304 THE CHEMISTRY OF THE SUN. [CHAP. 



(2.) The sun's atmosphere is not composed of strata which 

 thin out, all substances being represented at the bottom ; but of 

 true strata, like the skins of an onion, each different in compo- 

 sition from the one either above or below. Thus, taking the 

 sun in a state of quiescence and dealing only with a section, 

 we shall have (as shown in fig. 101) C, say, containing neither 

 D nor B, and B containing neither A nor C. 



FIG. 101. Layers in solar atmosphere. 



(3.) In the lower strata we have not elementary substances 

 of high atomic weight, lut those constituents of the elementary 

 bodies which can resist the greater heat of these regions. 



The conditions under which we observe the phenomena of 

 the sun's atmosphere have not, as a rule, been sufficiently borne 

 in mind, and it is quite possible that the notion of the strata 

 thinning out has, to a certain extent, been based more upon the 

 actual phenomena than upon reasoning upon the phenomena. 



