PORTION OF THE COSMOS. THE SUN. 285 



the small degree of density of gaseous strata, the longer 

 path traversed by the very oblique rays does not appear to 

 lessen their number and strength ; nor does the transition 

 to another medium on issuing forth at the surface appear 

 to produce polarisation by refraction. Now as the Sun's 

 light coming from its margin in a very oblique direction, 

 and at very small angles, also shews no trace of polarisation 

 when examined by the polariscope, it follows from this im- 

 portant comparison that the Sun's brightness does not pro- 

 ceed from its solid body nor from any liquid substance, but 

 from a gaseous self-luminous envelope. We have here a 

 highly important physical analysis of the photosphere. 



The polariscope has also led to the conclusion that the 

 Sun's light is not greater at the centre of the disk than at 

 the edges. If the two complementary coloured images of the 

 Sun, the red and the blue, are so placed over each other 

 that the margin of the one image coincides with the centre 

 of the other, a perfect white is produced. If the intensity 

 of light in the different parts of the solar disk were not the 

 same, if, for example, the centre of the sun were more 

 luminous than the limb, then in the partial superposition of 

 the images the conjoined segments of the blue and red 

 disks would appear not of a pure white but of a pale red, 

 because the blue rays would only be able to neutralize a 

 portion of the more abundant red rays. Remembering, 

 then, that in the gaseous photosphere of the Sun, quite in 

 opposition to what takes place in solid or liquid bodies, the 

 smallness of the angles at which the luminous rays come to 

 us from the edges of the Sun's disk does not lessen their 

 number, while the same visual angle comprehends a greater 



