the Motion oj Electrons in Gases. 



885 



have their volocities reversed. If s is very large the greater 

 proportion will pass by the molecule and their direction of 

 motion will be only slightly affected, and in this case the 

 average velocity after collision will have a component in 

 the original direction of motion. There is one value of s for 

 which the average component of the velocities of the elec- 

 trons after collision will be zero, and this is the value taken 

 in this investigation as <r, which may be called the radius of 

 the molecule for brevity. 



Fio-. 5. 



70 



60 



50 



40 



30 



20 



10 



































k 



















f 





/ 













/ 



/ 













/ / 



/ \ 











! 



// 



•7 

 / 



\ 







2 



P 





! 



10 



12 



Similarly if a large number of electrons move in the same 

 direction initially in a gas, the mean value of the components 

 of the velocities in any direction is zero after all the electron- 

 have collided with molecules, and the mean distance they 

 travel in the original direction of motion is the mean free 

 path I. 



12. With the above specification of the mean free path 



of 



an electron moving 



x eas under an electric force Z. 



