10 



Now, we have seen that water is continually flowing by means of 

 the rivers from the land to the seas. The process has been going on 

 for ages past. It evidently couldn't continue unless there was some 

 means by which the water came back from the seas and oceans to the 

 land. What is the road which it travels on this retiirn journey? To 

 discover it let us trace the rain to its origin. Eain comes from moist- 

 ure condensing in the clouds. Where do the clouds come from? 

 Some of them form from vapor which rises from the land, and some 

 from moisture that rises from the sea. Now this is the only known 

 path by which water returns from the ocean to the land. The vapor 

 rises gently and invisibly from the sea, and it seems almost incredible 

 that such huge masses of water can rise in this imperceptible form as 

 is carried by the Mississippi and all the innumerable rivers of the 

 earth. Yet such is the fact, and when we think of the immense cur- 

 rents that carry water from the land to the ocean we should at the 

 same time try to imagine the equally immense overhead rivers of 

 vapor which convey the water back from the ocean to the land. 



But water does not move of its own accord. To what great agency, 

 then, do we owe this tremendous activity of the water on the globe? 

 Firstly, to the heat of the sun, which falls silently on the waters of 

 the ocean, tearing particles free and raising them as vapor into the 

 air. It is really the sun, too, that starts into motion the winds which 

 carry this moisture over the land, where it falls as rain. Then we 

 have the assistance of gravity or the attraction of the earth, for it is 

 to this that the flow of the brooks from the hillside to the river is 

 due, and also the further flow of the rivers to the ocean. 



