318 Intelligence and Miscellaneous Articles. 



THE SOLAR ECLIPSE OF JULY 2i)TH, 1878. 

 BY PROFESSOR HENRY DRAPER, M.D. 



As I have recently been giving attention to the subject of solar 

 spectroscopy in consequence of my discovery of oxygen in the sun, 

 it seemed to be desirable to take advantage of the total eclipse of 

 July 29th, to gain as precise an idea as possible of the nature of 

 the corona, because the study of that envelope has been regarded 

 as impossible at other times. The main point to ascertain was 

 whether the corona was an incandescent gas shining by its own 

 light, or whether it shone by reflected sunlight. 



For this purpose I organized an expedition, and was fortunate 

 enough to secure the cooperation of my friends Professors Barker 

 and Morton and Mr. Edison. The scheme of operations was as 

 follows : — (1) the photographic and photo-spectroscopic work as 

 well as the eye slitless spectroscope were to be in charge of my 

 wife and myself ; (2) the analyzing slit spectroscope was in charge 

 of Prof. Barker, with the especial object of ascertaining the pre- 

 sence of bright lines or else of dark Fraunhofer lines in the corona ; 

 (3) the polariscopic examinations were confided to Professor Morton, 

 who was also to spend a few moments in looking for bright or dark 

 lines with a hand spectroscope ; (4) Mr. Edison carried with him 

 one of his newly invented tasimeters with the batteries, resistance 

 coils, Thomson's galvanometer, etc., required to determine whether 

 the heat of the corona could be measured. 



This entire programme was successfully carried out; and good for- 

 tune attended us in every particular. The results obtained were : — 

 1st, the spectrum of the corona was photographed, and shown to 

 be of the same character as that of the sun, and not due to a special 

 incandescent gas ; 2nd, a fine photograph of the corona was ob- 

 tained, extending, in some parts, to a height of more than twenty 

 minutes of arc — that is, more than 500,000 miles ; 3rd, the Fraun- 

 hofer dark lines were observed by both Professors Barker and 

 Morton in the corona ; 4th, the polarization was shown by Pro- 

 fessor Morton to be such as would answer to reflected solar light ; 

 5th, Mr. Edison found that the heat of the corona was sufficient to 

 send the index beam of light entirely off the scale of the galvano- 

 meter. Some negative results w^ere also reached, the principal 

 one being that the 1474K, or so-called corona line, was either very 

 faint or else not present at all in the upper part of the corona, 

 because it could not be observed with a slitless spectroscope, and 

 the slit spectroscope only showed it close to the sun. 



The general conclusion that follows from these results is, that 

 on this occasion we have ascertained the true nature of the corona, 

 viz. : — it shines by light reflected from the sun by a cloud of 

 meteors surrounding that luminary, and that on former occasions 

 it has been infiltrated with materials thrown up from the chromo- 

 sphere, notably with the 1474 matter and hydrogen. As the chro- 

 mosphere is now quiescent, this infiltration has taken place to a 

 scarcely perceptible degree recently. This explanation of the 



