There is thus a good agreement between the calculated and

observed values of the activity measured by the β rays.

The results are satisfactorily explained if it is supposed:—

(1) That the change B into C (half transformed in 21 minutes) does not give rise to β rays;

(2) That the change C into D (half transformed in 28 minutes) gives rise to β rays.

222. These conclusions are very strongly supported by observations of the decay measured by the β rays for a long exposure. The curve of decay is shown in Fig. 88 and Fig. 89, curve I.

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Fig. 89.

P. Curie and Danne made the important observation that the curve of decay C, corresponding to that shown in Fig. 88, for a long exposure, could be accurately expressed by an empirical equation of the form

where λ_{2} = 5·38 × 10^{-4} (sec)^{-1} and λ_{3} = 4·13 × 10^{-4} (sec)^{-1}, and α = 4·20 is a numerical constant.

I have found that within the limit of experimental error this equation represents the decay of excited activity of radium for a