678 
DR, W. HUGGINS ON THE PHOTOGRAPHIC SPECTRA OP STARS. 
line is H. K, if present at all, is thin and inconspicuous.* The nine lines which 
follow do not appear to be coincident with any of the stronger lines of the solar 
spectrum. These lines appear to be common to all the stars of this class, though it 
may be that some of the more refrangible lines are sometimes absent. 
For the sake of convenience of reference I have distinguished these nine hues by 
the letters of the Greek alphabet in the order of their refrangibility. 
I would wish to call attention to the remarkable arrangement in position in the 
spectrum of these lines. As the refrangibility increases the lines diminish in breadth, 
and the distance between any two adjacent lines is less. The group possesses a 
distinctly symmetrical character. The suggestion presents itself whether these lines 
are not intimately connected with each other, and present the spectrum of one sub¬ 
stance, t It is also of importance to notice that the spectrum does not end with the 
group. Beyond the last line, between M and N, the continuous spectrum runs on far 
beyond S in the ultra-violet. The wave lengths of these lines will be found under 
Vega. The spectrum of Vega may be taken conveniently as typical of the whole 
class of white stars, so that the distinctive features of the other stars of this class may 
be regarded as modifications or departures from this common typical form. There are 
principally three directions in which the changes take place : 
1 . In the breadth and greater or less marginal diffuseness of the typical lines. 
2 . In the presence or absence of K, and if present in its breadth and intensity 
relatively to H. 
3. In the number and distinctness of the other lines of the spectrum. 
* In 1876, Mr. Lockyer suggested that photographs of the spectra of the brighter stars might show 
modifications of this character of the lines of the calcium spectrum, and that such modifications would 
confirm his views as to the dissociation of this substance. (Proc. R.S., No. 168, 1876.) Mr. Lockyer gives 
a fuller statement of his views on this and other points in connexion with the different classes of the stars 
in Proc. R.S., Dec., 1878, see fig. 1. 
f [There is a high probability that this substance is hydrogen. The two lines in the visible part of the 
spectrum C and P forming part of the same group belong to hydrogen. Also, as stated above, the first 
two lines of the photographic group correspond to the line of hydrogen near G and to that at the position 
of h. Dr. H. W. Vogel has called my attention to a paper of his “ On the Spectrum of Hydrogen” in the 
‘ Monatsbericht der Konigl. Academie der Wissenschaften zu Berlin,’ July 10, 1879. Among other lines 
he gives the following, which agree in position with four of the typical lines:— 
Vogel’s numbers. 
X 3968 
3887 
3834 
3795 
My numbers. 
A 3968 H 
3887-5 * 
3834 j3 
3795 7 
Dr. Vogel says in his letter (February 18, 1880): “ In one of my last photographs I have another line 
A 3769, your next line is 3767'5.” 
January 24, 1880, I received the following note from Mr. Johnstone Stoney, F.R.S.:— 
“There can remain very little doubt that your typical lines are due to hydrogen. The evidence of 
their all being members of one physical system is made very plain when their positions are plotted down 
