The New Star in Perseus. 



123 



In the case of new stars, after the maximum of luminosity has been 

 reached, however high they ascend, short of the apex of the tem- 

 perature curve, this order must be reversed, and hence we should 

 expect to find the spectrum varying in accordance with the foregoing 

 sequence, but in the reverse order. 



In Nova Corona (1866), according to the observations of Sir William 

 Huggins and Dr. Miller, the absorption spectrum was very similar to 

 that of a Orionis, which is a star of the Antarian group, so that the 

 temperature attained was relatively low ; this indeed is demonstrated 

 by the fact that at present it shines faintly as an Antarian star, and 

 doubtless did so before the collision. The collision, therefore, probably 

 did not take Nova Coronse very much above its initial stage of tem- 

 perature, and when the disturbance was over it simply reverted to its 

 old conditions. 



The spectrum of Nova Cygni (1876) was not photographed, and as 

 special attention was given by most observers to the bright lines, 

 there is no satisfactory record of the absorption spectrum. 



This now appears as a nebula, and doubtless it was a nebula to begin 

 with, as Nova Coronas was a star to begin with. 



In Nova Aurigas (1892), as we have seen, the comparison with 

 a Cygni indicates that the Cygnian (a higher) stage was reached, 

 and in the final stages its spectrum corresponded with that of the 

 planetary nebulas, that is, a stage lower than that reached by Nova 

 Coronas. The intermediate stages, however, were not observed, 

 possibly because the star was never very brilliant, and partly because 

 of the difficulty of observing closely grouped lines, such as occur in 

 the Polarian and Alclebarian stages when they are rendered broad by 

 such disturbances as those which were obviously present in the Nova. 



The observed maximum magnitude in the case of a new star will 

 evidently depend upon the distance and size of the colliding masses, as 

 well as upon the temperature produced by the collision. It is not 

 remarkable, therefore, that there is no apparent relation between the 

 greatest brightness and the temperature indicated by the spectra, 

 Nova Coronas, with its relatively low temperature, shone for a time as 

 a 2nd magnitude star, while Nova Aurigas, with a much higher tem^ 

 perature, scarcely surpassed a star of the 5th magnitude. 



I now return to Nova Persei. If the idea that in the present Nova 

 the swarm which gives the dark line spectrum resembles a Cygni be 

 confirmed ; as its temperature is reduced we may expect it to pass 

 successively through some or all of the stages of temperature repre- 

 sented by stars of the Polarian, Aldebarian, and Antarian groups } 

 enhanced lines being first replaced by arc lines, and then by flutings. 

 AVhether it remains at one of these stages or undergoes a further back- 

 wardation into a nebula will be a point of the highest interest. 



If, like Nova Aurigse, the present Nova should end as a nebula, it 



VOL. LXVIII. L 



