By their measurements on the heating effect of the β-rays of Radium E, Ellis and Wooster(1) have proved that the continuous spectra of β-rays represent the actual β-rays of disintegration. Since the β-rays in the continuous spectrum have a wide range of energies, there arise problems which can best be understood by considering a particular series of disintegrations, which we may regard as typical; the most suitable series to consider is the following:

The main problem that arises is to reconcile the facts that the β-rays from Thorium B and Thorium C are emitted with a wide range of energies, while before, in Thorium A, and after, in Thorium C and Thorium C′, we have bodies which emit α-rays which are homogeneous, or, at most, consist of a few homogeneous groups [Rosenblum(2)].