246 W. G. Cady — Electric Arc between Metallic Electrodes. 



expected to limit the penetration of the oscillations to a like 

 extent, since the discharge is the source of the oscillations and 

 they are propagated in each direction from it. 



It was difficult to determine the effect on the frequency of 

 varying the length of the discharge, for this length was limited 

 by the available e.m.f. to about one millimeter, and it became 

 continually shorter as the discharge passed, on account of the 

 deposits of carbon dust on the electrodes. One would expect 

 an increase of length to cause an increase in resistance, and 

 thus to diminish the frequency of the oscillations. It can only 

 be affirmed that the possible variation in length was over too 

 small a range to affect the frequency appreciably. 



§ 25. Systems of harmonics. — Owing to the impossibility of 

 keeping the state of the discharge and intensity of current 

 constant long enough to obtain data for a full resonance curve, 

 only incomplete groups of harmonics can be shown, obtained 

 at different times, and under different conditions. The dis- 

 charge, and consequently the frequency, fluctuated so much 

 that the resonance curves were considerably flattened, as if the 

 oscillations had been damped. But in one or two signal 

 instances (see § 29), when the discharge was unusually steady, 

 curves for one or two frequencies of great sharpness were 

 obtained. 



In the following table some representative groups of har- 

 monic frequencies are shown. The figures in the first two 







Table IY. 







Observed 





No. of 



Fundamental 



frequency 



Eatio 



harmonic 





f 0-25 



0-98 



1 





! 0-465 



1-82 



2 



0-255 



« 



1-02 

 1-32 



4-0 



5-18 



4 

 5 







1-82 



7-1 



7 







L 2'22 



8-70 



9 





f0-237 



1-0 



1 





| 1-4 



5-91 



6 



0*237 



<j 1-68 



7-10 



7 





| 2-9 



12-2 



12 





^ 3-7 



15-6 



16(f) 





f 0-46 



2-09 



2 



0-22 



J 0-66 

 ] 0-84 



3-00 

 3-83 



3 

 4 





^ 1-12 



5-09 



5 





f 0*87 



302 



3 





| 1-18 



4-10 



4 



0-288 



<{ 1-70 



5-90 



6 





2-30 



7-99 



8 







2-88 



10-0 



10 



