Aston called his invention a mass-spectrograph because it sorted elements and isotopes of elements by mass much as an optical spectrograph sorts light by its frequency. The mass-spectrograph was immediately and sensationally a success. “In letters to me in January and February, 1920,” says Bohr, “Rutherford expressed his joy in Aston’s work,” which “gave such a convincing confirmation of Rutherford’s atomic
