Tivo Ions produced in Gases by Rontgen Radiation. 149 



free charge there, but near the plates, where most of the 

 charge exists, the changes are very rapid. When the poten- 

 tial between the plates is increased, the fall at the plates also 

 increases. 



+ 2 



Volts 



Fig. 13. 



Absolute 2 



-2 







Units A 



/ r 



300 







/ J^ 1 1 









/ s ' 



300 



cm 



/fi\ 



<0 







i 





! X 



// 















300 









-2 









300 



Thus, by using 6 cells the fall was practically three times 

 that obtained above with the 2 cells. 



The conditions affecting the amount of free charges at the 

 plates are necessarily applicable to the changes of potential 

 resulting from them. These have already been given in §9, 

 where it will be seen what effect surface-ionization and other 

 causes have upon the fall of potential near the plates. 



Having obtained the potential curve experimentally, it is 

 possible to calculate from it the density of the electrification 

 at the various points between the plates. 



Let V be the potential at a distance x from the point where 

 the curve (fig. 13) crosses the line of zero potential. Then if 

 p is the density of the electrification at the point x 



d 2 V 



7? = -**p 



as 



d 2 V = d 2 V =() 

 dy 2 dz 1 



