ALTERNATING-CURRENT ARCS 109 



to the fact that a potential difference of several volts is 

 necessary in order to produce any current at all through 

 the arc. 



As the current increases the voltage decreases slightly, 

 since it requires less voltage to maintain a large current 

 than a small one. The amount of the current during this 

 part of the cycle is determined chiefly by the resistance 

 and inductance in the other parts of the circuit. Near the 

 end of the phase the current rapidly approaches zero, since 

 the voltage has then become less 

 than that needed to maintain an 

 arc. 



There is given in Fig. 31 a curve 

 taken with an oscillograph where 

 the voltage curve aa' is given in 

 a negative direction in order that 

 it may not be confused with the 

 current curve W. These curves F 



were taken by Simon 1 with an 



arc between solid carbons 5 mm. in diameter placed 

 horizontally above a Bunsen burner, so that the arc was 

 in the flame of the burner. The arc was 2.5 mm. in length 

 and the current was 2.3 amperes with a frequency of 50 

 per second. 



The flaming arcs behave with alternating currents much 

 the same as the arc between cored carbons, although the 

 curves of the flaming arc taken with an oscillograph were 

 more similar to those of the solid than to those of the cored 

 carbon arcs. 2 Fig. 32 gives such curves when there was 

 non-inductive resistance in series with the arc. 



1 Phys. ZS., 6, 305; 1905. 



2 Blondel, Trans. Intern. Elec. Cong., 2, 744; 1904. 



