408 



Cady and Arnold — Electric Arc. 



rent increased and also as the length diminished. This may 

 have been due to increasing frequency, since Simon* has shown 

 the frequency to vary in the same manner. Adding non- 

 inductive resistance to the shunt circuit always greatly reduced 

 the deflections. 



The experiment of inserting in series with the condenser a 

 small coil having a self-inductance of 0*000 04 henry was also 

 tried. This always diminished the deflections when the cur- 

 rent was over 2 amp., but as the current was decreased, its 



c 



A 



to Bridge 



B 



L 



R 



K 



P 



240 Volt 

 Supply 



Fig. 6. 



damping effect was reduced until at small currents it sometimes 

 even caused an increase in the deflection. This points to the 

 existence of a sort of resonance between the arc and the shunt 

 circuit, and is probably related to the fact that a decrease in 

 the arc current tends to reduce the frequency. 



§37. Experiments with the Copper Arc, Lecher 's Method.- — 

 With no self-induction in the shunt circuit, closing the switch 

 of the latter always put the arc out unless the current was over 

 three amperes. Galvanometer deflections were not large, and 

 they grew smaller as the current increased. That Lecher 

 found no effect with copper is probably due to the lower sensi- 

 tiveness of his apparatus. 



With 0*000 04 henry in series with the condenser, the cur- 

 rent could be reduced to one ampere before the arc went out. 

 Deflections increased with decreasing current, and before the 

 arc was extinguished the light disappeared from the scale. 

 This illustrates the effectiveness of the copper arc at small cur- 

 rents for the production of high frequency oscillations. 



* Phys. Zeitschr., vii, 433, 1906. 



