114 LIGHT SCIENCE FOR LEISURE HOURS. 



observation were applied, Young inferred that a certain 

 green line belongs unquestionably to a region of 

 luminous matter not less extensive than the inner 

 corona. It appeared tolerably safe to conclude that 

 the inner corona was the actual source of hi s peculiar 

 light. And if the resemblance between this light and 

 that of the aurora borealis were admitted, it appeared 

 reasonable to infer that the inner corona is a perpetual 

 solar aurora, as had been suggested in 1869. 



But although the reasoning of Professor Young 

 was so nearly conclusive, that he must be regarded as 

 in effect the discoverer of the important facts just 

 mentioned, yet it seemed desirable to astronomers to 

 endeavour to obtain even more convincing evidence. 

 We have seen the difficulty which lay in their way ; it 

 remains to be shown how, during the recent eclipse, 

 that difficulty was overcome. 



They had hitherto dealt with the spectral line or 

 lines of the inner corona. Those lines are in reality 

 coloured images of the slit through which the spectro- 

 scopist admits the light which he proposes to examine ; 

 and therefore their shape can teach him nothing about 

 the source of light, their position (or which is the same 

 thing, 1 their colour) being all that the spectroscopist 

 considers. But suppose he uses no slit, then instead 

 of a series of images of a slit he will have a series of 



1 The same thing, because a bright line corresponding to any posi- 

 tion along the rainbow-tinted spectrum has the colour proper to that 

 position. In fact, spectroscopists indicate the position of a bright line 

 by reference to its colour saying a liae in the red, or in the blue 

 green, or the like. 



