392 COSMOS. 



reference to this question : 25 " Now, granting the existence 

 of such an atmosphere, its form, in obedience to the laws of 

 equilibrium, must be that of an oblate spheroid, the ellip- 

 ticities of whose strata differ from each other and from that of 

 the nucleus. Consequently, the equatorial portions of this enve- 

 lope must be of a thickness different from that of the polar, 

 density for density, so that a different obstacle must be thereby 

 opposed to the escape of heat from the equatorial and the 

 polar regions of the Sun." Arago is engaged at the present 

 moment in a series of experiments, by which he purposes to 

 test not only his own views, but also to reduce the results of 

 observation to accurate numerical relations. 



emission of polarized light from liquid iron is an effect of 

 refraction during its passage towards a medium of lesser 

 density. Wherever there is refraction, a small amount of 

 polarised light must be produced : gases do not emit polarized 

 light, because their strata do not possess the requisite amount 

 of density. When the Moon is followed through all its phases, 

 it will be found to afford evidences of polarization, excepting 

 at the full moon and the days immediately preceding and 

 following it. It is more especially during the first arid last 

 quarters that the unequal (mountainous) surface of our satel- 

 lite presents suitable inclinations for the polarization of solar 

 light by reflection." 



25 Sir John Herschel, Astron. Observ. made at the Cape 

 of Good Hope, 425, p. 434; Outlines of Astr. 395, 

 p. 234. Compare Fizeau and Foucault, in the Comptes Rendus 

 de I Acad. des Sciences, torn, xviii. 1844, p. 860. It is 

 remarkable enough that Giordano Bruno, wno was burnt 

 eight years before the invention of the telescope, and eleven 

 years before the discovery of the spots of the Sun, should 

 have believed in the rotation of the Sun upon its axis. Pie 

 considered, on the other hand, that the centre of the Sun was 

 less luminous than the edges. Owing to an optical deception, 

 he believed that he saw the disc turn round, and the whirl- 

 ing ec^ges expand and contract. (Jordano Bruno, par Christian 

 Bartholmess, torn. ii. 1847, p. 367.) 



