1. H. Haberlandt, B. Karlik and K. Przibram, Wien Ber., IIa, 143, 151; 1934. See also NATURE, 133, 99; 1934.
2. G. Jantsch and W. Klemm, Z. anorgan. Chem., 216, 80; 1933.
3. For the line-fluorescence of other trivalent rare earth salts, see R. Tomaschek and O. Deutschbein, Phys. Z., 34, 374; 1933 and M. Haitinger, Wien. Ber., IIa, 142, 339; 1933.