11 



gravity, which may thus be moved, varies as the 6th power of the velo- 

 city of the current. Thus if a current of 10 miles an hour will just 

 move a block of a certain form, whose weight is 5 tons, a current of 

 15 miles an hour would move a block of similar form of upwards of 

 55 tons. A current of 20 miles an hour would, according to the 

 same law, move a block of 320 tons, while a current of 2 miles an 

 hour would scarcely move a small pebble. 



In the previous calculations the relation between the magnitude of 

 the block and the velocity of the current has been determined on the 

 supposition that the current, at the instant it acquires its greatest 

 velocity, shall just be able to move the block, which would again be 

 left at rest without being moved through any sensible space. If the 

 velocity be greater or the mass smaller, the block will be transported 

 to a distance which the author has calculated. Let 

 o 2 be the velocity of a current just sufficient to move an assigned 



block ; 

 «! the velocity of the transporting current acting on the above block, 



o i being greater than o 2 ; 

 I the breadth of the great wave of translation producing the current ; 

 h the height of the highest point of the wave above the level of the 



ocean ; 

 H the depth of the ocean ; 

 s the space through which the block is transported by the wave. 



The following Table gives corresponding values of these quanti- 



