306 THE CHEMISTRY OF THE SUN. [CHAP. 



lengths of the lines in the spectrum of the strata C, B, A, will 

 give the heights to which the strata extend from the sun, and 

 show where B and A respectively thin out. As the material is 

 by hypothesis continuous down to the sun, the lines will be 

 continuous down to the spectrum of the sun seen below as 

 shown. 



Now take three concentric envelopes, A, B, C (fig. 103), so 

 that only A rests on the photosphere, B rests on A, and C on 

 B. The phenomena will in the main be the same as in the 

 former case, i.e., the line C .will still appear to rest on the 

 spectrum -of the photosphere, for it will be fed, so to speak, 

 from C' and C", though absent along the line CBA at B and 

 A. So also with B. 



Thus much having been premised with regard to the obser- 

 vations as conditioned by the fact that we are observing a 

 sphere, we can now proceed to note how the two hypotheses 

 deal with the facts. 



Old Hypothesis. New Hypothesis. 



1. The spectrum of each element as The spectra should not resemble each 

 seen in our laboratories should be other. 



exactly represented in the solar spec- 

 trum. 



FACT. There is a very wide difference between the spectra. 

 See ante, pp. 174 and 230. 



2. The spectrum of the base of the The spectrum of the liase should 

 solar atmosphere should most resemble least resemble the Fraunhofer spectrum, 

 the ordinary Fraunhofer spectrum. because at the base we only get those 



molecules which can resist the highest 

 temperatures. 



FACT. When we leave out of consideration the lines of 

 hydrogen, calcium, and magnesium, those seen at the base, 

 as a rule, are either faint Fraunhofer lines, or are entirely 

 absent from the ordinary spectrum of the sun. See p. 182. 



