iii the Solar Chromosphere. 



481 



2.10- 2.10" 



1 



3 



55 



17 



19 



52 



43 



83 



57 



91 



70 



94 



So 







93 





48 

 88 

 98 



7.10 

 5 



68 

 98 



-l 



Table VI. 

 Ionization of Barium (in per cents.). 

 U = 1'2 . 10 5 calories approximately. 



Pressure... 10. 1. 10 _1 . 10~ 2 . 10~ 3 . 10" 4 . 10~ 6 . 



Temp. 



2000° 



2500 



3000 



4000 



5000 17 



6000 62 



7000 15 



7500 22 



8000 30 



9000 47 



10000 65 



11000 97 



12000 99 



in 



6 . 10" 3 

 1-8. 10" 1 



1-6 



28 

 86 

 99 



Complete 

 Ionization. 



6 

 46 

 99 



We are not aware how the temperature and the pressure 

 (partial pressure for a particular element) vary with 

 height in the solar atmosphere. According to F. Biscoe *, 

 the temperature of the photosphere is about 7500° K., while 

 the pressure in the reversing layer varies, according to 

 different investigators, from 10 to 1 atmospheres. If we 

 suppose that the variation in temperature is entirely caused 

 by radiation, the temperature of the upper layers should 



tend to the limit -^- t? or a little more than 6000° K. 



2 T 



The partial pressure may be supposed to vary from 10 atmo- 

 spheres in the reversing layer to 10~ 12 atmosphere in the 

 outermost layers. 



An examination of Tables IV., V., VI. shows that, under 

 the above-mentioned assumptions, about 34 per cent, of the 

 Oa-atoms are ionized on the photosphere. When the pres- 

 sure falls to 10 ~ 4 atmosphere, almost all the atoms get 

 ionized, so that up to this point in the solar atmosphere, we 

 shall get combined emission of the H, K, and the '/-line, 

 but above this point, we shall have only the H, K lines. 

 This is in very good agreement with observed facts. 



* F. Biscoe, 'The Astrophysical Journal,' vol. xlvi. p. 355. 

 f Schwaraschild, Gott. Xachrichten, p. 41 (1906). 



