82 THE CHEMISTRY OF THE SUN. [CHAP.VI. 



takes place at a considerable elevation in the atmosphere of 

 the sun. His notion was that the sun we see is what gives 

 us the continuous spectrum the light of which is absorbed; 

 that above that there is a haze differing in structure from it, 

 and yet not competent to give us the absorption lines ; that 

 practically none of the absorption phenomena arise from that 

 stratum, but that ths absorption phenomena really take place 

 above this very luminous region of haze. Such was KirchhofF s 

 view. 



KirchhofF s explanation of the solar spots was that they are 

 clouds in the atmosphere of the sun. He shows that local 

 diminutions of temperature there, as in our own atmosphere, 

 must give rise to the formation of clouds. 



" When a solar cloud is formed, all the portions of the atmo- 

 sphere lying above it will be cooled down, because a portion of the 

 rays of heat which are emitted from the incandescent surface of the 

 sun are cut oft' by the cloud." x 



The result of this would be that the upper portions of the 

 clouds would rapidly increase and become cooler. The tempera- 

 ture of the cloud then falling below the point of incandescence 

 it would become opaque and form the dark nucleus of a spot. 

 He further supposed that the interposition of this dark cloud 

 would so cool the regions above it that a second cloud would 

 be formed of less opacity than the first, because the density 

 of the vapour at that elevation w r ould be less. This second 

 cloud would appear as a semi-opaque penumbra, 



1 Researches on the Solar Spectrum and the Spectra of the Chemical Elements, 

 part i. p. 26. 



