On ilie Ions produced in Air by Rontgen Rays. 435 



plates, and through a larger range of P.D., but to accomplish 

 this with the battery available was not possible. 



The following table contains the results of a set of obser- 

 vations : — 



Distance between the disks <^ = 0'45 cm. 

 Potential-difference used 1800 volts. 



Time of Fall without P.D. Ditto with P.D. 



X=0. X = 13-3E.S. units. 



sees. sees. 



(1) 23-6 (2) 17-8 



(3) 23-3 (4) 16-9 



(5) 23-9 (6) 17-0 



(7) 23-8 (8) 17-2 



Mean. ..23-65 Mean.. .17*22 



The numbers in brackets refer to the order in which the 

 observations were made. The above results give 



0*45 n , mQA cm. 

 ^2M5 =0019 °se^ 



„ 2= ^ =0-0262^ 

 17*22 sec. 



Consequently, since 



9 



we have 



Also 



e = 3'l xl0- 9 ^(« 2 -«!)■»!*, 



_ 3-1 x lO" 9 x 981 X 0-0072 x (0-019)* 



13-3 

 = 2-3 xl0- 10 E.S. units. 



- 3-1 x 10~ 9 Xiv = 8'l x 10- 12 gram. 



The method of experimenting can be varied by measuring 

 the velocity of fall first with the field in one direction and 

 then with the field in the opposite direction. If v 2 and w 3 

 are the velocities, then 



mg 4- Xe v 2 



mg — X<? ~~ t? 3 ' 



taking v 2 to be the velocity when Xe acts in the downward 

 direction. The mean of v 2 and v* gives the velocity when 

 X = 0. 



