in the Solar Chromosphere. 48. r > 



we have Vi#r , o f n \ /n\ _ '^ 



ZvO / , = J((. 7 ;)h-^' / 0h,— ^-, 



H -^ _3.4() * c 1 H = -1*6, 2i/C = *2 3 



U = 8*2.10 4 calories. 



K— — - — ? P, where P = total pressure, and a fraction x 



has been dissociated. We have thus 



log J* - P == - f 2 ' 1( ^ + 1-5 log T + '2. 

 a l-r 4*571 T ° 



Table VIII. shows the dissociation of hydrogen under 

 different pressures and temperatures (in per cents.): — 



Table VIII. 

 Dissociation of the H 3 -molecule. 

 l. io- 1 . io- 2 . 10- 3 . 



Pressure.. 

 Temp. 

 2000° .... 

 2500 .... 

 3000 .... 

 3500 .... 

 400O .... 

 5000 .... 



1 



11 

 46 

 85 

 96-5 

 100 



3 



35 



85 



9 



75 

 98-5 



29 

 97 



io- 



70 



Complete Ionization. 



Tiie table shows that under the conditions prevailing in 

 the Sun the dissociation is complete. Even in the umbra 

 of sun-spots, assuming that the temperature is 4000° K. 

 and the pressure is of the order of 1 atmosphere, the 

 dissociation is almost complete (96'5 per cent.). 



Ionization of Hydrogen. 



For a rigorous treatment of the case, we shoald start with 

 the process (D). But since in the Sun the hydrogen is 

 entirely in the atomic state, we may use the process (C). 

 The results will be but approximate, for the equation which 

 follows does not hold over the whole range of temperature. 



The case is quite analogous to the ionization of calcium. 

 We have only to put U = 3'2x 10 5 calories (approximately) 



* Reiche, Ann. d. Physik, vol. lviii. p. 057, and Leon Schames, PIi)/s. 

 Zeits. vol. xxi. p. 41. 



