138 LIGHT SCIENCE FOR LEISURE HOURS. 



the solar corona. The occasion was a very favourable 

 one for the purpose, many of the stations being high 

 above the sea level. While the corona as a whole had 

 thus shrunk in extent and increased in brightness, losing 

 also the complexity of structure it had shown in 1871, 

 it had changed still more significantly in another way. 

 Dr. H. Draper and Mr. Lockyer repeated the observation 

 which the latter had made in 1871, but they saw no 

 coloured images of the inner corona, and the spectro- 

 scopists sawno bright lines in the spectrum of the corona. 

 In fact, the corona no longer showed those signs of being 

 partly gaseous which had been recognised in 1869, 



1870, and 1871. Not only so, but the rainbow-tinted 

 background corresponding to the non-gaseous part of 

 the corona showed no dark lines. It was not, therefore, 

 reflected sunlight only or chiefly, as it had been in 



1871, when Janssen recognised the solar dark lines in 

 this part of the corona's light. It was, in fact, the light 

 which comes from glowing solid or liquid matter. The 

 inference seems clear that now, when the sun is without 

 spots, the corona, greatly shrunk in size, and, as it were, 

 drawn inwards towards the sun, is so intensely heated 

 as to be self-luminous a result not very surprising 

 when we remember that the heat, even at its outer- 

 most part, is 100,000 times that of vertical sunlight on 

 the earth. Singularly enough, on this occasion, when 

 first decisive spectroscopic evidence was obtained 

 respecting the intense heat of the minute particles 

 probably forming the corona, the heat received from 

 the corona was actually measured. The ingenious 



