THE SUN'S SPOTS. 391 



margin than in the centre. The last named of these distinguished 

 physicists and astronomers expresses himself as follows, in 



inegale (montagneuse) de notre satellite, des inclinaisons, de 

 plans convenables pour produire la polarisation par reflexion." 

 " The phenomena of chromatic polarisation afford evidence 

 that the margin of the Sun has the same intensity of light as 

 the centre ; for by placing in the polariscope a segment of the 

 margin upon a central segment, I obtain a pure white as the 

 complementary effect of red and blue. In a solid body (as 

 in an iron ball heated red-hot,) the same visual angle 

 embraces a larger extent of the margin than of the 

 centre, according to the ratio of the cosine of the angle: 

 but in the same ratio, the greater number of the material 

 points emit a feebler light, in consequence of their obliquity. 

 The ratio of the angles is naturally the same for a gaseous 

 sphere; but since the obliquity does not produce the 

 same amount of diminution in gases as in solid bodies, the 

 margin of the gaseous sphere would be more luminous than 

 its centre. That which we term the luminous disc of the Sun 

 is the gaseous photosphere, as I have proved by the entire 

 absence of every trace of polarization on the margin of the 

 disc. To explain the equality of intensity indicated by the 

 polariscope for the margin and the centre, we must admit the 

 existence of an outer envelope, which diminishes (extin- 

 guishes) less of the light which comes from the centre than 

 from the marginal rays having a longer way to traverse before 

 they reach the eye. This outer envelope forms the whitish 

 corona of light observed in total eclipses of the Sun. The 

 light which emanates from solid and liquid incandescent 

 bodies, is partially polarized when the rays observed form an 

 angle of a few degrees with the surface from whence they 

 emerge ; but there is no sensible evidence of polarization 

 when incandescent gases are seen in the polariscope. This 

 experiment proves, therefore, that solar light does not emanate 

 from a solid mass or an incandescent liquid. Light is not 

 engendered solely on the surface of bodies ; but a portion 

 originates within the substance itself, even when the experi- 

 ment is made with platinum. Light, therefore, is not pro- 

 duced by the decomposition of the ambient oxygen. The 



