384 



Dr. Norman Campbell : Experiments 



on 



of a magneto in which results much more concordant with 

 his theory were obtained. The curve which he gave showing 

 the relation between the peak potential and C x was marked 

 by well-defined minima such as are characteristic of the 

 theoretical curves. The discrepancy between his results and 

 those just described has to be explained. 



At first it was thought possible that the discrepancy 

 might arise from the methods adopted for measuring the 

 peak potential ; Prof. Jones employed a method depending 

 on a spark-gap. But a few experiments were sufficient to 

 show that the two methods gave precisely the same results 

 within the limits of their respective errors. It was then 

 noted that, in order to bring the frequency of the oscil- 

 lations within the limits of the instrument which he had 

 employed for measuring the wave-form, Prof. Jones had 

 inserted in series with the primary of the magneto a choking 

 coil with an air-core. Accordingly, the measurements which 

 had been made were repeated with a choking coil with an 

 air-core and a self-inductance of O'OOl henry inserted in 

 series with the primary. Curve A of fig. 12 shows the 



Fig. 12. 



:eoc- 



.2700 



C,(mf.) -o 



relation that was then obtained between the peak potential 

 and the primary capacity. The sharp minimum character- 

 istic of the theoretical curve is now clearly shown : the 



