Silent Electric Discharge 



79 



taken with this camera. The scale at the top and bottom gives the 

 number of electrical degrees passed through with respect to time in 

 the direction shown. The negative discharge appears as a line which 

 represents a concentrated glow on the needle point, while the positive 

 discharge gives the characteristic brush extending from the needle 



Fig. 3. Photograph of zinc plate showing effects of discharge on the metal. 



Fig. 4. Corona discharge in nitrogen taken with revolving mirror camera. 



point to the zinc plate. In the positive brush, a short distance from 

 the needle may be seen a dark space. This represents a space be- 

 tween the end of the neck and the brush where there is either no 

 radiation or where the radiation is of such wave length that it does 

 not affect the photographic film. Pictures taken without the zinc plate 

 show the luminous discharge extending from one needle to the other. 



