DR. A. SCHUSTER ON THE SPECTRA OF METALLOIDS. 
53 
that the line of the compound spectrum is more refrangible even than the edge of 
the atmospheric band, but I am not quite certain of this. I have left out therefore for 
the present the line from the list of the elementary line spectrum of oxygen. 
In a letter to ‘Nature’ (Dec. 20, 1877) I have drawn attention to the fact that 
the lower temperature spectrum of oxygen seems to be reversed in the sun, and I 
have tried to bring this fact into connexion with the statement made by Professor 
Draper, that the higher temperature lines of oxygen appear bright on the solar disc. 
I have now nothing to add to what I have stated in my letter to ‘ Nature,’ and only 
give the list of the exact wavedengths of the compound line spectrum, together with 
the wavedengths of the nearest solar lines. 
Oxygen. 
Width. 
Solar Lines. 
a 6156-86 
PO-3 
(A.) 
6156-70 
(S.) 
6156 - 69 
/3 5435-55 
+ 0-3 
5435-44 
5435-56 
7 5329-41 
+ 0-6 
5329-30 
5329-10 
C 4367-62 
4367-58 
The first column contains the wave-lengths of the compound line spectrum of oxygen ; 
the second column contains the number which has to be added to or subtracted from 
the wave-length, in order to get the edge of the lines, as it is their centres which are 
given in the first column ; the third and fourth columns give the wave-lengths of the 
corresponding solar lines as observed by Angstrom (A.) or myself (S.). In Plate 1, I 
have given a drawing of this spectrum, marked B. 
8. The Spectrum of the Negative Pole. 
This spectrum was first accurately described by Wullner. * When looked at, as he 
did, with low dispersive power, it seems to consist of four distinct, not shaded bands ; 
but, as I have already said, I was able to resolve the bands into separate lines. I have 
also in this case spared no trouble to show that the spectrum is really due to pure 
oxygen, and not either to impurities in the gas, to the nature of the electrode, or 
influence of the glass. It seems interesting to notice that in Experiment 6 (page 47), 
when the spectrum of the spark at atmospheric pressure was continuous, a purple point 
was seen on the negative electrode which gave the spectrum of the negative pole. 
The peculiar circumstances which favour the production of this spectrum always exist 
therefore at the negative pole, and are independent of the mode of discharge. 
When examined with low power, the bands of the negative pole seem to occupy the 
following wave-lengths. 
* Pogg. Ann., 147, page 357. 
