136 Further Observations on Nova Persei. 



with any degree of accuracy owing to lack of comparison photographs 

 showing lines in the same part of the spectrum, but it is probably 

 identical with the line at X 342 which von Gothard has independently 

 recorded.* 



The enhanced lines of iron, magnesium, c., which were such a con- 

 spicuous feature of the earlier photographs of the Nova spectrum, have 

 now entirely disappeared, and the probability is that the bright lines 

 of the present spectrum other than those of hydrogen and helimii 

 belong to gases the terrestrial equivalents of which have not been 

 found. It may be mentioned, however, that in their paper " On the 

 Spectrum of the more Volatile Gases of Air,"f Professors Liveing and 



Dewar reord weak lines at XX . ',, and 4636 which may possibly 



have the same chemical origin as the Nova lines 4364 and 4636. 



As there is no indication of the new lines forming a series similar to 

 those given by hydrogen and helium, there is probably more than one 

 gas involved. 



Characteristics of tin* Hytlroijen and other Lines. 



In the series of photographs under discussion, the hydrogen lines no 

 longer exhibit the curious structure described in previous communica- 

 tions, but are much fainter and rather narrower and devoid of any 

 apparent differences in density. Some of the bright lines notably 

 X 3868 anil A. 3970 are of about the same width as the adjacent 

 hydrogen lines were in the earlier photographs, and show a structure 

 somewhat similar to that illustrated in a previous note.J 



The lines in question appear as triplets, and in each case the most 

 refrangible member is slightly brighter than the others. The lines at 

 X 4364 and X 4720 are narrower and less intense than those just 

 mentioned, and put on the appearance of doubles, the brighter members 

 being still on the more refrangible side. 



Appearance of the Star. 



Visual examination of the star under high powers shows that the 

 Nova has a decidedly larger disc than is possessed by neighbouring 

 stars of similar magnitude. Photographs of the region of the Nova 

 taken on the nights of September 11 and 12, 1901, with a Dallmeyer 

 rectilinear objective of 6 inches aperture and focal length of 4 feet 

 6 inches, show the penumbral aureole very clearly. It has a fairly 

 definite outline, and is altogether different in character from the 



* ' Astro. Nach.,' No. 3738. 



t ' Boy. Soc. Proc.. ; vol. 67, p. 467. 



J ' Boy. Soc. Proc ,' vol. 68, p. 234. 



