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II. On the Spectra of Metalloids—Spectrum of Oxygen. 
By Arthur Schuster, Ph.D., F.R.A.S. 
Communicated by J. Clerk Maxwell, F.R.S., Professor of Experimental Physics 
in the University of Cambridge. 
Received April 25,—Read May 16, 1878. 
[Plate 1.] 
1. Introductory. 
Tee many unexplained phenomena attending the passage of electricity through gases 
will probably for some time to come occupy the attention of experimental physicists. 
It is desirable that the subject should be approached from as many different sides 
as possible. One of our most powerful instruments of research is the spectroscope ; 
but before it can be applied to the study in question, we have to settle the chemical 
origin of the different spectra which we observe in tubes, and to discuss in what way 
such spectra are liable to change under different circumstances. A special investiga¬ 
tion has to be made for each gas ; we have to study the effect of various impurities, 
the influence of the electrodes and that of the glass, which in the tubes generally used 
is considerably heated up by the spark. To make the investigation complete we have 
to vary as much as possible the pressure, the bore of the vacuum tube, and the strength 
of the spark. 
I have chosen Oxygen as a first subject of investigation. Though Plucker and 
Wullner have, as far as their experiments went, accurately described the phenomena 
seen in oxygen tubes, the following paper contains much that is new, and will put 
some of the older facts on a firmer basis. When I first began to work, it was my 
intention to take the gases in groups, and to study their mixture ; but as the follow¬ 
ing investigation has taken me a year’s nearly continuous work, and is complete in 
itself, I trust it will not be found unworthy of publication. I must, of course, at 
present confine myself to the purely spectroscopic point of view. As several of the 
observations which I shall have to record bear directly on the general theory of double 
spectra, I must briefly refer to our knowledge on that point. 
2. Multiple Spectra. 
We may roughly divide all known spectra into three kinds or orders : continuous 
spectra, line spectra, and, standing between them, spectra of fluted bands or channelled 
spaces, as they are commonly called. 
