78 



Proceedings of Indiana Academy of Science 



In nitrogen a very beautiful discharge is obtained which extends 

 from one needle to the other and is made up of many fine streamers 

 of glow discharge. 



The discharge in oxygen is scarcely visible up to the sparking 

 potential, which is almost double that of nitrogen. We were unable 

 to obtain a photographic record of this discharge as even the slight 

 glow of the points failed to show up on the photographic plates. 



The discharge in nitrogen with an insulated zinc plate placed 

 midway between the two needles is represented in figure 2. This picture 

 has been retouched and the uneven joint in the center of the discharge 

 chamber is cut out. The presence of the plate increased the sparking 

 potential about 50 per cent. If the discharge at the point is closely 

 studied it is seen that from the neck of the discharge many small 



-^m m^ 



37 Kv 15 



l-vi^een needles. 



DischarKC in nitiofjcn with zinc plate between needle electrodes. 



branches form at definite intervals. This formation seems to indicate 

 that the discharge is composed of a number of concentric cones. 



This structure of the discharge was still further substantiated by a 

 study of the zinc plate after it had been in the discharge for a short 

 time. Sections of the plate were roughened giving the concentric 

 circles sho\vn in figure 3. The light portion represents the roughened 

 surface and the darker portion indicates where the plate retained 

 much of its original polish. Due to the fact that most of the static 

 sparks struck within the inner circle this section is roughened more 

 than any other. 



Although the discharge, as represented in figure 2, appears con- 

 tinuous to the eye it is actually made up of two distinct types of 

 discharge, the images of which are superimposed. By means of a 

 special camera" these two can be separated and drawn out along a 

 time axis. Figure 4 represents the discharge in nitrogen at 60 cycles 



= McEachron, Karl B., "Two Photographic Methods of Studying High- Voltage Dis- 

 charges", Amer. Inst. Elec. Eng., Vol. 42, No. 10, 1923, pp. 1045-1050. 



