76 



WORLD-POWER AND EVOLUTION 



at night and a noon temperature approaching 50" ; or whether 

 it is a little higher, there seems to be little question that it is 

 distinctly lower than the physical optimum. A high civilization 



80% 



40% 



— r- 



Relative Humidity 

 60% 60% 70% 



80% 



— r— 



90% 

 — I — 



FiorRE 14. A. Unsmoothed Climograph of the Dry Interior of the 

 United States 



cannot be based either upon physical well-being or mental well- 

 being alone. The two seem to be equally necessary. Therefore 

 the best climate would apparently be one in which the winters are 

 cool enough so that there are several months with frost, while the 



