KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 43. N:o 10. 19 
stinguishable from stars, when the prisme is removed from the eyepiece, but a few 
of them have small dises. He points out that »the regions examined have been 
selected with the view of affording a fair means of learning something with regard 
to the distribution of these objects in the sky, and that it is remarkable that all 
those which have been found occur in or near the Milky Way.» He adds that »this 
was previously known to be the case with the larger planetary nebulze, having ga- 
seous spectra»> No further account as to the extent of the researches is given. 
10. On the Wolf-Rayet stars. 
These stars, having peculiar spectra, are of all celestial objects those which show 
the most decided concentration to the Milky Way. Indeed, of 55 known objects of 
this category all are situated within 9” to both sides of the Galactic circle. The 
distribution shows, according to W. W. CAMPBELL', two maxima at about 60” and 
about 246” of Galactic longitude, a fact which, to some degree, reminds of the 
distribution of sunspots on two opposite sides of the Sun's equator. 'These features 
are, however, not decisive for the planetary nebule, though a resemblance of the 
spectra was pointed out by PICKERING. Later CAMPBELL contradicts (1. c.) this si- 
militude of spectra, remarking (pag. 475) that »in conclusion the spectra of the 
Wolf-Rayet stars are not closely related to any other known type>. 
11. On large gaseous nebule in the Milky Way. 
Though the planetary nebule are not generally members of the Milky Way, 
there exist in it or in its neighbourhood, other gaseous nebulée of great extent. Such 
nebule are: the Orion Nebula; the great nebula G. C. 4616 in Cygnus, Roberts II, 
plate 21;? N.G. C. 281 Cassiop., Roberts IT, plate 22; N. G. C. 1499 Persei, Roberts 
II, plate 22; M 16 Clypei, Roberts II, plate 23; Neb. 37 Cygni, Roberts IT plate 24; 
Neb. 74 Cephei, Roberts II, plate 24; Nebule in the Pleiades; G. C. 600 Ceti, Ro- 
berts I plate 10, and others. These nebule are well to be distinguished from the 
planetary nebulee. 
12. Concluding facts and hypotheses. 
1. The Planetary Nebulce consist originally of rotating luminous shells filled 
with very thin matter. In the course of their evolution, the shells break down at 
their poles, forming apparent Ring Nebulme, with mostly distinguishable Nuclei. — At 
a further stage of development, a big, bright, and extended centre sometimes arises, 
1 The Wolf-Rayet stars, Astronomy and Astrophysics Vol. 13, 1894, pag. 450. 
> Isaac Roberts, Photographs of nebulx and clusters of stars, Vol. I, II, London 1893, 1899. 
