Resistance of the Electric Arc. 



413 



the resistance of the arc can be obtained directly in ohms as 

 the difference of two readings of the box R. 



Method II. is shown diagrammatically in fig. 2 ; the arc 



Fi-. 2. 



circuit in this case being shown to the right. X is the arc, 

 B the battery of accumulators, K the resistance, A the am- 

 meter, and v the voltmeter across the arc. B and K were 

 made large, K being about 11 ohms. The circuit shown on 

 the left consists of the alternator D, the transformer T, which 

 together with E is now used simply as a delicate alrernate- 

 current ammeter, a condenser F, and a commutator C. By 

 means of C we can put in circuit either the resistance R, 

 or the arc-lamp X in series with the resistance S. The alter- 

 nating current flowing through K is negligible compared 

 with that flowing through X on account of the high resist- 

 ance of K. The condenser F prevents any continuous current 

 due to the P.D. at the arc from passing through the alter- 

 nator. 



Method of Experimenting . 



If L is the self-induction of the circuit and F its capacity, the 

 impedance I of the circuit is given by \/ R'"' + 1 ™ — Lea] > 

 where o> = 2-7T x frequency. This is a minimum when LFar = 1. 



