AND ITS SELF-CONSEBVATION. 129 



toward a ; and a will appear to be moving away from c, 

 but also toward ~b. That is, b will have the appearance 

 of moving in the opposite direction from that of its 

 real velocity, while a will be moving in one direction 

 with reference to c, and at the same time in the oppo- 

 site direction with reference to Z>. 



Again, both a and c may be revolving about ~b with 

 any velocity, and, so long as their directions from one 

 another remain unchanged, this revolution could never 

 be detected save with reference to some body outside 

 the system (as we saw before in case of a system of 

 two bodies). 



Once more, suppose an ' ' infinite " sphere, of uniform 

 density, to occupy an otherwise empty space ; the sphere 

 might be revolving on its axis in any given direction 

 and with any velocity, while yet the fact of its revolu- 

 tion, and still more the velocity of its revolution, must 

 be absolutely undiscernible. And yet, at the same time, 

 its revolution must constantly involve motion in an 

 infinitude of opposite directions. That is, every point 

 not in the axis of motion must move in a direction 

 precisely opposite to that in which the corresponding 

 point on the other side of the axis moves. 



Nay, the revolution of such sphere must also involve 

 all possible velocities, from the " infinitely small," 

 at the axis, to the " infinitely great/' at the infinitely 

 removed " circumference." 



Finally, it is easy to see that this ' ' infinite sphere " 

 without differentiation of any kind, is but a material- 

 ized image of space itself, whose content is nothing 

 but the abstract and purely negative possibility of all 

 motion. 



