CLIMATE 309 



relative humidity is low than where it is high. Air of a given tem- 

 perature seems cooler when in motion than when quiet. 



Moisture as an element of climate. Climate takes account of 

 (1) the average amount of yearly precipitation, (2) the variations 

 of precipitation from year to year, (3) its average distribution 

 through the year and departures from this average, (4) the propor- 

 tions which fall as rain and snow respectively, (5) relative and (6) 

 absolute humidity (p. 255) even when there is no precipitation, 

 and (7) cloudiness. 



Uniform and variable climate. If the range of temperature is 

 small, the distribution of precipitation somewhat equal, the winds 

 nearly constant in direction and strength, the climate is uniform. 

 If, on the other hand, the variations of these climatic elements are 

 great, either in one year or in successive years, the climate is vari- 

 able. The climate of the middle and northern latitudes of the 

 United States is variable because (1) the annual range of tem- 

 perature is great, (2) because the range varies from year to year, 

 (3) because two summers or two winters may have very different 

 temperatures, (4) because changes of temperature may be very 

 sudden, and (5) because the amount and distribution of rainfall and 

 snowfall vary much from year to year, and from season to season. 



A variable climate varies in different ways. (1) A region which 

 is always dry during one season of the year and wet during another 

 has a climate which is variable within the year with reference to 

 precipitation; the climate of such a region may, however, be very 

 nearly the same from year to year. (2) A region which is hot at 

 one time of the year and cold at another is variable within the year 

 with respect to temperature. In such regions, too, one winter or sum- 

 mer may be much cooler or warmer than the next, giving a variation 

 from year to year rather than from season to season. (3) In some 

 regions the winds shift regularly from season to season, as where mon- 

 soons blow. The climates of such places are variable within the 

 year with respect to winds, and this makes them variable also with 

 respect to other elements of climate. The climates of such regions 

 may be uniform from year to year. 



The climate of a region may vary in other ways also. Thus 

 some summers or some winters mav be much warmer or much drier 



