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TEE POPULAR SCIENCE MONTELY.— SUPPLEMENT. 



coroDa in 1867 should have closely resembled the 

 corona of last July, if this theory were sound. 



It would be idle, I think, to seek for further 

 evidence either in favor of the theory we origi- 

 nally proposed to discuss, or against it : for the 

 evidence of the eclipse of 1867 disposes finally 

 of the theory in that form. I may note in pass- 

 ing that the eclipse of 1868 gave evidence almost 

 equally unfavorable to the theory, while the evi- 

 dence given by the eclipse of 1869 was neutral. 

 It will be desirable, however, to consider, before 

 concluding our inquiry, the evidence obtained in 

 1871 and last July, in order that we may see 

 what, after all, that evidence may be regarded as 

 fairly proving with regard to coronal variations. 



First, however, as I have considered two 

 eclipses which occurred when the sun-spots were 

 decreasing in number — namely, those of 1842 

 and 1851, midway (roughly speaking) between 

 the crest and hollow of the sun-spot wave on its 

 descending slope — it may be well to consider an 

 eclipse which was similarly situated with respect 

 to the ascending slope of a sun-spot wave. I 

 take, then, the eclipse of 1858, as seen in Brazil 

 by Liais. The picture drawn by this observer is 

 one of the most remarkable views of the corona 

 ever obtained. It is given at page 339 of my 

 book on the Sun. Formerly it was the custom to 

 deride this drawing, but, since the eclipse of 1871, 

 when the corona was photographed, it has been 

 admitted that Liais's drawing may be accepted 

 as thoroughly trustworthy. It shows a wonder- 

 fully complex corona, like that of 1871, extending 

 some 700,000 miles from the sun, and correspond- 

 ing in all respects with such a corona as our 

 theory (if established) would have associated 

 with the stage of maximum solar disturbance. As 

 in this respect the eclipse of 1S58, when sun-spots 

 were increasing, resembled those of 1S42 and 

 1851, when sun-spots were diminishing in num- 

 ber, we find no trace of any law ©f association 

 depending on the rate of increase or diminution 

 of solar disturbance. 



If we limited our attention to the eclipses of 

 1871 and of last July, we should unquestiona- 

 bly 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 

 differences in observing qualities. 



Mr. Lockyer recognized in 1871 a corona re- 

 sembling a starlike decoration, with its rays ar- 



ranged almost symmetrically — three above and 

 three below two dark spaces or rifts at the ex- 

 tremity of an 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 coro- 

 na. 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 tele- 

 scope. The complex structure of interlacing fila- 

 ments 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 spectroscope showed that the inner corona, 

 to this height at least (but Respighi's spectro- 

 scopic observations prove the same for a much 

 greater distance from the sun), was formed in 

 part of glowing gas — hydrogen — and the vapor 

 of some as yet undetermined substance, shining 

 with light of a green tint, corresponding to 1474 

 of Kirchhoff s 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 be- 

 low, forming the appearance as of a starlike 

 decoration, described by Mr. Lockyer ; insomuch 

 that it is rather strange to find Mr. Lockyer re- 

 marking that " the difference between the photo- 

 graphic and the visible corona came out strongly 

 . . . . and the non-solar origin of the radial 

 structure was conclusively established." The re- 

 semblance is, indeed, not indicated in the rough 

 copy of the photographs which illustrates Mr. 

 Lockyer's paper ; but it is clearly seen in the 

 photographs themselves, and in the fine engrav- 

 ing which has been formed from them for the 

 illustration of the eclipse-volume which the As- 

 tronomical Society proposes to issue (some time 

 in the present century, perhaps). 



Now, last July the corona presented an en- 

 tirely different appearance. Mr. Lockyer, in a 

 telegram sent to the Daily News, describes it as 

 small, of pearly lustre, and having indications of 

 definite structure in two places only. Several 

 long rays were seen ; but the inner corona was 

 estimated as extending to a height of about 70,- 

 000 miles from the sun's surface. Its brightness 

 was estimated as exceeding tenfold that of the 

 corona seen in 1871. The most remarkable 

 change, however, was that which had taken place 

 in the character of the corona's spectrum — or, in 



