1. A less rigorous derivation of the same result has been given by the author in Compt.Rend.,239, 1023 (1954).
2. we shall follow TolmanRelativity, Thermodynamics and Cosmology (Oxford, 1934)
3. Cfr. Einstein:The Meaning of Relativity (Princeton, 1953), p. 87.
4. cfr. de Broglie:Théorie générale des particules à spin (Paris, 1954), p. 191
5. Cfr.Tolman:Relavity, Thermodynamics and Cosmology (Oxford, 1934), p. 474.