50 



Mr. J. N. Lockyer. On the Classification [Apr. 12, 



the bands given by Duner in his admirable observations on these 

 bodies.* 



Duner in his map gives eleven absorption bands, chiefly flutings, 

 in Class Ilia, but in the case of the tenth and eleventh bands there is 

 some discrepancy between his map and the text, to which reference 

 will be made subsequently. His measurements are of the darker 

 portions of the flutings, speaking generally. 



It will be clear at once that in the case of the dark flutings the dark 

 bands should agree with the true absorption of the vapours, and that 

 when the amount of absorption varies, only that wave-length away 

 from the maximum of the flutings will vary. Thus, the same fluting 

 may be represented in the following manner, according to the quantity 

 •of the absorbing substance present. 



i i 



Fig. 12. — Diagram showing how an absorption fluting varies in width according to 

 the quantity of absorbing substance present. 



In the case of the bright flutings, however, the dark bands on either 

 side may in some cases be produced partly by contrast only, and the 



* " Les Etoiles a Spectres de la troisieme classe." — ' Kongl. Svenska Yetenskaps- 

 Akademiens Handlingar,' Band 21, Xo. 2, 1885. 



