dee 



Cambridge Philosophical Socieit/.} 



about 4 tons. If the polar axis == ^ths of the equatorial diameter, 

 the block will be just moved, protided its height be 3^ feet and its 

 weight 14 or 15 tons. i ,: ^ ,f:,,, j, , t. ,f I j,;i ^ 



In this part of the investigation it is shown that the power of 

 rapid currents to transport blocks of enormous magnitude is per- 

 fectly consistent with the almost inappreciable power of currents of 

 which the velocity does not exceed, for instance, 2 miles an hour ; 

 for it is shown that the weight of a block of given form and specific 

 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 ceitain 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 . ., ; . i 

 02 be the velocity 'of a current just sufficient to jmovei an assigned 



block; i :,; ; (!(1V. CO' ': 



Vi the velocity of the transporting current acting on the abov? block, 



1 being greater than Ug ; 

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

 h the height oftiie highest J^cmiJ.oJ ^fe w^e^abojreji^leypl^of^giglj 



°^^^'> , :',:•!,; 1 •' '■! - •• '■':ti:'-;;:vMU r!oi;<< ,t^brio:hioo aJ ,iol 

 H the depth of the ocean ; , .. , <m,> orii 



s the space through which the block is transported by the ■wa,v<?,[,.^ ^^.^ 



The following Table gives corresponding values of these quanti- 

 ties. The last column gives the corresponding value of the space (s^) 

 through which a particle of the water, or any body floating in the 

 w^tef^wiill he carried by the wave. The expressions for s and s^ are 



-il) :jl((B-Ii)Jji«iHO') ■: 1 (yj _ o,)2 



(J 10 noiJiJaq-'Ji n 



' A6sn'jbUuu'j 



it lo flirjil) 



[See opposite page.] ; 1 1 1 



In estimating the magnitude of a block which may be moved bya ' 

 given current, the transport is supposed to take place over a hori- 

 zontal surface sufficiently hard and even for the block to roll upon it 

 without impediment. In other states of the surface the transport 

 might be more or less impeded. The constant action of denuding 

 causes would be highly favourable to the transport by the successive 

 removal of local impediments. The author conceives that the ob- 

 jection to this mode of transport, founded on inequaUties of surface 



' s iy-iuia ,3iol . . 



il.iill W 2 



V being much greater than v 



V 



