198 OUTLINES OF FORESTRY. 



surface is higher in some places than it is in 

 others, in some places is covered with vegetation 

 and in others is bare, or is exposed to cold or 

 currents of wind or water in some places and to 

 warm currents in others. 



Differences in the elevation of the land cause 

 differences in the temperature of the air. An 

 elevation of three hundred and fifty feet will cause 

 the same lowering of temperature as a difference 

 of one degree of latitude, viz., of 1 Fah. 



The same changes of temperature are observed 

 in passing from the base to the summit of a high 

 tropical mountain as in passing along the earth's 

 surface from the equator to the poles. 



Portions of the earth's surface covered by water 

 heat or cool slowly; consequently, the air over 

 such portions does not change its temperature 

 rapidly, or, in other words, such portions of the 

 earth possess an equable climate. Portions of 

 the earth covered by land heat and cool rapidly ; 

 consequently, the air over such portions changes 

 its temperature rapidly, or, in other words, such 

 portions possess a variable climate. 



A surface covered with vegetation such, for 

 example, as a forest does not change its tempera- 

 ture as rapidly as it would if it were bare. Forests, 



