Elements in the Sun. 



817 



Ionization of Magnesium. 



Ionization Potential = 7' 6 5 Volts = 1*76 x 10 5 calories. 



Pressure 

 Temp. 



4000 .. 



5000 ... 



6000 ... 



7000 ... 



7600 ... 



8000 ... 



9000 ... 



10000 ... 



11000 ... 



12000 ... 



13000 ... 



14000 ... 



15000 ... 



16000 ... 



10 



-1 



10" 



10" 



10" 





2.10-3 



1 



2 



9 



5. 10-- 



1 



4 



11 



32 



2 



6 



18 



50 



87 



6 



20 



54 



89 



98 



11 



32 



73 



96 







17 



47 



85 



98 





34 



75 



96 







56 



90 



98 



1 





75 

 86 



96 , 

 98 















93 



96 



98 



99 





Complete 

 Ionization 









99 











As the ionization potential of magnesium is rather high, it 

 is ionized to a lesser extent than the other alkaline earths. 

 Total ionization is readied at a pressure of about 10 -6 to 

 10" 7 atm. in the chromosphere. This is in excellent accord 

 with observational results. 



The lines of ionized magnesium have been studied by 

 Fowler. The lines which should theoretically * turn out 

 to be the strongest, all lie in the ultra-violet, as the following 

 table shows ■ — 



(l, 5 )-(2, i ; 1 ) 2795-5 A.U. 



-(2,jp 2 ) 2802-7 



(2 ?Pl )-(3,^i) 2798-1 



(8,p0-(3,4) 2790 



(Mi)-(4,/) ^81, 



so that the only line available for observation is the leading- 

 member of the Bergmanu series X — 4481 A.U. According 

 to observation, this reaches a level of 450 km. only. 



According to the considerations presented in paper C, 

 lines of this description under all circumstances require 

 not only a higher stimulus, but also a high density of the 



* Fowler, Phil. Trans, vol. ccxiv. The intensity given for 4481 is 

 relatively much greater than the intensity of the (1, s)— (2, p) lines. 



