1. Fleck, Lord et al. 1965, Radio Astronomy, H.M. Stationery Office, London.
2. Gold, T., Messel, H. 1964, Nature, 204, 18.
3. Lovell, A. C. B. 1964, Biog. Mem., Roy. Soc., 10, 229.
4. Smith-Rose, R. L. 1964, Nature, 203, 7.
5. Smith, F. G., Smith-Rose, R. L. 1966, IUCAF Document no. 87, URSI Information Bulletin no. 155, P. 49.