﻿in Total Eclipses of the Sun, 235 



of thousands of miles from the sun's photosphere, in regions 

 where, if any solar atmosphere exist, the results of recent obser- 

 vations with the spectroscope by Lockyer and Frankland lead us 

 to believe that it can only be the faintest possible trace of it, we 

 must infer that the light of the corona is of electric origin. 



In the hands of Prof. Young and Prof. Winlock the spectro- 

 scope has obtained direct evidence of a physical correspondence 

 between the solar corona and terrestrial auroras. Prof. Young 

 observed in the spectrum of the corona a bright line, the position 

 of which he gives as 1474 on KirchhofFs scale, and which proves 

 to be in coincidence with a small line marked as iron onKirchhoff 's 



o 



and Angstrom's maps. He remarks that " it turns out also to 

 coincide very closely, if (which is much more probable) it is not 

 absolutely identical, with a line recently discovered, by Prof. Win- 

 lock of Cambridge, in the spectrum of the aurora borealis. He 

 also saw two other, fainter lines in the spectrum of the corona 

 which coincided quite closely with other lines reported by Prof. 

 Winlock as visible in the spectrum of the aurora. In view of 

 these results of spectroscopic observation he remarks as follows: — 

 " At present it seems pretty likely that the spectra of the corona 

 and the aurora borealis are identical, with only such differences 

 in the intensity of their lines as we might naturally expect, and 

 that very probably the identity extends to the essential nature 

 of the phenomena themselves." 



The detection of the same iron line in the aurora and corona, 

 taken in connexion with the well-established fact that the vapour 

 of iron is present in the photosphere and chromosphere of the 

 sun, and that the magnetic features of the aurora lead to the 

 natural conclusion that some form of ferruginous matter consti- 

 tutes the substance of auroras, for which no terrestrial origin 

 can reasonably be assigned, conducts to the inference that the 

 terrestrial auroral matter is derived from the sun, and adds to 

 the weight of accumulative evidence in support of the theory I 

 have advocated, that the corona is made up of material emana- 

 tions from the sun. 



Note. — Some persons have conjectured that the corona might be 

 produced by the passage of the sun's rays through the earth's atmo- 

 sphere ; but it may readily be shown that this is impossible. When 

 one reflects that the half width of the moon's shadow, in the larger 

 eclipses, is as great as the estimated height of the atmosphere, it will 

 be seen that, to an observer on the central line of the eclipse, the 

 line of sight will not fall upon the illuminated portion of the atmo- 

 sphere exterior to the shadow, unless inclined under a large angle to 

 the line of direction of the centres of the sun and moon. The corona, 

 therefore, if of terrestrial atmospheric origin, ought to present, to- 

 ward the middle of the eclipse, the appearance of a halo entirely de- 



