Nipher — Nature of the Electric Discharge. 3 



formed when the windmill was placed in this gap, and a 

 faint motion of the air towards the copper plate was then 

 shown by the windmill.^ 



In Fi^. C, a strongly marked glow is shown on the 

 surface of the positive knob. It covers the hemisphere 

 which faces the copper plate. This glow differs from 

 the negative glow at the other knob. It gives the front 

 of the knob the appearance of being at a red heat. Scin- 

 tillations are occasionallv visible over this luminous sur- 

 face. They are perhaps the beginnings of drainage 

 streamers. It seems evident that air molecules in con- 

 tact with this luminous part of the knob are delivering 

 corpuscles to the knob, but the drainage luminescence 

 does not extend beyond the layer in close contact with 

 the knob. If the contacts at either a or 'a are disturbed 

 so that any luminous effects exist at these gaps, this posi- 

 tive glow partly ,or wholly disappears and one or more 

 luminous streamers shoot out from the positive knob, as 

 in Fig. A. The drainage inflow to the positive terminal 

 is then through and along these conducting channels. If 

 the gap at a in the positive line is slightly increased in 

 length, the luminous streamers appear in arc-like forms 

 from points around the central line of discharge, as is 

 seen in Fig. B. These streamers are continually vibrat- 

 ing as is the case when convection and conduction winds 

 in opposite directions exist side by side. Fig. B of Plate 

 I shows that these luminous conduction streamers have 

 their origin at the positive knob, in zones which are con- 

 centric with the central axis through the two knobs. In 

 the air around the discharge gap, these streamers appar- 

 ently lie in co-axial cones, having dark spaces sandwiched 

 between them. In these dark spaces the air is evidently 

 drifting towards the positive knob, and into the luminous 

 streamers on either side, where the conduction transfer 

 is taking place, and where the air molecules are moving 

 away from the positive knob. The action is similar to 



1 The front edge of the plate is not in focus, and its image is rather 

 imperfectly reproduced in the original, and does not appear in this figure. 



