1. Harang, L., and Stoffregen, W., Z. Hochfrequenztech., 55, 105 (1940), On 41 Mc./s. Lovell, A. C. B., Clegg, J. A., and Ellyett, C. D., Nature, 160, 372 (1947), On 46 and 72 Mc./s. Forsyth, P. A., Petrie, W., Vawter, F., and Currie, B. W., Nature, 165, 561 (1950), On 32.7 Mc./s. Aspinall, A., and Hawkins, G. S., J. Brit. Astro. Assoc., 60 (1950), On 72 Mc./s. Hellgren, G., and Meos, J., Tellus, 4, 249 (1952), on 30.3 Mc./s.
2. Chapman, S., J. Atmo. Terr. Phys., 3, 1 (1953).