1. Becquerel, E.,Ann. de Chim. et Phys., 1859,57, 125; 1861,62, 90.
2. Lecoq de Boisbaudran,Compt. Rend., 1887,103, 1107, 1224; 1824,104, 330, 478, 554.
3. Du Bois, H., and Elias, J.,Ann. d. Phys., 1908,27, 233; 1911,35, 635.
4. Schmidt, G. C.,Ann. d. Phys. U. Chem., 1904,15, 622.
5. Mendenhall, E. C., and Wood, R. W.,Phil. Mag., 1915,30, 316.