YET A YEAR LATER. 87 



But the spectrum of iron contains upwards of 400 lines, 

 while even the simpler spectrum of the aurora contains 

 several lines ; that of the corona, on the other hand,, 

 has not been proved to contain any other bright lines 

 except the one just mentioned. Others have been sus- 

 pected, but the degree of their brightness has not been 

 such as to prove beyond all possibility of question that 

 they belong to the solar corona. 



However, as Professor Young remarks on this point 

 (writing in 1871), ' considered as a demonstration of 

 self-luminosity one bright line is just as conclusive as 

 many.' 



It was in fact demonstrated by this observation 

 alone that the corona, for a considerable part at least 

 of its extension, is a self-luminous object. * Nor can 

 there be any doubt,' I may add with Professor Young,, 

 'as to the location of the self-luminous matter. It 

 cannot be in our atmosphere, for no possible reason 

 can be assigned why the particular molecules of the 

 air that happen to lie near the lines which join the 

 eye of the observer with the edge of the moon should 

 become luminous rather than others in a different 

 portion of the sky. Nor can it be at the moon ; 

 otherwise, of course, it would always be visible round 

 her disc.' * Accordingly,' he adds, ' it is now universally, 

 I think I may say, acknowledged that one important 

 element of the corona consists of a solar envelope of 

 glowing gas reaching to a considerable elevation* 

 Mr. Lockyer, who is still disposed to assign to the 

 solar element of the corona a lower relative importance 



