Dr. and Mrs. Huggins. 



[May 19, 



Photograph of the Ultra- Violet part of the Spectrum. — On February 

 22 and March 9 we took photographs of the star with a mirror of 

 speculum metal and a spectroscope of which the optical part is made 

 of Iceland spar and quartz. 



The photograph taken on February 22 with an exposure of If hour 

 surprised us in showing an extension of the star spectrum into the 

 nltra-violet, almost as far as the limit imposed upon the light of 

 celestial bodies by the absorption of our atmosphere. 



Not only the hydrogen lines near Gr and at h, but also H and K, 

 together with the complete hydrogen series which appears dark in 

 the white stars, came out bright, each with its corresponding absorp- 

 tion line on the blue side. There are some inequalities of brightness 

 in these lines, especially in the line 8, which is brighter than 7 or /3, 

 which probably arise from lines of other substances falling upon 

 them. On this night K was followed by an absorption, which was 

 less intense than the absorption at H. 



Beyond the hydrogen series the spectrum is rich in bright lines, 

 which, in most cases, are accompanied by lines of absorption. Neces- 

 sarily, from the long range of spectrum included on the plate, the 

 scale is small, and for this reason, and from the faintness of the 

 more refrangible portion of the spectrum when observed under the 

 measuring microscope, the positions given to the stronger groups, 

 which alone have been inserted in the map, must be regarded as 

 approximate only. 



Below the spectrum of the Nova, the spectrum of Sirius has been 

 placed for comparison. The group near the more refrangible limit of 

 the spectrum* has been drawn in. Numerous other lines between 

 this group and the end of the hydrogen series have been detected in 

 our photographs of Sirius, but have not yet been measured with 

 sufficient accuracy to justify us in putting them into the map. 



In this map no attempt has been made to show the shift of the 

 spectrum of the Nova. The bright lines in the star have been put 

 at the places of the hydrogen lines. 



To the extreme limit of the spectrum a faint continuous spectrum 

 shows itself. 



The photograph of March 9, exposed for \\ hour, was rather faint, 

 as the state of the sky was unfavourable. 



The apparently Multiple Character of the Lines. — On February 2 we 

 noticed that the F line was not uniform throughout its breadth, and 

 soon came to the conclusion that it was divided, not quite symmetric- 

 ally, by a very narrow dark line. The more refrangible component 

 was brighter, and rather broader than the other. Later on in Feb- 



fall into Balmer's formula for the hydrogen series. We must regard them, doubt- 

 less, as members of that series and due to hydrogen. — June 10.] 

 * « Roy. Soc. Proc.,' vol. 48, p. 216. 



