96 



potentials between the excitation- and tlie ionization-potential and for 

 the low pressures used here. Things are different above approx.16 volts, 

 the ionization potential of ai-gon. This already' can be observed at 

 the curves for argon at higher pressures in tig. 5, by a bend in 

 the curves at Hi volts; consequently the ratio of corresponding 

 pressures is no more accurately constant there, as is to be seen in 

 fig. 6 at the curves for 18 volt. At the same time this curve shows, 



0,6 



fli4 



Ol? 



0,08 ■% 



OiOZ 0i04 



HOêTm 



0,6 



0.4 



Oi 



0p2 



OjB( 



0.06 ""/m 



Fig. 6. 



that for the lower pressures the number of ionising impacts is so 

 small as to play no part, so that there is no objection against 

 deducing the ratio of the mean free paths from the ratio of the 

 slopes of the first straight parts of the curves. 



As a result of the measurement, the values for the ratio of the 

 mean free paths of electrons in neon and argon obtained in this 

 way aie shown in fig. 7 as a function of the potential corresponding 

 to the velocity of the electrons; in fig. 8 they are plotted as a 

 function of the root of this potential, being proportional with the 



