8-4 THE NEW AGRICULTURE. 



v 



three times greater than that of the land. All this rain gradually 

 mingles with the salt water, and can then be no longer recognized. 

 It thus helps to make up for the loss which the sea is always suf- 

 fering by evaporation, for the sea is the great evaporating sur- 

 face whence most of the vapor of the atmosphere is derived. 



" On the other hand, the total amount of rain which falls upon 

 the land of the globe must be enormous. It has been estimated, 

 for example, that about sixty-eight cubic miles of water annually 

 descend as rain even upon the surface of the British Isles, and 

 there are many much more rainy regions. If you inquire about 

 this rain which falls upon the land, you will find that it does not 

 at once disappear, but begins another kind of circulation. Watch 

 what happens during a shower of rain. If the shower is heav}% 

 you will notice little runs of muddy water coursing down the 

 streets or roads, or flowing out of the ridges of the fields. Follow 

 one of the runs. It leads into some drain or brook, that into some 

 larger stream, the stream into a river; and the river, if you follow 

 it far enough, will bring you to the sea. Now think of all the 

 brooks and rivers of the world, where this kind of transport of 

 water is going on, and you will at once see how vast must be the 

 part of the rain which flows off the land into the ocean. 



" But does the whole of the rain flow off at once into the sea in 

 this way ? A good deal of the rain which falls upon the land 

 must sink underground and gather there. You may think that 

 surely the water which disappears in that way must be finally 

 withdrawn from the general circulation which we have been trac- 

 ing. "When it sinks below the surface, how can it ever get up to 

 the surface again? 



" Yet, if you consider for a little, you will be convinced that what- 

 ever becomes of it underneath, it can not be lost. If all the rain 

 which sinks into the ground be forever removed from the surface 



