1871J The Eclipse of Last December, 237 



line 1474 and 72 for the line c. Only one explanation is 

 available, namely, that the area of the region supplying 

 light whose spectrum shows the 1474 line must exceed the 

 area of the region whose light shows the c line, in the pro- 

 portion which 100 x (from 25 to 50) bears to 72, or from 35 

 to 70 times. Professor Young, assigning to the coloured sierra 

 and prominences an apparent area equivalent to a ring a 

 quarter of a minute high round the sun, concludes that the 

 self-luminious corona would be "equivalent to another ring 

 from 8' to 14' high." * The irregular nature of the 

 inner part of the corona would also seem to leave no escape 

 from the conclusion that this portion cannot suffice to give 

 all the light showing the 1474 line, unless we suppose the 

 inner corona to extend in places considerably more than 8' 

 from the sun. Professor Young, therefore, concludes that 

 "we have surrounding the sun, beyond any farther reasonable 

 doubt, a mass of self-luminous gaseous matter, whose 

 spectrum is characterised by the green 1474 line. The precise 

 extent of this it is hardly possible to consider as determined, 

 but it must be many times the thickness of the red hydrogen 

 portion of the chromosphere ; perhaps on an average 8' 

 or io' with occasional horns of twice that height. It is not 

 at all unlikely that it may even turn out to have no upper 

 limit, but to extend from the sun indefinitely into space." t 



As respects other spectroscopic evidence, little need be 

 said. None of the other observers save Lieutenant Brown 

 obtained results which differ essentially from those already 

 recorded. Lieutenant Brown was unable to detect the 1474 

 line, but as he used a single-prism spectroscope, whereas 

 the invisibility of the line depends on a certain amount of 

 dispersion being obtained, his failure can be readily inter- 

 preted. The Italian observers at Agosta saw tv/o very 

 brilliant bands. "Father Denza," writes Secchi, "executed 

 the part assigned him to admiration. He saw the protu- 



* In " Nature " this is written 8' to 16' high," but this is obviously- 

 due to a mistake ; and Professor Young probably wrote the passage as I 

 have put it. A ring 16' high round the sun's disc would exceed a ring one 

 quarter of a minute high, about 80 times in extent, instead of about 70 times. 



f In one of the most humorous paragraphs I ever remember to have read in 

 a scientific paper, Professor Young assures the advocates of the atmospheric 

 glare theory that "in the main" he concurs with their views " with the exception 

 that he is disposed to" negative the only remaining special point which 

 they had not conceded. The corona had been gradually admitted to be 

 solar as respe&s a greater and greater extension from the sun ; but for all above 

 6' or 7' from the sun, and specially for the radiations, a contest was still 

 maintained with the object of proving these parts to be terrestrial. Professor 

 Young placidly hands over to the sun these last remaining portions of the corona, 

 assuring the advocates of the terrestrial theory that in all other respects he 

 agrees with them. 



