40 Mr. E. M. Wellisch on the Motion of 



aj few examples of the latter type being given in fig. 4. 



The 



free electrons were more numerous in each of these gases 

 than in air at the corresponding pressure : this point is 

 brought out by the fact that with the same frequency of 

 commutation the electrons appeared at much higher pressures 

 than in air, e. g. it was just possible to detect electrons in air 

 at 8 cm. pressure, whereas in C0 2 they appeared in large 

 numbers at a pressure of 14 cm., and in H 2 they were readily 



Fig. 4. 



JOO 120 



observable at atmospheric pressure (v. curve A, fig. 4, w T hich 

 was obtained with a frequency of only 42 6; also curve in 

 fig. 5). This result was to be expected from the conclusions 

 of previous experimenters who had found that the abnormal 

 increase in the ionic mobility set in for these gases at higher 

 pressures than for air. It should be remembered that we 

 cannot form any definite inference as to the relative number 

 of electrons by comparing the ionization currents in the 

 E curves for different gases at the same pressure because these 

 currents are due to the electrons which have passed through 

 the meshes of the gauze electrode, and the fraction of electrons 

 which accomplish this depends upon the gas concerned. 



When the pressure of the 00 2 or H 2 was relatively high, 

 the free electrons appeared to be extremely sensitive to the 

 presence of impurities in the gas under consideration ; the 

 number of free electrons was greatly decreased if the gas 



