Ix] EXCITED RADIO-ACTIVITY 285 
plate can be conveyed to it, and the rest, in the course of several 
succeeding alternations, are carried to the other plate. 
When the plate B is negatively charged, the E.M.F. between 
the plates is #, — #,, when B is positive the E.M.F. is A, + 44. 
Let d = distance between the plates, 
T = time of a half alternation, 
p =ratio of the excited radio-activity on the plate B to the 
sum of the radio-activities on the plates A and B, 
K = velocity of the positive carriers for a potential-gradient 
of 1 volt per centimetre. 
On the assumption that the electric field between the plates is 
uniform, and that the velocity of the carrier is proportional to the 
electric field, the velocity of the positive carrier towards B is 
and in the course of the next half alternation 
i, + &, 
ae VK 
towards the plate A. 
If x, is less than d, the greatest distances 2,, 7, passed over by 
the positive carrier during two succeeding half alternations is thus 
given by 
£,-f, L,+#, 
d agente 
Suppose that the positive carriers are produced at a uniform 
rate of gq per second for unit distance between the plates. The 
number of positive carriers which reach B during a half alter- 
nation consists of two parts: 

KT, and «= KT. 
“= 
(1) One half of those carriers which are produced within the 
distance «, of the plate B. This number is equal to 
4a,g0. 
(2) All the carriers which are left within the distance 2, from 
B at the end of the previous half alternation. The number of 
these can readily be shown to be 
