ALTERNATING-CURRENT ARCS 



119 



current arc between carbon and a metal were taken by 

 Blondel 1 by means of the oscillograph. He found that 

 when there was inductive resistance in the circuit, the arc 

 was extinguished for a longer time than when there was 

 none. 2 Fig. 36 gives a good idea of such curves. During 



FIG. 36. 



one half period the current and potential difference curves 

 are much the same as with ordinary alternating-current 

 arcs. In the other the voltage rises to its normal value, 

 but there is no corresponding current. 



This phenomenon is the same as that described on page 69 

 where the peculiarities of the direct-current arc between 

 unlike terminals were discussed, and the explanation of this 

 is, of course, the same as that given in that discussion. 



Alternating-current Arc in Other Gases than Air. 

 There have been but few experiments performed on the 

 alternating current in other gases than air. The results 

 obtained from these are such as one would expect from 

 those on the direct-current arc in different gases. Thus it 

 has been observed that it is very difficult to maintain an 



1 C. R., 128, 727; 1899. 



2 See also Duddell and Marchant, Journ. Inst. Elec. Eng., 28, i; 1899. 



