Page:Radio-activity.djvu/384

 Fig. 80.

The theoretical and observed values thus agree within the limit of error in the measurements. The theoretical curve is shown in Curve A, Fig. 80 (with the observed points marked, for comparison). The curve B shows the theoretical curve of the decay of the activity of Th X and the emanation, supposing there is no further change into the active deposit. Curve C shows the difference curve between the curves A and B, i.e. the proportion of the activity at different times due to the active deposit. The activity due to the latter thus rises to a maximum about two days after removal of the Th X, and then decays with the time at the same rate as the Th X itself, i.e. the activity falls to half value every four days. When t exceeds four days, the term e^{-(λ_{2} - λ_{1})t} in the theoretical equation is very small.