Chap. VII.] GRAVITATION AND INERTION. 91 



tion. These motions result from the efforts of the 

 particles of matter to maintain the positions in rela- 

 tion to each other which the extraneous force dis- 

 turbs ; whereas the motion of the stone in the sling 

 is caused directly by the extraneous force carrying 

 the stone onwards in accordance with its laws, in 

 spite of the resistance of vis-inertiae. The stone is 

 hurled through the air in direct opposition to the 

 force of gravitation ; and after it is released from 

 the sling the motion communicated to it must, sooner 

 or later, be spent by the continuous resistance of 

 vis-inertiae. 



An increase of the velocity of rotation which 

 revolv^es the cork and the water above mentioned 

 will cause the particles of water and the cork to 

 recede from the centre along tangents backwards from 

 the successive points to which the revolving force en- 

 deavours to carry them in the circles of revolution 

 (as shown by the diagram on page 88) ; because, 

 as has been shown in the preceding chapter, the 

 retarding force of astral gravitation increases as the 

 square of the velocity of the motion which it resists ; 

 and it wdll therefore carry the revolving particles 

 backwards from the centre of ' revolution until the 

 disturbed equilibrium is readjusted in consequence 

 of the revolving force decreasing as the cube of the 

 distance from the centre increases. 



As the water recedes alons^ the tano-ents it exem- 

 plifies the overwhelming of lesser forces by greater. 



