CHAPTER XVIII 

 CLIMATE 



Something has been said concerning climate in preceding chap- 

 ters, but the subject will be summarized here, and studied in con- 

 nection with the zones of the earth. 



Definition. Climate is the average succession of weather condi- 

 tions for a long period of time. The average weather of a place 

 for ten years would give some idea of its climate; but the average 

 weather for twenty years would be better, and the average for 50 

 or 100 years would be better still. The distinction between climate 

 and weather is correctly recognized by such expressions as these: 

 The winter climate of Chicago is cold and windy; but the winter 

 weather of Chicago in 1905-6 was mild. 



The Elements of Climate 



The principal elements of climate are temperature, moisture, 

 and wind. 



Temperature as an element of climate. In speaking of the 

 climate of a region, account is taken not only of (1) the average 

 temperature of the year and (2) the average temperature of the 

 several seasons, but also of (3) the temperature of exceptional sea- 

 sons, and (4) the extremes of temperature during the season. 

 Sensible temperature, or the temperature as it feels to us, and abso- 

 lute temperature, as shown by a thermometer, are also to be taken 

 into account. Moist air of a given temperature seems much warmer 

 than dry air of the same temperature when the temperature is 

 high, and much colder when the temperature is low. Sunstroke is 

 much more common where'the relative humidity is high than where 

 it is low. Sunstrokes are rare, for example, in the arid west, even 

 with temperatures much above those of Chicago or New York. 

 Sudden changes of temperature are also less harmful where the 



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