1. Wigner, Phys. Rev., 51, 106 (1937).
2. Fermi, E., Ric. Sc., 7, 2 (1936).
3. Frisch, Halban, Koch, NATURE, 170, 895 (1937).
4. Dunning, Manley, Hoge, and Brickwedde, Phys. Rev., 52, 1076 (1937); Halpern, Esterman, Simson and Stern, Phys. Rev., 52, 142 (1937); Schwinger and Teller, Phys. Rev., 52, 286 (1937).
5. See Bethe and Bacher, Rev. Modern Physics, 8 (1936). For the number given here the scattering cross-section was assumed to be 18 × 1024 cm.2 for free protons and slow neutrons, and the difference of the magnetic moments of proton and neutron 4.2 nuclear magnetons.