Theory of Metallic Conduction. 293 



value of this same component after collision is 



r*2ir f*a 



\ \ [£(1-2 cos 2 O )+ vA 2 -f sin 20 o cos ^pdpdylr 



~£! JO JO 



Jo )j d P d + 



%V~a 2 j C0 ** e *P d p)> 



and similar results hold for the other components, the factor 

 being the same in each case. 



We may therefore conclude that the coefficient of per- 

 sistence of the velocities of the electrons after the collisions 

 is quite generally 



4 C a 

 6=1 r, I cos 2 6 pdp *. 



a Jo 

 We have therefore 



1- 



4 C a 

 — - a \ cos 3 o p dp. 



CI ! A 



In this case, however, the mean time between two colli- 

 sions is 



U 1 



so that 



1-6 



hrnu I cos 2 p dp, 



and the general formula is to be used with this expression. 

 We may, however, before adopting it proceed to the limiting 

 case, where a is infinite, so that the most general equation is 

 to be used with 



1-6 f°° 



= 47rm/ 1 cos 2 6 pdp. 



Tm Jo 



It is for many reasons more convenient to interpret this 

 result in terms of the constant a, introduced above instead of 



* Or at least the statistical effect of the collisions may be so inter- 

 preted. The average value of the velocity component after collision is 

 just as if the number in each partial group were reduced by this factor. 

 The argument here is purposely stated indefinitely, as it is probably of 

 an extremely tentative character. 



