1. P. Lenard:Hand. der Exp. Phys.; Fluorescenze und Phosphorescenz, p. 976.
2. M. Curie andM. Prost:Compt. Rend.,223, 1125 (1946).
3. This effect has been also observed byJ. Trinks:Ak. Wiss. Wien,147, Abt. IIa. 5 and 6, 226 (1938).
4. P. D. Johnson andF. Williams:Phys. Rev.,95, 69 (1954).
5. G. Tricomi:Atti R. Accademia delle Scienze di Torino,76, 288 (1941).