488 Ionization in the Solar Chromosphere. 



Summary. 



1. In the present paper it has been shown from a dis- 

 cussion of the high-level chromospheric spectrum that this 

 region is chiefly composed of ionized atoms of Calcium, 

 Barium, Strontium, Scandium, Titanium, and Iron. In the 

 lower layers both ionized and neutral atoms occur. 



2. An attempt has been made to account tor these facts 

 from the standpoint of JSTernst's theorem of the " Reaction- 

 isobar," by assuming that the ionization is a sort of reversible 

 chemical process taking place according to the equation 

 Ca~T~^Oa + + e — IT. The energy of ionization U can be 

 calculated from the ionization-potential of elements as 

 determined by Franck and Hertz, and MacLennan. For 

 determining Nernst's chemical constant and the specific 

 heat, the electron has been assumed to be a monatomic gas 



having the atomic weight of j^g- 



3. The equation shows the great influence of pressure on 

 the relative degree of ionization attained. The almost com- 

 plete ionization of Ca, Sr, and Ba atoms in the high-level 

 chromosphere is due to the low pressure in these regions. 

 The calculated values are in very good accord with observa- 

 tional data and the laboratory experiments of King. 



4. Hydrogen has been shown to be completely dissociated 

 into atoms at all [joints in the solar atmosphere. 



5. It has also been shown that the greater the ionization 

 potential of an element, the more difficult ionization will be 

 for that element under a given thermal stimulus. Calculations 

 have been made in the case of hydrogen (V = 13'6 volts) and 

 helium (V = 20'5 volts), which show that these elements 

 cannot get ionized anywhere in the Sun to an appreciable 

 extent. Helium can have appreciable ionization only in 

 stars having the highest temperature (> 16,000° K.), which 

 only are therefore capable of showing the Rydberg line 4686 



and the Pickering lines i> = N ^ — ; — p^ . 



|_2 2 (m+ij^J 



In conclusion, I beg to record my best thanks to my 

 students for their valuable help in the calculations, and to 

 my friend Dr. J. C. Ghosh for revising the proofs. 



Calcutta, India, 



March 4, 1920. 



