SIR NORMAN LOCKYER 369 



Like the lowest hottest layer, for some reason or other, this upper 

 layer does not write its record among the lines which build up the 

 general spectrum. 



GENERAL RESULTS REGARDING THE LOCUS OF ABSORPTION 



IN STELLAR ATMOSPHERES 



We learn from the sun, then, that the absorption which defines the 

 spectrum of a star is the absorption of a middle region, one shielded 

 both from the highest temperature of the lowest reaches of the atmos- 

 phere, where most tremendous changes are continually going on and 

 the external region where the temperature must be low, and where the 

 metallic vapors must condense. 



If this is true for the sun it must be equally true for Arcturus, 

 which exactly resembles it. I go further than this, and say that in the 

 presence of such definite results as those I have brought before you it 

 is not philosophical to assume that the absorption may take place at 

 the bottom of the atmosphere of one star or at the top of the atmos- 

 phere of another. The onus prohandi rests upon those who hold such 

 views. 



So far I have only dealt in detail with the hotter stars, but I have 

 pointed out that we have two distinct kinds of coolest ones, the evi- 

 dence of their much lower temperature being the shortness of their 

 spectra. 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 accompany- 

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

 and bright ones. 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 nebulae, we cannot 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 



