250 Mr. E. Rutherford on the Electrification 



of air was about 10 ~ 4 electrostatic units. In the case of the 

 better conducting gases and vapours the volume-density is 

 greater. For the vapour of methyl iodide the volume- 

 density would be over 20 times as great. 



The facility with which the electrified gas is discharged by 

 metals and insulators may at first sight lead to the conclusion 

 that we are dealing with electrified dust, which, as is well 

 known, is completely discharged by glass wool, and also 

 readily gives up its charge to whatever it comes in contact 

 with. It has been shown, however, that the amount of 

 electrification is quite independent of the amount of dust in 

 the air, and that therefore the electrification can be in no way 

 due to electrified dust. 



The theory has been advanced that the discharge of elec- 

 tricity from the surface of a metal under the action of ultra- 

 violet light is due to the disintegration of metallic particles or 

 vapour from the surface, and that these carry off the charge. 

 The discharge of electrification by the Rontgen rays might pos- 

 sibly be due to a similar cause, and this was fully investigated. 

 In the first place, there are many experiments which negative 

 this view. It has been shown in a previous paper that the 

 current through a gas conducting under the x-tsljs increases 

 with the distance between the electrodes although the surface 

 exposed to the gas is unaltered. The amount of electrification 

 obtained from a gas was found to be quite independent of the 

 nature of the electrodes. The inside electrode (fig. 1) of the 

 cylinder was coated with paraffin or wax, and provided we 

 do not allow the charge to collect on the surface of the insu- 

 lator, the amount of electrification was unaltered. Similarly, 

 if the inside of the cylinder was coated with an insulator,, no 

 difference in amount could be detected immediately after the 

 rays were turned on ; but after the rays had been acting for 

 a short time the amount decreased, owing to the charging of 

 the surfaces of the insulators. These conclusions show that 

 the conductivity in a gas is independent of the nature of the 

 surface of the electrodes, for it is extremely improbable that 

 the same amount of dust would be dislodged by the rays from 

 the surface of all metals and insulators. 



The most conclusive experiments on this subject are some 

 which I recently made on the diminution of the intensity of 

 the Rontgen rays due to the absorption in their passage 

 through gases and vapours. 



Absorption of Energy uy Gases and Vapours. 



Since gases all conduct under the influence of the .r-ravs, 

 it was interesting to investigate the relative absorption in 



