1. Pierce, J. R., et al., Astrophys. J., 134 (1961).
2. McClain, E. F., Sci. Amer., 202, 45 (1960).
3. Kraus, J. D., Nash, R. T., and Ko, H. C., Inst. Rad. Eng. Trans., AP-9, 4 (1961).
4. Khaikin, S. E., and Kaidanovskii, N. L., Paris Symp. Radio Astronomy, edit. by Bracewell, R. N., 166 (Stanford University Press, Stanford, 1959).
5. Swenson, G., and Bracewell, R. N., Sky and Telescope, 22, 77 (1961).