of Electricity through Gases exposed to Rontgen Rays. 401 

 the gas, we have from equation (2), 



N 



-«}'. 



where N represents the number of conducting particles at 

 this stage ; after the rays have ceased, we have 



dn 9 



dt ' 



or l_^ =zut 



if t is the time which has elapsed after the rays have stopped, 

 when £ = T, ?i = j?N, hence 



1 T- 



substituting for N its value, we get 



or 1 le 



Substituting for q and a. the values just found, equation (4) 

 becomes 



l-l _ lh 2 € 



le ~ITVE 2 U 2 ' 



74 2 



1(1— *) = x 2 E 2 U 2 ^ 



Thus in the straight part of the curve, where i is small com- 

 pared with I, we have approximately 



Now EU/7 is the sum of the velocities of the positively 

 and negatively charged particles in the electric field. Hence, 

 equation (6) shows that the current bears to the maximum 

 current the same ratio as the space described by the charged 

 particles in time T bears to the distance between the elec- 

 trodes. In an experiment where I was about 1 cm., the rate 

 of leak through air for a potential-difference of 1 volt was 

 about ^\y of the maximum rate of leak, hence the charged 



