May 10, 1888] 



NATURE 



3i 



SUGGESTIONS ON THE CLASSIFICATION OF 

 THE VARIOUS SPECIES OF HEAVENLY 

 BODIES. ' 



IV. 



IV.— ON THE SPECTRA OF STARS OF GROUP II. 



IN the previous part of this memoir I have attempted to 

 give a general idea of that grouping of celestial bodies 

 which in my opinion best accords with our present know- 

 ledge, 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 upon it when, in addition to 

 general grouping, it is used to show us how specific 

 differences are arrived at. 



I. General Discussion of Duner's Observations. 



In the paper communicated to the Royal Society on 

 November 17 I pointed out that the so-called "stars" 



Fig. 6. — Diagram showing how an absorption fluting varies in width according 

 to the quantity of absorbing substance present. 



of Class lU.a were not masses of vapour like our sun, 

 but swarms of meteorites ; the spectrum being a com- 

 pound one, due to the radiation of vapour in the inter- 

 spaces and to the absorption of the light of the red- or 

 white-hot meteorites by vapours volatilized out of them 

 by the heat produced by collisions. 



I also showed that the radiation was that of carbon 

 vapour, and that some of the absorption was produced by 

 the chief flutings of Mn and Zn. 



Dune'r 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. 



' Th« Ba'<er'an Lecture, delivered at the Royal Society on April 12, by 

 J. Ncrman Lock; er, F.R.S. Continued from p. ir. 



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

 flutings the dark bands should agree with the ixwz. absorp- 

 tion of the vapours, and that when the amount of absorp- 

 tion varies, only that wave-length away from the maximum 

 of the flutings will vary. Thus, the same fluting may be 

 represented as in Fig. 6, according to the quantity 

 of the absorbing substance present. 



In the case of the £r/4 r ///flutings,however, the dark bands 

 on either side may in some cases be produced partly by 

 contrast only, and the brighter and wider the bright flutings 

 are the more they will appear to vary, and in two ways : 

 first, they will dim by contrast when the bright fluting 

 is dimmer than ordinary ; and secondly, the one on the 

 side towards which the bright fluting expands from its 

 most decided edge will diminish as the bright fluting 

 expands (see Fig. 7). 



There is also another important matter to be borne in 

 mind. As these spectra are in the main produced by the 

 integration of the continuous spectra of the meteorites, 

 the bright flutings of carbon, and the dark flutings pro- 

 duced by the absorption of the continuous spectra by the 



Fig. 7.— Diagram showing the variation in width of a bright fluting, and the 

 consequent variation in width of the contrast band at th; fainter edge. 



vapour surrounding each meteorite ; the proportion of 

 bright fluting area to dark fluting area will vary with the 

 reduction of the spacing between the meteorites. 



If any bright or dark flutings occur in the same region 

 of the spectra when the spaces are' greatest, the radia- 

 tion effect will be stronger, and the absorption fluting will 

 be " masked ;" where they are least the radiation itself 

 will be masked. This reasoning not only applies to 

 flutings but to lines also. 



The Radiation fluting r. 



We will first deal with the radiation flutings— those of 

 carbon. The brightest less refrangible edge of the chief 

 one is at wave-length 517, where it sharply cuts off the 

 tail end of the absorption of the magnesium fluting the 

 darkest edge of which begins at 520, as the carbon light 

 from the interspace pales the absorption. The same 



