1. Bassett, I. M., Box, M. A., and Hewitt, R. G. L., Search, 5, 182–186 (1974).
2. Urbach, F., Berger, D., Robertson, D. F., and Davies, R. E., in Proc. third CIAP Conf., Cambridge, Massachusetts (1974).
3. Cutchis, P., Science, 184, 13–19 (1974).
4. Schulze, R., in Proc. Int. Conf. Struct. Composition and General Circulation of the Upper and Lower Atmospheres and Possibly Anthropogenic Perturbations, 479–493, Melbourne, Australia (1974).
5. Robertson, D. F. in The Biologic Effects of Uultraviolet Radiation (edit. by Urbach, F.), 433–436 (1969).