MOTION OF GASEOUS IONS IN STRONG ELECTRIC FIELDS 251 



in second order, using (156), (157) and (158) 



p(2) ^ -10.542 



g(2) _ +14.993 5^2) _ Q 



/^^ = -4.408 

 in third order, using (156), (157), (158) and (159) 



p(3) = -0.8710 



q^'^ = +1.1754 



r^'^ = +1.0140 



s^'^ = -0.5809 



The longitudinal diffusion coefficient results from these numbers by the 

 use of (23), (24) and (160). With the notation (155) the formula becomes 



£>,, = -a^^V^{l, 1} (161) 



The formula (154) yielding {1, 1) from go(w) is s = 2, v = 



{1,1} = m, 0) + 4(3, 1) - i(l, 1)(2, 0) (162a) 



or numerically from the Table II 



{1, 1) = i{3, 0) + 0.6433 (162b) 



The result is 



{1, 1}^'^ = -0.3695 (163a) 



{1, 1)^'^ = -0.2075 (163b) 



{1, 1)^'^ = -0.2198 (163c) 



The numbers do not extrapolate too reliably but one would guess that 



{1, 1) = -0.22 



is essentially correct. Hence we have 



i),l = 0.22a" V (164) 



In order to gain an appreciation of the value obtained it is worthwhile 

 to compare it with the value that would have been predicted from the 

 generalized Nernst-Townsend relation (148). The mobility concept is 

 ambiguous for all but the cases discussed then. It would seem that the 

 appropriate concept here is the differential mobility because comparison 



