702 Dr. B. van der Pol on Oscillation Hysteresis in a 



possible in the mode of vibration in which it is already oscil- 

 lating, though the other mode of vibration is possible for the 

 same parameters. 



Fig. 2. 



I, 



Fiar. 3. 



1 







y/A? 



! B 





J. 



r 



i 

 i 

 i 





' ^^v. 



^^ 



***^r 



i 







E 



i 



i 





D 



ov. 



6UU 



These phenomena were noticed by the author in February 

 1920, bat it was felt that no satisfactory explanation could 

 be given unless progress was first made in the development 

 •of a non-linear theory of sustained oscillations. For it is 

 obvious that, when the problem is treated with linear 

 differential equations, the principle of superposition is valid, 

 .and in t i is case oscillations in the one mode are uninfluenced 

 by oscillations in the other. It is therefore somewhat sur- 

 prising that up to the present, though several theoretical 



