THE SUN'S TRUE ATMOSPHERE. 99 



principles of spectrum analysis. He put forward the 

 theory that the absorptive action takes place below the 

 level of the sun's surface as we see it. 



But observations made by Fr. Secchi at Rome pointed 

 to a view so different from Mr. Lockyer's, as to lead to 

 a controversy which filled many pages of the Comptes 

 Rendus, of the Philosopical Magazine, and of other 

 publications a controversy Conducted, as too many 

 philosophical discussions have been, with a somewhat 

 unphilosophical acrimony. 



Fr. Secchi had noticed that when the very edge of 

 the sun's disc is examined with the spectroscope, the 

 dark lines disappear from the spectrum, which thus 

 becomes a simple rainbow-tinted streak. He judged, 

 accordingly, that the absorbing atmosphere exists above 

 the sun's real surface ; for he believed that just at the 

 edge the bright lines corresponding to the light from 

 the vapours themselves so nearly equal in intensity the 

 light of the solar spectrum, that no signs of difference 

 can be detected ; or, in other words, that the dark lines 

 are obliterated. On the other hand, the glowing atmo- 

 sphere cannot, he argued, reach much above the sun's 

 surface, since otherwise the spectroscope would show 

 the bright lines belonging to that atmosphere's light. 

 Now, no such lines are visible. So far as the spectro- 

 scopic evidence is concerned, it would appear as though 

 immediately above the sun's surface, as we see it, there 

 came the sierra that low range of prominence-matter, 

 which, strangely enough, some have regarded as an 

 atmospheric envelope. The spectrum of the sierra 



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