158 EVOLUTION OF THE EARTH 



seasons and comparing these with the weather. All of these 

 methods yield substantially the same results. So far as 

 temperature is concerned they indicate that people's health Is 

 best and their physical energy greatest when the average 

 temperature for day and night together is from 60° to 68° F., 

 which means when the noon temperature ranges from about 



65° to 75°. 



Among the methods mentioned above the study of deaths 

 seems to be the best thus far employed. As this method has 

 never before been used on a large scale, it may be well to con- 

 sider it somewhat fully. Death is one of the few occurrences 

 which takes place in all parts of the world and can easily be 

 reduced to accurate statistics. Such statistics are kept by all 

 of the more advanced governments, so an enormous body of 

 valuable facts is easily available, and needs only to be tabulated 

 in order to give most significant results. Accordingly, I shall 

 here give a resume of the detailed study of about 9,000,000 

 deaths In Italy, France, and the United States, and of the more 

 cursory but no less exact study of a much larger number in 

 Belgium, Germany, Sweden, Finland, and Japan. The most 

 important result of these studies is a series of "cllmographs'* 

 like Figures 31 to 33. Figure 31 is based on 2,500,000 deaths 

 in the part of the United States north of the fortieth parallel 

 and east of the Missouri River during the years 1900-19 12. 

 Figure 32 is based on 2,200,000 deaths in France from 1901 

 to 19 10, and 1,500,000 in Italy from 1899 ^^ 19 13. Figure 

 33 is based on 142,000 deaths in four California cities, namely, 

 San Francisco, Sacramento, Los Angeles, and San Diego, from 

 1900 to 19 1 2. The diagrams show to what extent the deaths 

 during months with any specified temperature and humidity 

 fell short of or exceeded the normal. Temperature is indi- 

 cated at the left and humidity at the top. The heaviest shad- 

 ing means that on an average the deaths during months having 

 the conditions included within its area were at least 10 per cent 



