1. M. Fierz andW. Pauli:Proc. Roy. Soc., A173, 211 (1939).
2. H. A. Buchdahl:Nuovo Cimento,10, 96 (1958). The formalism here is the same as that used in A.
3. H. Umezawa:Quantum Field Theory, Ch.iv (Amsterdam, 1956), p. 66.
4. TheS-tensor spinor and any other quantities not explicitly defined here are defined in the following paper:H. A. Buchdahl:Australian Journ. Math., (in press). This paper will be referred to as S.
5. A. S. Eddington:The Mathematical Theory of Relativity (Cambridge University Press, 1924), ch.vi, p. 176, eqs. (74.33) and (74.43).