592 Original Articles. | Oct., 
spectrum does not contain every possible ray, from the red at the one 
end to the violet at the other, but that the appearance it presents is 
that of a luminous ground crossed by black lines, which denote the 
absence of certain rays. 
The origin of these lines was for a long time a most perplexing 
question. Sir David Brewster was the first who prepared the way for 
its solution, by showing that analogous (not identical) lines might be 
artificially produced by interposing a jar containing nitrous acid gas in 
the path of the ray. His inference was that the solar lines do not denote 
rays originally wanting in the light of the sun, but are due rather to the 
absorption produced by some substance interposed between the source 
of light and the spectator. His subsequent researches in conjunction 
with those of Dr. Gladstone and others led, on the whole, to the belief 
that this absorption was probably not due to the earth’s atmosphere, 
and of course the only remaining field for such an influence was the 
atmosphere of the sun. But it remained for Kirchhoff, a distinguished 
German philosopher, to set the matter at rest, not however before the 
true explanation had been divined by Professor Stokes. This belongs 
to another part of our subject : in the meantime we shall describe what 
has been already accomplished in delineating these wonderful phe- 
nomena, the lines. 
In the solar spectrum, as in the starry firmament, every new 
accession of magnifying power enables us to reap a fresh harvest of 
discovery. Thick lines split themselves up into a bundle of thin 
ones; nebulous bands resolve themselves into distinct lines; new 
groups spring into existence, and the appearance of things is so entirely 
altered, that an observer accustomed to a small instrument would not 
be able to recognize those very parts of the spectrum with which he 
used to be most familiar. This cannot be better exemplified than by 
referring to the double line known as “p,’ a prominent line between 
Hic. 3; 
the orange and the yellow. Fraunhofer only just succeeded in recog- 
nizing its duplicity. Kirchhoff, in his admirable map of the spectrum 
recently published, a small portion of which is represented in Fig. 3, 
