EVAPORATION OF THE SEA. 49 



The water which the ocean loses by evaporation 

 is returned to it in full measure by rains and rivers. 

 It is not so, however, in the case of certain interior 

 seas, completely isolated from the ocean, or only 

 coramunicating with it by means of a narrow channel. 

 The winds which blow upon such a sea may be de- 

 spoiled of their humidity by their passage across 

 gi-eat continents, and the rivers themselves may not 

 bring a sufficient tribute to supply the loss caused 

 by a powerful evaporation ; or it may happen that the 

 quantity of water returned by rains and rivers is 

 exactly equal to that which is lost by evaporation ; 

 or, finally, the supply may exceed the loss. In 

 either case, the result, as regards the saltness of the 

 sea, is obvious. In the first case its water will be 

 Salter than that of the ocean; in the second, it will 

 be about the same ; in the third, less. 



If the interior sea communicates with the ocean, 

 there will generally be a current in the channel 

 which unites them. This current will float sliips 

 into the interior sea if that sea loses moie water 

 than it receives; but it will bear them towards the 

 ocean if it receives more water than it loses. The 

 Mediterranean and the Red Sea both receive the 

 waters of the ocean. The Black Sea and the Baltic 

 are, so to speak, too rich ; they contribute tlieir 

 excess of water to the neighbouring seas. 



