1. J. L. Synge, The General Relativity, North-Holland Publishing Co., p. 367, 1960.
2. G. Tauber, Canad. Journal of Phys.,35, 477, 1957.
3. E. T. Newman, E. Couch, K. Chinnapared, A. Exton, A. Prakash andR. Torrence, Journal of Math. Phys.,6, 918, 1965.
4. A. Papapetrou, Ann. Inst. Henri Poincaré, IV. 83, 1966.
5. See [1],J. L. Synge, The General Relativity, North-Holland Publishing Co., p. 311. 1960.