XXII.j 



LAYERS. 



305 



I have referred to this point before, p. 164, but recur to it here 

 for greater clearness. 



FIG. 102. Lines produced by layers are of different lengths. 



Take three concentric envelopes of the sun's atmosphere, A, 

 B,C (fig. 102), so that C extends to the base of A, and B also to 



Sun's Spectrum 



FIG. 103. But lines of different length do not necessarily indicate that the sub- 

 stances producing the longer of them extend down to the photosphere. 



the base of A, that is, in both cases to the photosphere. Then, 

 whether we deal with the sphere or with a section of it, the 



x 



