52 
DR. A. SCHUSTER OH THE SPECTRA OF METALLOIDS. 
elementary line spectrum is best studied. The mere insertion of a Leyden jar, I find 
makes hardly a difference ; the jar does not seem to be charged at all. If in addition 
to the jar we insert a movable air break, which cam be opened or closed at will, while 
we look through the spectroscope, we shall be able to see alternately two perfectly 
distinct spectra. If the air break is closed the four lines of the compound spectrum 
only are seen; if the ah’ break is opened these four lines will disappear entirely, and 
the elementary line spectrum will come out. We have here as complete a transforma¬ 
tion as we have from the band to the line spectrum of nitrogen taking place under 
exactly the same circumstances. We have, therefore, the same right to consider the 
two line spectra of oxygen as two distinct spectra, as we have in the case of the two 
spectra of nitrogen. 
There are two reasons why the existence of a separate line spectrum of oxygen 
might have escaped the notice of previous observers. The blue line of the compound 
line spectrum is very near a bright line of the elementary line spectrum, and cannot 
be distinguished from it unless a high dispersive power is used, and even then only 
when special attention is paid to the line. 
To an observer who looks at this fine with small power, it would seem as if on the 
introduction of the air break other lines spring up to its right and left, which are 
brighter than the blue line he is looking at; but he would not notice that the blue line 
itself has disappeared, and has been replaced by another line a little more refrangible 
and of about the same brightness. 
Again, in tubes of rather wide capillary bore, as that of which the dimensions have 
been given on page 43, under the heading B, it is impossible to get rid altogether of 
the lines of the compound line spectrum. The effect of the jar and air break is only to 
widen the lines considerably; not to extinguish them. If the pressure in a tube is 
large, these lines widen to a considerable extent, and finally fuse together so as to 
form a continuous spectrum. This has been well described by Wullner, who likened 
the lines in this respect to the hydrogen lines. The observations which refer to the 
disappearence of these lines must therefore be made under low pressure when the 
continuous spectrum has disappeared, and the phenomenon then is very striking. If 
a spark is taken through oxygen at atmospheric pressure, a strong red but flushy 
line is seen very nearly coincident with the red line of the compound spectrum. I 
confess I have not been able to find out with certainty whether the two lines are 
identical or not. The compound line spectrum widens considerably with increased 
pressure, and chiefly towards the less refrangible side. At first sight the atmospheric 
line is decidedly less refrangible than the line of the compound line spectrum, and the 
measurements by Thalen and Huggins of the line in the atmosphere give a wave¬ 
length sensibly larger than that which I have obtained for the line of the compound 
spectrum. Yet if account be taken of a one-sided widening, so that the line has to 
be compared with the edge of the atmospheric band, not with its middle, I am inclined 
to think that the two may prove identical. It appeared to me sometimes, it is true, 
