444 



BELL SYSTEM TECHNICAL JOURNAL 



experiment. The two cases computed are for the system operating 

 with cod and aj„ exactly the frequencies of electrical and mechanical 

 resonance and for operation with cod 21 cycles higher than resonance. 

 In the latter case aj„ is determined by the requirement — noted by Mr. 

 Hartley — that the phase angles of the impedances be equal. The 

 actual change in co^ is only a fraction of a cycle. The two cases are 

 given because it was not possible, with the equipment available, to 

 determine co^ with sufficient accuracy to distinguish between them. 



5 

 ? 8 



5 6 



4 6 6 7 8 9 10 II 12 13 



JMPRESSED POTENTIAL (RMS) IN VOLTS 



Fig. 2 — Electrical current components. 



< UH 



[. OUJ 



1 2 3 4 5 6 7 e 9 10 II 12 13 14 15 16 17 18 



IMPRESSED POTENTIAL (RMS) IN VOLTS 



Fig. 3 — Mechanical displacement. 



While the frequency difference between them is only 20 cycles out of 

 v30,000 it will be noted that, because of the critical character of the 

 impedances, the results differ considerably in amplitudes of the com- 

 ponents and in the threshold value. 



The second case checks very closely as far as the electrical results 

 are concerned and the mechanical results are of the same order of 

 magnitude. The discrepancy can reasonably be laid to the inac- 

 curacies in the indirect method of measuring the mechanical amplitude. 

 More important is the verification of the outstanding properties pre- 

 dicted by the analysis. There is a threshold \oltage above which 



