ASTRONOMY: W. H. WRIGHT 
591 
strong lines appear with greatly reduced exposure. None of the lines 
exhibit any tendency to undue localization in the nuclei. The fourth 
strong line from the right is 4686A, whose origin has so engaged the 
attention of physicists in recent years. It is quite as long as Hues of 
equal strength in other parts of the spectrum. Flanking this line on 
either side are groups of fainter lines which should be noted, as they 
play important parts in the discussion which is to follow. 
FIG. 1. SPECTRA OF NEBULAE 
The nebula N. G. C. 7662, whose spectrum follows, consists of a 
nucleus surrounded by an elliptical ring, the whole lying on a somewhat 
complicated background of fainter nebulosity. The increased bright- 
ness of most of the nebular lines where they cross the ring is plainly 
evident, particularly where the hues are not over-exposed. The line 
at wave-length 4686A and its neighbors are shorter than the others. 
They terminate sharply at the ring, and do not extend out into the faint 
outlying nebulosity and their brightness at contact with the ring itself 
is not greatly increased, which shows that they are relatively bright in 
