216 Neio Group of Lines in Photographic Spectrum of Sirius. 



[7 and the stronger lines of the group, it may arise from some optical 

 or photographic cause."* 



We now learn that this difference between two parts of the lines 

 indicates probably a different condition of the nebula on the two 

 sides of the -star-spectra. 



Other lines besides those described in this note are present, not only 

 between Gr and F, but also on the more refrangible side of the strong 

 line about X 3725. 



The importance of the new points which have come out from these 

 photographs makes us regret that we must postpone a fuller examina- 

 tion and discussion of the spectrum of different parts of the nebula 

 until its return next year. 



" Ou a new Group of Lines in the Photographic Spectrum of 

 Sirius." By WILLIAM HUGGINS, D.C.L., LL.D., F.R.S., and 

 Mrs. HUGGINS. Received April 25, Read June 12, 1890. 



In 1879,t I gave an account of a series of broad lines in the photo- 

 graphic region of the spectrum which was found to be characteristic 

 of Sirius, Vega, and other white stars, and which was identified as a 

 continuation of the spectrum of hydrogen beyond H.J In the photo- 

 graphs of Sirius which I had taken up to that time, I was not able to 

 be certain if the two most refrangible of the lines, 6 and , were 

 present. This uncertainty has been set at rest by photographs taken 

 since, in which the complete series of the hydrogen lines, including 

 and i, come out with great distinctness. 



I have long suspected the presence of another group of broad lines 

 some distance further on in the ultra-violet region, bnt until this year 

 we have not been able to see them in the photographs with sufficient 

 distinctness to be able to make even roughly approximate measures 

 of their positions. 



On April 4th, a photograph of the spectrum of Sirius was taken 

 with a long exposure, the slit being made very narrow, in the hope of 

 bringing out this new group of lines with greater distinctness. This 

 plate shows, on examination, that the spectrum of Sirius, after the 

 termination of the hydrogen series, remains, as far as we can see at 

 present, free from any strong lines until a position as far in the ultra- 

 violet as about X 3338 is reached, at which place appears the first of 

 a group of at least six lines, all nearly as broad as those of the hydro- 

 gen series. The third line of the group about X 3278 appears to be 



* ' Roy. Soc. Proc.,' vol. 46, p. 54. 

 f ' Phil. Trans.,' 1880, p. 669. 



t H. W. Vogel, ' Berlin, Akad. Monatsber.,' 1879, July 10 ; and Cornu, ' Journal 

 de Physique,' 2nd ser., vol. 5, 1836, p. 100. 



