700 BELL SYSTEM TECHNICAL JOURNAL 



\ — A = ^° I 1 + — 



where Za represents the impedance of Zq and Zi in parallel. Again 

 only the bracketed term can yield undamped transients so that the 

 criterion involves plotting — ZjZin over the frequency range; if the 

 resultant curve does not enclose (1,0) the circuit is stable. 



It may be remarked that these results are applicable to circuits in- 

 cluding two-terminal negative impedances such as the oscillating arc 

 and the dynatron, which are of the series and the shunt type respec- 

 tively. 



Acknowledgments 



The authors are indebted to Mr. L. W. Hussey for discussions of 

 theoretical points, and to Mr. P. A. Reiling for his cooperation in the 

 experiments. 



