L. VEGARD. 



M.-N. Kl. 



If Nitrogen in the auroral region is present in the form of clusters or 

 small particles, such conditions are indeed different from those as yet 

 experimented upon in laboratories. It might, however, be possible to 

 reproduce similar conditions by cooling Nitrogen in Liquid Hydrogen and 

 bombarding it with electric rays. 



The disappearance of lines in the band-series is a rather interesting 



fact. According to the 

 theory of light emission 

 given by Bohr, the 

 number of lines in 

 an ordinary line-series 

 should increase when 

 the mutual distance 

 between the molecules 

 increases, and the same 

 rule may probably hold 

 also for band-series. If 

 then the gas in the 

 auroral region consisted 

 of free molecules we 

 should — considering 

 the extremely small 

 density — expect a 

 great many lines in the 

 series. If, however, the 

 molecules are packed 

 together into small par- 

 ticles, the molecules are 

 not free, and thus the 

 conditions will be un- 

 favourable for the for- 

 mation of alarge number 

 oflinesofthe band series. 

 That the number of 

 lines emitted by Nitro- 

 gen, when bombarded with cathode rays, decreares at very law temperatures, 

 is shown by some laborator}' experiments vecently carried out. The result 

 will be seen from Fig. 3. The spectrum Fig. 3 a corresponds to room 

 temperature Fig. 3 b to that of liquid air. We notice the great reduction 

 of the number of lines at the law temperature. The Helium spectrum is 

 used for comparison. Fig. 4 a is a reproduction of an auroral spectrum 

 taken with the quartz spectrograph. A Cd. spare is used for comparison. 

 Fig- 4 b gives the strongest lines of the aural spectrum, in the blue and 

 violet part, taken with the big glass spectrograph. 



Fig. 3 and 4. 



