1U 



Sir Norman Lockyer. 



red. 



No doubt the differences in the appearances are due to the fact that 

 at He we are dealing with the lines both of hydrogen and calcium. 



Bough measurements on the bright line H/3 show that the interval 

 between the centres of the two extreme maxima shown in the light 

 curve corresponds to about 25 tenth-metres. This would give a 

 differential velocity of 960 miles per second between the different 

 sets of hydrogen atoms in the bright-line swarm itself. 



It may be then that the appearances described as reversals of the 

 hydrogen lines on February 25th, were but the beginning of the sub- 

 sequent changes. 



The comparisons with stars which have been taken with the slit 

 spectroscope on each evening of observation, indicate that no great 

 change in the velocity of the dark-line component has occurred. 



So much, however, cannot be said of the bright lines, in which a 

 change has been observed. In addition to the hydrogen lines the 

 strong lines in the green already ascribed to iron, appear to be double 

 in the photographs most recently obtained. 



Comparison with oc Cygni. 



The view of the apparent similarity between the spectra of Nova 

 Persei and Nova Aurigse, to which I drew attention in my previous 

 paper, has been strengthened by the comparisons which have since 

 been made. 



The bright lines in the spectrum of Nova Persei are so broad, 

 especially in the blue and violet, that accurate determinations of their 

 wave-lengths are difficult to obtain. The lines less refrangible than F, 

 however, besides being more isolated, are narrower than those in the 

 more refrangible part of the spectrum. A direct comparison of these 

 with the lines in the spectrum of a star which is known to contain the 

 enhanced lines of iron, &c, has been considered a better method of 

 arriving at some definite conclusion as to the connection between the 

 Nova lines and the enhanced lines, than that of determining the wave- 

 lengths of the broad lines and comparing the results with the known 

 wave-lengths of the enhanced lines. 



