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



According to this view the orb would be regarded as a dark 

 body, surrounded at a certain distance by an atmosphere 

 which might be compared to that enveloping the earth when 

 composed of a continuous bed of opaque and reflecting 

 clouds. To this first atmosphere w^ould succeed a second, 

 luminous in itself, and which has been called photosphere. 

 This photosphere, more or less removed from the interior 

 cloudy atmosphere, would determine by its circumference the 

 visible limits of the orb. According to this hypothesis, spots 

 upon the sun would appear as often as there were found in 

 the two concentric atmospheres corresponding vacant por- 

 tions, which would permit us to see exposed the dark central 

 body. 



Those who have studied these phenomena with powerful 

 instruments, professional astronomers, and competent judges, 

 acknowledge that the hypothesis of which I have just spoken, 

 concerning the physical constitution of the sun, supplies a 

 very satisfactory account of the facts. Nevertheless, it is 

 not generally adopted ; recent authoritative works describe 

 the spots as scoriae floating on the liquid surface of the orb, 

 and issuing from solar volcanoes, of which terrestrial vol- 

 canoes are but a feeble type. 



It was desirable, then, to determine, by direct observation, 

 the nature of the incandescent matter of the sun. 



But when we consider that a distance of 95 millions of 

 miles separates us from this orb, and that the only means 

 of communication with its visible surface are luminous rays 

 emanating therefrom, even to propose this problem seems 

 an act of unjustifiable temerity. 



The recent progress in the science of optics has, however, 

 furnished the means for completely solving the problem. 

 My readers will pardon some necessary details which will 

 render its solution evident. 



None are now ignorant that natural philosophers have 

 succeeded in distinguishing two kinds of light, viz., natural 

 and polarized. A ray of the former of these lights exhibits, 

 on all points of its surface, the same properties ; whilst, with 

 regard to the polarized light, the properties exhibited on the 

 different sides of its rays are different. These discrepancies 



