Atoms and their Packing Fractions

@article{AstonAtomsAT,
  title={Atoms and their Packing Fractions},
  author={Francis William Aston},
  journal={Nature},
  volume={120},
  pages={956-959}
}
THE original mass-spectrograph was set up in the Cavendish Laboratory in 1919. Its resolving power was suffint to separate mass lines differing by about 1 in 130, and its accuracy of measurement was about 1 in 1000. These capabilities sufficed to determine with fair certainty the isotopic constitution of more than fifty elements, and to demonstrate that, with the exception of hydrogen, the masses of all atoms could be expressed as integers on the scale 0=16 to one or two parts in one thousand… 
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Isotopes of Stable Elements
The development of mass spectrographs in the 1920s was instrumental in the identification of multiple stable isotopes in many elements. The discovery of all stable isotopes including isotopes

References

Bakerian Lecture.— A new mass-spectrograph and the whole number rule
The original mass-spectrograph was set up in the Cavendish Laboratory in 1919. Its resolving power was sufficient to separate mass lines differing by about 1 in 130 and its accuracy of measurement