148 PHYSIOGRAPHY 



The climatic effects of lakes. The great number of lakes in 

 the northern parts of the United States and Europe have some little 

 influence upon the climate of the regions in which they occur. They 

 increase its humidity to some slight extent at least, and, since 

 water is heated less rapidly than the land and also gives up its heat 

 less readily, the lakes have the effect of tempering the climate. 

 Until they freeze over, they tend to keep the temperature of their 

 surroundings a little higher than it would otherwise be in the 

 autumn and early winter, and they tend to reduce the temperature 

 of spring. The climatic effects of a small lake are insignificant, 

 but the effects of large lakes such as Michigan or Superior, are 

 distinctly felt. Their temperature effects are felt chiefly on the 

 sides toward which the prevailing winds blow from the lake. 



Economic advantages and disadvantages. Are lakes helpful 

 or harmful to mankind? Various considerations have a bearing on 

 this question. 



1. The Great Lakes make cheap transportation possible, for 

 freight can be carried by boats more cheaply than by rail.' In this 

 way lakes serve a good purpose. 2. Many cities, like Chicago, 

 draw their water-supply from lakes. 3. Lakes yield fish which are 

 of some importance as food. 4. Large lakes affect the climate and 

 so modify, to some extent, the crops which may be raised about 

 them. Thus the prevailing westerly winds change the climate of 

 the east shore of Lake Michigan so as to make it favorable for fruit- 

 growing, while the west side of the lake is not adapted to fruit. In 

 these and other ways the lakes seem to benefit mankind. 



On the other hand, it is to be remembered that lakes cover land, 

 much of which might have been good farming land if the lake had 

 not been present. Lake Michigan, for example, has an area- of 

 about 22,450 square miles. The value of such an area (more than 

 14 millions of acres) of good farming land would be hundreds of 

 millions of dollars. Small lakes are of little consequence to com- 

 merce, but they have a value of another sort. They beautify the 

 landscape, and afford the means for rest and recreation which 

 could not well be spared. The actual value of such considerations 

 cannot be estimated in dollars and cents. 



Lakes seem to have been of advantage to primitive peoples, for 



