THE SALTS OF THE SEA. 185 



would constantly accumulate, as tliis very shrewd author remarks, 

 were it not for the shells and insects of the sea and other agents 

 mentioned. 



503. " The case of the sea," says Fowner, " is but a magnified 

 representation of what occurs in every lake into which rivers flow, 

 but from which there is no outlet except by evaporation. Such 

 a lake is invariably a salt lake. It is impossible that it can be 

 otherwise ; and it is curious to observe that this condition disap- 

 pears when an artificial outlet is produced for the waters." 



504. How, therefore, shall we account for this sameness of 

 compound, this structure of coral (§ 498), this stability as to ani- 

 mal life in the sea, but upon the supposition of a general system 

 of circulation in the ocean, by which, in process of time, water 

 from one part is conveyed to another part the most remote, and 

 by which a general interchange and commingling of the waters 

 take place ? In like manner, the constituents of the atmosphere, 

 whether it be analyzed at the equator or the poles, are the same. 

 By cutting off and shutting up from the general channels of cir- 

 culation any portion of sea water, as in the Dead Sea, or of at- 

 mospheric air, as in mines or wells, we can easily fill either with 

 gases or other matter that shall very much affect its character, 

 or alter the proportion of its ingredients, and affect the health of 

 its inhabitants ; but in the open sea or open air, no. 



505. The principal agents that are supposed to be concerned in 

 giving circulation to the atmosphere, and in preserving the ratio 

 among its components, are light, heat, electricity, and magnetism. 

 But with regard to the sea, it is not known what office is perform- 

 ed by electricity and magnetism, in giving dynamical force to its 

 waters in their system of circulation. The chief motive power 

 from which marine currents derive their velocity has been ascribed 

 to heat ; but a close study of the agents concerned has suggested 

 that an important — nay, a powerful and active agency in the sys- 

 tem of oceanic circulation is derived from the salts of the sea water, 

 through the instrumentahty of the winds, of marine plants, and 

 animals. These give the ocean great dynamical force. 



506. Let us, for the sake of illustrating and explaining this 

 force, suppose the sea in all its parts — in its depths and at the sur- 



