20 THE OCEAN. [Book II. 



as far as our present purposes are concerned, be con- 

 sidered equal in volume, and the velocity of one of 

 those equal masses is greater than the velocity of the 

 other. 



But, in the case of a stream of water meeting with 

 an obstruction in its course, where the different parts 

 of the water are moved with unequal velocities ', the 

 check given to the onward motion which brings those 

 unequal velocities into conflict, is not given as in 

 Plate III. at a central axis, necessarily brmging a 

 volume on one side of the axis into conflict with an 

 equal volume on the other side, but this check is given 

 at the end of each line of motion ; so that, although 

 unequal velocities are brought into conflict, yet, as 

 far as the demonstration in connection with Plate III. 

 is concerned, there might nevertheless be no over- 

 whelming of lesser forces by greater forces ; because, 

 by a greater volume of the water moved at the lesser 

 velocities opposing itself to a lesser volume of that 

 moved at the greater velocities, the quantities of 

 motion brought into opposition might be equalised ; 

 thereby preventing the overwhelming of lesser forces 

 by greater forces in the manner demonstrated in 

 connection with Plate III. 



But that, though the onward motion of the fluid 

 be checked at the end of each line of motion, there 

 will nevertheless be an overwhelming of lesser forces 

 by greater forces, may be demonstrated by holding a 

 goblet containing water in an inclined position, as in 



