carried by the Ions produced hy Rbntyen Rays, 541 



and putting 



«=-14, # = 981, //, = l-8xl0- 4 , 

 we find 



a 2 = 1.1-5 Xl0" 8 , 



6i = 3-39 xlO" 4 , 

 -47ra 3 = l-63xl0- 10 . 

 As the radius of the drop is considerable compared with 

 the mean free path in air at atmospheric pressure we may 

 feel some confidence that equation (1) will be true for drops 

 of this size. 

 Hence 



^ira 6 



This is the number of ions in 1 cub. centim. of the ex- 

 panded gas ; the number in 1 cub. centim. of the gas before 

 expansion 



= 2-94 x 1-36 xl0 4 = 4xl0 4 . 



We now consider the electrical part of the experiment. 

 The electrometer gave a deflexion of 90 scale-divisions for 

 two Leclanche cells, the capacity of the system consisting of 

 the cell containing the gas exposed to the rays, the connecting 

 wires, and the quadrants was 38, on the electrostatic system 

 of units. The diameter of the circular electrodes between 

 which the leak took place was 3*6 centim., and the distance 

 between them 2 centim. When the rays were on, and the 

 potential- difference between the electrodes that due to two 

 Leclanches, the leak was at the rate of 9 scale-divisions per 

 minute ; hence if E is the electromotive force of a Leclanche 

 cell, the quantity of electricity passing in one second through 

 a cross-section of the discharge-tube is equal to 



300 

 But this is equal to 



Aneu W 9 

 where A is the area of the electrodes and equals 7r(l*8) 2 , 

 n the number of ions per cub. centim. = 4x 10 4 , e the charge 

 on an ion, u the mean velocity of the positive and negative 

 ion under unit potential gradient, Mr. Rutherford found this 

 to be 1*6 x 3 x 10 2 . E' is the potential gradient, assumed to 

 be uniform, in our case it was E. Substituting these values, 

 we get 



J^E = 7r(l-8) 2 x4xl0 4 x*x4-8xl0 2 xE; 



hence e = fr'd x 10" 10 . 



Phil. Mag. 8. 5, Vol. 46. No. 283. Dec. 1898. 2 P 



