THE FACTORS WHICH DETERMINE CLIMATE 291 



among the clouds. He survives extreme exposure and retains 

 his health, strength, and bodily vigor while engaged at the 

 hardest labor for many hours each day. As long as he labors 

 out of doors in the fresh air and in the sunshine, receives an 

 abundance of nourishment, and sleeps eight hours each night 

 in the open air, he outstrips nearly every other type of animal 

 life in health, bodily vigor, and power of endurance. 



Usually, it is when man violates one or more of these condi- 

 tions that he becomes a puny, delicate creature, an easy prey 

 for disease. The experience of every polar expedition in 

 history is positive evidence of the truth of this statement. 

 Pioneer life, with all its exposure and privations, has always 

 developed a people of exceptional vigor and hardiness. 



It is almost wholly man's unwise and unintelligent attempts 

 to protect himself against the inclemency of weather and cli- 

 mate which have produced conditions favorable to the trans- 

 mission of disease from one person to another and at the same 

 time have so weakened his bodily resistance that he easily 

 succumbs to almost any disease. Among all classes, from the 

 wealthy to the very poor, two other causes of ill health are 

 evident: (1) Lack of sufficient and suitable nourishment; and 

 (2) lack of proper amount cf sleep and rest. The wealthy 

 suffer from these causes because of self-indulgence, the poor 

 suffer because of their poverty. 



III. THE FACTORS WHICH DETERMINE CLIMATE 



A. TEMPERATURE 1 



315. Seasonal Changes in Temperature. 



Exercise 69. Study of the Average Temperature Maps of United States 

 for July and January (Figs. 218 and 219.) 



What and where is the highest average temperature for July? 

 What and where is the lowest average temperature for July? 

 What and where is the highest average temperature for January? 

 What and where is the lowest average temperature for January? 

 In which month, then, July or January, is found the widest differ- 

 ence of temperature within the boundaries of the United States? 

 1 See foot note page 196. 



