Chapter XIII 



THE EFFECT OF CLIMATE AND WEATHER 



Ellsworth Huntington 



THE climatic FACTORS 



WEATHER, as everyone knows, is the natural 

 atmospheric changes from day to day; climate is 

 the sum total of the weather year after year. In 

 studying their combined physiological effects it is advisable 

 to begin with the individual factors of which they are 

 composed. Temperature is the most important of these. 

 Ordinary experience gives some idea of how temperature may 

 influence human health and activity. It is not so easy, how- 

 ever, to appreciate the effect of changes of temperature, for 

 changes often produce effects totally different from what the 

 actual temperature as measured by the thermometer would 

 lead one to expect. Humidity probably comes next in 

 importance, but it is difficult to differentiate between the 

 direct effect of atmospheric moisture itself upon the 

 skin, nerves, mucous membrane and the like, and its 

 indirect effect upon the sensible or "feelable" temperature. 

 When the thermometer reads 70°f., unmoving air that is satu- 

 rated with water feels warm, for its sensible temperature is 

 high, but perfectly dry air feels cool because evaporation 

 causes the sensible temperature to be too low for comfort. 



The effects of wind are even harder to isolate than those of 

 humidity. That the movement of the air has a direct 

 physiological effect in addition to its cooling power is 

 evident to anyone whose eyes have watered in a high wind. 

 The wind also does much harm by carrying dust and other 

 impurities. Yet its most important physiological effect is 

 tojower the sensible temperature. Sunlight, the fourth great 

 climatic factor, resembles both humidity and wind in 

 being^highly important because of its effect on our feelings of 

 warmth or the reverse, and yet in producing its own 

 individual effects of quite a different kind. The moment the 

 sun's rays are intercepted we feel cooler, but the complete 



