1. J. R. Oppenheimer:Phys. Rev.,38, 725 (1931).
2. R. Mignani, E. Recami andM. Baldo:Lett. Nuovo Cimento,11, 568 (1974).
3. E. Majorana:Scientific Manuscripts, unpublished, deposited at the « Domus Galilaeana », Pisa: Quaderno 2, p. 101/1; 3, P. 11, 160; 15, p. 16; 17, p. 83, 159 (1928-1932).
4. E. Majorana:Nuovo Cimento,5, 171 (1937). See alsoE. Amaldi:La vita e I’opera di E. Majorana (Rome, 1966).
5. See alsoJ. R.Oppenheimer:Lectures on Electrodynamics, edited byB. S. de Witt (New York, N.Y., 1970).