146 ELEMENTS OF GENERAL SCIENCE 



considerable depth (fig. 75), the exact distance depending on 

 the clearness of the water. If the water is clouded by sedi- 

 ment, 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 reflected 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 surface waters with the cool deeper layers, thus 



scattering the 

 heat widely. 

 For these rea- 

 sons, although 

 as much heat 

 will be received 



upon a square 

 foot of water 

 as of land, no 

 part of the 

 water is heated 



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



The 

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



are mostly absorbed at the surface. The water reflects some and most im- 

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



considerable depths portant reason 



is found in the 



effect of a given amount of heat upon different substances. 

 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 water 

 are placed on the stove and exposed equally to the heating 

 surface, it will be found after a short time that the iron is 

 much hotter than the water. The same amount of heat has 

 much less effect on the water than on the iron, so far as 

 raising its temperature is concerned. The amount of heat 

 which will warm a pound of iron 1 C. will warm a pound of 

 water only 0.11 of 1 C.; that is, it takes over nine times as 



