20 ROUGH WAYS MADE SMOOTH. 



of July, 1878, we should unquestionably be led to adopt the 

 belief that the corona during a year of many spots differs 

 markedly from the corona when the sun shows few spots, or 

 none. So far as the aspect of the corona is concerned, I 

 take the description given by the same observer in both 

 cases, as the comparison is thus freed as far as possible from 

 the effect of personal differences. 



Mr. Lockyer recognised in 1871 a corona resembling a 

 star-like decoration, with its rays arranged almost symmetri- 

 cally three above and three below two dark spaces or rifts 

 at the extremity of a horizontal diameter. The rays were 

 built up of innumerable bright lines of different length, with 

 more or less dark spaces between them. Near the sun this 

 structure was lost in the brightness of the central ring, or 

 inner corona. In the telescope he saw thousands of inter- 

 lacing filaments, varying in intensity. The rays so definite 

 to the eye were not seen in the telescope. The complex 

 structure of interlacing filaments could be traced only to a 

 height of some five or six minutes (from 135,000 to 165,000 

 miles) from the sun, there dying out suddenly. The spec- 

 troscope showed that the inner corona, to this height at 

 least (but Respighi's spectroscopic observations prove the 

 same for a much greater distance from the sun), was formed 

 in part of glowing gas hydrogen and the vapour of some 

 as yet undetermined substance, shining with light of a green 

 tint, corresponding to 1474 of Kirchhoffs scale. But also 

 a part of the coronal light came from matter which reflected 

 sunlight ; for its spectrum was the rainbow-tinted streak 

 crossed by dark lines, which we obtain from any object 

 illuminated by the sun's rays. It should be added that the 

 photographs of the corona in 1871 show the three great 

 rays above and three below, forming the appearance as of a 

 star-like decoration, described by Mr. Lockyer ; insomuch 

 as it is rather strange to find Mr. Lockyer remarking that 

 ' the difference between the photographic and the visible 

 corona came out strongly, . . . and the non -solar origin 

 of the radial structure was conclusively established.' The 



