CLIMATIC INFLUENCES OF BODIES OF WATER 141 



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

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

 soil, that at a depth of comparatively few feet the temperature 

 does not change, summer or winter. On the other hand, the 

 sun's rays penetrate into the water to a considerable depth 

 (fig. 75), the exact distance depending on the clearness of the 

 water. If the water is clouded by sediment, the rays of the 

 sun do not penetrate very far. A second reason is that, since 

 the sun's rays are reflected from the water more than from the 

 land, much of 

 the heat is re- 

 flected also 

 and does not 

 actually enter 

 the water. A 

 third reason 

 lies in the fact 

 that the water 

 moves easily. 

 Waves and 

 currents mix 

 the warm sur- 

 face waters 

 with the cool 

 deeper layers, 



thus scattering the heat widely. For these reasons, although 

 as much heat will be received upon a square foot of water as 

 of land, no part of the water is heated so highly. 



The fourth and most important reason is found in the effect 

 of a given amount of heat upon different substances. If we ex- 

 pose equal amounts of two different substances to equal heat 

 for the same time, the two bodies will not usually be equally 

 heated. If a kettle of water and a flatiron are placed on the 

 kitchen range at the same time, the iron will be heated more 

 rapidly than the water. If a pound of iron and a pound of 



FIG. 75. Action of the sun's rays on land and water 



When the sun's rays fall upon the surface of the land, they 



are mostly absorbed at the surface. The water reflects some 



of the light and heat, and the remainder may penetrate to 



considerable depths 



