158 
DR. T. R. MERTON AND PROF. J. W. NICHOLSON ON 
a still greater distance from the cathode. Of particular interest is the beha^dour of 
the characteristic “ spark ” line A4686, 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 X4686 appear in the 
6,6^6 
B 
5,8 Z'e 
B 
5,015 
-3<,9Z£ 
Ik? 
4<7I3 
3 
3 
4,422. 
4432 
4,368 
fi/ 
5.042 
4 , 686 ^ 
4,359 
4143 
Hg: 
4,026 
B 
3.965 
3,686 
B 
4,121 
Ilg'4,042 
3 
He 
Fig. 3. 
glow around the cathode. Whilst confirming this, we see that the band spectrum is 
localised in 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, l)ut it is interesting to note that over a definite region X4686 and 
