98 , WORLD-POWER AND EVOLUTION 



he most needs a stimulant. I know that this sounds extreme. Yet 

 what else can be the meaning of the fact that the days when the 

 temperature falls most in New York are accompanied by an 

 improvement of 10 per cent, 20 per cent, and even 40 per cent 

 in the deathrate? I know, too, that different diseases may act 

 differently, and that this whole matter needs far more thorough 

 investigation than has yet been possible. Physicians are the ones 

 to carry on this investigation, and already some of them are at 

 work on it. 



The principles discussed in this chapter enable us to answer 

 another important practical question: What climate is really 

 the best? I have discussed this question in "Civilization and 

 Climate," and the answer there given is strongly reenforced by our 

 studies of the deathrate. We have seen that a mean temperature 

 of 64°, a mean humidity of about 80 per cent, and frequent 

 changes of temperature are the most desirable conditions for 

 purely physical health. We have seen that in factory work where 

 physical effort is the chief item, but where mental activity takes 

 a certain share, the best conditions seem to be the same except 

 that the optimum temperature should apparently average about 

 60°F for day and night together instead of 64°. Finally for 

 purely mental work the conditions of humidity and variability 

 should apparently be about the same as in the other cases, but 

 the mean temperature should be much lower, perhaps 40°. The 

 only way to get all these conditions is to live in a climate which 

 has several frosty but not cold months in winter, several warm but 

 not hot months in summer, and a constant succession of storms at 

 all seasons. No part of the world fulfills all these conditions. 

 England is admirable in temperature and has a great deal of 

 variety although not quite enough. New Zealand in many ways 

 rivals England as a candidate for first place. The northeastern 

 United States is variable enough, but its winters are too cold and 

 its summers too hot. Germany falls in the same class with the 

 United States, but in both regions the nervous stimulus seems to 



