1896.] Electricity thro Dielectrics traversed by Rontgen Rays. 131 



following may serve as specimens of such experiments ; the method 

 used was B, and the gas in the tube was air. 



These numbers show that the rate of leak and the current 

 through the gas is almost independent of the electromotive 

 force. If we regard the conduction as electrolytic the gas 

 being ionised by the Rontgen rays, the fact that the current 

 is independent of the electromotive force indicates that the 

 velocity of the ions is independent of this force. This result is 

 consistent with the law connecting the conductivity with pressure 

 for we saw that this implied that the conductivity was propor- 

 tional to the number of ions but independent of their mean free 

 path. Now if the conductivity depended upon the velocity ac- 

 quired by the ions under the action of the electromotive force 

 it would depend upon the coefficient of viscosity between the ions 

 and the molecules, and hence upon their mean free path. The 

 current increases with the potential difference when this is small, 

 but soon attains a maximum value. This effect would result if 

 the passage of the Rontgen rays through the gas produced chains 



