98 LIGHT SCIENCE FOR LEISURE HOURS. 



as it seems to me, he would have avoided had he taken 

 into account the enormous pressure at which an atmo 

 sphere so extensive as the corona would necessarily 

 exist under the influence of the sun s mighty attractive 

 energies. It may easily be shown that if the outer 

 parts of the corona were as rare as the contents of our 

 so-called vacuum-tubes, or even a thousand times rarer, 

 yet according to the la,ws which regulate atmospheric 

 pressure, the density even at vast heights above the 

 sun s surface would attain to many hundred times that of 

 our heaviest gases. The pressure would, indeed, be so 

 great that we can see no way of escaping the conclu 

 sion that, despite the enormous heat, the gases com 

 posing the imagined atmosphere would be liquefied or 

 even solidified. 



When the observers of the Indian eclipse of 1868 

 found that the coloured prominences are masses of 

 glowing hydrogen, with other gases intermixed, and 

 when the prominence-spectrum was found to show the 

 hydrogen lines as these appear when hydrogen exists 

 at very moderate pressures, KirchhorFs view had to be 

 abandoned as altogether untenable. Wherever the 

 vapours exist which produce the solar dark lines, they 

 are undoubtedly not to be looked for in the corona. 



But there the lines are. The absorptive action is 

 exerted somewhere. The question is Where are the 

 absorptive vapours ? 



At this stage of the inquiry, a very strange view was 

 expressed by Mr. Lockyer a view which appears to 

 have been founded on a slight misapprehension of the 



