[Footnote 38:  An actinium X was also discovered by Professor Giesel (Jahrbuch d.  Radioaktivitat, i. p. 358, 1904).  Since the above was written, another product has been found to intervene between the X substance and the emanation in the case of actinium and thorium.  They have been named radio-actinium and radio-thorium respectively.—­ED.]

It is not possible to give a complete table which should, as it were, represent the genealogical tree of the various radioactive substances.  Several authors have endeavoured to do so, but in a premature manner; all the affiliations are not at the present time yet perfectly known, and it will no doubt be acknowledged some day that identical states have been described under different names.[39]

[Footnote 39:  Such a table is given on p. 169 of Rutherford’s Radioactive Transformations.—­ED.]

Sec. 4.  THE DISAGGREGATION OF MATTER AND ATOMIC ENERGY

In spite of uncertainties which are not yet entirely removed, it cannot be denied that many experiments render it probable that in radioactive bodies we find ourselves witnessing veritable transformations of matter.

Professor Rutherford, Professor Soddy, and several other physicists, have come to regard these phenomena in the following way.  A radioactive body is composed of atoms which have little stability, and are able to detach themselves spontaneously from the parent substance, and at the same time to divide themselves into two essential component parts, the negative electron and its residue the positive ion.  The first-named constitutes the beta, and the second the alpha rays.

The emanation is certainly composed of alpha ions with a few molecules agglomerated round them.  Professor Rutherford has, in fact, demonstrated that the emanation is charged with positive electricity; and this emanation may, in turn, be destroyed by giving birth to new bodies.

After the loss of the atoms which are carried off by the radiation, the remainder of the body acquires new properties, but it may still be radioactive, and again lose atoms.  The various stages that we meet with in the evolution of the radioactive substance or of its emanation, correspond to the various degrees of atomic disaggregation.  Professors Rutherford and Soddy have described them clearly in the case of uranium and radium.  As regards thorium the results are less satisfactory.  The evolution should continue until a stable atomic condition is finally reached, which, because of this stability, is no longer radioactive.  Thus, for instance, radium would finally be transformed into helium.[40]

[Footnote 40:  This opinion, no doubt formed when Sir William Ramsay’s discovery of the formation of helium from the radium emanation was first made known, is now less tenable.  The latest theory is that the alpha particle is in fact an atom of helium, and that the final transformation product of radium and the other radioactive substances is lead.  Cf.  Rutherford, op. cit. passim.—­ED.]