C/'ooker — Influence of a Seizes Spark. 281 



Art. XIX. — Influence of a Series Spark on the Direct 

 Current Corona; by Sylvan J. Crookee. 



In the paper entitled "Some Brush Discharge Phe- 

 nomena Produced by Continuous Potentials," S. P. Far- 

 well 1 published some experiments in which he noted 

 changes in the appearance of the direct current corona 

 between coaxial cylindrical electrodes when a short spark 

 was placed in series with the corona tube. The typical 

 negative corona discharge with constant voltage consists 

 in more or less evenly spaced bright beads ; the positive 

 glow (the wire being positive) is uniform in most cases. 

 If now a short spark is introduced in series with the 

 corona tube, this difference in the discharge is largely 

 wiped out, and the discharge appears almost the same 

 whether the wire is positive or negative. This effect of 

 the spark is well illustrated by the last four photographs 

 of fig. 2 of the mentioned article. Farwell was inclined to 

 attribute this effect to oscillations or surges set up in the 

 system by the spark. He found indeed that an induction 

 coil gave rise to the same kind of discharge in the corona 

 tube as the spark in series, but at the same time he 

 remarked that the resistance in the corona tube was so 

 high as to exclude oscillations. A condenser in parallel 

 with the tube also gave rise to the beaded discharge 

 characteristic of the direct current. The question was 

 then open whether there were oscillations or not and it 

 was the purpose of this investigation to decide this ques- 

 tion, if possible, to measure the frequency and the 

 amplitude of the oscillations and to perform further 

 experiments which might throw light on the nature of 

 the phenomenon. 



A part of Farwell 's experiments were repeated by 

 means of the same tube and the same dynamos. The 

 electrodes of the spark gap were polished brass spheres 

 one centimeter in diameter fastened to brass rods which 

 were supported by hard rubber blocks on a solid hard 

 rubber base. One of the electrodes was supplied with a 

 micrometer screw and an insulated handle which per- 

 mitted an easy adjustment of the spark distance. The 

 connection of the corona tube with the auxiliary appa- 

 ratus is shown in fig. 1. 



1 Physical Eeview, vol. 4, p. 31, 1914. 



