1. Gorter, C. J., Phys. Z., 35, 923 (1934).
2. Kurti, N., and Simon, F. E., Proc. Roy. Soc., A, 149, 152 (1935).
3. Simon, F. E., in “Le Magnetisme”, 3, 1 (Strasbourg, 1940).
4. Halban, H., Nature, 140, 425 (1937).
5. Spiers, J. A., “Directional Effects in Radioactivity” (Ontario: National Res. Coun. Canada, 1949).