1. Cope, P. G., J. Brit. Interplan. Soc., 19, 285 (1964).
2. Russell, P. C., Nature, 205, 684 (1965).
3. Russell, P. C., Nature, 206, 281 (1965).
4. Unpublished photographs from SL 303, flown on April 9, 1965.
5. Möllenstedt, G., von Grote, K. H., and Jonsson, C., in X-ray Optics and Microanalysis, edit. by Pattee, Cosslett and Engstrom, 73 (1963).