INTELLIGENT BILLIARD BALLS. 



when D strikes and stops, and it will appear 

 to start with the speed with which D finished, 

 so that it will run as far against friction as 

 D would have done, if, instead of striking 

 C, it had been uninterrupted. 



Now how is it that only A moves ? And 

 how is it that, in all variations of the speed 

 of D, or of the number of balls in the stationary 

 row, A knows just how fast to start, and so 

 how far to go ? D loses the whole of its 



FlQ. 10. EQUAL MOVEMENT TRANSMITTED TO EQUAL 

 NUMBER OF BALLS. 



energy of movement, which has finally been 

 transferred to A. But this cannot have hap- 

 pened without B and C having moved also. 

 How is it that they do not share in the final 

 movement ? Why is this final movement not 

 divided equally between A, B, C, and D, all 

 of them moving together, though much more 

 slowly, and for a shorter distance than when 

 the movement is all concentrated in A ? 



But this is not the most surprising part 

 of the paradox. If there be a longer row of 

 stationary balls, four, five, six, or seven, and if 



37 



