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XVII.—On the Constitution of the Lines forming the Low-Temperature 
Spectrum of Oxygen.. By Priazzi Smytu, Astronomer Royal for Scotland. 
(Read 30th January 1882.)—Ordered by the Council to be issued with Professor Smyru’s paper on “‘ Gaseous Spectra.” 
I had added (at p. 140 of my paper on “Gaseous Spectra”) to the “small 
dispersion” account therein given of the above mentioned spectrum of lumin- 
ous oxygen gas,—that two, if not four, of its very few and scanty lines appeared, 
when viewed with much higher dispersion, to be double ; but that I hoped to 
give a more exact account of them, after completing some arrangements then 
in progress for increasing both the dispersion and magnifying power of my 
spectroscope. 
These improvements, together with a great advance in definition, were 
finished last November, and almost the first result they yielded was, to much 
more than confirm what I had only suspected before ; and to do so, moreover, 
with such vigour and certainty, as to make me inquire right and left for several 
weeks to ascertain if what I then saw, was really a new discovery, or had 
perhaps been known long before to older and better spectroscopists. 
So far as I have been able to gather, the thing is new, and promises to be 
important to theorists in molecular vibrations, on account of what it fulfils. 
To explain this, let me refer to Dr. ARTHUR ScHUSTER’s valuable paper in the 
“ Transactions of the Royal Society,” London, for 1879, “ On the Spectra of the 
Metalloids ; Spectrum of Oxygen.” Beginning his exposition of the low- 
temperature spectrum—after having treated very fully of the exceedingly 
different high-temperature spectrum, of oxygen,—with the late Prof. PLUCKER’s 
account of it, and concluding with his own confirmatory observations, Dr. 
Scuuster shows that the low spectrum had always been found to consist of only 
four single, wide-apart lines,—viz., one in the orange, one in the citron, another 
in the green, and another still in the indigo-violet ; and to that spectrum, con- 
taining only four such solitary, single, simple lines, the learned Doctor gave the 
second or aias name of “ the compound-line” spectrum of oxygen. 
The reason for such an apparent misnomer, or /ucus a non lucendo, was, that 
at the very moderate temperature of electric illumination at which this trifling 
lined spectrum of oxygen appears, most other gases do give forth very com- 
pound-line spectra indeed ; spectra with hundreds or even thousands of lines, 
arranged in peculiar bands or parcels, and known generally as “fluted 
spectra.” Hence Dr. ScuusTEr’s name for what he saw in oxygen, while prin- 
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