1. P. J. Kellogg andM. Weed,Balloon Measurement of Ionospheric Electric Fields, inS. C. Coroniti andJ. Hughes,Planetary Electrodynamics, Gordon-Breach, New York etc. 1969, vol. 2, p. 431?436.
2. F. S. Mozer andR. Serlin,Magnetospheric Electric Field Measurements with Balloons, Univ. of California, Berkeley, report Feb. 21, 1969.
3. R. E. Bourdeau, E. C. Whipple Jr., J. F. Clark,Analytical and Experimental Electric Conductivity between the Stratosphere and the Ionosphere, J. Geophys Res.64 (1959), 1363.
4. E. C. Whipple Jr.,Electricity in the Terrestrial Atmosphere, inS. C. Coroniti,Problems in Atmospheric and Space Electricity (Elsevier Publ. Co.,) p.p. 123?139, 1965.
5. A. Pedersen,Measurements of Ion Concentrations in the D-region of the Ionosphere, Uppsala Ionospheric Observatory, Report no. 15 (1966).