48 THE OCEAN. [Book II. 



course under the action of tlie force of gravitation. 

 This force of gravitation acts with equal force upon 

 all the particles of the stream, but those at the sides 

 and bottom of the stream are checked by friction, 

 which is therefore a force acting in opposition to that 

 force of gravitation which tends to draw the stream 

 onwards ; and it is because the particles at the 

 surface of the deep and central parts of the stream 

 are comparatively free from the opposing action of 

 this friction that they are drawn onwards more 

 rapidly by the force which impels the stream on its 

 course. We need not here investigate the abstract 

 nature of the force which causes the particles near 

 the sides or bottom to resist more than those at the 

 surface of the deep and central parts of the stream, 

 the force which tends to set them equally in mo- 

 tion. We are here only concerned with the fact 

 that it is a force which opposes the action of any 

 force which may tend to set the water in motion. 

 It is for the present sufficient that the force de- 

 scribed as friction tends at the sides and bottom 

 of the ocean to check the action of vis-inertia3 in 

 those parts, leaving it comparatively unobstructed 

 at the surface of the deep and central parts of the 

 ocean ; and that therefore the unobstructed ac- 

 tion of vis-inertise at the surface of the deep and 

 central parts of the ocean, being a greater force, 

 must overwhelm, to a greater or lesser extent, the 

 lesser forces near the shores and bottom of the ocean. 



