The Limiting Polarization of Downcoming Radio Waves Traveling Obliquely to the Earth's Magnetic Field

The paper is a theoretical discussion of the limiting polarization of downcoming electromagnetic waves propagated at oblique angles to the earth's magnetic field. The main conclusions arrived at are: (a). The polarization of the downcoming wave tends to a definite limit on leaving the Kennelly-Heaviside layer. The limiting polarization has been shown to be very nearly independent, for conditions that are likely to hold in practice, of the presence of large numbers of heavy negative ions in addition to the electrons, and of the occurrence of collisions between electrons and gas molecules. (b). The shape of the ellipse of polarization is determined by the frequency of the wave relative to the critical frequency, and by the angle between the direction of propagation and the lines of force of the earth's magnetic field. (c). The orientation of the ellipse is such that the principal axes are perpendicular to the direction of propagation, the major axis being in the plane containing the direction of the earth's magnetic field and the direction of propagation. (d). The sense of rotation of the electric vector contained by the ellipse is left-handed when the direction of propagation of the "ordinary" downcoming ray makes an acute angle with the earth's field; the rotation is right-handed when the angle is obtuse.