The Mighty Deep 



evaporation or drying-up of water-surfaces. 

 This is remarkably seen in the Red Sea. An 

 amount of water passes away from that sea in 

 a single year, sufficient to bring down its level 

 some fifteen or twenty feet, — which it would do, 

 but for a powerful current always flowing In from 

 the Indian Ocean. 



When sea-water thus passes off in vapour, 

 it leaves the salt behind. Were this amount 

 of evaporation to go on steadily in the Red Sea, 

 without any fresh supplies of water being re- 

 ceived, about two thousand years would suffice 

 to dry up the whole Sea, nothing but a great 

 mass of salt remaining in its bed. 



If the Red Sea alone loses in one year a slice 

 of water, fifteen or twenty feet thick, imagine 

 what the enormous quantity must be which is 

 raised, year by year, from the surfaces of all 

 tropical oceans, and in a less degree from the 

 seas in colder regions. The weight of the whole 

 could only be told in hundreds of millions of 

 millions of tons. And this vast mass is drawn 

 up, gently and mildly, particle by particle ; to 

 be wafted by breezes to regions where water is 

 urgently required, and there to be poured down 

 as rain upon the thirsty ground. Thus the 

 great exchange is carried on, with steady se- 



94 



