The New Star in Perseus. 



121 



of the plates, indicates that the middle portions of the bright lines are 

 not far from their normal positions ; those of the dark ones, however, 

 are displaced by some 15 tenth-metres towards the violet, thus indi- 

 cating a differential movement of something like 700 miles a second. 



Movements more rapid and disturbances more violent than those 

 observed in Nova Aurigae are therefore indicated ; both by the greater- 

 displacement of the dark lines relatively to those that are bright and 

 the greater breadth of the bright and dark lines. 



The comparison of spectra shows us that we are dealing with two 

 swarms, one of which, the less dense, gives us broad bright lines and is 

 almost at rest with reference to the line of sight ; the denser swarm, 

 indicated by the dark lines, is in most rapid movement in the line of 

 sight towards the earth. 



An interesting feature of the spectrum is the presence of fine dark 

 lines down the middle of each of the bright lines of hydrogen and 

 calcium ; these are most probably reversals, and if this be so, they will 

 be of great service for accurate determination of the wave-lengths of 

 the other bright lines. The dark hydrogen line Hy, and perhaps H/2 

 and HS, are also possibly reversed. 



Eye observations showed among the chief lines a group of four in 

 the green; one probably H/3, the others near XX 492, 501, and 517 ; a 

 bright line at or near D, and a brilliant red line probably correspond- 

 ing to Hoc. Each of these was accompanied by a dark broad line on 

 its more refrangible side. Other lines of less brightness were observed 

 both in the green and red. 



It at first seemed probable that two of the bright lines in the green 

 (XX 492 and 501) might be due to asterium, while that in the orange 

 was perhaps the helium line D 3 . Subsequent investigation, however, 

 suggested as an alternative origin that these lines might be the 

 enhanced lines of iron at X 4924*1 and 5018*6, which are very nearly 

 in the same positions as the asterium lines. This view was tested by 

 inquiring whether other prominent enhanced lines of iron so strongly 

 visible in the spectrum of a Cygni were present. 



A comparison with the spectrum of this star photographed with the 

 same instruments suggested that many lines between F and h in the 

 Nova probably correspond with lines in a Cygni. Certainty could not 

 be arrived at in consequence of the great breadth of the lines in the 

 Nova. 



Hence, as the Nova bore some resemblance to both Nova Aurigag and 

 a Cygni, a reference was suggested to the lines recorded in the spectrum 

 of Nova Aurigse which were observed when the light of that star was 

 on the wane, and when the lines were thinned enough to be easily mea- 

 surable. I may also add that these observations were made before the 

 work on enhanced lines was undertaken. 



The importance of this reference was strengthened by the considera- 



