Ions and Electrons through Gases. 45 



cannot be regarded as a maximum, as a greater degree of 

 purification would probably result in still higher values. 



Fig. 6. 



There is some evidence of an indirect character that the 

 electron does not move with a velocity which is strictly pro- 

 portional to the applied field, but traverses with an accelerated 

 motion distances comparable with the distance between the 

 electrodes. The close approach for small potentials of the E 

 curves in fig. 6, which refer to C0 2 at the same pressure 

 (137 mm.) but with different alternation frequencies, sug- 

 gests very large values for the velocities of the electrons; 

 this is more readily understood if we apply the formula 



i' = i (/— prv J, where i' is the current for potential V when the 



alternating field is employed and i is the current for potential 

 Y directly applied. If we take the velocity calculated fromV 

 at the higher frequency, viz. £ = 1336 at 137 mm., the above 

 formula (with d = 2) gives tY/V — 4'1 for V = 5'78 volts, 

 where the suffixes 1 and 2 refer to the low and high 

 frequency respectively; the value obtained from the experi- 

 mental curves is only 1/3. Similarly for V=6*96 volts we 

 obtain a calculated ratio of 2*6, whereas that obtained 

 experimentally is 1*2. These considerations would seem to 

 imply that the value £ = 1336 is too small, and that the 

 critical potential is really smaller than the value (V = 4* 5) 

 apparently obtained. 



In this connexion it is a significant fact that several of the 



