ABSTRACT
The experimental evidence collected during the last few years has strongly supported the view that the α particle is a charged helium atom, but it has been found difficult to give a decisive proof of the relation. The number of α particles from one gram of radium have been counted, and the charge carried by each determined. The values of several radioactive quantities, calculated on the assumption that the α particle is a helium atom carrying two unit charges, have been shown to be in good agreement with the experimental numbers. If the α particle is a helium atom, helium should gradually diffuse from the glass and mercury into the exhausted space, and its presence could then be detected spectroscopically by raising the mercury and compressing the gases into the vacuum-tube. A number of blank experiments were made, using samples of the lead-foil which had not been exposed to the α rays, but in no case was any helium detected.
