1889.] of the various Species of Heavenly Bodies. 251 



The blue colour of some of the more advanced members of 

 Group I, which are all faint, is probably due to the bright blue 

 fluting of carbon which stands out beyond the end of the continuous 

 spectrum. They are really blue, and not apparently so because of 

 any absorption of the red. That in the case of double stars this 

 colour is not due to optical causes or complementary colours is shown 

 by the fact that there are some equally faint stars which are seen to 

 be red under similar contrast, and instrumental, conditions. 



Pechule has observed the spectrum of one faint blue star, and his 

 observation bears out my view of their nature. He says : 



" 15' au Nord de cette etoile je trouve une etoile de 7 m- , 



qui a un spectre tres singulier ni du III ni du IV type- La 

 partie moins refrangible du spectre n'est qu'indistinctement coupee 

 t un peu plus lumineuse du cote du rouge. Apres un large intervalle 

 noir vient une zone etroite d'un eclat tout-a-fait predominant qui 

 s'eteint rapidement du cote plus refrangible, et forme la fin du 

 spectre. La couleur de 1'etoile est bleuatre." (Pechule, 'Expedition 

 Danoise,' 1882, p. 40.) 



The green colour of the unadvanced members of Group I is pro- 

 bably due to the magnesium radiation ; thus, the Ring Nebula in 

 Lyra is green, and we find that its radiation consists almost entirely 

 of the magnesium fluting at wave-length 500. The bodies in the 

 same group which are white, or pale grey, in all probability add the 

 radiation of carbon and incandescent meteorites to the foregoing. 

 How far spectroscopic observations made with the assistance of large 

 telescopes will confirm these views or prove them to be erroneous 

 remains to be seen ; for the present, however, we may take the 

 colours associated with bodies in Group I as I have stated them. 



The colours which I have associated with Groups II and VI are 

 those given by Duner. 



The prevailing tints in bodies of Groups III and V are white, 

 yellow and orange, so that when we see a yellow star we cannot say 

 from colour alone what group it belongs to. 



The later species of Group III will be white and greenish white, 

 the latter being the most advanced. With a further increase of 

 temperature, stars of Group IV are formed, the colour becoming 

 bluish white owing to the increase of blue light. After this the 

 temperature begins to fall. The first species of Group V will also 

 be greenish white on account of the reduction of blue light, and the 

 next species will be white. After this, the various species of the 

 group will vary from yellowish white to orange. 



The stars of Group IV, a Lyrae, and Sirius being the most brilliant 

 types, are bluish white. 



The bodies of Group VII have little or no inherent luminosity. 



