42 TEE BOTTOM OF THE SEA. 



THE WATER OF THE OCEAJv. 



1. Composition of Sea- water — Biot's Apparatus. 



Seas are the products of atmospheric vapour, con' 

 densed into fresh-water. But the earth, with which 

 the water came into contact, contains various soluble 

 matters. These were dissolved by the water, and 

 its purity was irrevocably lost. 



The vapour wliich is lifted from the seas by the 

 action of the atmospheric currents may be said to rise 

 in a pure state ; in other words, it is fresh water that 

 is raised. But, again, it falls in the form of rain or 

 snow upon the soil, over wliich it passes slowly to its 

 destination, and thus becomes charged anew with 

 salts which it conveys into the sea. Every time 

 evaporation takes place, the vapour returns in the 

 form of water laden with fresh matter from the sur- 

 face of the earth. This alternate migration of vapour 

 and water must tend to augment continually the salt- 

 ness of the sea, and if there were no countervailing 

 cause, its saltness would increase to the extreme point 

 of saturation. 



