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TUB POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



phcric nature of the corona). Xo one now doubts 

 that the corona is a solar appendage. But the 

 demonstration of this fact was worth absolutely 

 nothing, because the fact had been demonstrated 

 before. The demonstration had not been ac- 

 cepted by ail ; in fact, it could not be accept- 

 ed by those who could not understand it ; and 

 to some it appeared as utterly ridiculous ' to 

 assert that the corona belongs to the sun, as it 

 still appears to Mr. Hampden to assert that the 

 earth is a globe. But as we should not recognize 

 the least value in a series of researches which 

 convinced Mr. Hampden that the earth is a globe, 

 so we cannot recognize any value in the demon- 

 stration of the already demonstrated fact that the 

 corona is a solar appendage, even though the new 

 demonstration should be so simple as to be easily 

 understood by persons to whom the other had 

 been as " caviare to the general." The true value 

 of the photographs taken by Mr. Davis and by 

 Colonel Tennant resides, not in the circumstance 

 that they place the solar nature of the corona be- 

 yond all possibility of doubt or cavil, but in, the 

 fact that they throw new light on the structure 

 of the corona. Now, if six photographs, each ob- 

 tained from an exposure of about one-sixth the 

 duration of totality, are thus instructive (each 

 telling the same thing, be it noticed), how much 

 more instructive would one photograph have 

 been to obtain which advantage had been taken 

 of the entire duration of totality ! 



In April, 18*75, an opportunity occurred for re- 

 deeming this error to some degree. It could not 

 be wholly redeemed on that occasion, because in 

 1870 and 1871 the sun had been in a highly dis- 

 turbed condition, whereas in 1875 he was pass- 

 ing through the stage of least disturbance. All 

 the more desirable was it, however, that a record 

 of the condition of the solar corona should be 

 obtained in 1875 for comparison with the records 

 obtained in 1870 and 1871, and with more satis- 

 factory records to be obtained at the next time of 

 maximum disturbance in 1882— '84. Unfortunate- 



1 This is ijot exaggerated. Not many months be- 

 fore the evidence was obtained which proves in a man- 

 ner " easily undorstanded of the people " that the co- 

 rona belongs to the sun, the enunciation of this fact by 

 myself was characterized by Mr. Lockyer ns " simply 

 ridiculous," and by no means because the fact was 

 obvious, but because it could not be a fact. 



ly, however, another mistake was made in 1875i 

 in the face of the clearest possible evidence that 

 failure must result. Instead of making it a point 

 that, whatever else might be done, the corona 

 should be photographed well and carefully, above 

 all things, those who planned our English expedi- 

 tion on that occasion devised an ingeniously elab- 

 orate arrangement for photographing the spec- 

 trum of the corona in a way which had not the 

 remotest chance of success. 



We may well hope that the American observers 

 of the eclipse of the 29th inst. will not make any 

 mistakes of this sort. The minimum sun-spot pe- 

 riod is still in progress, so that a good photograph 

 of the corona will have great value. This I trust 

 they will in the first instance provide for effectual- 

 ly. Secondly, we may hope that they will make 

 good spectroscopic observations of the corona. 

 It has been shown that the spectrum of the coro- 

 na is partly indicative of gaseity ; but besides the 

 bright line or lines having this interpretation, 

 there is a rainbow-tinted background implying 

 that the corona shines in part by reflecting sun- 

 light. Janssen in 1871 thought he could recog- 

 nize the solar dark lines in this spectrum. Of 

 course they should be seen if it is really the spec- 

 trum of reflected sunlight. It is to be hoped that 

 the observers of the approaching eclipse will ob- 

 tain more decisive evidence on this point. 



If any American observers care to try the ex- 

 periment suggested in 1875, for photographing the 

 spectrum of the corona, they may do so : they will 

 be able to prove, perhaps, what is already certain, 

 that the experiment is bound to fail if carried out 

 in the proposed manner. 



Lastly, the occasion is one when an attempt to 

 recognize, I will not say the true extension of the 

 corona, but somewhat more of its real extension 

 than has hitherto been perceived, may be usefully 

 made by persons unable to employ large telescopes, 

 or to effect any spectroscopic or photographic re- 

 searches. For success in such an attempt, it will be 

 necessary — 1. To select a station as high as pos- 

 sible above the sea-level; 2. To protect the eye 

 carefully from sunlight before totality begins, and 

 from the light of the prominences, sierra, and in- 

 ner corona, during totality ; 3. To use either a 

 very low magnifying power, or to trust altogether 

 to the unaided eye. — Gentleman 's Magazine. 



