Rutherford envisioned the proton in 1914 when experiments on alpha-particle scattering led him to suggest that the hydrogen nucleus was the carrier of both positive charge and mass in the structure of all heavier atoms. This was supported by his discovery in 1919 that bombardment by alpha particles expelled hydrogen from nitrogen. In 1920, he proposed the name proton for the hydrogen nucleus in this role but refrained from using it, perhaps from what he considered a lack of direct experimental evidence. That constraint continued as he and Chadwick found hydrogen expelled from most other light nuclei. He abandoned it at last when Blackett's cloud chamber showed the capture of the alpha particle by a nitrogen nucleus at the time the proton was emitted.