158 



DR. T. B. MERTON AND PROF. J. W. NICHOLSON ON 



a still greater distance from the cathode. Of particular interest is the behaviour of 

 the characteristic " spark " line X4686, and the band spectrum, of which only the 

 more prominent heads are visible. 



Tt has been known for some time that the band spectrum and X4G86 appear in the 



B 



5876 

 B 



5,015 



I 4JL43 



4P26 



B 



3,965 



3,688 



4922 

 H/i 



4713 



B 

 B 



5.047 



t.686 



fix 



4,359 



B 



Hg-4,047 



B 

 He 



Fig. 3. 



glow around the cathode. Whilst confirming this, we see that the band spectrum is 

 localised m a restricted region at some distance from the cathode. On the other 

 hand, X4686 has its seat of maximum emission in a region where the band spectrum 

 is only just visible, but it is interesting to note that over a definite region X4686 and 



