PHYSIOLOGICAL PARADOXES. 



to green, and immediately afterwards P Q R 

 to red and G H I to green. 



There will now be no red at A I, where the 

 red spot originally was. It will be at J R 

 having travelled by successive jumps through 

 the positions D L and G O. But these jumps 

 have been to a spectator on the distant moun- 

 tain so small and quick that they have not 

 appeared as jumps. The individual move- 

 ments have been imperceptible to him, and 

 it has appeared to him that the spot moved 

 quickly, but smoothly and continuously, from 

 A I to J R. 



Now let S T U turn red, P M J simul- 

 taneously turning green again, and so with 

 V W X and Q N K and with Y Z and 

 R O L. The spot of red will appear to have 

 changed its direction and moved steadily to 

 U Y ; and it might continue moving in this 

 direction for twenty or one hundred yards, or 

 change its direction again and move towards 

 any other point. Through all these movements 

 the spectator on the distant mountain would 

 appear to have seen the red spot change its 

 position much as we think we see a fly crawl 

 over the window-pane or a player run over the 

 cricket ground, sometimes faster, sometimes 

 more slowly, sometimes in one direction, some- 

 times in another, but always with continuity 

 that is to say, never passing from one posi- 

 tion to another without having been at each 



280 



