130 



Sir iSTorman Lockyer. 



Specific difference a in the Spectra. 



In considering the question of variations of spectra with temperature 

 in these stars, the importance of taking differences of magnitude into 

 account must not be lost sight of. 



A general examination of Dun^r's observations indicates that there 

 are two marked differences in the spectra of the different stars. (1) 

 Some of them give secondary bands, whilst in others they are absent. 

 (2) Some of them have longer continuous spectra than others, as 

 indicated by the number of zones " visible. 



If the continuous spectrum extends far enough towards the violet, 

 the three dark flutings of carbon will divide the spectrum into four 

 bright zones. If it does not extend beyond the most refrangible of 

 the flutings (X473) only three zones will be visible, and the continuous 

 spectrum will appear to end sharply at wave-length 473. In one case 

 it does not extend beyond the fluting at X517, and then only two 

 zones are visible. 



These diff*erences might evidently depend upon diff'erences of mag- 

 nitude of the stars concerned, but a detailed examination of the 

 observations shows that some of the diff'erences do not depend upon 

 brightness. If we consider the visibility of the secondary bands 

 according to Dimer, we have the following result : — 



No. of band. 



Ware-leBgth. 



Magnitude of stars 

 in which it is seen. 



Magnitude of stars in 

 whicli It is not seen. 



1 



656-0 



5 -4—6 -2 



6-0—9-5 



2 



621 



5-4—8-1 



6-0-9-5 



3 



604-8 



5 -4—8 -1 



6-0-9 -5 



4 



589 -8 



5 4—8-5 



6-6—9-5 



5 



576-0 



5 -4-8 -1 



7 '5— 9 5 



7 



551-0 



5-4—6-5 



6 0—9 -5 



8 



528-3 



5-4—7-0 



6 -0—9 -5 



This table shows that the visibility of the secondary bands is not 

 altogether dependent upon the magnitudes of the stars observed. 

 Thus the bands 2 and 3 are seen in some of the stars of the group as 

 low as magnitude 8-1, whilst they are absent from some of the stars of 

 the sixth magnitude. 



If we consider the question of the length of the continuous spectrum, 

 we have the follo^ving result, the maximum number of zones referring 

 to the longest continuous spectrum : — 



