432 



. \V. K. Ayr-ton and Dr. W. E. Surapner. [Apr. 9, 

 Table III. 





Comparing V with the E.M.P. of the dynamo, we see that the arc 

 and the condenser together acted as a condenser on the whole ; bat, 

 comparing V with V\ + Ft, we see that the arc acted as an induction 

 and not as a capacity. 



It having been conclusively proved that a hissing arc with uncored 

 carbons acts as an induction, it was interesting to compare the im- 

 pedance it produces with the impedance produced by the ordinary 

 regulating electromagnet of the lamp. The arc itself seen in fig. 3 

 was, therefore, short-circuited, and the following measurements made, 

 F! now being the square root of the mean square of the P.D. 

 between the terminals of the regulating electromagnet, F as 

 before that between the terminals of the non-inductive resistance, 

 and F that between a and c, the arc, as already explained, being 

 short-circuited. The frequency was maintained at 200 periods per 

 second. 



Table IV. 



We have, then, P.D. measurements giving the phase difference of 

 current and P.D. with the arc alone (Table I and fig. 2) ; with the 

 arc and regulating electromagnet (Table II and fig. 3) ; and with 

 the electromagnet alone (Table IV). Defining impedance in the 

 usual way as the ratio of the square root of mean square of P.D. to 

 the square root of mean square of current, we find from the two 

 sets of results given on Table I, that 



