i'Si; 



Crodker — Influence of a Series Spark 



When a condenser is placed in parallel with the corona 

 tube, the positive streamers do not appear and the nega- 

 tive heads are not broken up. The results obtained with 

 the telephone are compatible with the assumption that 

 the corona current with a spark in series is only inter- 

 mittent and not oscillatory. 



More evidence in favor of this view is arrived at by 

 means of Boys' method. It consists in photographing 



BOYS 



Fig. 4. 



METHOD 



Plate 



Lenses 



Spark 



-o + 



=4] 



Motor Tube 



Fig. 4. Arrangement for photographing the spark. 



the spark directly as the image from it sweeps across a 

 photographic plate. C. V. Boys 2 used a system of six 

 revolving lenses set in one solid disc. Each lens was 

 mounted a little offset from the center of the disc as 

 compared to the adjacent ones so that the image from it 

 would not overlap the others. The arrangement of the 

 apparatus is shown in fig. 4. All of the lenses have the 

 same focal length so the spark gap can be focused on the 

 plate through any one of them. The spark gap and the 

 photographic plate are stationary but since the lenses 

 move the focus of the spark shifts from one point to 

 another across the plate leaving its record of instanta- 

 neous images. 



A small motor drives the lenses at a speed of about 



2 Phil. Mag., vol. 30, p. 253 ; Proe. Phys. Soc, London, vol. 9, p. 1, 1890. 



