| |
| 1910–13 |
| |
| Bertrand Russell (1872–1970) and Alfred North Whitehead (1861–1947) published Principia Mathematica, carrying out the reduction of arithmetic to symbolic logic. This work is the foundation of the calculus of propositions and modern symbolic logic. | 1 |
| |
| 1911 |
| |
| Robert A. Millikan (1868–1953) established that electric charge always consists of an integral multiple of a unit charge, which he determined with great accuracy in his oil-drop experiment. | 2 |
| |
| 1911 |
| |
| Ernest Rutherford (1871–1937) introduced the nuclear model of the atom, that is, a small positively charged nucleus containing most of the mass of the atom and surrounded by electrons. | 3 |
| |
| 1911–13 |
| |
| Ejnar Hertzsprung (1873–1967) studied double stars and their colors, especially in the Pleiades, and with Henry Norris Russell (1877–1957) devised the Hertzsprung-Russell Diagram, a graphic way of grouping stars by the relation between their absolute magnitudes and spectral types. | 4 |
| |
| 1912 |
| |
| Max von Laue (1879–1960) discovered x-ray diffraction, a powerful technique for directly observing the atomic structure of crystals. | 5 |
| |
| 1913 |
| |
| Niels Bohr (1885–1962) devised a new model of the atom by applying quantum theory to Rutherford's nuclear atom. Although this model violated classical electromagnetic theory, it successfully accounted for the spectrum of hydrogen. | 6 |
| |
| |
