The regularity of the phenomenon is so
great that it can be used to measure time: in 3985 seconds[36] the
activity is always reduced one-half.
[Footnote 36: According to Professor Rutherford, in 3.77 days.--ED]
Radioactivity induced on any body which has been for a long time in
presence of a salt of radium disappears more rapidly. The phenomenon
appears, moreover, more complex, and the formula which expresses the
manner in which the activity diminishes must contain two exponentials.
To find it theoretically we have to imagine that the emanation first
deposits on the body in question a substance which is destroyed in
giving birth to a second, this latter disappearing in its turn by
generating a third. The initial and final substances would be
radioactive, but the intermediary one, not. If, moreover, the bodies
acted on are brought to a temperature of over 700 deg., they appear to
lose by volatilisation certain substances condensed in them, and at
the same time their activity disappears.
The other radioactive bodies behave in a similar way.
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