Two other bodies, polonium and actinium, the one characterised by the special nature of the radiations it emits and the other by a particular spectrum, seem likewise to exist in pitchblende.  These chemical properties have not yet been perfectly defined; thus M. Debierne, who discovered actinium, has been able to note the active property which seems to belong to it, sometimes in lanthanum, sometimes in neodynium.[33] It is proved that all extremely radioactive bodies are the seat of incessant transformations, and even now we cannot state the conditions under which they present themselves in a strictly determined form.

[Footnote 33:  Polonium has now been shown to be no new element, but one of the transformation products of radium.  Radium itself is also thought to be derived in some manner, not yet ascertained, from uranium.  The same is the case with actinium, which is said to come in the long run from uranium, but not so directly as does radium.  All this is described in Professor Rutherford’s Radioactive Transformations (London, 1906).—­ED.]

Sec. 3.  THE RADIATION OF THE RADIOACTIVE BODIES AND THE EMANATION

To acquire exact notions as to the nature of the rays emitted by the radioactive bodies, it was necessary to try to cause magnetic or electric forces to act on them so as to see whether they behaved in the same way as light and the X rays, or whether like the cathode rays they were deviated by a magnetic field.  This work was effected by Professor Giesel, then by M. Becquerel, Professor Rutherford, and by many other experimenters after them.  All the methods which have already been mentioned in principle have been employed in order to discover whether they were electrified, and, if so, by electricity of what sign, to measure their speed, and to ascertain their degree of penetration.

The general result has been to distinguish three sorts of radiations, designated by the letters alpha, beta, gamma.

The alpha rays are positively charged, and are projected at a speed which may attain the tenth of that of light; M.H.  Becquerel has shown by the aid of photography that they are deviated by a magnet, and Professor Rutherford has, on his side, studied this deviation by the electrical method.  The relation of the charge to the mass is, in the case of these rays, of the same order as in that of the ions of electrolysis.  They may therefore be considered as exactly analogous to the canal rays of Goldstein, and we may attribute them to a material transport of corpuscles of the magnitude of atoms.  The relatively considerable size of these corpuscles renders them very absorbable.  A flight of a few millimetres in a gas suffices to reduce their number by one-half.  They have great ionizing power.

The beta rays are on all points similar to the cathode rays; they are, as M. and Madame Curie have shown, negatively charged, and the charge they carry is always the same.  Their size is that of the electrons, and their velocity is generally greater than that of the cathode rays, while it may become almost that of light.  They have about a hundred times less ionizing power than the alpha rays.