246 OBSERVATIONS AT THE SUMMIT OF MONT BLANC. 



that belong to it, but it has another bearing of a still more lofty 

 order. It reveals to us a new harmony in the constitution of the 

 system. 



We already know the grand outlines of the sun's constitution and 

 the admirable conditions realized to assure both the abundance and 

 the duration of the radiation with which it supplies the planets. We 

 know how, as M. Faye's fine theory teaches, the incandescent surface 

 of excessive thinness in which resides its radiating virtue is itself 

 regenerated by the vast reserves of heat of the great central mass. 



We know too, that this radiating surface is protected from rubbing 

 against the icy void of space by a number of gaseous envelojies. Of 

 these envelopes, or atmospheres, the highest, and doubtless the most 

 efficacious, is the coronal atmosphere, which, during total eclipses, pro- 

 duces the splendid plienomenon of the glory of the corona. 



This atmosphere is principally composed of hydrogen, the lightest 

 and most transparent of known gases. The capital function of radia- 

 tion, which is the rational end of the central luminary, is then assured 

 by that transparent and protecting atmosphere. But we now see that, 

 by an arraugement no less admirable, the body which could in a moment 

 compromise this function has been removed with care. 



Thus it is that science as she advances reveals to us at every step 

 unknown laws and harmonies in the constitution of the world. 



The observatory which now rears its head above the summit of Mont 

 Blanc has Just contributed a little part to this work. It promises in 

 the future much larger results. The building is the realization of the 

 thought and the desire of numbers of distinguished men of science 

 who have worked on the renowned mountain. Since the memorable 

 ascent of De Saussure, Mont Blanc has formed acquaintance with the 



But tLongh this is striking, it is the comparison with tubes placed under optical 

 conditions as identical as j)ossible which alone can lead to any certain conclusion. 

 These comparative experiments have been commenced in the laboratory of the 

 Observatory of Meudou. They lead to the same result, to wit, the disappearance of 

 the groups A, a, and B at the limits of the atmosphere. But because of the impor- 

 tance of the question they will be tahen up anew and completed. 



It might be asked whether the elevated temperatures to which are submitted the 

 gases and vapors of the solar atmospheres are not capable of modifying their power 

 of selective absorption, and in particular whether oxygen, which might be in those 

 atmospheres, would not have a spectrum quite different from that which we recog- 

 nize in our experiments at ordinary temperatures. 



I have already instituted experiments with a A'iew to meeting this objection. I 

 shall report them to the Academy, but I wish to say that the absorption spectra of 

 oxygen, wJiether that with irresolvable bands or that with lines, do not appear to 

 be appreciably modified when the oxygen is carried to 400'^ or 500'^. 



On the whole I may say that the observations which have lieen made at the sum- 

 mit of Mont Blanc put the question of the telluric origin of the oxygen groups of 

 the sol.ar spectrum upon a new footing much more precise and lead to the answer 

 indicated. 



