1. L. Pauling, Phys. Rev. 36, 430 (1930).PHRVAO0031-899X
2. R. Pohlman, Zeits. f. Physik 79, 394 (1932).
3. P. E. Shearin, Phys. Rev. 48, 299 (1935).PHRVAO0031-899X
4. G. Hettner, Zeits. f. Physik 78, 141 (1932).
5. E. K. Plyler and P. E. Shearin, J. Opt. Soc. Am. 28, 61 (1938).JOSAAH0030-3941