xiii.] COMPOSITE ATMOSPHERE. 167 



lines visible in the solar spectrum ; and on this ground the 

 name " reversing layer " was given to it. 



Still, undoubtedly some absorption was produced in the upper 

 region of the solar atmosphere, for with each eclipse, against 

 authority, against chemical arguments based upon the low 

 atomic weight of the substances in the chromosphere, the 

 corona grew and grew. In 1870 we had hydrogen 8' from the 

 sun, " far above .any possible atmosphere ;" l and in 1871 this was 

 carried higher still ; while towering above the hydrogen lines 

 was another line, the famous 1474, which indicated something 

 else existing in the exterior reaches of the atmosphere. 



What, then, was the totality of the knowledge which had been 

 acquired a few years ago with regard to the chemical nature of 

 the sun's atmosphere taken as a whole the sun's atmosphere 

 from the upper reaches of the coronal atmosphere down to the 

 region where, doubtless, the spot phenomena are located ? The 

 view of the sun's atmosphere, in 1873, was one something like 

 this : We had, let us say, first of all an enormous shell of 

 some gas, probably lighter than hydrogen, about which we 

 know absolutely nothing, because so far none of it has 

 been found here. Inside this we had a shell of hydrogen ; 

 inside this one of calcium, another of magnesium, another of 

 sodium, and then a complex shell which has been called the 

 reversing layer, in which we got all the metals of the iron 

 group plus such other metals as cadmium, titanium, barium, 

 and so on. 



The solar atmosphere then, from top to bottom, consisted, it 

 was imagined, of a series of shells, the shells being due not to 

 the outside substance existing only outside, but to the outside sub- 

 stance extending to the bottom of the sun's atmosphere, and 

 encountering in it, at a certain height, another shell which 

 again found another shell inside it, and so on; so that the 



1 Young. 



