18 



Art. 3. — K. Hirayama : 



This will be very easily understood by the geometrical representa- 

 tion of the motion. 



•7/3 



23. The sign of -rr for different types will be discussed now. 

 ■tu 

 The point at which -^ changes its sign is determined by the 



equation 



s'ex—pi cos 0=0 



combined with the equations (15) and (16). Eliminating e and 

 cos 6, we get easily 



x^+2s'Ex+^=0 

 



or 



(25) x==-s'E±Js'^E'~ 



The corresponding values of e are given by 



