Hydrogen, and some of its Compounds, 375 



electrodes and these tubes are exhausted to a pressure of from 

 one to two millimetres, the resultant spectra are very similar. 

 The following gases have been studied in the neighbourhood 

 of the great H H lines of the solar spectrum : 



Hydrogen, 



Oxygen, 



Nitrogen. 



In the hydrogen tube the only lines that appeared in the 

 region from 4320 to 3200 were: 



4268 very intense, 

 3922 faint, 



The tube was very thoroughly heated while it was being 

 exhausted. The above-mentioned lines do not generally 

 appear with hydrogen in tubes with metallic electrodes ; but 

 with a tube with platinum electrodes, filled with hydrogen, 

 and heated for two hours during exhaustion at a temperature 

 of 350° C, the same two lines appeared, and in addition the 

 following very faint lines : 



3871 



3886 



These same four lines also appear in carbon tubes when 

 filled with oxygen. In addition, the following lines are 

 present : 



3936 



3971 



4077 



All these lines appear in the nitrogen-tube, and, in addition: 



3883 

 3876 

 3868 

 3856 

 3849 

 3841 



None of these lines appear in tubes with metallic electrodes 

 filled with nitrogen ; and they are, therefore, not nitrogen 

 lines. All the lines in the nitrogen-tube are more intense 

 than those in the oxygen-tube, and it is possible that with a 

 longer exposure these additional lines would come out in the 

 oxygen. 



To study the effect of the carbon terminals, the following 

 gaseous carbon compounds were put into wide tubes provided 



2C2 



