produced in Gases by Rontgen Rays Sfc. 425 



reading was steady at 0*5 of the initial reading. The electro- 

 meter was then discharged by metallic connexion and again 

 charged positively. Its reading remained steady after three 

 minntes at 0*63 of the initial charge. In the third and fourth 

 experiments the readings after three minutes were '81 and 

 •90 of the initial charges respectively. 



The ball was next charged negatively. When the rays 

 were played on it a steady reading was obtained after four 

 minutes at *18 of the initial charge. In the second, third, 

 and fourth experiments the steady readings after four 

 minutes were *45, "70, and *78 of the initial charges re- 

 spectively. 



The paraffin was then removed and the brass ball polished 

 with emery-paper; whether the charge was positive or 

 negative it fell in about five seconds to one definite position, 

 •437 of a volt, on the positive side of the metallic zero, when 

 the rays were played on the charged ball. 



These experimental results demonstrate that, for the low 

 potentials — usually 2 or 3 volts — we here used, the Rontgen 

 rays did not produce conductance between the brass bail, 

 when it was coated with paraffin, and the surrounding metal 

 box. We have already seen in § 2 that air is rendered 

 temporarily conductive by the rays, and Rontgen 's com- 

 parison of the effect of the rays with that of a flame show r s 

 that our experimental results are explained by the augmenta- 

 tion of the electrostatic capacity (quasi - condenser) of the 

 brass ball by the outside surface of its coat of paraffin being- 

 put into conductive communication w r ith the surrounding 

 lead box and the connected metals. 



In our second series of experiments we endeavoured to 

 eliminate the influence of the varying capacity of the quasi- 

 condenser. For this purpose we placed a strip of metal 

 connected to the insulated terminal of the electrometer inside 

 an aluminium cylinder ; the space between the metal and the 

 cylinder was first filled with air, afterwards with paraffin. 

 The aluminium cylinder was connected to the case of the 

 electrometer, and inductive disturbances were avoided by sur- 

 rounding the copper wire connected to the insulated terminal 

 with a lead sheath in metallic connexion with the electrometer 

 case. 



In our first experiments with this apparatus we had air, 

 instead of the main mass of paraffin, separating the insulated 

 metal from the surrounding aluminium cylinder, as shown in 

 fig. 6, and we had only small disks of paraffin serving as 

 insulating supports for the ends of the metal, and not played 

 on by the Rontgen rays. When the metal thus supported 



