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.