204 



Prof. E. Rutherford on the Charge 



experiments on the charge carried by the a rays, half the 

 algebraic sum of the currents observed with reversal of the 



Fig. 2. 



potential represents the value ne, where n is the number of 

 (3 particles escaping from the central electrode per second, 

 and e the charge on each particle. 



The value of ne was found to decrease with the time at the 

 same rate as the rod lost its /3 activity , measured in the usual 

 way by an electroscope. Knowing the curve representing 

 the variation of the /3 ray activity with time, the value of n e 

 at any time can be expressed in terms of the value of ne at 

 the moment of removal of the rod from the emanation. 



The following numbers illustrate the experimental method. 

 At the moment of removal, the 7 ray activity of the rod 

 corresponded to 4*20 milligrams of radium bromide. The 

 value of n e was determined after the rod had been removed 

 33 minutes. From comparison with the known curve, the /3 

 ray activity had during that time fallen to 74 per cent, of the 

 initial value. The value of ne, reduced to the initial value, 

 was found to be 1'05 x 10 -li ampere. Taking e as 

 1*13 x 10 — 19 coulomb, the value of n is thus 9*3 x 10 7 . 



This is the number corresponding to 4*2 milligrams oi' 

 radium bromide. Remembering that half of the j3 particles 

 are projected into the lead which absorbs most of them, it can 



