1888.] 



of the various Species of Heavenly Bodies. 



27 



perature. The various species will be marked by 

 increasing simplicity of spectrum. 



Group IV. — Simplest line absorption predominant. 



Group V. — Line absorption predominant, with decreasing tempera- 

 ture. The various species will be marked by de- 

 creasing complexity of spectrum. 



Group VI. — Carbon absorption predominant. 



Group VII. — Extinction of luminosity. 



It will be seen from the above grouping that there are several 

 fundamental departures from previous classifications, especially that 

 of Vogel. 



The presence of the bright flutings of carbon associated with dark 

 metallic flutings in the second group, and the presence of only absorb- 

 ing carbon in the sixth, appears to be a matter of fundamental 

 importance, and to entirely invalidate the view that both groups (the 

 equivalents of Ilia and III& of Vogel) are produced from the same 

 mass of matter on cooling. 



This point has already been dwelt upon by Pechiile. 



Another point of considerable variation is the separation of stars 

 with small absorption into such widely different groups as the first 

 and fourth, whereas Vogel classifies them together on the ground of 

 the small absorption in the visible part of the spectrum. But that 

 this classification is unsound is demonstrated by the fact that in these 

 stars, such as 7 Cassiopeiae and j8 Lyra?, we have intense variability. 

 We have bright hydrogen lines instead of inordinately thick dark 

 ones ; and on other grounds, which I shall take a subsequent 

 opportunity of enlarging upon, it is clear that the physical conditions 

 of these bodies must be as different as they pretty well can be. 



It will be seen also that, with our present knowledge, it is very 

 difficult to separate those stars the grouping of which is determined 

 by line absorption into the Groups III and V, for the reason that 

 so far, seeing that only one line of temperature, and that a descending 

 one, has been considered, no efforts have been made to establish the 

 necessary criteria. I noted this point in the paper to which I have 

 already referred in connexion with the provisional curve. 



Part III. — Sub-Groups and Species of Group I. 

 I. Sub-Group. Nebula. 



Having, in the preceding part of this memoir, attempted to give a 

 general idea of that grouping of celestial bodies which in my opinion 

 best accords with our present knowledge, and which has been based 

 upon the assumed meteoric origin of all of them, I now proceed to 

 test the hypothesis further by showing how it bears the strain put 



