DR. W. HUG GIN'S ON THE PHOTOGRAPHIC SPECTRA OF STARS. 
G79 
One of these modifications which possesses great suggestiveness, consists of the 
absence or difference of character presented by the line K. In all the stars of this 
class this line is either absent or is very thin as compared with its appearance in the 
solar spectrum, at the same time that H remains very broad and intense. In the 
spectrum of Arcturus, a star which belongs to another class, which includes our sun, 
this line K has passed beyond the condition in which it occurs in the solar spectrum, 
and even exceeds the solar K in breadth and intensity. 
The spectra of these stars may therefore be arranged in a continuous series, in which 
first we find this line to be absent. Then it appears as an exceedingly thin line. We 
then pass to another stage in which it is distinct and defined at the edges; in the 
solar spectrum it becomes broad and winged; and lastly in Arcturus there is further 
progress in the same direction, and the line, now a broad band, exceeds in intensity H. 
as in the following diagram, for it there becomes more conspicuous that they lie on, or very near, a 
definite curve, which could not happen by chance. 
e 
>) 
K 
t 
5 
V 
p 
a 
Hi 
h 
Gi 
F 
C 
This question of whether they lie actually on, or only near, a definite curve is, if I mistake not, of very 
great significance in the theory. If they lie on a curve obeying any exact mathematical law, their con¬ 
nexion must, I think, be attributed to their corresponding to the consecutive partial tones of some vibrating 
system (like those of an elastic rod or bell, for example). If, on the other hand, they lie near but not on 
the curve this circumstance would support the hypothesis (which seems to accord with other facts) that 
the visible lines are members of harmonic series, most of the members of which are invisible, those only 
being seen whose positions chance nearly to fulfil a definite condition—a state of things which I have 
shown to exist in some acoustic arrangements, and which wherever it prevails exalts the intensity of the 
harmonics whose positions nearly fulfil the requisite condition. 
To ascertain which of the two foregoing alternatives is the true account of your typical lines, I con¬ 
verted the wave lengths as you determined them into wave frequencies (the reciprocals of the wave 
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