394 
ASTRONOMY: E. E. BARNARD 
the successive stages characteristic of Novae into one very strongly 
resembling that of planetary nebulae; and then, by the gradual elimina- 
tion of the nebular lines and their replacement by Wolf-Rayet bands, 
into a spectrum identical with this characteristic type of stellar spectra. 
It appears very probable from the observations of Nova Aurigae and 
Nova Persei that this stage of development is to be considered as in the 
nature of a permanent one. It is of interest to note, however, that 
the period required to reach this condition may be quite variable for 
different stars, since the nebular lines X 5007 and X 4960 were still by 
far the most prominent feature of the spectrum of Nova Lacertae (1910) 
as recently as the autumn of 1913. It seems entirely possible that the 
nebular lines found in the case of Novae are extraneous to the stars 
themselves and due to material in which they are involved. Of especial 
importance in this connection is the recent discovery by Wrighf* that 
the central star in certain planetary nebulae has the Wolf-Rayet type 
of spectrum. 
1 Stellar Movements and the Structure of the Universe, p. 156. 
^Astr. Nachr. Kiel, 177, 113 (1908). 
^Contrih. Mt. Wilson Solar Obs., No. 87; Aslrophys. J., 40, 294 (1914). 
^Astrophys. 40, 466 (1914). 
A SINGULAR DARK MARKING ON THE SKY 
By E. E. Barnard 
YERKES OBSERVATORY. UNIVERSITY OF CHICAGO 
Read before the Academy. April 20. 1915. Received. June 4, 1915 
In the search for dark or vacant regions in the sky I have photo- 
graphed a number of very remarkable places, such as those near p 
Ophiuchi and 6 Ophiuchi, and elsewhere. 
These regions are generally connected with the presence of diffused 
nebulosity, but I have found several cases in which a well defined dark 
object seems superposed on the sky itself without any visible presence 
of ordinary nebulosity. One of these, and perhaps the most remarkable 
on account of its well defined character and singular form, is in the po- 
sition: (1855.0)o; = 20 h. 48m.; 5 = +59°.6, in Cepheus (see Plate). It 
resembles an irregular, roughly torn and curved opening through which 
a darker region is visible. It is one degree long and narrows down to 
something like 3' across at its western end. It seems to be a part of the 
background of the sky independent of the starry stratum (there are no 
indications whatever of nebulosity immediately about it), and is appar- 
