Two Tons produced in Gases by Rdntgen Radiation. 135 



produced between the parts at the boundary and those more 

 distant, which causes a diffusion of both kinds of ions towards 

 the place of lesser concentration (equations for this kind of 

 diffusion are given by Townsend, Phil. Mag., June 1898); and 

 this is more rapid for the negative ions than for the positive. 

 A larger number of negative ions thus impinges upon the metal 

 and this becomes negatively charged, while the air is left 

 positive due to the excess of ions of that sign. 



The effects obtained experimentally under ordinary con- 

 ditions are appreciable though small, and to increase them 

 it must be remembered that the accumulation of each of the 

 charges tends to counteract further separation, and that 

 since the effects are due to action at a boundary, an 

 increase in the surface of the metal will increase the amounts 

 obtained. 



The arrangement of the apparatus used is shown in fig. 6. 



Fig-. 6. 



To E/ectntmeter 



F 



WSM/S/M/SJMM//;/M»//W , /WVJ t JTp )V//MMJ//*/UI//J T IM/UH/IJU/////U//r/r//jr T7 . 



u 





LL is an aluminium tube 45 centim. in length and I centim. 

 in diameter. At one end, insulated by E, is the aluminium 

 cylinder D, which has in its centre a plug of glass-wool S, 

 and is connected to a pair of quadrants of an electrometer. 

 A gas-bag is connected, by means of the tube T, to the 

 aluminium cylinder A, which is filled with glass-wool to 

 prevent dust and all stray electrification from entering the 

 apparatus. C is a spiral made out of a 9 centim. wide sheet 

 of thin aluminium which is wound so that the separate spirals 

 are 1 millim. to 2 millim. apart. The tube D and the wires 

 leading to the electrometer are metallically shielded, and 

 everything except D is connected to earth. 



The rays from the source pass through the aluminium 

 window H of the lead box II, then through the tube LL at 

 B, and are finally all stopped by the lead piece F, which covers 

 closely that part of the apparatus. 



If now a current of air is blown from the bag through the 

 apparatus when the rays are not acting, or if the rays are 

 turned on when there is no air-current, the electrometer 

 connected to D receives no charge. 



