8 Hemsalech, spectrum of the Glow Discharge. 



the conditions presented by the glow discharge. In the 

 nitrogen glow the H and K lines are very strong, 

 K especially is very marked whereas the blue line at 

 4226 is feeble. In hydrogen, on the other hand, the blue 

 line is very strong and the H and K lines rather faint. 

 In oxygen the blue line is also very strong but of the H 

 and K lines only K is just visible. 



5. — Conclusions. 



The effect of heating a wire is to ionise the gas in its 

 neighbourhood, and the ionisation is at the surface of the 

 heated metal, and does not extend to any considerable 

 distance in the gas. When the charge on the cathode 

 leaps across the air gap, the electrons will not only 

 break through at the end nearest to the anode, but will 

 force their way out at all places within a certain distance 

 from the end, and, shooting through the thin layer of 

 ionised gas, will stimulate its ions to send out vibrations, 

 and thus give rise to the glow round the cathode. 



The results obtained with the glow discharge and the 

 ordinary coil discharge in air tempt us to draw some 

 conclusions as to a possible origin of the three types of 

 nitrogen spectra, viz., the line spectrum, the negative^ and 

 the positive band spectra. 



From the researches of Schuster, J. J. Thomson, and 

 others, we know that the spark discharge is initiated by 

 the expulsion of positive ions from the anode, and of 

 electrons from the cathode. The positive ions bombard 

 the cathode, and help to disentagle the electrons from 

 the surface of the cathode. The positive ions will be 

 densest near the anode, and the negative ions will be 

 very dense near the cathode. Now when the discharge 

 takes place the electrons, by virtue of their greater 

 velocity, will for the most part shoot through the layer of 



