8 BOHLIN, ON THE GALACTIC SYSTEM WITH REGARD TO ITS STRUCTURE. 
3. On spectra of gaseous nebulce. 
It is obvious that the gaseous nebul&e exhibit examples of such a very exag- 
gerated state of matter, here supposed once to have characterised the body, of which 
the Galaxy is the present product. At first, the extraordinary brightness of many 
of them, namely of the »blue nebule>», shows that the intrinsic luminosity of these 
bodies far exceeds that of condensed stars at even the highest temperatures. But, 
furthermore, the known constitution of their spectra plainly exhibits the same thing. 
In fact, the continuous spectrum, frequently accompanying the gaseous lines in the 
nebular spectra, seems to be at any rate foreign to the true nebulous state. In the 
planetary nebul&e G.C. 4234, 4373, 4390, 4628, VoGEL' observed the continuous spec- 
trum, more or less weakly developed from about 07.600 to 0v.470, while, according 
to the same author, the continuous spectrum is wanting in the planetary nebulze 
G.C. 4510, 4532, 4572. 
The nebulous lines themselves, of which, according to CAMPBELL, there exist a 
considerable number,” two of which, however, are to be regarded as characteristic, 
are principally four, viz. 
nh, = 0.5007 first chief nebular line 
hj, = 0.4959 second ; ? 
3 = 0.4862 
I, = 0.4341, 
The line å, = 6v.4862 is generally and the line >, =0v.4341 frequently present in the 
spectra of gaseous nebul&e. These lines correspond, according to HuGGINns” and 
GOTHARD '", resp. to the hydrogen lines Hz and H.. The first chief line was originally 
ascribed by HUGGINS” to nitrogene. But as the latter is seen to be double, the ne- 
bular line being single, the coincidence must be accidental. 'The second chief line, 
nearly coinciding on the one side with a barium-line and on the other with an oxygen- 
line, cannot be indentified with any known substance.” It is, moreover, to be noti- 
ced that the first of the hydrogen-lines, + = 0".656 = H, is absolutely absent from the 
nebulous spectrum. This is also the case with many of the variable stars, as R An- 
dromed&e, V OCassiop., and B Lyre. According to KEELER”, the lines of the nebu- 
lous spectrum are due to a very high temperature of the nebulous matter. He adds 
that the first chief nebulous line seems to be absolutely monochromatic, which, in 
fact, will support the idea of an extremely exaggerated state of matter in the ne- 
bulous bodies. 
! Astron. Nachr. N:o 1864 and N:o 2854. 
2? W. W. CAMPBELL, Spectra of the great nebula in Orion and other wellknown nebul:e. Astronomy and 
Astrophysics Vol. XIII, 1894 pag. 494. 
3 Philosophical Transactions 1868. 
1 Astronomy and Astrophysics, Vol. XII, 1893, pag. 55. 
> J. E. KEELER, Spectroscopic observations of Nebulr, Publications of the Lick Observatory, Vol. III, 1894. 
