"I knew it could not have been a proton. Since a proton is 1800 times as heavy as an electron it would have produced a much thicker line [trail]... [I]t could not have been a neutron since neutrons have no electric charge and, therefore, are incapable of producing any kind of line... [T]he line was exactly what would have been produced by an ordinary electron except that electrons had always been found to have a negative electric charge and, therefore, should have turned to the right. This one turned to the left... an electron with a positive charge ...a positive electron!"