4 Trans. Acad. Sci. of St. Louis. 



the diseliarges across a gap shorter than the critical 

 spark length as discussed in a former paper.^ 



The zones on the positive knob in which the luminous 

 drainage streamers take their origin are shown in Fig. 



A, Plate II. The camera exposure and development were 

 so adjusted that the streamers themselves shown in Fig. 



B, Plate I, did not develop on the plate. No flashlight 

 was made in this exposure. The same exposure, followed 

 by a flashlight is shown in Fig. B, Plate II. It will be 

 observed that the central point of the knob-face, nearest 

 to the copper sheet, is in these two figures, a non-lum- 

 inous area.^ 



Figures C and D, Plate II, show two photographs of 

 the positive knob, taken through a small hole in the cop- 

 per plate. The knobs and the brass rods on which they 

 were mounted were laterally displaced, in order to make 

 room for the camera. The length of the spark-gap at a, 

 appears to determine the number and arrangement of 

 these luminous zones from which the streamers spring. 

 In Figs. C and D, the exposure was somewhat increased, 

 and traces of diverging streamers are shown. 



It seems evident that these dark spaces lying between 

 the luminous cones springing from these luminous zones, 

 are in the nature of Faraday dark spaces. They are 

 tubes of discharge within which supercharged molecules 

 of air from the copper plate, mingled with molecules hav- 

 ing a normal charge, move towards the positive knob. 



Wlien the conditions exist which are shown in Fig. C, 

 Plate I, they actually deliver their charge to the knob 

 itself. When the drainage streamers have formed, these 

 super-charged molecules pass into them. Their charge 

 then continues by conduction to the positive knob, while 

 they move back in an opposite direction towards the 

 copper plate, along the luminous streamers. That a sim- 



2 These Trans. XIX, No. 4, pp. 67-8. 



3 In Fig. B a reflection of the flash from the polished surface of the 

 knob is seen, as well as a sharply defined image of a wire screen back 

 of the flash. 



