1. Costain, C. H., Lacey, J. D., and Roger, R. S., Pub. Dominion Observatory Ottawa, 25, No. 3 (1969).
2. Thielheim, K. O., and Beiersdorf, R., J. Phys. A: Gen. Phys., 3, 79 (1970).
3. Allan, H. R., Clay, R. W., Jones, J. K., Abrosimov, A. T., and Neat, K. P., Nature, 222, 635 (1969).
4. Barker, P. R., Hazen, W. E., and Hendel, A. Z., Phys. Rev. Lett., 18, 51 (1967).
5. Hazen, W. E., Hendel, A. Z., Smith, H., and Shah, M. J., Proc. Eleventh I U P A P Cosmic Ray Conf., Budapest, 1969, Acta Physica Hungarica (in the press).