250 POINTER READINGS 



opposite side of the mountain is tunnelling to meet his 

 less philosophically minded colleagues. The important 

 thing is not to confuse the two entrances. 



Nature of Exact Science. One of the characteristics of 

 physics is that it is an exact science, and I have generally 

 identified the domain of physics with the domain of 

 exact science. Strictly speaking the two are not synony- 

 mous. We can imagine a science arising which has no 

 contact with the usual phenomena and laws of physics, 

 which yet admits of the same kind of exact treatment. 

 It is conceivable that the Mendelian theory of heredity 

 may grow into an independent science of this kind, for 

 it would seem to occupy in biology the same position 

 that the atomic theory occupied in chemistry a hundred 

 years ago. The trend of the theory is to analyse com- 

 plex individuals into "unit characters". These are like 

 indivisible atoms with affinities and repulsions; their 

 matings are governed by the same laws of chance which 

 play so large a part in chemical thermodynamics; and 

 numerical statistics of the characters of a population are 

 predictable in the same way as the results of a chemical 

 reaction. 



Now the effect of such a theory on our philosophical 

 views of the significance of life does not depend on 

 whether the Mendelian atom admits of a strictly physical 

 explanation or not. The unit character may be contained 

 in some configuration of the physical molecules of the 

 carrier, and perhaps even literally correspond to a chem- 

 ical compound; or it may be something superadded which 

 is peculiar to living matter and is not yet comprised in 

 the schedule of physical entities. That is a side-issue. 

 We are drawing near to the great question whether there 

 is any domain of activity — of life, of consciousness, of 



