THE CHEMISTRY OF THE STARS. 175 



In one of these groups we deal with absorption alone, as in those 

 already considered; we find an important break in the phenomena 

 observed; helium, hydrogen, and metals have practically disappeared, 

 and we deal with carbon absorption alone. 



But the other group of coolest stars presents us with quite new phe- 

 nomena. We no longer deal with absorption alone, but accompanying 

 it we have radiation, so that the spectra contain both dark lines and 

 bright oues. Now, since such spectra are visible in the case of new 

 stars, the ephemera of the skies, which may be said to exist only for an 

 instant relatively, and when the disturbance which gives rise to their 

 sudden appearance has ceased we find their places occupied by neb- 

 ula?, we can not be dealing here with stars like the sun, which has 

 already taken some millions of years to slowly cool, and requires more 

 millions to complete the process into invisibility. 



The bright lines seen in the large number of permanent stars which 

 resemble these fleeting ones — new stars, as they are called — are those 

 discerned in the once mysterious nebulae which, so far from being stars, 

 were supposed not many years ago to represent a special order of 

 created things. 



Now the nebulae differ from stars generally in the fact that in their 

 spectra we have practically to deal with radiation alone; we study them 

 by their bright lines; the conditions which produce the absorption by 

 which we study the chemistry of the hottest stars are absent. 



A NEW VIEW OF STARS. 



Here, then, we are driven to the perfectly new idea that some of the 

 cooler bodies in the heavens, the temperature of which is increasing and 

 which appear to us as stars, are really disturbed nebula?. 



What, then, is the chemistry of the nebulas? It is mainly gaseous; 

 the lines of helium and hydrogen and the flutings of carbon, already 

 studied by their absorption in the groups of stars to which I have 

 already referred, are present as bright ones. 



The presence of the lines of the metals iron, calcium, and probably 

 magnesium, shows us that we are not dealing with gases merely. 



Of the enhanced metallic lines there are none; only the low temper- 

 ature lines are present, so far as we yet know. The temperature, then, 

 is low, and lowest of all in those nebula? where carbon flutings are seen 

 almost alone. 



A NEW VIEW OF NEBULAE. 



Passing over the old views, among them one that the nebula? were 

 holes in something dark which enabled us to see something bright 

 beyond, and another that they were composed of a fiery fluid, I may 

 say that not long ago they were supposed to be masses of gases only, 

 existing at a very high temperature. 



Now, since gases may glow at a low temperature as well as at a high 



