of Ionization by Collision. 



971 



different forces and pressures have been determined. Hence 



the values of /jl may be represented by a curve in terms of 



y 



jr, when a is small. The curve is shown in fig. 4. 



The connexion between /j, and the quantity p, which is 

 determined experimentally, may easily be found. Let n be 

 the number of ions set free by the photo-electric effect, w l9 

 n 2 , and n 3 the numbers of negative ions generated by collisions 

 in the spaces S 1} S 2 , and S 3 respectively. 



Then 



A*= 



ft 



n x -\-n 2 + n 3 qi + q 2 + qz' 



?0 + ? 2 



also 



n Y + n 2 + n 3 -f n Q = ?i e 2 \ 



Hence ^_(P + 1X/^1) 



/*0> + l)-l ' 



(4) 



Fk. 5. 



•1 



•s 



*r 

 •* 



Taking the case in which e 2a =l approximately, so that 

 is independent of a. and is given bv the curve in lip-. 5 in 



fi is independent of a, and 



s given by the curve in fig. 5 i 



