1. Watts, J. M., and Davies, K., J. Geophys. Res., 65, 2295 (1960).
2. Knecht, R. W., and Davies, K., Nature, 190, 797 (1961).
3. Davies, K., Proc. Inst. Rad. Eng., 50, 94 (1962).
4. Dungey, J. W., “Electrodynamics of the Outer Atmosphere”, The Physics of the Ionosphere, 229 (Physical Society, 1955).