682 
DR, W. HUGGINS ON THE PHOTOGRAPHIC SPECTRA OF STARS. 
to supplement my eye observations of 1864 of the gaseous nebulae by photographs 
of the more refrangible parts of their spectra. Such photographs, taken together with 
those described in this paper, and combined with our knowledge of the visible spectra of 
these bodies, would help us probably to a better understanding of the typical changes 
in the order of time through which a star passes. 
In the hope of throwing some light on these and other questions which suggest 
themselves, I have taken for comparison a number of terrestrial spectra under various 
physical conditions. As I am still pursuing this inquiry I prefer at present to reserve 
an account of this part of my work. 
§ IX. Vega (a Lyrce). 
The photographic exposure with sensitive gelatine plates was from 15 minutes to 
80 minutes. Recently, with more sensitive plates, these times have been reduced. 
The photographs of this star show with great distinctness the twelve strong typical 
lines. There is a thin line at the position of K. In one photograph of this star I 
suspected the presence of a very delicate line between the lines H and K, but as 
I cannot be sure of its existence I have not inserted this line in the map. The lin e, 
if present, would be about A 3945. A circumstance of great importance is the entire 
absence of any lines in the spectrum beyond i, X 3698. The spectrum, which then 
becomes continuous, is strong, and extends beyond S in the ultra-violet. In solar 
photographs taken with the same apparatus the lines of this region are well-defined 
for some distance beyond S, and therefore this abrupt cessation of lines cannot be 
referred to an instrumental cause. All the lines are broad, and winged at the edges. 
After H the lines become less intense, and also better defined in the order of 
refrangibility. 
Lines. 
W.L. 
W.L. 
H 4340 
£ 3767'5 
h 4101 
e 3745-5 
Hj 3968 
r 3730 
K 3933 very thin. 
>] 3717-5 
x 3887-5 
0 3707-5 
13 3834 
i 3699 
7 3795 
§ X. Sirius. 
In the photographs of this star we have a spectrum very similar to that of a Lyras. 
I am not able to detect any line at the position of K, but as the altitude of the star 
is low the definition in the photograph is not quite so good as that of Vega, It is 
probably due to this cause that I have not been able to be sure of any lines beyond §. 
