1. Fricke, Amer. J. Roent. Rod. Ther., 18, 430 (1927); Phys. Rev., 31, 1117 (1928). Fricke and Morse, Phil. Mag., 7, 129 (1929).
2. Fricke and Hart, J. Chem. Phys., 3, 60 (1935).
3. For example, Stenström and Löhmann, Radiology, 18, 322 (1931).
4. Shishacow, Phil. Mag., 14, 198 (1932).
5. Gray and Weigert (unpublished data).