1904 - 5 .] On Prof. Seeliger’s Theory of Temporary Stars. 523 
admitting enormous atmospheric expansion in temporary stars. 
The correctness of this view will be more fully evidenced if we 
now investigate the effects of such a rapidly expanding gaseous 
envelope on the appearance of the spectrum. Almost at a glance 
we notice that a satisfactory explanation of one of the most 
enigmatic features of the Nova spectrum is here offered. 
To show this in a few words, let us consider the star immediately 
after the collision, when its surface is in a state of high incandes- 
cence, and when the gaseous matter evaporating from the surface 
expands in radial directions outwards. Let the circle A A' repre- 
sent the boundary of the star nucleus in a plane passing through 
the observer, 0 E being the line of sight. We suppose the outside 
boundary of the expanding atmosphere at this particular moment 
to he at B C C' B' D' D. We may also assume the star to he so 
far removed that the light of its photosphere ( = incandescent 
star surface) and of the surrounding atmosphere is thrown simul- 
taneously upon the slit of the spectroscope. Now, obviously, 
all the rays leaving the photosphere in the direction OE, i.e. 
towards us, have to pass through that part of the atmosphere 
which lies within the area ADD' A'. The natural assumption 
being that the gases of the outside layers at D D', in consequence 
E 
