generated in a High-tension Magneto. 



159 



spark could be depended upon to appear regularly — on 

 a given occasion and with a given capacity — at practically 

 the same value of the primary current. 



Included in the primary circuit was also an air-core coil 

 of small self -inductance (0*00099 henry). Without this 

 it was not found possible to obtain a curve having any well- 

 marked features ; the optimum capacity was very small — 

 apparently between O'Ol and 0*02 microfarad — and it could 

 not be determined with any accuracy. Probably the spark 

 method is not sufficiently delicate to enable one to detect 

 small fluctuations in the curve when the capacity is very 

 small. 



With the series inductance, however, a curve showing 

 clear indications of the arches was easily obtained. The 

 curve is shown in fig. 5. In this experiment the gap was 



Fig. 5. 



J. 



L 



6-0 



S-5 



5-0 





01 -02 -03 04 -05 -06 -07 08 -09 I Microfarad. 



C, 

 Capacity -potential curve for a magneto. 



0*1 mm. wide, and the points on the curve were obtained by 

 adjusting the current until the spark passed at one-half the 

 number of breaks. A curve showing the same features was 

 also obtained with a gap of 0*2 mm. The points may also, 

 less conveniently, be determined by finding the smallest 

 current required to produce the spark. 



The curve shows two maxima, at about Ci = 0*0475 and 

 d = 0*0115 microfarad, the minimum between them being 

 at about C\ = 0*018 microfarad. The rise in the curve from 

 0*018 to 0*0115 microfarad was verified on many occasions, 

 and there can be no doubt that it corresponds with one of 

 the arches of the (u, U sin <f>) curve. 



