ASTRONOMY: W. H. WRIGHT 
593 
Wolf-Rayet bands, in addition to that at 4686A. One of these shows 
very faintly at 4057A. While the nucleus is undoubtedly to be con- 
sidered a Class O star, I am in some doubt as to its exact position in 
the Harvard scale. 
The spectrum of N. G. C. 6543 very much resembles the one immedi- 
ately above it, except that the nebulous envelope is comparatively much 
larger. Five of the critical lines in the vicinity of 4686A are very short, 
while two of them: 4641 and 4713 are of medium length. The nucleus 
band, 4057A, visible only with difficulty in N. G. C. 6572, is strongly 
developed here. Unlike the one at 4686A, this band does not appear 
to have its counterpart in a true nebular spectrum, that is, it has not 
been observed except as a broad band confined to nebular nuclei, or 
other Class O stars. As in most of the other spectra the lines are of 
various lengths, helium being intermediate in extent between 4686A and 
hydrogen. The other lines fall in their usual order of length. 
The following subject is the spectrum of the central region of N. G. C. 
6826. The spectrum of the nucleus resembles that of the preceding 
object, but has the additional feature of interest that the nucleus band 
at 4686A, and probably the bright hydrogen lines, are accompanied on 
their more refrangible edges by dark lines in the spectrum of the nucleus. 
Dark ^ Puppis fines are also present, though faint, and H and K (Cal- 
cium) are also dark. In addition to 4686A, 4658 and perhaps 4650 
occur as bright bands in the nucleus. 
As has already been remarked, the nebula N. G. C. Index 418, situated 
in the southern part of the constellation of Orion, was found by Camp- 
bell to have a hydrogen atmosphere of greater extent than that of its 
'nebulium atmosphere. The photograph confirms this result, and 
shows in addition the restricted occurrence of helium. The details of 
the nucleus spectrum are lost on this plate, through overexposure, so 
that it is necessary to state that 4650 and 4686A are present as broadened 
bands confined to the nucleus, the first named line being much the 
stronger. In the downward progression this line has developed from 
a comparatively insignificant nebular line into the strongest band in 
the spectrum of the nucleus. 
The spectrum immediately below is that of the well-known Wolf- 
Rayet star B.D. -f30°3639 which Campbell found to be surrounded 
by a hydrogen atmosphere. As announced a year ago it is in reahty 
a planetary nebula with a highly complicated nucleus. The fine 4686A 
and most of the neighboring lines which occur as nebular lines in N. G. C. 
7027 are here represented by broad bands in the nucleus. Helium is 
in the nucleus, while hydrogen is still outstanding in the nebula. 
