24 EXTENT AND DEPTH OF OCEAN. 



a quart of fresh water was thus obtained; which, 

 though not very palatable, was sufficiently good to 

 relieve the thirst of the ship's crew. Many ships 

 are now regularly supplied with apparatus for dis- 

 tilling sea water; and on the African coasts and 

 other unhealthy stations, where water is bad, the 

 men of our navy drink no other water than that 

 which is distilled from the sea. 



The salts of the ocean have something to do 

 with the creating of oceanic currents; which, in 

 their turn, have a powerful influence on climates. 

 They also retard evaporation to some extent, and 

 have some effect in giving to the sea its beautiful 

 blue colour. 



The ocean covers about two-thirds of the entire 

 surface of the Earth. Its depth has never been 

 certainly ascertained ; but from the numberless 

 experiments and attempts that have been made, we 

 are warranted in coming to the conclusion that it 

 nowhere exceeds five miles in depth, probably does 

 not quite equal that. Professor Wyville Thomp- 

 son estimates the average depth of the sea at about 

 two miles. 



Of the three great oceans into which the sea is 

 naturally divided the Atlantic, the Pacific, and 

 the Arctic the Atlantic is supposed to be the 

 deepest. There are profundities in its bosom which 

 have never yet been sounded, and probably never 

 will be. 



The difficulty of sounding great depths arises 



