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



the two of which we have just spoken ; for these clouds can- 

 not be sustained in vacuo. '^ 



Every one now knows the uncertainty which still remains 

 upon one point, truly remarkable, concerning the physical 

 constitution of the sun. When we think that the phenomena 

 which might decide all doubts are habitually invisible, that 

 they can only be seen during total eclipses of the sun, which 

 total eclipses are of rare occurrence, so much so, that since 

 the invention of telescopes the astronomers of Europe and 

 America have scarcely had an opportunity satisfactorily to 

 observe six ; no one will be astonished that in the middle of 

 the nineteenth century the question raised by the mysterious 

 red flames upon which so much has been said, still remains 

 to be investigated. 



After these explanations, the length of which I must beg 

 you to excuse, we shall indicate, in a few w^ords, by what series 

 of measurements and deductions, science has succeeded in 

 fixing the true place of the sun in the totality of the universe. 



Archelaus, who lived in the year 448 B.C., was the last 

 philosopher of the Ionian sect ; he said, regarding the sun, — 



* That these clouds may be sustained in vacuo, it is necessary that the cen- 

 trifugal force resulting from their circular movement shall incessantly equal 

 the gravitation w^hich would cause them to fall towards the sun. One would 

 need to transform them into real planets, revolving with extreme rapidity 

 around the sun. Such, in substance, is the explanation of the prominences of 

 1842, which M. Babinet has given at the meeting of the Academy of Sciences 

 on the 16th of February 1846. > [W^p,^ bfnori- 



The reader will perceive, in the memoir of the learned Academician, the in- 

 genious considerations upon which this theory is based, and how analogous it 

 is to the cosmogonic system of Laplace. I think, now that the phenomenon 

 has been minutely observed, that M. Babinet will find more than one difficulty 

 in reconciling the immense velocity which he is compelled to attribute to the 

 matter of the prominences, with the relative immobility of those which have 

 been observed in 1851, and the change of height which they have presented. 

 These difficulties will no longer exist when the spots are assimilated to clouds 

 floating in a solar atmosphere, endowed with a slight rotatory movement. 



I would, moreover, remark, that the existence of this third atmosphere is 

 established by phenomena quite of another nature, namely, by the comparative 

 intensity of the border and the centre of the sun, and also in some respects by 

 zodiacal light, so perceptible in our climate during the equinoxes. But the 

 question, considered from this point of view, requiteu details from which I am 

 forced to abstain. u .: i .JlJ^J ' ii^.:.iu ; ...i : ^ 



