M. Arago on the Physical Constitution of the Sun. 201 



After having proved that the sun is composed of a dark 

 central body, of a cloudy-reflecting atmosphere, and of a pho- 

 tosphere, we should naturally ask if there is nothing besides ; 

 if the photosphere terminates abruptly and without being 

 surrounded by a gaseous atmosphere less luminous in itself, 

 or feebly reflecting \ Generally, this third atmosphere would 

 disappear in the ocean of light with which the sun always 

 appears surrounded, and which proceeds from the reflexion 

 of its own rays upon the particles.o£ which the teiTestrial 

 atmosphere is composed. liVm-A oi; 



A means of removing this doubt presented itself ; it was 

 selecting the moment wherein, during a total eclipse, the moon 

 completely obscures the sun. 



Almost at the moment when the last rays, emanating from 

 the margin of the radiant orb, disappeared under the opaque 

 screen formed by the moon, our atmosphere, in the region 

 which is projected between the moon, the earth, and the 

 neighbouring parts, ceased to be illuminated. 



Every one now knows what was the principal object of the 

 astronomers, who in 1842 repaired to the south of France, to 

 Italy, to Germany, and to Russia, where the eclipse of the 

 sun of the 8th of July would be total. 



In all our researches, innumerable unexpected appearances 

 invariably present themselves : thus the observers were not 

 a little surprised when, after disappearance of the last direct 

 rays of the sun behind the margin of the moon, and after the 

 light reflected by the surrounding terrestrial atmosphere had 

 also disappeared, to see rose-shaped prominences from two 

 to three minutes in height, dart, as it were, from the circum- 

 ference of our satellite. 



Each astronomer, following the usual bent of his own ideas, 

 arrived at an independent opinion regarding the cause of these 

 appearances. Some attributed them to the mountains of the 

 moon ; but this hypothesis would not bear a moment's exami- 

 nation. Others wished to discover in them certain effects of 

 difl^raction or of refraction. But the touchstone of all theories 

 is calculation ; and uncertainty the most indefinite must fol- 

 low, in reference to their application to the remarkable phe- 

 nomena specified, those, namely, of which we have just been 



