8 Proceedings of the Royal Society of Victoria. 



6. — Later History of the Star. 



On March 19th the nova entered upon the third stage of its 

 life history, so far as we can ever know it. The decline in its 

 luminosity, previously very rapid, became extremely slow ; but 

 the star now assumed the character of an irregularly periodic 

 variable of rapidly lengthening period, its brightness fluctuating 

 between the 4th and 6th magnitudes.^ With this variation in 

 brightness was associated a variation in the spectrum, which 

 showed two well-marked types ; the first type agreed with the 

 spectrum already described, save that the metallic lines were 

 steadily weakening ; the second type differed from the first by 

 the absence, or at least the great relative weakness, of the 

 continuous spectrum, the absence of dark bands, and the gradual 

 emergence of new bright ones. The conditions of change from 

 one spectrum-type to the other were very carefully studied by 

 Sidgreaves^, who found that it was associated with the absolute 

 brightness of the star, and not with the phase of the light- 

 variation ; whenever the magnitude sank below 4*57 the second 

 type appeared, whenever it rose above that value the first type 

 was re-established. Pickering'^ to a certain extent supports this 

 conclusion, as all the second type photographs secured by him, 

 ■with one exception, were taken at minima ; the exception is 

 important, as he records that " the magnitude of the star was the 

 same on 12th and 13th April, but the spectrum was different;" 

 there appears, however, to be a possibility of error on his part, as 

 the light-curves of Lockyer and Cliild agree in showing that, on 

 both dates, the brightness was near to Sidgreave's critical value, 

 being slightly below it on the 12th and above it on the 13th ; 

 the same thing is shown by Rambant's observations^, which give 

 the magnitude on 12th April as 4"67, and on 13th April as 449 ; 

 on the whole, Sidgreaves seems to be right. 



The most noteworthy of the early changes in the spectrum of 

 the second type are the disappearance of the " enhanced " 

 metallic lines and the gradual emergence of characteristic nebular 



1 Lockyer (M.N., Ixi., App. p. 59) and Child (M.N. Ixi., p. 4S3) ^'ive drawiiiffs of the light 

 curve for February, March, and April. 



2 Loc. cit. 



3 Ap. J., xiv., p. 80. 



4 M.N., Ixi., p. 467. 



