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



the doublets also varying periodically. Each doublet would 

 occupy a volume c/co cube, and so would give interference 

 effects. It is also seen that if: both polarized rays are 

 eliminated by crossed nicols no energy will get through, 

 and it would be impossible to have " longitudinal radiation" 

 by itself. 



A source of radiation of frequency co would consist of a 

 number of rotating doublets. Energy would be dissipated 

 in two ways : — (1) A doublet losing all its energy, as its 

 periphery is moving with velocity r, would send out a pulse 

 to infinity — if all the doublets were rotating in phase, the 

 disruption of a number at a fairly steady rate would give 

 the ordinary periodic radiation and interference effects ; 

 (2) a doublet owing to a "collision" would leave the 

 cluster and travel as a whole in a straight line from the 

 source until through another collision it gave up all its 

 energy — its velocity would be less than e, but would 

 probably give effects that would appear instantaneous. 

 Accordingly, it seems that a source could be very weak 

 and give interference effects, and yet be able to start the 

 photoelectric effect in an inappreciable time. 



LXXXV. On Oscillation Hysteresis in a Triode Generator 

 antli Two Degrees of Freedom. By Balth. van der Pol 

 Jun., D.Sc* 



WHEN two oscillatory circuits are linked together by 

 means of a magnetic, electrostatic, or resistance 

 coupling, it is well known that the circuit combination 

 possesses two degrees of freedom. If one of these oscillatory 

 circuits is, moreover, a part of a triode generator, it is 

 natural to ask whether the tw r o modes of vibration can exist 

 simultaneously or, if this is not the case, whether the one or 

 the other mode of vibration will obtain for any particular 

 conditions. 



Now it is found experimentally that, when the system 

 oscillates in one of the two modes of vibration and the 

 natural frequency of the secondary circuit is varied gra- 

 dually, the system suddenly jumps at a certain point from 

 the first mode of vibration to the other. If afterwards 

 the natural frequency of the secondary is varied in the re- 

 verse direction it is found that the system jumps from the 

 second into the first mode of vibration, but at a point which 

 is not identical with the first one mentioned above, and thus 

 * Communicated by Professor H. A. Lorentz, For.M.R.S. 





