592 ASTRONOMY: W. H. WRIGHT 
the comparatively dark area within. 4363 A is longer than the mem- 
bers of this group but shorter than the hydrogen (H/3, H7, H5, He) 
and nebuhum (N2-1) lines. Although the exposure extended over 17 
hours the continuous spectrum of the nucleus is only faintly recorded, 
a fact which may be due, in part, to poor observing conditions. 
Both in form and in spectrum the object N. G. C. 7009 bears a strik- 
ing resemblance to 7662, and the purpose of exhibiting the spectrum 
is partly to call attention to this fact. Both of these spectra appear to 
bear a strong resemblance to that of the ring nebula in Lyra as de- 
scribed by Max Wolf, and it may be that in general objects of this form 
have a characteristic spectrum. The spectrum of the nucleus of N. G. C. 
7009 is continuous, but the record is not strong enough to prove the 
presence or absence of dark lines. 
N. G. C. 2392 is the nebula in Gemini which consists of two con- 
centric rings of nebulosity surrounding a very bright nucleus. The 
usual nebular lines, including those due to hydrogen and helium, are 
present in the outlying nebulosity, but in the nucleus the hydrogen 
and helium lines are reversed, that is, they appear as dark lines. 4686 A 
on the contrary is brightened and probably broadened on crossing the 
spectrum of the nucleus. One might expect, from this apparent ten- 
dency of the line to concentrate in the nucleus, to find it comparatively 
short in the nebula, but as a matter of fact it appears to be quite as long, 
in this object, as any of the other lines. In fixing the position of the 
spectrum in an order, the controlling factor of whose arrangement is the 
degree of concentration of the line 4686A, there is therefore some doubt 
as to which of these phenomena should control. As a nebular line the 
one in question is relatively longer in this nebula than in N. G. C. 7662, 
which should place it before that object, while its increased breadth 
in the nucleus would seem to indicate a position intermediate between 
N. G. C. 7009 and 6572. In the dilemma I have tentatively assigned it 
to the latter position. In addition to the dark lines referred to above, 
the .t Pup pis series is also dark in the spectrum of the nucleus. 
The nebula N. G. C. 6572, or Struve 6, is a small object which bright- 
ens gradually to a hazy nucleus near the center. It will be noticed that 
the Hne 4686A is confined to the nucleus, and that it has completely 
lost its monochromatic character. It has the appearance of a hazy 
ball. The hues flanking it on either side are very short, and some of 
them are broadened. The lines of these groups become very active in 
the novae and some of them play important roles in the Wolf-Rayet 
(Class O) spectra. The well-known lines 4634 and 4650A are among 
them. The spectrum of this nucleus has several of the characteristic 
