Sune 12, 187 3] 
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ry 
NATURE 
127 
THE CORONAL ATMOSPHERE OF THE SUN* 
I 
I PROPOSE to bring before you rapidly the principal 
results obtained by me during the last total eclipse 
of the sun which I observed in Hindostan, at a point not 
very far distant from the place where I observed the 
great eclipse of 1868, which opened up such new horizons 
with regard to the constitution of the sun. 
The last eclipse took place on December 12, 1871. 
The chief interest of the phenomenon is connected with 
the problem of the luminous corona which surrounds the 
sun during total eclipses. When that body is eclipsed by 
the interposition of the moon, you know that indepen- 
dently of those jets and luminous expansions which are 
known as protuberances, there is seen around the dark 
disc of our satellite a magnificent luminous phenomenon, 
resembling a glory or crown, which extends to 8’, 12’, 15’, 
and more from the lunar limb, and the frequent strange 
forms of which are variable at each eclipse. The obser- 
vation of the eclipse which now occupies our attention, 
had for its object to definitely fix for us the nature of this 
_ singular phenomenon, 
The corona is the luminous manifestation which is 
| predominant during a total eclipse, and thus it must, at 
all times, attract the attention of observers. We possess, 
indeed, descriptions by Plantade, by Halley, by Louiville, _ 
and by others, which go back to the commencement of 
| the 18th century ; of course these observers did not indi- 
cate the cause of the phenomenon, 
| Arago and his school forma period in the history of 
_the attempts which have been made to discover the 
| nature of the corona. Our great physical astronomer 
applied the polariscopic methods to these investigations, 
| but he as well as his successors were baffled. In the 
“ Astronomie Populaire,” published in 1856 (tome iii. 
p- 604), we read the following conclusion upon this 
subject ; “I regret to say that the disagreement which 
has been found to exist between the observations made | 
in different places by astronomers equally competent, on | 
the luminous corona, in one and the same eclipse, has 
covered the question with such obscurities, that it is in 
the meantime impossible to arrive at any certain conclu- 
sion on the cause of the phenomenon.” 
By means of spectrum analysis the question has | 
entered on a new phase. In 1868, while the nature of 
the protuberances was discovered, the spectrum of the | 
corona was also obtained; it is true the observers found it 
continuous, not an exact observation according to me, 
which retarded the solution of the question. 
In the following year the Americans took up the 
* Translation of paper'read by M. Janssen at the Bordeaux meeting of 
the French Association for the Advancement of Science. 
+ Let us mention the observation of M. Rayet, who found luminous pro- 
longation on the principal lines of the spectrum of a protuberance. 
| matter.* They still found the continuous spectrum, but 
they established the existence of that celebrated green 
line (1474 in Kirchhoft’s scale) which is the prevailing 
manifestation in the spectrum of the corona, and the 
meaning of which has yet to be discovered. We owe, 
moreover, to the Americans some very beautiful photo- 
graphs of the protuberances, which show also the actinic 
power of the coronal light. 
The eclipse of 1870 was marred by the bad weather. 
The few observations which could be made confirmed in 
general the observations of 1869.+ 
Thus, in 1871, we already possessed some very im- 
portant data on the corona. Unfortunately these data 
were as yet incomplete, and above all inconsistent ; for 
* The total eclipse of August 7, 1869, visible in N. America. 
+ We should mention, nevertheless, the beautiful observations of Mr. 
Young on the reversion of the lines at the base of the chromosphere. 
