88 WORLD-POWER AND EVOLUTION 



Figures 8 and 9, with those of the eastern and central United 

 States, Figures 12 to 14. In the milder French climate the lines 

 of the diagrams are closer together and the contrast between the 

 health of summer and winter much greater than in the more 

 rigorous climate of the northern United States. If southern 

 Italy were the only place to show a high deathrate in winter, we 

 might attribute it to lack of care and to poor medical service. 

 When Los Angeles, San Francisco, and Seattle follow suit, however, 

 such an explanation is untenable. 



The real explanation of the unexpectedly favorable conditions 

 in rigorous climates seems to be that the rigorous climates are also 

 highly variable. In "Civilization and Climate" I have described 

 a series of studies of factory operatives and students which bear 

 on this point. Both mental and physical work appear to be 

 stimulated by changes in temperature. In general, if today's 

 temperature is the same as yesterday's, people do not work so 

 well as when there is a change. When winter and summer are 

 averaged together a rise of temperature seems to be slightly 

 stimulating to physical activity, although it is distinctly harmful 

 to mental. A fall of temperature, on the contrary, appears to 

 be stimulating under all conditions, although an extreme fall is 

 not so good as one of more moderate dimensions. 



I have now tested this conclusion by means of the records of 

 daily deaths in New York City from 1877 to 1884. These deaths 

 number approximately 300,000, and the number of days concerned 

 is approximately 3,000. Hence the body of data on which we 

 shall base our conclusions is large enough to give thoroughly 

 reliable results. These results agree with those obtained from 

 the study of students, but fail to show any favorable effect corre- 

 sponding to the slight stimulus which a rise of temperature seems 

 to exert upon factory operatives. AU three types of investiga- 

 tion, however, namely, studies of deaths, factory operatives, and 

 students, agree in indicating that changes of temperature are, in 

 general, a stimulus, and this is the main point. 



