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.
