1869.] 



of AugiLst 18, 1868. 



69 



the red flames almost as accurately as if the observer had the benefit 

 of a perpetual eclipse. 



In this manner Mr. Lockyer has sketched the protuberance 

 shown in the following figure : — 



Fi-. 7. 



When the slit is adjusted so as to fall on a, the brilliant rays 

 are seen entirely separated from the solar spectrum. 



We come uow to the curious du23lex nature of this discovery. 

 In describing his spectrum observations of the eclipse prominences 

 of the 18th August last, M, Janssen said : — 



"The most important result of these observations is the dis- 

 covery of a method of which the principle was conceived during 

 the eclipse itself, and which will allow of the study of protuberances 

 and of the regions surrounding the sun at all times, without its 

 being necessary to have recourse to the interposition of an oj^aque 

 body before the sun's disc. This method is founded upon the 

 spectral properties of the light of the protuberances — hght which 

 resolves itself into a small number of very luminous pencils, cor- 

 responding to the obscure rays of the solar spectrum." 



M. Janssen describes his discovery in the following words : — 

 "It struck me immediately that it would be possible to see the 

 rays without an echpse. During the night the method and means 

 of execution were clearly arranged in my mind. The next morning, 

 the 19th, the sun rose very brightly. By means of the finder 

 attached to the large telescope, I placed the slit of the spectroscope 

 in part on the solar disc, and part beyond ; the sht therefore gave 

 two spectra, that of the sun, and that of the region of the protu- 

 berances. The brilliancy of the solar spectrum was a great difii- 

 culty, 1 therefore tm'ned the apparatus so as to remove from the 

 field the red, green, and blue, the most brilliant portions of the 

 solar spectrum. All my attention was directed to the line o which 

 was dark in the sun's spectrum, but brilliant in that of the protu- 

 berance. Suddenly 1 perceived a small brilliant red ray, one or 

 two minutes in height, forming a rigorous prolongation of the black 

 line G of the solar spectrum. Upon moving the slit of the spec- 

 troscope in such a manner as to sweep methodically the region that 

 I was examining, this line was persistent, but it became modified 

 in length and in the brilliancy of its various parts, thus showing 



