86 LIGHT SCIENCE FOR LEISURE HOURS. 



It cannot be doubted that the observers in 1871 

 will have a much more difficult task than those who 

 have added so importantly to our knowledge during 

 the eclipses of the last three years. This will appear 

 on a brief consideration of the progress and present 

 position of the problem with which the observers are 

 to deal. 



In 1868, the observers of the great Indian eclipse 

 discovered that the solar prominences are vast masses 

 of glowing vapour, hydrogen being the chief constitu- 

 ent of these marvellous objects. But the solar corona, 

 that glory of light which appears around and beyond 

 the coloured prominences, did not at that time receive 

 its interpretation. In 1869, the American observers 

 directed their chief attention to this beautiful phe- 

 nomenon ; and they were singularly successful in their 

 observations. One result of a very remarkable cha- 

 racter was obtained by several observers. The light of 

 the corona when analysed in the spectroscope was 

 found to be in large part monochromatic, the coronal 

 spectrum showing one bright line. Now the reader is 

 doubtless aware that in spectrum analysis the essential 

 point is to determine where any bright or dark lines 

 may lie along the range of that rainbow-tinted streak 

 which we call the solar spectrum. In this instance 

 the position of the bright line has been most satisfac- 

 torily determined by a very skilful spectroscopist, 

 Professor Young, of America. The line agrees in posi- 

 tion with one of the lines in the spectrum of iron, a 

 line also seen in the spectrum of the aurora borealis. 



