lONIZATION BY NEGATIVE IONS 13 



When the cylinder is negative new ions are produced 

 as the force increases, so that when the potential differ- 

 ence between the wire and cylinder is 360 volts the 

 current is ten times as great as that which is due to 

 the ions that are produced by the direct action of the 

 rays. 



When the cylinder is positive there is no appreciable 

 change in the current until the potential of the cylinder 

 is more than 300 volts above the wire, and with 360 volts 

 the current increases only by one-fifth of its initial value. 



These results show that in the previous experiments 

 with parallel plate electrodes the increase of conductivity 

 must have been due to negative ions. 



6. Negative ions generated by various methods have the 

 same ionizing power. 



Without considering the absolute values of a that 

 have been found, it is possible to deduce some interest- 

 ing conclusions as to the properties of negative ions. 

 Since a is independent of the distance between the 

 plates I, the new ions must generate others by collisions 

 to exactly the same extent as the original ions by which 

 they are themselves produced. From this it follows that 

 the negative ions generated by collisions in any gas must 

 in each case be the same as those produced by the 

 external agencies., 



Now when ultra-violet light is used, the ions set free 

 from the zinc plate are the same for different gases ; 

 hence the negative ions produced by collisions from the 

 molecules of different gases and vapours must be all 

 the same, being identical with those set free from the 

 negative electrode. The gases for which the values of 

 a have been determined by experiments in which the 



