NATURAL PHILOSOPHY. 137 



whiteness in the glass ? then they are necessarily gaseous. The incan- 

 descent bodies which have been studied by a polariscope, the light 

 being emitted under angles, are the following : of solids, forged iron 

 and platinum ; of liquids, fused iron and glass. From these experi- 

 ments it may be said, you have a right to affirm, that the sun is neither 

 fused iron nor glass ; but what authority have you further to general- 

 ize ? My response is this ; following the two explanations that have 

 been given of the abnormal polarization which presents rays emitted 

 under acute angles, all ought to be the same, with the exception of the 

 quantity, whatever be the liquid, provided that the surface of emer- 

 gence lias a sensible reflecting power. There would remain only the 

 case, in which the incandescent body would, as to its density, be anal- 

 ogous to a gas ; as for example, the liquid of an almost ideal rarity, 

 which many geometricians have been led to place hypothetical!}*, at 

 the extreme limit of our atmosphere, where the phenomena of polar- 

 Nation and colorization may perhaps disappear. I shall however, 

 Anticipate a difficulty which may suggest itself. It ought to be observed, 

 that the lights proceeding from two liquid substances, may, according 

 to the special nature of these substances, not be identical in reference 

 to the number and position of the black bands of Frauenhofer, and 

 which these prismatic hues offer to the eye of the philosopher. These 

 discrepances are of a nature to be considerably augmented by the 

 differently constituted atmospheres through which the rays have to 

 travel before reaching the observer. 



Observations made any day of the year, looking directly at the sun, 

 with the aid of powerfully polarizing telescopes, exhibit no trace of 

 colorization. The inflamed substances then, which defines the circumfer- 

 ence of the sun, is gaseous. We can generalize this conclusion, since, 

 through the agency of rotation, the different points of the surface of the 

 sun come in succession to form the circumference. This experiment 

 removes out of the domain of simple hypothesis the theory we have 

 previously indicated concerning the constitution of the solar photo- 

 sphere. These results, let it be loudly proclaimed, are entirely due 

 to the united efforts of the observers of the 17th and 18th centuries, 

 and also in a certain measure to those of our cotemporary astrono- 

 mers. And, here, let me make a remark, which, when endeavoring 

 to determine the physical constitution of the stars, we shall have occa- 

 sion to apply. If the material of the solar photosphere were liquid, 

 if the rays emitted from its margin were polarized, the two images 

 furnished by the polarizing telescope would not only be colored, but 

 they would be different in different parts of the circumference. Is 

 the highest point of one of these images red, the point diametrically 

 opposite will be red also. But the two extremities of the horizontal 

 diameter will each exhibit a green tint, and so on. If, then, one suc- 

 ceeds in concentrating to a single point, the rays emitted from all parts 

 of the sun's limb, even after their decomposition in the polarizing tel- 

 escope, the mixture will be white. 



The constitution of the sun, as I have just established it, may equally 

 well serve to explain how, on the surface of the orb, there exist some 



