252 NEW STARS IN ANDROMEDA AND ORION. 
discovery. It gave what is called a double spectrum. 
Upon a background of a ITI,, there appeared four bright 
lines, twe of which coincided plainly with hydrogen 
lines. The spectrum of the Vova Cygni was examined 
shortly after its discovery both at Paris and Potsdam, 
and was found to be very like that of the Corona star, 
bright lines (indicating hydrogen) on a continuous back- 
ground. This spectrum implies a sudden and enormous 
outburst of luminous hydrogen; corresponding, per- 
haps, to the red prominences of our sun, though neces- 
sarily exceeding them vastly in number and extent. 
These bright lines were discernible after the continuous 
spectrum upon which they lay was no longer seen. 
They were followed until the star, in. the case of V 
Cygni, had fallen to the tenth magnitude, when but one 
line in the green could be detected. This green line is 
the one prominent in the spectra of gaseous nebule. 
This would suggest that we may have here a case of re- 
version to the nebulous state. Prof. Proctor, who 
believes that new stars have some intimate connection 
with nebule, assumes that a small planetary nebula, 
hitherto unnoted, exists in this place, and that the green 
line indicates only the comparatively permanent condi- 
tions under which the temporary presented itself. But 
Prof. Pickering says, in his annual report of 1880, 
that the spectrum of the WVova Cygni has become that 
of an ordinary star, though exceedingly faint. 
The two new stars, therefore, whose spectra have been 
examined are characterized by bright lines on a con- 
tinuous background. 
Of the nebule whose spectra have been examined 
(mainly by Huggins), about one-third give only bright 
lines and thus proclaim themselves to be of a gaseous 
nature. The Andromeda nebula does not fall into this 
third. , It gives a continuous spectrum, without visible 
lines and with the red end wanting. 
1386 
