Propagation of Electric Waves over the Earth

The comparatively poor transmission of radio waves of two or three hundred meters indicates some sort of selective effect in the atmosphere. Such an effect is found to result from the existence of free electrons in the atmosphere when the magnetic field of the earth is taken into account. In the earth's magnetic field, which is about one-half gauss, this selective effect will occur at a wave length of approximately 200 meters. Ionized hydrogen molecules or atoms result in resonant effects at frequencies of a few hundred cycles, this being outside of the radio range. The paper, however, takes into account the effects of ionized molecules as well as electrons. The result of this combination is that the electric vector of a wave traveling parallel to the magnetic field is rotated. Waves traveling perpendicular to the magnetic field undergo double refraction. Critical effects are observed in rotation, bending of the wave and absorption at the resonant frequency. The paper develops the mathematical theory of these phenomena and gives formulas for the various effects to be expected.