1888.] of the various Species of Heavenly Bodies. 



15 



that the difference between comets and the stars now under discussion 

 is more instrumental than physical. 



Supposing that the cometic nature of these bodies be conceded, 

 laboratory work will eventually show us which flutings and lines 

 will be added to the nebula spectrum upon each rise of tempera- 

 ture. 



The difficulties of the stellar observations must always be borne in 

 mind. It will also be abundantly clear that a bright fluting added to 

 a continuous spectrum may produce the idea of a bright line at the 

 sharpest edge to one observer, while to another the same edge will 

 appear to be preceded by an absorption band. 



III. Stars with Bright Flutings accompanied by Dark Flutings. 



I also showed in the paper to which reference has been made that 

 the so-called " stars " of Class Ilia of Vogel's classification are not 

 masses of vapour like our sun, but really swarms of meteorites ; the 

 spectrum being a compound one, due to the radiation of vapour in 

 the interspaces and the absorption of the light of the red- or white- 

 hot meteorites by vapours volatilised out of them by the heat produced 

 by collisions. The radiation^ is that of carbon vapour, and some of 

 the absorption, I stated, was produced by the chief flutings of manga- 

 nese. 



These conclusions were arrived at by comparing the wave-lengths 

 of the details of spectra recorded in my former paper with those of 

 the bands given by Duner in his admirable observations on these 

 bodies.* 



The discovery of the cometic nature of the bright-line stars greatly 

 strengthens the view I then put forward, not only with regard to the 

 presence of the bright flutings of carbon, but with regard to the actual 

 chemical substances driven into vapour. From the planetary nebulas 

 there is an undoubted orderly sequence of phenomena through the 

 bright-line stars to those now under consideration, if successive stages 

 of condensation are conceded. 



I shall return to these bodies at a later part of this memoir. 



I 



IV. Stars in which Absorption Phenomena predominate. 



I do not suppose that there will be any difficulty in recognising, that 

 .if the nebulae, stars with bright lines, and stars of the present Class 

 Ilia are constituted as I state them, all the bodies more closely 

 resembling the sun in structure, as well as those more cooled down, 

 must find places on a temperature curve pretty much as I have placed 



* " Les IStoiles a Spectres de la troisieme classe." — ' Kongl. Svenska Vetenskaps- 

 Akademiens Handlingar,' Band 21, No. 2, 1885. 



