97 



velocitj' of (lie electrons. The dotted line in lig. 8 shows for comp- 

 arison the valnes of this ratio as deduced from Ramsaukk's measure- 

 ments. It will be seen that our measurements verify not only the 

 fact of the variation of the mean free path of the electrons with 

 their velocity, as found by Ramsaukk, but also the general ciiaracier 

 of this variation. The maximum of the curves was found in the 

 present measurements at a potential about 2 volts less than in 

 Ramsauers. 



The action of the slowest electrons is theoretically of special interest. 

 As however the accuracy of such measurings decreases for ex- 

 tremely slow electrons an extrapolation in the direction of the 



Fig. 7. 



Fig. 8. 



velocity zero is always doubtful. If we stipulate, according to the 

 results of Ramsauer that the electrons in neon show nearly normal 

 values of the mean free path, it appears that, according to the here 

 obtained results, the mean free path of electrons in argon on 

 approaching zero-velocity, do not reach an infinite value, but one 

 about 3 times that calculated from the kinetic theory for very 

 rapidly moving particles of infinitesimal small dimensions. This figure 

 can however, by no means lay claim to accuracy. 



The number of collisions of an electron passing through a unit 

 length under the infiiience of an electric field E, in a gas, in which 



its mean free path is ^, is 



E 



— — , that is, inversely proportional 

 e ^^ 



m 



of the square of the mean free path. In argon the mean free path, just 

 below 12 volts, the excitation potenlial, i-eaches ils minimum of about 

 V, of the value derived from the kinetic theory. We can therefore 

 conclude that an electron of this velocity in ^irgon in passing 



