204: RADIO-ACTIVE EMANATIONS [CH. 
134. Increase of current with time. The current due to 
the emanation does not reach its final value for some time after 
the active matter has been introduced into the closed vessel. The 
variation with time is shown in the followimg table. The satura- 
tion current due to thorium oxide, covered with paper, was observed 
between concentric cylinders of 5:5 cms. and ‘8 cm. diameter. 
Immediately before observations on the current were made, a 
rapid stream of air was blown through the apparatus. This removed 
most of the emanation. However, the current due to the ionization 
of the gas by the emanation, as 1t was carried along by the current 
of air, was still appreciable. The current consequently does not 
start from zero. 
Time in seconds Current 
O 9 
23 25 
53 49 
96 67 
125 76 
194 88 
244 98 
304 99 
484 100 
The results are shown graphically in Fig. 38 Curve B. The 
decay of the activity of the emanation with time, and the rate of 
increase of the activity, due to the emanation in a closed space, are 
connected in the same way as the decay and recovery curves of 
Th X and Ur X. 
With the previous notation, the decay curve is given by 
and the recovery curve by 
ty 1—e, 
0 
where 2X is the radio-active constant of the emanation. 
This relation is to be expected, since the decay and recovery 
curves of the emanation are determined by exactly the same con- 
ditions as the decay and recovery curves of Ur X and ThX. In 
both cases there is: 
