44 ' INORGANIC EVOLUTION. [CHAP. IV. 



or gases extended above the sun could be obtained ; early observations, 

 in fact, showed the existence of glare between the observer and the 

 dark moon ; hence it must exist between us and the sun's surround- 

 ings. 



The prismatic camera gets rid of the effects of this glare, and its 

 .results indicate that the effective absorbing layer that namely, which 

 gives rise to the Fraunhofer lines is much more restricted in thickness 

 than was to be gathered from the early observations. 



We learn from the sun, then, that the absorption which defines its 

 ordinary spectrum is the absorption of a middle region, one shielded 

 both from the highest temperature of the lowest reaches of the atmo- 

 sphere where most tremendous changes are continually going on, and 

 from the external region where the temperature must be low, and 

 where the metallic vapours must condense. 



This is the first great teaching of the test-spectrum. The next 

 chapter will deal with the second. 



