1. Allen, L. R., et al., Mon. Not. Roy. Astro. Soc., 124, 477 (1962). Rowson, B., ibid. (in the press).
2. Matthews, T. A., et al., Amer. Astron. Soc. meeting, New York, 1960; Sky and Telescope, 21, 148 (1961). Greenstein, J. L., and Munch, G., Ann. Rep. Dir. Mt. Wilson and Palomar Obs., 80 (1961).
3. Matthews, T. A., and Greenstein, J. L., Conf. Radio Sources, Nat. Aeronaut. Space Admin., Goddard Inst. Space Studies, New York (Dec. 1962) (unpublished).
4. Greenstein, J. L., and Matthews, T. A., Nature, 197, 1041 (1963).
5. Hazard, C., Mackey, M. B., and Shimmins, A. J., Nature, 197, 1037 (1963).