the Electrical Conduction produced by it. 113 



field the positive ions travel towards the negative plate and 

 the negative ions towards the other plate, and consequently 

 a current will pass through the gas. Some of the ions 

 will also recombine, the rate of recombination toeing pro- 

 portional to the square of the number present. The current 

 passing through the gas for a given intensity of radiation will 

 depend on the difference of potential between the plates, but 

 when the potential-difference is greater than a certain value 

 the current will reach a maximum. When this is the case 

 all the ions are removed by the electric field before they 

 can recombine. 



The positive and negative ions will be partially separated 

 by the electric field, and an excess of ions of one sign may be 

 blown away, so that a charged gas will be obtained. If the ions 

 are not uniformly distributed between the plates, the potential 

 gradient will be disturbed by the movement of the ions. 



If energy is absorbed in producing ions, we should expect 

 the absorption to be proportional to the number of ions pro- 

 duced and thus depend on the pressure. If this theory be 

 applied to uranium radiation we should expect to obtain the 

 following results : — 



(1) Charged carriers produced through the volume of the 



(2) Ionization proportional to the intensity of the radiation 



and the pressure. 



(3) Absorption of radiation proportional to pressure. 



(4) Existence of saturation current. 



{>)) Rate of recombination of the ions proportional to the 

 square of the number present. 



(6) Partial separation of positive and negative ions. 



(7) Disturbance of potential gradient under certain con- 



ditions between two plates exposed to the radiation. 



The experiments now to be described sufficiently indicate 

 that the theory does form a satisfactory explanation of the 

 electrical conductivity produced by uranium radiation. 



In all experiments to follow, the results are independent of 

 the sign of the charged plate, unless the contrary is expressly 

 stated. 



§ 4. Complex Nature of Uranium Radiation. 



Before entering on the general phenomena of the conduction 

 produced by uranium radiation, an account will be given of some 

 experiments to decide whether the same radiation is emitted 

 by uranium and its compounds and whether the radiation is 



Phil. Mag. S. 5. Vol. 47. No. 284. Jan. 1899. I 



