OCEANIC CURRENTS. 451 



of oil. There has been much question raised 

 upon the supposed effects of oil in calming the 

 waves of the sea, and no doubt its power has 

 been much exaggerated ; but it appears certain 

 that pouring oil on the surface, by neutralizing 

 the force of the wind, has a certain tranquil, 

 lizing influence upon the agitated waters. The 

 same degree of adhesion does not exist between 

 oil and air, as between air and water. 



We must now advert to movements in the 

 waters of a different kind to those hitherto 

 spoken of these are Currents. It may be 

 surprising to learn, that in a body of water 

 apparently so little exposed to causes likely 

 to create a current as is the ocean, currents 

 of determinate direction, and of considerable 

 velocity, actually exist. There are mighty 

 rivers in the ocean as well as on land. Some 

 of these currents are merely due to the me- 

 chanical action of the wind ; others are ascrib- 

 able to differences of temperature; thus the 

 melting of a large iceberg, or of an ice-field, 

 would set up, during the whole period occu- 

 pied in the process, various irregular currents 

 caused by the cold water descending, while 

 its place becomes occupied by the lighter and 

 warmer fluid. In these respects, however, we 

 can trace little analogy between the phenomena 

 exhibited by the air and those of the ocean. 



