1. Altenhoff, W., Mezger, P. G., Wendker, H., and Westerhout, G.: 1961,Ver�ff. Univ. Sternw. Bonn, Nr. 59, part IV.
2. Baars, J. W. M., Mezger, P. G., and Wendker, H.: 1965,Z. Astrophys. 61, 134.
3. Bolton, J. G., Gardner, F. F., and Mackay, M. B.: 1964,Austral. J. Phys. 17, 340.
4. Conway, R. G., Kellerman, K. I., and Long, R. G.: 1963,Monthly Notices Roy. Astron. Soc. 125, 261.
5. Day, G. A., Shimmins, A. J., Ekers, R. D., and Cole, D. L.: 1966,Austral. J. Phys. 19, 35.