Manchester Memoirs, Vol. xlviii. (1904), No. 10. 9 



negative ions, and in this way cause the glow which gives 

 the negative band spectrum. After having passed through 

 the negative ions, they will encounter near the anode the 

 positive ions, moving at a much slower rate ; they will 

 collide or combine with some of them, giving rise to a 

 spectrum peculiar to the anode and its neighbourhood, 

 namely, the line spectrum of nitrogen. The positive ions, 

 after their encounter with the electrons, will now meet the 

 negative ions, which also move at a slower rate than the 

 electrons, and their collisions with each other, or with 

 complete molecules of the gas, will set up vibrations all 

 along the spark gap, which will constitute the positive 

 band spectrum. The existence of some rays of the line 

 spectrum in the glow may be explained by the positive 

 ions, which bombard the cathode to free the electrons. 



Thus, on the above view, the spectra of nitrogen may 

 be accounted for in the following manner : 



1. The line spectrum is the result of the, possibly 



interior, vibrations of the positive ions, brought 

 about by collision or combination with electrons. 



2. The negative band spectrum is the result of 



encounters between negative ions and electrons. 



3. Th-Q positive band spectrum is the result of encounters 



between positive and negative ions, or between 

 ions and molecules. 



Deslandres has recently given an explanation of these 

 spectra,^ which differs slightly from the above. He does 

 not distinguish between ions and atoms, and according to 

 his view the vibrations are caused by encounters, com- 

 binations, or decompositions of electrons, atoms, and 

 molecules. 



1 Deslandres, Comptes Renaits, t. 137, p. 1013, 1903. 



