August 29, 1878] 



NATURE 



459 



this instrument would have been something like Fig. 4, 

 provided I had a clockwork arrange7nent to drive it. 

 Without this contrivance the image and spectra will 

 travel along the plate in the direction of the sun's 

 motion — Let us suppose as here in Fig. 5. 



It will be thus clear that, with this simple contrivance, 

 the result obtained, if clock-work be employed, will be 

 very similar in kind to that arrived at in Dr. Draper's 

 more elaborate arrangement, to which attention has been 

 drawn. 



In the spectra, then, thus obtained, we had only one 

 question to solve, as we all thought : we had to deter- 

 mine the position of the rings photographed in the first 

 and second order spectra, or, at all events, in the first. 

 Long before I developed my plate I knew what had hap- 

 pened. Dr. Draper, Prof. Thorpe, and myself, had 

 photographed the spectrum — this I never doubted — but 

 we had photographed as continuous a one as if a 

 platinum wire, or ball, in a state of incandescence, had 

 been in front of our instrument, instead of a shell of 

 hydrogen gas 6' high, as in 1869, and 10' high, as in 

 1871. 



Dr. Draper's plate was exposed during the whole of 

 totality, to make assurance doubly sure. The continuous 

 spectrum has no trace of a ring, though the plate was 

 considerably over-exposed. In my own little photograph 

 the continuous spectrum only is shown, and very clearly. 

 While my plate was being exposed I held a duplicate 

 grating close to the eye, expecting to see the rings as I 

 saw them through five prisms in 187 1. In first, second, 

 and third order it was all the same — 



Continuous spectrum. 

 Continuous spectrum, 

 Continuous spectrum ; 



and it was this which told me of the gigantic change 

 which had taken place in the atmosphere of the great 

 body we were studying. 



The remarkable phenomenon thus photographed was 

 of course as remarked by the eye observers ; still 

 bright lines were seen in the corona spectrum by one 

 observer, using the term corona to represent everything 

 outside the photosphere, and I make this remark because, 

 whether the spectrum observed was that of the pheno- 

 menon which was visible or not I cannot say. 



Prof. Young himself and many other observers saw the 

 reversal of many lines at the moment of totality, there- 

 by endorsing Pye and Maclear's observations of 1870 and 

 1 87 1. After this, to all but Prof. Young the lines 

 vanished utterly, and this was so absolute that in three 

 parties there was consternation and fear, when nothing 

 but a continuous spectra was seen, that something had 

 gone wrong with the instruments. 



Prof. Young saw 1474 very faint, F without C, and 

 strangest of all, the H and K lines without the long 

 calcium line. This is one of the most remarkable results 

 of the eclipse, and must set students of solar physics to 

 work on a new hne. Young thinks the H and K hnes 

 were brilliant enough to suggest that the ring in this part 

 of the spectrum photographed in the eclipse of 1875 was 

 really due to them, and I am inclined to agree with him, 

 though why the H and K lines should appear minus the 

 longest line of calcium, passes comprehension, unless 



calcium is dissociated there from some cause of which at 

 present we have no idea. 



The discovery of a line in the ultra red by means of a 

 thermopile, is another victory gained, and I sincerely hope 

 that at the next eclipse Capt. Abney may use some " red 

 molecules" to photograph it. Mr. Edison, with his 

 wonderful tasimeter, also found indications of heat in the 

 corona, but as he did not use a spectrum, he did not 

 imitate Prof. Young in determining the exact position of 

 the radiation. 



We next come to the Dark Lines observed in the 

 corona spectrum. 



Janssen was the first to announce the fact that in the 

 corona spectrum the chief Fraunhofer lines were to be 

 seen. This observation Avas made on the Indian eclipse 

 of 1871. The natural interpretation of this observation is 

 that in the coronal atmosphere there are molecules suffi- 

 ciently complex to reflect rays of every refrangibility, and 

 that they do in reality reflect the solar light to us as it 

 reaches them. 



The observations on this point are a little doubtful, 

 though it is held generally that the balance of evidence 

 is in favour of their appearance. Prof. Barker, who 

 observed with Dr. Draper at Rawlins, saw these lines 

 at the moment that he was dumbfounded, as were most of 

 the observers, at the absence of the bright ones. . On the 

 other hand at Prof. Newcomb's camp at Separation they 

 were not traced. Commander Sampson seeing. nothing 

 but a perfectly continuous spectrum ; 1474, F, and even 

 C being utterly invisible. If the corona gives us light 

 containing the Fraunhofer lines, it can only do so because 

 it reflects solar light. Let us next see, then, what t'ne 

 evidence as to Polarisation is. 



When all the observations on this subject are collected 

 we may hope for much new knowledge, but the matter 

 was not finally settled 'this time, for here again was a 

 surprise. 



Professors Morton and Hastings had arranged to deter- 

 mine the quality of the polarisation observed. Prof. 

 Harkness was to attempt to photograph the phenomena, 

 while Prof. Wright set himself the difficult task of quan- 

 tifying it. One observer was specially told off to settle 

 the questions raised by Prof. Pickering's observations of 

 1870. I may commence by saying that these last obser- 

 vations suggest that in 1870 the instrument used by Prof. 

 Pickering was out of order, so that now everybody 

 agrees that there is polarisation. 



I have not yet been able to learn anything of the 

 results obtained by Professors W^right and Harkness as 

 the latter used dry plates which were to be developed 

 here, and the Las Animas party took a long mountain 

 trip to shake off the bad effects of a long camping on an 

 alcali plain, and so did not put in an appearance at 

 Denver. 



Prof, Morton got radial polarisation most distinctly as 

 I did in India in 1871. The amari aliquid is to be found 

 in Prof. Hastings' results, which will be best seen from 

 the following account obligingly placed at my disposal by 

 Prof. Bass, one of his party: — 



" The most important and unexpected result of the 

 expedition was reached by Dr. Hastings in his polari- 

 scopic observations. It Avill be remembered that in pre- 

 vious expeditions, and by many observers in the present 

 eclipse, only a few seconds were devoted to the examina- 



