﻿1134 Prof. M. N. Saha on Temperature Ionization of 

 The diminution in entropy 



S =&W= — Kln(n a n b ), 

 so that instead of equation (A) we shall have 



ba + tafc — b a 5 — ^0= Jy ; 



hence the equation of ionization takes the form, assuming 

 that only one species of atom is present, 



x 2 U 5 



lo &' i~2 P =" ~ ^M + 2 l0g T ~ 6>5 + l0g (jlan ^' 



The effective ionization potential I ~'now becomes 



U-2*3RTlog(w«n 5 ) 



For the electron and the alkalies we can take n b = l. For 

 alkaline earths, if we follow Boltzmann, n a = 2, but this 

 evidently does not suffice in the present case. It may be 

 pointed out that the present case is entirely different from 

 that considered by Boltzmann, for we are considering the 

 combination between an ionized atom and an electron, 

 whereas Boltzmann considered the combination of two atoms. 

 There is no reason why the steric factor should have the same 

 value in both cases. 



IV. 



On the basis of the above formula, let us consider the 

 effective LP. of helium and the alkaline earths at different 

 temperatures. Taking w = 2, 4, 6, 8 respectively, we have for 



n = 2, i e = I — -060m,") 



= 4, I e =I — '119 m, ! the temperature being 



= 6, I e = I — "158m, f ??i-thousands. 



= 8, I, = I--180mJ 



Russell is inclined to take the temperature of the spot = 

 4000° K. and that of photospheric emission = 6000° K. If 

 this view be correct, the temperature of the spot is only 

 slightly above that of the arc. But we find that in the arc 

 the Ba line X = 5535 is quite strong, while it is entirely 

 absent from the spot. The discrepancy can, of course, be 

 explained by assuming that the temperature of the arc is not 

 uniform; the absorption of \=5535 is due to the cooler 

 mantle of gaseous barium next to the air. But more ex- 

 tended research is required to test this point. 



