CHAPTER VI 

 THE IMPORTANCE OF VARIABILITY 



IT is not enough to understand man's extremely sensitive 

 adjustment to temperature and humidity. We must under- 

 stand the effect of changes. A variable climate has utterly 

 different effects from ^ uniform climate even though both have the 

 same average temperature and humidity. Change'? in the atmos- 

 phere appear not only to cause the fluctuations of business which 

 we have been studying, but to be among the most potent forces in 

 making some nations strong and others weak. When I began the 

 present investigation and discovered how much harm is done by 

 our cold northern winters I reasoned that in places with uniform 

 climates like southern Italy and California, where the winters 

 differ only a little from the summers, the conditions of health at 

 the two seasons must be nearly the same. The difference between 

 summer and winter, however, is relatively far greater in the mild 

 climates than in those that are more rigorous. In northern 

 France, Figure 8, for example, the range from the lowest death- 

 rate to the highest is only about 25 per cent; in southern Italy, 

 Figure 11, it amounts to 45 per cent. In the United States simi- 

 lar contrasts prevail. The rigorous northeastern section. Figure 

 12, where the temperature for a month at a time may average 20°, 

 shows a difference of only 20 per cent between the best months 

 and the worst. On the other hand, southern California, Figure 

 17, where the coldest month does not average below 50°, shows a 

 difference of over 25 per cent between summer and winter. A com- 

 parison of individual cities, such as Boston and Los Angeles, or 

 New York and San Francisco, emphasizes this contrast still more 

 strongly. So, too, does a comparison of the French diagrams. 



