CLIMATIC INFLUENCES OF BODIES OF WATER 145 



heated as it flows across the land, and rises as it is displaced 

 by more air from the lake. Thus there is a continuous flow 

 of air across the shore line from water to land as long 

 as the land is hotter than the water, excepting when local 

 breezes are counteracted by stronger and more general move- 

 ments of the air. The breeze gets well started about the 

 middle of the forenoon, the time the land ordinarily be- 

 comes heated. During the night the land may be cooler than 



When the land is warmer than the water, cool and heavy air from the water flows 



over the land, pushing the lighter, warm air upward. Such movement of the air 



is known as a lake breeze or sea breeze 



in the daytime ; sometimes so much cooler than the water 

 that the air flows from the land to the water, but this land 

 breeze is much less noticeable than the water breeze. 



161. Causes of unequal heating of land and water. The 

 more rapid heating of the land is due, first, to the fact that 

 it is not transparent. All the heat of the sun is received on 

 the surface of the land, and the upper few inches are very 

 rapidly heated, while the lower parts receive the heat slowly. 

 Indeed, so slowly is heat transmitted to the deeper layers of 

 the soil that at a depth of a comparatively few feet the tem- 

 perature does not change either in summer or winter. On 

 the other hand, the sun's rays penetrate into the water to a 



