286 EXCITED RADIO-ACTIVITY [CH. 
The remainder of the carriers, produced between A and B 
during a complete alternation, will reach the other plate A in the 
course of succeeding alternations, provided no appreciable recombi- 
nation takes place. This must obviously be the case, since the 
positive carriers travel further in a half alternation towards A than 
they return towards B during the next half alternation. The 
carriers thus move backwards and forwards in the changing electric 
field, but on the whole move towards the plate A. 
The total number of positive carriers produced between the 
plates during a complete alternation is 2dq7’. The ratio p of the 
number which reach B to the total number produced is thus 
given by 

p= aga TT Ree 
Substituting the values of #, and x, we obtain 
2(H,+ £,) @? 
TOO Dp eI Dpy) TEI 
In the experiments the values of £,, /,, d, and T' were varied, 
and the results obtained were in general agreement with the above 
equation. 
K= 

The following results were obtained for thorium : 
Plates 1:30 cms. apart. 




: 7 
j £ | Alternations Bs 
| Boyt tin |) Het | persecond | P is 
| | 
| 152 LO | 57 27 | 1:25 
225 150 | 57 | +38 1:17 
| 3800 200 | 57 | :44 1-24 
| 

Plates 2 cms. apart. 




= | Alternations | a 
| Bot By | By dh | per second | P | a 
| = | 
| 973 207 | 44 37 | 147 | 
| 300 200 | 53 *286 1°45 | 
| | 


