MOTION OF GASEOUS IONS IN STRONG ELECTRIC FIELDS 22 1 



The justification for the method rests therefore on an empirical basis at 

 this point. 



Assuming isotropic scattering, as in the "Monte Carlo" calculation 

 we express our results in terms of the dimensionless variable w defined 

 in (75). The equation system (51) becomes then 



(2. - i)(i - (isAxms, v) = 



(78) 

 = v{v + s-\- l)(s -l,v-l)-\-{p+ l){v - s){s - 1, 1/ + 1) 



where the abbreviation (s, p) has been introduced for (ly'P, (cos t>)) 

 and the quantities (/«.f(x)) are simple numbers computable from (48b) 

 and the assumption of isotropic scattering. The first truncated relation 

 is s = J/ = 1. It yields 



(1, 1> = 2 

 Reducing it with the relation (78) for which s = 2, j/ = we get 



(2, 0) = 8 (79) 



The next truncated relation is s = v = 2^ which yields 



and the reduction gives 



Similarly in the next stage 



(80) 



(81) 



As an example of an average which cannot be had explicitly we may 

 take the mean absolute value of the speed, that is (1, 0). We find this 



