178 Mr. Appleton and Dr. B. van der Pol on a Type of 



oscillatory circuit. The form of the oscillation characteristic 

 may be varied within fairly large limits by adjusting the 

 applied electrode potentials of the triode and the reaction 

 coupling, and thus many interesting problems arise. For 

 example, we may ask ourselves : What must be the shape of 

 the oscillation characteristic such that for some particular 

 set of circuit conditions there may be more than one possible 

 stable amplitude? In such a case we should expect the 

 particular amplitude obtaining to depend on the method of 

 approach to the set of conditions in question. We shall 

 deal here only with the answer to the question for a case in 

 which two stable amplitudes are possible for any given set 

 of circuit constants, but it would not be difficult to extend 

 the analysis to more complicated cases. For example, we 

 find that for two stable amplitudes to be possible, one of which 

 is zero, the expression for the oscillation characteristic, when 

 developed as a Maclaurin series, must have a positive fifth 

 differential coefficient and a negative third differential 

 coefficient. In the case of ordinary receiving triodes we 

 have found it quite easy to obtain characteristics of this 

 particular type, and thus have been able to compare the 

 theoretical results with experiment. 



The circuit used throughout the experiments was of the 

 simple type shown in iig. 1 A. 



Fig. 1. 



:.-}^ 



U 



m a 



As is well kaown, the anode current of a triode is a 

 function of both the anode and grid potentials with respect 

 to the filament. But in the circuit of fig. 1 there is a definite 

 relation between the variable parts (v a and v g ) of the anode 



