THE ECLIPSE OF 1871. IO7 



to be wanting, the streak being seen to be crossed 

 transversely by multitudes of dark lines. This had, 

 however, been known for many years, and even the 

 general interpretation of the fact had been ascertained 

 for nearly a quarter of a century, before the true 

 nature of the complex atmosphere was understood. 

 Kirchhoff, the eminent German physicist who detected 

 the secret of the solar spectrum, conceived that the 

 sun's corona is the atmosphere which produces the 

 darjr~- lines. In other words, he supposed an atmo- 

 sphere some two or three millions of miles in depth to 

 be in question instead of an atmosphere only a few 

 hundred miles deep. 



But when the study of the sun's coloured pro- 

 minences had shown that at a height of forty or fifty 

 thousand miles there is no glowing iron, or copper, or 

 zinc no atmospheric matter, in fact, which can by any 

 possibility account for the dark lines in the solar 

 spectrum, KirchhofFs theory was seen to be untenable. 

 It was clear that, if the absorbing vapours lay above 

 the visible surface of the sun at all, they must needs 

 occupy a shallow region, unrecognised hitherto either 

 by the observers of the eclipse or by spectroscopists. 



Now Father Secchi announced in 1869 that he had 

 detected traces of just such an atmosphere. For when 

 he examined with his spectroscope the very border of 

 the sun, he found that the dark lines could no longer 

 be seen ; as though the light of the glowing vapours 

 themselves which, examined alone, could show bright 

 lines precisely where the solar dark lines appear 



