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POPULAR SCIENCE MONTHLY.
detail. The residual activity at first mainly consists of β rays, and the activity measured by them does not change appreciably during the period of one year. The α ray activity is at first small, but increases uniformly with the time for the first few months that the activity has been examined. These results receive an explanation on the hypothesis that radium C changes into a product D which emits only β rays. D changes into a product E which emits only α rays. This view has been confirmed by separating the α ray product by dipping bismuth-plate into the solution containing radium D and E. The probable period of these changes can be deduced from observations of
