to the second law 

 of thermo-dynamics." 



The point of view of the demon is so different from that 

 of the physicist that one of the truest generalisations of the 

 latter would be declared absolutely false by the former ; 

 yet no one remains blind for a moment to the fact that the 

 contradiction of their respective statements is only apparent, 

 and is due to the radical difference in their points of view. 



Now I believe that the difference between the point of 

 view of the Mendelian and the biometrician is very like the 

 difference between that of the demon and that of the physicist. 

 The biometrician, with a new weapon of observation, is only 

 concerned with mass phenomena ; the individuals which go 

 to swell his correlation tables are, like the atoms of the 

 physicist, units of which no knowledge is required to attain 

 the result at which he aims. But I need not dwell on the 

 exactness of the parallel when we have these words from 

 " the inventor of the term biometry " : l " Our 2 knowledge 

 of atoms and our application of atomic and molecular hypo- 

 theses to problems in heat, elasticity, and cohesion is essen- 



1 Nature, Oct. 27, 1904, p. 626. 



2 Karl Pearson, " Grammar of Science/' 2nd. Ed., pp. 500-1. 



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