14 



ON THE CAUSES OF THE 



without rotatory motion. But if air with its lightness and 

 elasticity thus rapidly acquires the motion of the part of 

 the earth on which it rests, how much more decidedly must 

 heavy and comparatively inelastic water do so ? Yet it is 

 very probable that the opinion so generally adopted, that 

 the tropical trade winds were caused by the earth leav- 

 ing the air behind it, countenanced, if it did not give 

 birth to the belief, that the solid earth, in its rotation, 

 left the waters of the ocean behind. I am not aware 

 of any proof having been furnished of the superior rota- 

 tory velocity of the bed of the ocean, as compared with 

 that of the water resting on it. It appears to have been 

 voluntarily assumed, in order to assign a cause for the great 

 oceanic currents, as no other adequate cause could be found. 

 But when it is seen that wind has sufficient power to produce, 

 not only the great eastern oceanic currents, but also the other 

 currents which run in different directions, and with great 

 velocities, and that wind is always in action wherever the 

 currents are found, such an assumption becomes unnecessary 

 and may be discarded. 



The waters of the ocean are partially confined within basins 

 having bottoms unequal in depth, with sub-marine mountains 

 and vallies, bounded by land of irregular forms; and an ocean 

 current created by wind within any basin may obviously have 

 its direction altered by a sub-marine valley or mountain, just 

 as the direction of wind itself may be changed or modified in 

 passing through a valley above the level of the sea. And 

 when a force like the action of wind, in some particular 

 locality, raises water much above its natural level, as it 

 does in the Gulf of Mexico, the gravity of the water imme- 

 diately acts to restore the equilibrium of pressure, and may 

 thus produce new currents. It is not, however, the object of 

 this paper to pursue secondary oceanic currents through their 

 various courses, — that object having been only to point out 

 the real primary cause that puts in motion the waters whose 



