1. A. É. Becquerel, La Lumière, Paris (1867).
2. P. Lenard, Handbuch der Experimental Physik (ed. by W. Wien and F. Harms), Vol. 23, Akademische Verlagsgesellschaft, Leipzig (1928), p. 2.
3. J. W. Draper, Phil. Mag., 11:160 (1881).
4. E. Lommel, Ann. Phys. Chem., 3:251 (1878).
5. A. Dahms, Ann. Phys. (Leipzig), 13:425 (1904).