THE SUN'S SPOTS. 387 



stitution of the central body of our planetary system. "A 

 ray of light which reaches our eyes, after traversing many 

 millions of miles, from the remotest regions of heaven, 

 announces, as it were of itself, in the polar iscope, whether 

 it is reflected or refracted, whether it emanates from a 

 solid or fluid or gaseous body ; it announces even the degree 

 of its intensity. (Cosmos, vol. i. p. 33, and vol. ii. p. 715.) 

 It is essential to distinguish between natural light, as it 

 emanates directly from the Sun, the fixed stars, or flames 

 of gas, and is polarized by reflection from a glass-plate at 

 an angle of 35 25'; and that polarized light, which is 

 radiated as such from certain substances (as ignited bodies, 

 whether of a solid or liquid nature). The polarized light 

 which emanates from the above-named class of bodies, very 

 probably proceeds from their interior. As the light thus 

 emanates from a denser body into the surrounding attenuated 

 atmospheric strata, it is refracted on the surface ; and in this 

 process a part of the refracted ray is reflected back to the 

 interior, and is converted by reflection into polarized light, 

 whilst the other portion exhibits the properties of light 

 polarized by refraction. The chromatic polariscope distin- 

 guishes the two by the opposite position of the coloured 

 complementary images. Arago has shewn, by careful 

 experiments extending beyond the year 1820, that an 

 ignited solid body (for instance, a red-hot iron ball), or a 

 luminous, fused metal, yield only ordinary light, in rays 

 issuing in a perpendicular direction, whilst the rays which 

 reach our eyes from the margins, under very small angles, 

 are polarized. When this optical instrument, by which the 

 two kinds of light could be distinguished, was applied to gas 

 flames, there was no indication of polarization, however 

 small were the angles at which the rays emanated. If even 

 the light be generated in the interior of gaseous bodies, the 

 length of way does not appear to lessen the number and 



VOL. IV. H 



