Arnold Sommerfeld (left, 1868-1951) and Neils Bohr (1885-1962), German and Danish theoretical physicists. Bohr made numerous contributions to physics

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Arnold Sommerfeld (left, 1868-1951) and Neils Bohr (1885-1962), German and Danish theoretical physicists. Bohr made numerous contributions to physics during his career, but it was his work on the structure of atoms that won him the 1922 Nobel Prize in Physics. Following Ernest Rutherford's discovery of the nucleus, Bohr described the atom as a small, positively charged nucleus surrounded by waves of electrons with discrete (quantised) energies. Sommerfeld developed this idea, using elliptic orbits instead of Bohr's circular ones, and by showing how relativistic effects would be seen in the fine structure of atomic spectra. Photographed in 1919.

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