Two Tons produced in Gases by Pontgen Radiation. 147 



§11. Potential Gradient between tico Plates, 

 It lias been shown in §!> how the free electrification is 

 distributed between two plates between which conduction 

 is taking place through air, and it is evident that this electri- 

 fication must exert a marked influence upon the electric field 

 be t ween the plates. 



The variation of the potential between two such plates has 

 been investigated by means of the following apparatus. A 

 and IS in fig. 12 are the two parallel, 11 em. square plates 

 situated above and being perpendicular to the top of the lead 

 box which contains the induction-coil and the tube. 



Fiff. 12. 



To 



The rays coming out through an aluminium window pass 

 through the air between the plates, covering a volume indi- 

 cated by the dotted lines. 



The plates are connected to the two poles respectively of a 

 battery C, whose middle point is to earth. 



To determine the potential at different points between the 

 plates when the rays are acting, a fine wire M, of the same 

 metal as the plates, was used. It was stretched between two 

 insulated parts R and S of a glass frame N, as is shown 

 in the lower figure, and was connected to a pair of quadrants 

 of an electrometer by means of the wire K. For small 

 voltages the other pair of quadrants was connected to earth. 



L 2 



