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XVIII. On the Photographic Spectra of Stars. 
By William Huggins, D.C.L., LL.D ., F.R.S. 
Received December 11,—Read December 18, 1879. 
[Plate 33.] 
§ I. Introduction. 
In the year 1876 I presented to the Royal Society a preliminary note on the “ Photo¬ 
graphic Spectra of Stars.”* I beg now to give an account in greater detail of my 
methods of work and of the photographs which I have obtained. 
The importance of supplementing the observations by the eye of the spectra of 
stars by photographs of the violet and ultra-violet portions of their spectra was so 
obvious, that as early as the year 1863 my friend Dr. W. Allen Miller and I made 
the attempt to obtain such photographs in addition to our eye-measures of star spectra.f 
With the apparatus then at our command we were not able to get any clear definition 
of lines, but a dark streak only upon the negative plate. 
Other investigations which I then took up prevented me from resuming this line of 
work. I was also not encouraged to proceed further with photography at that time, 
as the clock-motion driving the telescope did not work with the accuracy that was 
necessary. 
In the year 1875 Mr. Grubb replaced the driving clock by a new one, in which 
there is a secondary control by means of a pendulum in electrical connexion with a 
standard clock. | I am able to speak in terms of high praise of the performance of 
this new clock. 
The early attempts at photography of the spectra of stars were made with the 8-inch 
refractor by Alvan Clark, then in my observatory. On receiving the new clock the 
refractor of the instrument lent to me by the Royal Society was dismounted and the 
Cassegrain telescope, with a metallic speculum of 18 inches diameter, was put in its 
place upon the equatorial stand. After many preliminary trials I adopted the following 
arrangements of the spectral apparatus and methods of work. 
* Proceedings R.S., No. 176,1876. Since the publication of my preliminary note, Professor H. Draper 
lias written two notes on this subject, ‘American Journal of Science,’ vol. xiii., Jan., 1877, and Nov. 27, 
1879, p. 83. 
t Phil. Trans. R.S., 1864, p. 428. 
X Proceedings R. Dublin Society, April 21, 1879. 
MDCCCLXXX. 4 R 
