6 Hemsalech, Spectrum of the Glow Discharge. 



through the wire electrode and the latter thus became 

 heated, the glow gradually developed and finally extended 

 for one centimetre or more along the electrode, running 

 up both branches of the wire. The glow seems to be 

 confined to the surface and is of a brilliant grey colour. 

 When the current through the wire was stopped the 

 glow disappeared. It is not necessary that the wire 

 should be heated to a red heat in order to obtain the 

 glow. 



Sometimes the spark itself became surrounded by a 

 deep blue glow forming a hollow envelope round the 

 spark. The origin of this blue envelope and the condi- 

 tions which determine its appearance are still unknown. 



A glow was also obtained on the other electrode (not 

 heated) at the point where the stream of electrons strike 

 the brass sphere. 



When the glow was produced on a copper wire, 

 a green vapour was constantly seen over the opposite 

 electrode. The spectrum of this vapour has not yet been 

 examined ; it looks as if the copper wire disintegrated by 

 the action of heat and the matter, instead of being 

 deposited on the opposite electrode, is repelled from it 

 and forms a luminous cloud above it. 



A very interesting case of metallic deposition was 

 observed with a heated platinum wire. When the glow 

 discharge had been kept up for about half an hour or 

 even less a very bright deposit of metallic platinum was 

 obtained on the other electrode. On a polished surface 

 this deposit acquires the same polish as the surface. The 

 diameter of this deposit was about 3 to 5 mm., it is 

 surrounded by platinum black. I do not know whether 

 this metallic deposit at atmospheric pressure has been 

 observed before ; possibly it may be an ordinary case of 

 " Zerstaubung." 



