Strutt suggested that the rays might be analogous to the canal rays of vacuum-tubes. Rutherford succeeded in showing the action of a magnetic field upon the rays and in making a preliminary measurement of the deviation. Becquerel confirmed the results obtained by Rutherford and gave a new measurement of the phenomenon. Des Coudres measured the electrical and magnetic deviation of the rays in a vacuum.
From these investigations it is seen that the α-rays act like projectiles having a great velocity and charged with electricity. The deviation in a magnetic field and in an electric field is the opposite of the deviation of the cathode rays.
The α-rays form an apparently homogeneous group, all being deflected to the same extent and, hence, not giving a spread-out spectrum as the rays do. The formulas (1) and (2) are applicable. According to the measurements of Des Coudres in a vacuum,
Hence the velocity of the particles is twenty times less than that of light. If we assume that the charge of a particle is the same as that of an atom of hydrogen, in electrolysis, it is found that its mass is of the same order of magnitude as the hydrogen atom (the ratio,
/
, is equal to 9650 for hydrogen in electrolysis). It may well be supposed that these particles, which are greater than the electrons and have a lower velocity, would be less capable of penetration.
According to the experiments of Becquerel, the curvature of the path of the α-rays moving in a uniform magnetic field is not constant when in air at the atmospheric pressure. At first the curvature is the same as that obtained in a vacuum, but it becomes less and less as the ray recedes from its source. This phenomenon can be explained by supposing that new particles attach themselves to the projectiles that make up the rays while the latter move through the air. This hypothesis explains why the absorbing power of a screen for the α-rays increases as it is removed farther from the radiant source.