40 



THE OPAL SEA 



Franklin 

 and Maury. 



teenth century to be influenced by the move- 

 ment of the sun, and by others to be a contin- 

 uation of the flow of the Mississippi River; 

 but our wise Dr. Franklin made a more com- 

 mon-sense explanation in saying it was caused 

 by the Trade Winds forcing the sea water into 

 the Gulf of Mexico and that its outward flow 

 was but the natural working of the law of 

 gravity. When the further common-sense of 

 Lieutenant Maury was applied to the ocean cur- 

 rents there was no longer any place for specula- 

 tion or superstition. 



Perhaps the chief cause of all ocean circula- 

 tion is the prevailing winds. By long and 

 steady pressure of the winds exerted upon the 

 surface of the waters the upper stratum is 

 forced into a sluggish movement which gradu- 

 ally increases in velocity until a well-estab- 

 lished bent or direction is given to it. The 

 current thus set in motion is not deep. On 

 the contrary, it is a surface drift which affects 

 the intermediate depths but slightly, and the 

 great depths probably not at all. The winds 

 that produce the chief currents are the well- 

 known Trades that blow steadily across the 

 Atlantic from east to west. In the Northern 

 hemisphere they are turned to the north and 

 flow back in a counter current to the east; in 



The Trade 

 Winds. 



