70 WORLD-POWER AND EVOLUTION 



15 per cent isopract, is not experienced until the temperature 

 falls to 30°, the coldest ever experienced in northern France. A 

 little further practice will make it easy to read the climographs. 

 Remember that the shading and the isopracts merely indicate the 

 average healthfulness of months having the temperature and 

 humidity indicated in the margins. Other circumstances cause 

 a month to vary from the average, but the diagrams show what 

 may be expected normally. 



Now compare Figures 8 to 11. Each of them shows a small 

 black dot where the temperature is 64° and the humidity 80 

 per cent. These conditions seem to be the best. They represent 

 what may be called the optimum or ideal. In each of the climo- 

 graphs the dot lies not far from the center of the heaviest shading. 

 Now turn to Figures 12 to 15, four climographs for the eastern 

 and central parts of the United States. Here, too, the general 

 aspect of the drawings is similar to the climographs for France 

 and Italy, and the black dot lies not far from the middle of the 

 darkest shading. Finally look at Figures 16 and 17 representing 

 the Pacific Coast in the Puget Sound region, and Figures 18 and 

 19 representing deaths among white people and negroes respec- 

 tively in the eastern part of the United States. In two of these 

 the black dot comes close to the center of the darkest area, while 

 in the other two it falls outside the darkest area and at a lower 

 temperature. In these two exceptional cases, however, the 

 climographs are based on relatively few deaths. Moreover, the 

 failure of these two to conform to the rest amounts to only 6° in 

 Figure 17 and 4° in Figure 19. In both it is due to special cir- 

 cumstances, for in California the breeziness of the hottest months 

 makes them more favorable than the slightly cooler months, while 

 in Figure 19 we are dealing with negroes whose ancestors come 

 from a hot country. 



These twelve climographs, representing nearly 9,000,000 

 deaths, agree with the results obtained from a less careful study 

 of over 50,000,000 other deaths in Belgium, Finland, Sweden, 



