Manchester Memoirs, Vol. xlviii. (1904), No. 10. 3 



Fig. I of Plate VI. The image of the spark, which was 

 placed parallel to the slit, was projected on to the latter, 

 and thus permitted one to follow the changes in the 

 spectrum along the spark gap, according to Lockyer's 

 method. The bands, which are seen to go right across 

 from the anode (top) to the cathode (bottom), form the 

 positive band-spectrum of nitrogen. From the anode are 

 also seen to emerge certain lines of the line spectrum of 

 nitrogen ; these do not go right across, but only traces of 

 them can be seen in the glow of the cathode. The most 

 brilliant spectrum is seen in the cathode glow (bottom), 

 where, in addition to the positive bands, two new bands 

 appear, whose heads are at X = 39i4"4 and X = 4277*8. 

 These are the characteristic bands of the negative band- 

 spectrum of nitrogen, and of the glow discharge in air. 



2. — Spectrum of the Glow Discharge in Air. 



The glow was obtained by heating the electrode, and 

 an image of the glow was projected on to the slit of a glass 

 prism spectrograph. A remarkable feature of this spectrum 

 {Fig. 2, glow on Cu electrode) seems to be the great energy 

 concentrated in the heads of the principal negative bands. 

 This is perhaps an indication that the stimulation of the 

 nitrogen ions is effected impulsively and momentarily. 

 Some of the brighter air lines of the line spectrum are also 

 seen in the glow, their appearance is very hazy ; also the 

 principal metal lines are faintly visible. 



In the following table are contained the chief bands 

 of the spectrum of the glow discharge in air, the wave 

 lengths referring to the heads of the bands. For the sake 

 of comparison I have added a list of the radium glow 

 bands (deduced from the photograph published by Sir W. 

 and Lady Huggins, l.c) and of the negative and positive 

 bands as observed in vacuo. My observations which werej 



