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 regained its activity. A long series of measurements was then undertaken to examine the time-rate of these processes of decay and recovery of activity.

Fig. 47.

The results are shown graphically in Fig. 47, where the final activity of the thorium and the initial activity of the Th X are in each case taken as 100. The ordinates represent the activities determined by means of the ionization current, and the abscissae represent the time in days. It will be observed that both curves are irregular for the first two days. The activity of the Th X increased at first, while the activity of the thorium diminished. Disregarding these initial irregularities of the curves, which will be