Eclipses 



total eclipses. What chiefly attracts our atten- 

 tion are the radiating plumes of the halo ; these 

 plumes give in the spectroscope a continuous 

 spectrum, which appears to have a double 

 origin. In the regions most remote from the 

 sun this spectrum appears identical with the 

 spectrum of the photosphere, showing, like it, 

 black lines on a continuously coloured ground, 

 shading from red to violet ; but, as the chromo- 

 sphere is approached, the spectrum of the halo 

 becomes brighter, while the black lines become 

 narrow. This fact suggests that the halo con- 

 sists of solid dust, which sends light to us in 

 two distinct ways; first, it diffuses into space 

 in all directions the radiations received from 

 the photosphere and thus produces the dark 

 line spectrum, and, secondly, it emits light 

 directly, as in the case of incandescent solid 

 bodies, that is to say, in the form of a continuous 

 spectrum free from lines. The predominance, 

 according to the region observed, of emitted 

 light or of diffused light explains the effects 

 actually observed. 



What causes these solid incandescent dusts 

 to remain at such great distances from the sun? 



215 



