1. W. Pauli, quoted repeatedly since 1931, to be published shortly in "Rapports du Septième Conseil Solvay, Brussels", 1933.
2. C. D. Ellis and N. F. Mott, Proc. Roy. Soc., A, 141, 502; 1933.
3. E. Fermi, La Ricefca Scientifica, 2, No. 12; 1933.
4. This point of view was first put forward by I. Curie and F. Joliot, at the Conseil Solvay, 1933.
5. I. Curie and F. Joliot, NATURE, 133, 201, Feb. 10, 1934.