1. C. Cattaneo:Nuovo Cimento,10, 318 (1958). This paper will be in the following quoted as I.
2. Latin indexes vary from 1 to 4; greek indexes vary from 1 to 3.
3. It is the same tensor employed in the transverse covariant derivation. This tensor had already been considered in general relativity; see, for instance:A. Lichnerowicz:Théories relativistes de la gravitation et de l’életromagnétisme (Paris, 1955), p. 9;C. Møller:The theory of relativity (Oxford, 1952), p. 238.
4. By means of the standard definitions, the gravitational field does not enter explicitely in the definition of the dynamical quantities: it has only a direct influence on the space and time measurements. Occasionally we remember that the adoption of the standard spatial tensor and the standard relative time gives to ds2 the form [I, (68)]: any optic anisotropy of the space disappears. the speed of the light being equal toc in every direction.