1. T.H. Osgood, Phys. Rev. 30, 567 (1927).
2. M.A. Dauvillier, J. Phys. Radium, Ser. VI T VIII, No. 1, 1 (1927).
3. J. Bergengren, Compt. Rend. 171, 624 (1920); Z. Phys. 3, 247 (1920).
4. A.E. Lind, Compt. Rend. 172, 1175 (1921); ibid.
175, 25 (1922).
5. T. Magnusson, doctoral thesis, Uppsala University, 1942.