1. Gold, T., Nature, 218, 731 (1968).
2. Finzi, A., and Wolf, R. A., Astrophys. J. Lett., 155, L107 (1969).
3. Cohen, J. M., Langer, W., Rosen, L., and Cameron, A. G. W., Astrophys. Space Sci., (in the press).
4. Thirring, H. T., Phys. Zeit., 19, 33 (1918).
5. Cohen, J. M., J. Math. Phys., 8, 1477 (1967).