■it '2 M. I. Pupin — -Electrical discharges through poor 



discharge through. A camera was placed in front of the bulb 

 as indicated in tig. 10, and the discharges photographed. Figs. 

 1, 2, 3, 4, 5, 6, (in the plate facing p. 462) are photographs of 

 the discharges obtained in this manner but in various degrees 

 of rarification. 



I shall discuss the discharge given in fig. 6 first. In this case 

 the vacuum was very poor (about 60 mm pressure). The dis- 

 charge started in the form of four large streamers together with 

 a very large number of short luminous jets, which were more 

 or less uniformly distributed over the sphere. In consequence 

 of these jets the appearance of the sphere reminded one very 

 much of the granular structure of the sun's disc as revealed 

 by Rutherfurd's; Janssen's, and Yogel's photographs of the 

 sun. Yery luminous spots appeared from time to time at sev- 

 eral points of the surface, which reminded one very much of 

 the sun's faculiBe. Both the jets and the large streamers 

 rotated rapidly. This rotation is indicated very plainly in the 

 photograph ; for the number of streamers in each wing repre- 

 sents the number of maxima in the alternating discharge dur- 

 ing the time of the exposure, which was a small fraction of a 

 second. The thickest streamers indicate the place where the 

 discharge started. It is evident that the streamers were dis- 

 tributed nearly symmetrically over the sphere at the start of 

 the discharge and that then one-half of them were gradually 

 and almost uniformly displaced in the direction of motion of 

 the hands of a watch, the other held in the opposite direction. 

 The peculiar curvature of some of these streamers indicates 

 the presence of two kinds of motion, one a translational along- 

 the prolongation of the radii of the small sphere and the 

 other a rotational. It was this rotational motion which led me 

 to assume that there must be some sort of repulsive action 

 between the streamers of a vacuum discharge. The existence 

 of this action was demonstrated conclusively by the experi- 

 ment described in the paper cited above. Additional re- 

 searches in this direction lead me to the conclusion that two 

 discharge streamers tend to blow each other out owing to the 

 motion of the cooler gas between them, this motion being pro- 

 duced by the enormous heating effect of the discharge. The 

 result is that the particles of the gas which at any moment 

 form the path of a discharge are continually displaced (partic- 

 ularly in a discharge through a poor vacuum), and since every 

 successive discharge prefers the particles through which the 

 preceding discharge passed (for reasons given above) it fol- 

 lows that a sort of rotary motion is set up in the various parts 

 of the discharge. 



An additional evidence in favor of a translational motion 

 along the paths of the streamers is furnished by the fact that 



