90 THE OCEAN. [Book IH, 



relation to eacli other. When, then, the object in the 

 centre of the basin is made to rotate, those particles 

 of water adjoining the rotating surface endeavour to 

 maintain their position in relation to the part of the 

 rotating surface against which they rested, and also 

 in relation to those particles next beyond them ; and 

 therefore draw towards the part of the surface caused 

 by the action of the extraneous force to tend from 

 them, and also towards those particles next beyond 

 them, these latter towards those next them, and so 

 on ; and thus all the particles, each endeavouring to 

 maintain its connection with those next to it, draw 

 or gravitate towards each other. Thus' the gravita-. 

 tion of the particles one towards another draws the 

 whole mass onwards in a motion of rotation, each 

 endeavouring to maintain its position in relation to 

 the particles set in motion by the action of the ex- 

 traneous force : and therefore, as the object in the 

 centre of the basin is made to rotate, the force of 

 gravitation causes the cork to revolve in the same 

 direction. This is analogous to the motion of the 

 moon revolved eastwards in its orbit by the force of 

 its gravitation towards the surface of the earth ro- 

 tating eastwards. In the case of the moon, as in the 

 case of the cork, the motion is caused directly by 

 gravitation, which is the effort of vis-inertise to 

 maintain matter in a state of rest : — it is the force 

 exerted in the endeavour to resist the action of any 

 forces which tend to cause a change of form or posi- 



