16 ARMSTRONG LAST SOLAR ECLIPSE. [Yol. vii. 



The condition of our knowledge of the spectra of the Corona 

 ,and Halo at the time of the eclipse of 1870, are well stated in 

 Professor Young's summary. He considered that the spectrum 

 of the Corona and Halo consisted of: — 



1. "A continuous spectrum without lines, either bright or 

 •'' dark, due to incandescent dust — that is, particles of solid or 

 ■" liquid meteoric matter near the Sun." 



2. "A true gaseous spectrum consisting of one (I4Ti) -or 

 ^*more lines, whicli may arise from the vapour of the meteoric 



^' dust, but more probably from a solar atmosphere through 

 ^' which the meteoric particles mov^e as foreign bodies." 



3. " A true sunlight spectrum, icltli its dark lines, formed by 

 '' photospheric light reflected from the solar atmosphere and 

 " meteoric dust. To this reflected sunlight is undoubtedly due 

 ^' most of the Polarization." 



4. " Another component spectrum that is due to the light re- 

 ^- fleeted from the particles of our own atmosphere. This is a 

 '• mixture of the three already named, with the addition of the 

 ^' chromosphere spectrum, for while at tlie middle of the eclipse 

 -" the air is wholly shielded from photospheric sunlight, it is of 

 ^' course exposed to illumination from the prominences and upper 

 -'' portions of the chromosphere." 



5. " If there should be between us and the Moon at the mo- 

 ^' ment of the Eclipse, any cloud of cosmical dust, the light re- 

 '' fleeted by this cloud would come in as a fifth element." 



Such a spectrum, as will be seen, is, to use again Professor 

 Young's words, " exceedingly complex." 



The correctness of these views was, as has been previously 

 .hinted, fully established during the late Eclipse. And among 

 the observations then made the chief place in importance must 

 be given to those of Respighi and Janssen. The former, when 

 .observing, adopted the original method of Fraiinhofer and placed 

 the prism in front of the object glass, instead of in the position of 

 .the eye piece of his telescope ; an arrangement whereby a series of 

 overlapping coloured images of the observed object itself are 

 formed, and not merely a number of coloured reproductions of 

 the slit that is usually employed. M. Janssen on the other 

 hand, while using the spectroscope in the place of the eye piece, 

 did so without a slit ; — as did also Mr. Lockyer, who observed at 

 Bekul. The telescope employed by Janssen was specially adapted 

 to ensure a very much increased illumination of the image in its 



